The Project Gutenberg eBook of The Motor Rangers' Cloud Cruiser, by John Henry Goldfrap

The Project Gutenberg eBook, The Motor Rangers' Cloud Cruiser, by John Henry Goldfrap, Illustrated by Charles L. Wrenn

CHAPTER I.

Joe Hartley turned to Nat Trevor as he spoke, and scanned the face of the young leader of the adventure-seeking Motor Rangers with some anxiety.

But the stout and placid Joe’s unwonted look of apprehension found no reflection on the firm countenance of Nat Trevor, who stood as steadily at the wheel of the Nomad as if that sixty-foot, gasolene-driven craft was not, to use Joe’s phrase of a few moments before, pitching and tumbling “like a bucking broncho.”

“It does look pretty ugly for a fact, Joe,” rejoined Nat, after he had scrutinized the horizon on every side.

“And this is a part of the Pacific where we were warned before we left the Marquesas that we must look out for squalls,” returned Joe, still looking worried.

“Oh, well, the Nomad has weathered many a good hard blow, not to mention those waterspouts,” commented Nat. “I guess she’ll last through whatever is to come.”

At this moment a third boyish countenance was suddenly protruded from a hatchway leading to the Nomad’s engine-room.

“S-s-s-s-say, y-y-y-you chaps,” sputtered our old acquaintance, William—otherwise and more frequently Ding-Dong—Bell, “w-w-what’s in the w-w-w-wind?”

“A bit of a storm, I guess, Ding-Dong,” returned Nat, watching his steering carefully, so as to send the Nomad sliding easily over the long, oily swells, “but don’t you mind, old chap. She’ll stand it, never fear. How are your engines running?”

“L-l-l-like a d-d-d-dollar w-w-watch,” returned Ding-dong, with a note of pride in his tones.

“Good. Now if only we were farther to seaward of that island yonder, I’d feel easier,” commented Nat.

“Say, Nat,” struck in Joe, as Ding-dong dived below once more, “it seems to me we are a long time passing that island.”

“I agree with you, Joe. That is what made me ask Ding-dong about his engines. At the pace they are turning up, we should have left it behind us long ago, yet there it is, still on our starboard bow.”

“And we are getting closer in to it all the time, you’ll notice,” rejoined Joe.

“There must be some powerful currents hereabouts,” said Nat, looking for the first time a little bit troubled. “There’s something queer about that island, anyhow. I can’t find it on the chart. According to that, this part of the mid-south Pacific is absolutely free from islands or rocks.”

“Hullo,” cried Joe suddenly, “that’s odd! Look, Nat, the island isn’t really one island at all. It’s two of them.”

This paradoxical speech was really a correct explanation of the case, as it now appeared. The Nomad had, by this time, made some little progress over the rising sea, and as the bit of land “opened out,” it could be seen that there were, as Joe had said, two islands, with a narrow channel running in between them.

“Phew!” whistled Nat. “This complicates the situation. To make matters worse——” He stopped short.

“Never mind,” replied Nat; and then in an undertone he added to himself: “I may be wrong, but I’ll bet the hole out of a doughnut that we are being dragged round toward that passage.”

That such was actually the case, he realized to his dismay an instant later. Head the Nomad’s bow round as he would, some invisible force still dragged her in toward the two islands. It soon became apparent, too, that the narrow channel was, in reality, more in the nature of a cleft between the two masses of land. Its walls were steep and sheer and formed of grayish rock. It could now be seen that the water in this abyss was boiling and bubbling as if in a caldron.

Nat and Joe exchanged glances of dismay. It was no longer possible to disguise the fact that they were momentarily being sucked, as though by invisible yet resistless forces, toward this ominous looking chasm.

The three youths had set out for the California coast, on which was their home, some days before, from the Marquesas group of islands, where they had had some surprising adventures. What these were will be found set down in the third volume of this series, “The Motor Rangers on Blue Water.” It may be said here, briefly, that their experiences in the South Seas had included the routing of a rascally band, who had made a headquarters on one of the Marquesas Group, and the discovering of the rightful owner of some valuable sapphires which had come into their possession in a truly remarkable way.

Of how they acquired these sapphires, and of the adventures and perils through which they passed before they gained full possession, details will be found in the second volume of the Motor Ranger Series, namely, “The Motor Rangers Through the Sierras.” In that volume, we followed our youthful and enterprising heroes through the great Sierra range, and learned of their clever flouting of the schemes of the same band of rascals whom they re-encountered in the South Seas. Among other feats, they located and caused the destruction of the hitherto secret fortress of Colonel Morello, a notorious outlaw. This earned them his undying enmity, which he was not slow to display. In this volume, too, it was related how the lads found, in a miner’s abandoned hut, the wonderful sapphires.

It now remains, only briefly, to sketch the earlier experiences of the three lads, to give our readers a grasp of their characters. In the first volume of this series, then, which was called “The Motor Rangers’ Lost Mine,” the three lads set out for Lower California on a mission which was to involve them in unlooked-for complications.

This errand grew out of Nat’s employment as automobile expert by Mr. Montagu Pomery, the “Lumber King,” as the papers called him, who made his winter home at Santa Barbara. Nat, who lived with his mother, was, at that time, very poor, and much depended on his situation with the millionaire, in charge of his several cars. But Ed Dayton, who considered that Nat had superseded him in the place, made trouble for him. Aided by Donald Pomery, the lumber king’s son, a weak, unprincipled youth, he hatched up a plot, which, for a time, put Nat under a cloud. But Mr. Pomery himself proved Nat’s firm friend.

Owing to Mrs. Pomery’s interference, the millionaire was compelled to discharge Nat, but he almost immediately re-employed him on the confidential mission of which we have spoken. This was to visit Lower California and investigate conditions on his timber claims there. Much rare and valuable wood had been going astray, and Mr. Pomery suspected his superintendent, Diego Velasco. He lacked proof, however, and Nat he selected as a bright, trustworthy lad, who could carry out an investigation painstakingly.

Nat recalled that his dead father had been interested, in his youth, in a rich mine in Lower California, and the prospect of the trip, therefore, had a double fascination for him. Mr. Pomery provided an automobile, equipped in elaborate fashion, for the long trip, much of which was to be made through desert country. With Mr. Pomery’s permission, Nat invited his two chums, Joe Hartley, son of a well-to-do department store keeper, and William Bell, the stammering lad, to accompany him. The latter’s mother and the former’s father at first demurred considerably to the trip, but at last they gave their consent. Nat, for his part, had some trouble winning his mother over. But soon all was arranged, and they set out. How they discovered the Lost Mine, and Nat became rich, was all told in that book, together with many other adventures that befell them. The reader is now in a position to understand our chief characters, sturdy, intelligent Nat Trevor, with his curly black hair and dancing blue eyes; stout, red-faced Joe Hartley, always good-natured, though inclined to be a bit nervous, and Ding-dong Bell, the cheery, stuttering lad, whose eccentricities of speech provided much amusement for his companions.

The day on which this story opens was the seventh since their departure from the Marquesas on their return voyage to the Pacific Coast. They had left behind them their fellow adventurers, some of whom wished to return by steamer, while others were anxious to continue their travels in the fascinating South Seas. So far, smiling skies and sunny seas had been encountered. But this particular day had dawned with a smoky, red horizon, through which the rising sun blazed like a red-hot copper ball.

It had been oppressively hot—torrid, in fact. But although the air was motionless and heavy, the sea was far from being calm. It heaved with a swell that tossed the Nomad almost on her beam-ends at times. That some peculiar kind of tropical storm, or typhoon, was approaching, Nat felt small doubt. A glance at the barometer showed that that instrument had fallen with incredible rapidity. A candle, held in the thick, murky air, would have flamed straight skyward without a flicker.

Dinner was eaten without a change being observable in the weather conditions, and, on coming on deck to relieve Joe at the wheel while he went below to eat, Nat sighted the bit of land toward which they were now being drawn like a needle to a lodestone. In the meantime the weather had been growing more and more extraordinary. The copperish sky had deepened in color till a panoply of angry purple overspread the heaving sea. The sun glared weakly through the cloud curtains as through a fog. But still there had come no wind.

Hardly had the two lads on the bridge of the Nomad realized that they were inexorably being drawn toward the two islands, however, when from far off to the southwest there came a low, moaning sound. It seemed almost animal in character; like the lowing of an angry bull, in fact, was the comparison that occurred to Nat. The sound increased in violence momentarily, while the sky from purple changed to black, and a blast like that from an open oven door fanned their faces. Through this awe-inspiring twilight the Nomad continued her inexplicable advance toward the two islands.

“Here it comes!” shouted Joe suddenly, as, from the same quarter as that from which the wind had proceeded, there came a sudden, angry roar.

“Hold tight for your life!” flung back Nat over his shoulder, gripping his steering wheel with every ounce of strength he possessed.

And thus began hours of stress and turmoil, which the Motor Rangers were ever to remember as one of the most soul-racking experiences of their young lives.

CHAPTER II.

Spray, flying like dust through the dense mid-afternoon twilight, stung his face. The wind whipped out his garments stiff, as if they had been made of metal, and half choked the words back down his throat.

Nat made no reply. He clung grimly to his wheel, striving with might and main to head the Nomad into the furious waves. Ding-dong Bell had emerged on deck an instant before, but had been promptly ordered below again.

“Keep your engines doused with oil; give them plenty of gasolene, and stand by for signals,” had been the young captain’s orders.

Below, beside his shining, laboring engines, Ding-dong was valorously striving to carry those orders out. But the strain on the motors was as great as they had ever been called upon to bear, even in the memorable encounter with the waterspouts.

Besides heading into the storm, Nat was “bucking” the strange current that set toward the island chasm. But powerfully as the Nomad’s propeller churned the driving seas, the unseen tide was more powerful still.

“Nat, we’re bound to be drawn into that gorge within a few minutes, unless——”

Joe’s comment and Nat’s rejoinder were both shouted above the storm. Their voices sounded feeble as whispers amid the fury of the conflicting elements.

Hardly a hundred yards now separated the storm-battered Nomad from the towering walls and boiling waters of the chasm. Inevitably, unless the miracle of which Nat had spoken occurred, they must, in a few moments, be laboring in the midst of that ominous-looking place. While the thought was still pulsating through their minds, and their hearts beat high with apprehension, the dreaded thing happened.

The Nomad was suddenly caught, as if by hands bent on causing her dissolution, and hurtled straight into the cleft between the islands. Nat, hardly conscious of what he was about, directed her course so that the craft was not instantaneously dashed to bits against the side of the cliffs. Joe, too alarmed to utter a word, simply clung tight to the rail. Below, in the engine-room, Ding-dong Bell was thrown from his feet and smashed up against a steel stanchion.

The blow knocked him senseless. And so, with her engineer unconscious, another member of her crew almost useless from fright, and only one guiding spirit on board her, the Nomad hastened forward into what seemed certain annihilation.

Within the cleft it was black as night. The angry seas that boiled and gnashed between the steep walls, for an instant completely hid the Nomad from view. But presently she gallantly emerged, fighting like a live thing for her life.

The wind, compressed within those narrow confines, blew with a force and fury almost incredible except to those who have passed through a South Pacific storm. It would have been impossible to cry out and make one’s voice heard. The most powerful shout would not have been audible a foot away. The situation of the Motor Rangers appeared to be almost desperate.

Such were the thoughts that galloped through Nat’s excited brain. He rang the electric signal for “more power,” but no response came from the engine-room, where Ding-dong lay senseless beside his motors.

Then he turned about to look for Joe. Now that his eyes had grown used to the darkness it was possible to see—as one sees on a night when the moon is obscured by heavy clouds. The young captain’s heart leaped into his mouth as his eyes pierced the obscurity.

A coil of light but strong rope was looped to the bridge in front of Nat. Without an instant’s hesitation, he tied one end of it about his waist. He had reached a desperate determination. If he got a chance, he had made up his mind to save Joe Hartley if it were humanly possible. The other end of the coil he knew was made fast to the bridge rail, so that a final testing of the knot about his waist was all that was necessary to put his daring scheme into execution. But first Nat fixed the wheel by means of the metal grips provided for that purpose.

Then, with every nerve a-quiver, every muscle flexed, he waited for another summons. Suddenly it came.

A smother of foam swept glimmering past the Nomad. It was luminous with phosphorescence. Amidst the greenish, ghastly glare, was plainly perceptible a darker spot. It was a human head.

“Hold on, Joe! I’ll be with you!” shouted Nat, and then, without hesitation, he mounted the bridge rail at the port side and plunged into the mass of spume.

Fortunately for those interested in the adventures of the Motor Rangers, at that instant a freak of the current spun Joe’s body about and flung him, like a bit of driftwood, toward the side of the Nomad. In a flash Nat’s strong arm was about him. It was just in time, too, for Joe, who had been swept from the bridge unseen when the Nomad encountered the angry maze of cross currents and tide rips, was almost exhausted.

In this condition he was not in full possession of his ordinary presence of mind. He clung to Nat desperately, with a grip that threatened to pull both rescuer and rescued under water together.

Nat, battling with the sharp, angry waves, as choppy and angular as giant fangs, had all he could do without struggling with Joe. Again and again he tried to break the other’s grip, but without avail. The hold of a drowning man or boy is the most tenacious known. It is almost impossible to loosen it.

But Joe only clung in a more leech-like fashion. What with the other lad’s dead weight clinging to him, and the conditions against which he was laboring, Nat, strong as he was, felt his strength being rapidly sapped.

Luckily, so intense had been the heat, the lads wore only light tropical trousers and sleeveless undershirts. Had they been incumbered with ordinary clothes, they could not have survived a quarter of the time that Nat and Joe did.

Nat began hauling in on his line, but with Joe gripping him so tightly, it was too much of a task.

“Joe, I hate to do it,” he said at length, “but I must, old fellow, I must!”

With these words, Nat did what he would have done with anybody else when first he realized the conditions. He struck Joe a blow on the head that completely robbed him of his senses. The lad’s vise-like grip relaxed. Under these circumstances, Nat could handle him easily.

By strong, rapid, over-hand motions, he hauled himself and his burden closer and closer to the side of the Nomad. At last they reached it. And now came the most difficult part of Nat’s enterprise. He had to get back on board, and, more than that, to get Joe there, too.

The Nomad was rolling and plunging till she was almost rail under at every roll. A sudden lurch of extra violence gave Nat his opportunity. It brought the bridge rail within reach of his free hand. He grasped it with a tenacious grip. But the next instant he was almost flung back into the sea again, as the little craft righted, and the lad, with his unconscious burden, was carried high above the boiling waters.

But Nat’s muscles had been trained to nickel steel suppleness and strength. He managed to hold on somehow, and the next roll to port of the Nomad gave him an opportunity to get one foot on the edge of the bridge. Thus he clung till the next wild roll in the opposite direction was over.

Then exerting a reserve force he had never before had occasion to bring into play, the young captain drew up Joe’s limp form and bundled it bodily within the bridge railings. This done, he clambered over himself. But he felt queer and dizzy. He could hardly keep his feet, even though he hung on to the rail. His head spun like a teetotum.

Nat did not conclude his sentence in words. Instead, he enacted it by giving a crazy plunge backward and collapsing in a heap, almost alongside the unconscious Joe.

CHAPTER III.

Nat sat upright with a strange singing sound in his ears. It was insufferably hot. He fairly panted as he opened his eyes. The sweat ran off him in rivulets. For an instant recollection paused, and then rushed back in an overwhelming flood.

“We were in that channel between those two queer islands,” mused Nat; “and we—gracious, where are the islands?”

He had staggered dizzily to his feet and was looking about him. He knew he could not have lain senseless very long, for his garments were still wet, despite the intense heat. But the islands were nowhere to be seen.

It was still partially dark, a murky twilight replacing the former deeper blackness. But an indefinable change had taken place, somehow, in the atmosphere. Nat drew in his breath with difficulty. It seemed to scorch his lungs.

He glanced over the side of the craft and then drew back with an alarmed cry. The water all about them was bubbling and eddying furiously. A shower of spray from one of the miniature waterspouts struck Nat in the face. It was this that caused his exclamation and made him step back hastily, just as if, in fact, he had been struck a blow in the face.

“Well, we certainly have landed in a surprising sort of fix this time,” muttered Nat to himself.

He bent over Joe. The lad had not yet regained his senses. But he was breathing heavily, and this stilled a dreaded fear, which, for a moment had almost caused Nat’s heart to stop beating.

“This air is suffocating,” gasped Nat presently. “It smells like it does when they are fumigating a room.”

He ran his tongue around his dry mouth in an effort to moisten it, for it felt parched and cracked. The reek of sulphur in the air, too, caused his throat to contract and his nose and eyes to tingle unmercifully.

But this stench also told Nat something. It furnished him with a partial explanation of the extraordinary occurrences that, as it seemed, were not yet over.

“This whole disturbance is volcanic,” reasoned the boy. “That is the cause of this awful sulphur smell. But that doesn’t account altogether for the sudden disappearance of those islands. I wonder——” But here he broke off his meditations.

Joe was plainly in need of immediate attention, and Nat devoted his efforts to trying to raise the recumbent lad. He wanted to get him below to the cabin, where there was a well-stocked medicine chest and a supply of reasonably cool water.

“What’s the matter with me, anyhow?” he asked himself half angrily. “This sulphur stuff must have knocked all my senses out of my head. Where’s Ding-dong, I wonder?”

He rang the engine-room call sharply. But there was no response. No Ding-dong appeared.

“Maybe the signal is out of whack,” muttered Nat, who had noticed some time before that the engine had stopped running. “Guess I’ll go below and see what’s the matter.”

It was the work of an instant to reach the hatchway leading below, and dive into the engine room. What met Nat’s eyes there made him jump almost as violently as he had when the boiling water struck him.

“Great Scott!” he exclaimed, as his gaze fell on the unconscious engineer, “if this isn’t worse and more of it. Poor Ding-dong is knocked out, too; cut on the head. It doesn’t seem to be a bad gash, but it has deprived him of his senses. Well, if this isn’t a fine kettle of fish! In the midst of a boiling sea with two unconscious chaps on my hands!”

On the wall of the engine room was a tap leading from the drinking water tanks of the craft. Nat saturated his handkerchief under this faucet and bathed Ding-dong’s wound. Then he applied the water plentifully to the lad’s face, and, opening his shirt, doused him with it.

“Hullo, Nat!” he exclaimed, like one awakening from a long sleep. “What’s up? What on earth has happened? Where are we? What makes it so hot?”

As usual, under strong excitement, Ding-dong forgot to stutter, as Joe termed it.

“I can only answer two of your questions,” replied Nat. “‘What’s up’ is that poor Joe is lying senseless on the bridge. He was washed overboard in that chasm. You’ve got to try to help me get him to the cabin. ‘What on earth has happened,’ is this: We have, apparently, passed through the chasm, and the islands have vanished in some mysterious fashion, although we can’t be far from where they were. The sea all about us is boiling hot, and I guess we are in the very core of some strange volcanic disturbance or other.”

“Cc-c-c-crickets!” sputtered Ding-dong, rising dizzily but pluckily to his feet, “we do seem to run into some mighty queer adventures, don’t we? Come on. I’ll give you a hand with poor old Joe. But, by the way, what have you been doing all this time?”

“Oh, I-I-guess I went to sleep for a while, too,” responded Nat, rather confusedly, and without mentioning his heroic rescue of Joe from the waters of the rift.

He was spared answering further questions, for it required their united strength to carry Joe to the cabin. Ordinarily, this would not have been so, but the heat was so terrific that it had sapped the strength of both boys till they had but half of their accustomed energy and vim.

Joe was laid on a locker and restoratives applied. Presently he was able to sit up, and then out came the story of Nat’s rescue. The lad colored brilliantly as Joe and Ding-dong both poured out their praise unstintedly.

“But, say,” exclaimed Joe, rubbing his head and looking suddenly bewildered, “I’ve got an awful bump here. I guess I must have hit my head before your brave——”

“I hit it for you to keep you quiet,” burst out Nat; “and if you don’t shut up now, I’ll bust it again.”

Going on deck, the three lads found that it had grown lighter. But the water still boiled about them furiously. Clouds of sulphurous steam arose from it, making them cough and choke.

In the brighter light they had quite an extensive view of their surroundings. But, of the islands, not a trace appeared. They had vanished as if they had been the fabric of a dream.

“By George! I have it!” cried Joe suddenly. “Those islands were of volcanic origin. Didn’t you notice how bare and bleak they were? I’ll bet that in this disturbance, whatever it is, they have subsided as suddenly as they arose.”

“Such cases are not uncommon,” rejoined Nat. “Only last year, Captain Rose, of the missionary schooner Galilee, of San Francisco, reported seeing an island of some extent arise and then vanish again before his very eyes.”

“W-w-w-well,” sputtered Ding-dong, with a grin and a return to his old manner, “w-w-w-we can r-r-r-report the same thing; but as t-t-this isn’t a go-go-gospel schooner maybe nobody w-w-w-will believe us.”

“My suggestion is, that we get the engines going and get out of this without delay,” said Nat.

“Here, too,” agreed Joe Hartley. “There’s nothing to hang about here for.”

An examination of the engines showed that, in falling, Ding-dong had shut off the gasolene supply valve, and had thus stopped the motors. This was soon remedied and the motors set going again. As the Nomad cut her way through the boiling sea where lately the twin islands had stood, they all felt like raising a fervent prayer of thanks to Providence for their wonderful deliverance.

“I’ve often heard of such things on the Pacific, but I never expected to live through one,” was Nat’s comment.

“Nor I,” was Joe’s rejoinder; “and I don’t know that I should care to repeat the experience. But hullo!” he broke off suddenly, “what’s that? No, not over there; off this way!”

He pointed excitedly to a small black object, which, in the now clear atmosphere, was visible at the distance of about a mile to the southeast of them.

“It’s a boat,” announced Nat, after a brief scrutiny of the strange object.

CHAPTER IV.

“So it is. What on earth can it be doing out here? Wait a jiffy, I’ll go below and get the glasses.”

Joe, now fully recovered, dived into the after cabin and soon reappeared with a pair of powerful binoculars.

Nat focused them on the distant object, which, by this time, was visible, even to the naked eye, and reported it to be a small boat, painted white, and looking like a ship’s dinghy, or small lifeboat.

Excitement ran high on board the Nomad when Nat proclaimed that he was almost certain he had seen an arm wave from the small craft.

“I couldn’t be quite sure, though,” he admitted. “Here, Joe, you take a look.”

“By ginger, Nat, you’re right!” he exclaimed. “There is someone on board. There must be something the matter with them, though, for they seem to be collapsed in a kind of bundle on the thwarts.”

“We must make all speed to their aid,” said Nat, signaling for more power. “Poor fellows, if they have been adrift in all that flare-up, they must be about dead.”

As they neared the boat, Nat began blowing long blasts on the electric whistle, to let the occupants know that aid was at hand. In response, a figure upreared itself in the drifting craft, waved feebly once or twice, and then subsided in a limp-looking heap.

“I reckon we’re only just about in time,” said Nat grimly, coaxing another knot out of the Nomad.

As they drew alongside the boat, they saw that not one but two persons occupied it. The one who had signaled them from a distance proved to be a short, stocky little man, with a crop of brilliant red hair and a pair of twinkling blue eyes. The merry flash in those optics had not been dulled, even by the terrible ordeal through which, it was apparent, he and his companion had passed.

“Hullo, shipmates! Glad to see you!” he chirruped, grinning up at the boys on the bridge with a look of intense good humor.

His white duck clothes were scorched, and his rubicund hair, on close inspection, proved to be singed, but nothing appeared capable of downing his amiability.

His companion was of a different character entirely. He was dressed in duck trousers and black alpaca coat. White canvas shoes adorned his extremely large feet. But it was his face that attracted the boys’ attention. It was large, round and learned looking, with a thin-lipped mouth cutting the lower part of it like a gash. Above this, a huge, bony nose protruded, across which was perched a pair of big, horn-rimmed spectacles. A crop of sparse gray locks crowned his high forehead and was scattered sparingly over his large, but well-shaped head, which was bare.

“God bless my soul, George Washington Tubbs, but I’ve lost my hat again!” he exclaimed to his companion, as the Nomad drew alongside.

“We’d have lost more than that, I fancy, if it hadn’t been for this here craft,” observed George Washington Tubbs, with a wink at the boys. “We’d have been a pair of buckwheat cakes, well browned, professor, when they found us.”

“I wish I could find my hat,” muttered the spectacled individual in a contemplative tone, peering about under the seats.

“It was blown off when the island busted up,” rejoined Mr. Tubbs. “But we’re keeping these gentlemen waiting. I presume,” he went on, addressing the boys, “that it is your intention to rescue us?”

Nat could hardly keep from laughing. His first impression was that they had encountered a pair of harmless lunatics. But something in the manner of both men precluded this idea almost as soon as it was formed.

It seemed as inadequate a remark as Stanley’s famous one to Livingston in the wilds of Africa; but, for the life of him, Nat couldn’t have found other words.

“Thanks; yes, we will,” responded Mr. Tubbs, with decisive briskness. “Oh, by the way! Don’t move! Don’t stir! Just as you are, till I tell you!”

Mr. Tubbs bent swiftly, and picked up what looked like a large camera from the bottom of the boat. Only it was unlike any camera the boys had ever seen. It was a varnished wooden box, with a big handle at the side. Mr. Tubbs gravely set it up on its tripod and began turning the handle rapidly.

“Now, you can move about! Let’s get action now!” he shouted, waving his free hand.

“This will be a dandy film!” he continued, addressing the world at large. “Gallant rescue of Professor Thaddeus Grigg and an obscure individual named Tubbs, following the disappearance of the volcanic isles.”

In good-natured acquiescence to Mr. Tubbs’ orders, the boys began bustling about. Ding-dong Bell, who had come on deck when he got the signal to stop his engines, was particularly active.

“Without my hat?” moaned the professor; but he nevertheless clambered over the side of the Nomad, the boys helping him, while Mr. Tubbs kept up a running fire of directions.

“Keep in the picture, please. Look around now, professor. Fine! Good! Great!”

These last exclamations came like a series of pistol shots, and seemingly proclaimed that the speaker was well satisfied with the pictures he had made. The professor being on board, Mr. Tubbs followed him, the boys helping him up with his machine, and with a box which, so he informed them, contained extra films.

Professor Grigg, as the red-headed, moving-picture man had called him, was too much exhausted to remain on deck, but retired to the cabin escorted by Ding-dong. As he went he was still murmuring lamentations over his hat.

“It’s his weakness,” explained Mr. Tubbs, who seemed to be in no wise the worse for his experience, “he’s lost ten hats since we left ’Frisco in the Tropic Bird.”

The name instantly recalled to Nat an item he had read in the papers some months before, concerning the setting forth on a mysterious expedition of Professor Grigg of the Smithsonian Institute and one George Washington Tubbs, a moving-picture photographer of some fame. The object of the expedition had been kept a secret, and the newspapermen could elicit no information concerning it. It had been rumored, however, that its purpose was to record the volcanic phenomena of the South Pacific.

“Is—is that the Professor Grigg?” asked Nat, in rather an awestruck tone.

“It is,” responded Mr. Tubbs, “and this is the Mr. Tubbs. I’ve taken moving pictures of the Russo-Japanese war, of the coronation, of the Delhi Durbar, of the fleet on battle practice, of—of everything, in fact. I’ve been up in balloons, down in submarines, sat on the cowcatchers of locomotives, in the seats of racing automobiles, hung by my eyebrows from the steel work of new skyscrapers; but I’ll be jiggered if this isn’t the first time I ever took a moving picture of an island being swallowed up alive—oh, just like you’d swallow an oyster.”

“Swallowed? I should say so. And with a dose of boiling water, too. But I got my pictures! I got my pictures!” concluded Mr. Tubbs triumphantly.

“But where’s your schooner? How did you come to be drifting about in an open boat?” inquired Nat.

“Ah, as Mr. Kipling says, ‘that’s another story,’” said Mr. Tubbs. “I guess I’ll have to leave that part of it to the professor. But—hullo, here he comes now. I guess he’s feeling better already. Possibly he’ll tell you the story for himself.”

“I shall be very glad to,” said the professor, who, after partaking of some stimulants from the Nomad’s medicine chest, already felt, as he said, “much revived.”

“You see in us, young men,” he continued, “the sole members of the volcanic phenomena expedition of the Smithsonian Institute and the British Royal Geographical Society, who adhered to the duty before them. Would you care to hear how we came to be adrift as you found us?”

“Then I——” began the professor, and then broke off and felt his bare head. “Can—can any one lend me a hat?” he asked.

CHAPTER V.

He was speedily furnished with a peaked yachting cap belonging to Nat. It sat oddly, almost comically, on his large head, but none of the boys was inclined to laugh at the professor just then. They were far too interested in hearing what the eccentric man had to tell about the voyage of the Tropic Bird.

“We sailed from San Francisco, as you no doubt know from the papers,” said the professor, “without the object of our mission being divulged. There is no harm in telling it now.

“It had been ascertained that a certain phase of the sun spots would be reached on this present day. As you are perhaps aware, it has long been a theory of scientific men that there was some intimate relation between that phenomenon and the volcanic disturbances and earthquakes that occur in these seas from time to time.”

“I think that we learned something like that in physics,” said Nat, nodding.

“It was my duty, assigned to me by the Smithsonian Institute and the British Royal Geographical Society, working in concert, to investigate such a disturbance and make elaborate reports thereon. At my suggestion, it was also decided to engage a moving-picture operator to take photos of the whole scene, which must prove of inestimable benefit to scientific knowledge. The Tropic Bird was chartered to convey the expedition, and Mr. Tubbs was placed under contract to take the pictorial record of the scene, if we were fortunate enough to encounter one.

“We cruised about for some time, awaiting the exact condition of the sun spots which would indicate that a phenomenon of the kind I was in search of was about to be demonstrated. Some days ago my observations showed me that the desired condition was at hand. As fortune would have it, on that very day we sighted these islands—or rather those islands, for they have completely vanished as I predicted they would.

“We landed, and found the islands to be of distinctly volcanic origin, and, seemingly, of recent formation. At any rate, they are not charted.”

“Of course there was no trace of habitation. But a few creepers and shrubs of rapid growth had taken root in the clefts of the lava-like rock, of which the islands were composed. I saw at once that it was here, if anywhere, that a seismic disturbance would result, in all probability, providing the conditions were favorable. That night, on our return to the ship, the captain of it waited on me.

“After much beating about the bush, he informed me that his crew was aware of my belief that the islands would be the center of a volcanic disturbance, and that they refused to remain in the vicinity. He denied being alarmed himself, however. I succeeded in calming the crew’s fears, and we remained at anchor off the islands for some days. At last, signs of the storm which broke to-day began to make themselves manifest on my instruments. I realized that the great moment was at hand.

“I warned Mr. Tubbs, here—a most valuable assistant—to be ready at any moment. I was confident that with the breaking of the storm the islands would vanish. But nothing was said to the crew. Quite early to-day Mr. Tubbs and I embarked in that small boat and lay off the islands. I was certain that the storm would be magnetic in character, and would break with great fury.”

“She is fitted with air chambers, and specially built to weather any storm,” was the reply. “But to resume: The cowardly captain, when he saw the storm coming up, sounded a signal for us to return on board. When we did not, he hoisted sail and made off, leaving us to our fate. The storm broke, and there was a spectacle of appalling magnificence. Mr. Tubbs behaved with the greatest heroism throughout.”

“I guess it was watching you kept me from feeling scared,” he declared, addressing the professor; “but anyhow, I got my pictures.”

“We have some faint idea of what the storm was,” put in Nat; “but can you explain something to us?” and he described to the professor the manner in which the Nomad had been drawn toward the volcanic islands.

“Pure magnetism,” declared the scientist, “a common feature of such storms.”

“Yes, but your engines, being metallic, of course, overcame that resistance. You are fortunate, indeed, not to have been drawn down when the islands vanished. It was a terrific sight.”

Nat explained that during that period they were all unconscious and then went on to tell of the experiences through which they had passed.

“Oh, why wasn’t I on board your craft?” moaned Mr. Tubbs, as he concluded. “What a picture that chasm would have made! It’s the opportunity of a lifetime gone.”

The boys could hardly keep from smiling over his enthusiasm; but Nat struck in with:

“It’s an opportunity I don’t want to encounter again,” an opinion with which everybody but Mr. Tubbs—even the professor—concurred.

“And now,” said the man of science suddenly, “I don’t wish to alarm you, young men, but it is possible that there may be some reflex action exerted by this storm. In other words, there may be a mild recurrence of it. In my opinion we had better get as far away from this spot as possible.”

The others agreed with him. Ding-dong dived below to his engines. Nat took his station on the bridge.

“By the way, what about the boat?” asked Nat suddenly, referring to the craft from which they had rescued the scientist and his assistant.

“Unless you want it, we will let it drift,” said the professor. “It is too large for you to hoist conveniently, and it would impede your speed if you towed it.”

And so it was arranged to leave the boat behind, but Mr. Tubbs took a series of pictures of it as the Nomad sped away. The professor also waved the craft, in which they had weathered so much, a farewell. But, when doing so, in some manner the peak of his borrowed cap slipped from between his fingers. The headpiece went whirling overboard, and fell into the sea with a splash.

“God bless my soul, I’ve lost my hat!” he exclaimed for the second time that day, as the catastrophe happened.

“He’ll use up every hat on board. You see if he don’t,” confided Mr. Tubbs to Nat, while the professor gazed fondly at the spot where the cap had vanished.

CHAPTER VI.

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.

“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.”

“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.”

“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.

“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.”

“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——”

“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.

“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.

“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.

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

CHAPTER VII.

“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.”

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

“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.”

“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.”

“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——”

“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.”

“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.”

“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?”

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.

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,” 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——”

“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.

“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.

CHAPTER VIII.

“Why! why, that’s the Tropic Bird!” exclaimed the scientist in astonishment, as they drew nearer rapidly to the vessel Nat’s keen eyes had espied.

“It is, indeed,” reiterated Mr. Tubbs, his red hair seeming to bristle. “Oh, the cowardly pack of rascals! I’d just like to run alongside and give them a bit of my mind.”

“They deserve it, certainly,” admitted the professor; “but I think we had better ignore them.”

But as they came close enough to the schooner to perceive her clearly, they saw that she carried her ensign reversed. This is a signal of distress which there is no ignoring at sea, and is the universal sign of imperative need on the part of the craft displaying it.

“We must see what they want,” declared Nat, setting his wheel over and changing the course of the Motor Rangers’ vessel.

The man who uttered the appeal was a powerfully built fellow, with a plentiful crop of black whiskers, which gave him a ferocious expression.

At the same instant, the skipper of the Tropic Bird appeared to recognize the professor.

“Why, surely that’s Professor Grigg?” he cried out, apparently in great astonishment.

“Yes, it is, you cowardly rascal,” burst out the professor, his anger overmastering his usually placid disposition. “What do you mean by deserting us in the manner you did? We might have perished if it had not been for these brave lads and their vessel.”

“Well, I’m sorry,” muttered the man, as the Motor Rangers’ vessel drew in close alongside, “but I couldn’t help myself.”

“Couldn’t help yourself?” echoed the scientist, still angry. “How was that, pray?”

“Why, I felt my schooner being drawn in toward the islands. If I hadn’t ‘cut stick’ when I did, we’d all have been lost, and I don’t see how that would have helped you.”

“You’ll have to ask ‘those kids,’ as you call them,” said the professor, with some disgust.

“How much do you want?” asked Nat, who felt less and less liking for the captain of the Tropic Bird.

“Oh, a few gallons will do. I know an island not more than a day’s sail from here, where I can refill my tanks.”

At this point, another man—a short, stout fellow, like the captain—came bustling up.

“Hullo, there, professor!” he hailed in an impudent voice. “So you came out all right, after all. Are you coming on board?”

“I am coming on board to get my things, Mr. Durkee,” was the response, “but I am not going to continue my voyage on the Tropic Bird.”

“Oh, come now,” he said, “let bygones be bygones. I should be in a fine fix if I sailed home without you.”

“You ought to have thought of that when you deserted us in that cowardly fashion during the magnetic storm,” rejoined the professor.

The deck of the Nomad was almost on a level with the top of the schooner’s bulwarks, so it was easy for the professor to step from one craft to the other. He now did so, disdaining the proffered aid of Captain Lawless and his mate.

Mr. Tubbs joined him, and the two went immediately into the after-cabin of the schooner, where they had lived while on board.

While they were collecting their belongings, Nat and Joe filled a twenty-gallon keg with drinking water, and it was hoisted to the schooner’s deck. It was really more than they could spare, but Nat was a generous lad, and figured that, if necessary, they could go on short allowance till the South American coast was reached.

During the time that the boys were about this work, Captain Lawless and his mate had been holding a consultation in the lee of the deckhouse, just aft of the foremast.

“It’s going to make lots of trouble for us if we arrive in America without the professor or that chap Tubbs,” said the mate. “Besides that, too, we’ll have lost our chance of sharing in that hunt for a lost city. There ought to be enough loot in that to make us both rich.”

“That’s so,” agreed the captain. “If what those papers of the professor’s say is right, that place must be paved with gold, and when it rains it must drop diamonds.”

“Pretty near,” grinned the mate, in appreciation of his superior officer’s humor. “I wish I’d had time to go over the papers more thoroughly before that kid’s craft overhauled us. That was a good guess of yours that they’d pick up the old gent and that chap Tubbs, and the reversed ensign was a good way to get ’em to come alongside.”

“Well, now that we’ve gone this far, we may as well take the next step,” observed the captain.

“And what’s that?” asked the mate, with a peculiar glint coming into his little rat-like eyes.

“Why, fix it so that it won’t be possible for old Grigg to make trouble for us in the States.”

“Simple enough. We can easily overpower those kids, and as for the professor and Tubbs, we’ll lock ’em in the cabin.”

“Say, cap, you are a schemer!” observed the mate, in rather sarcastic admiration, “and then I suppose we’ll sail for home and be arrested and imprisoned as pirates?”

“Not at all,” was the reply. “We don’t need to go home. South America’s good enough for me. It’s Chile that the old cove is headed for, ain’t it?”

“All right, then. We’ll make the whole bunch prisoners, land ’em on an island some place, and then we’ll sail on to Chile ourselves, and have a try at finding this old lost city. By the way, did you make a tracing of that map you found in the professor’s desk?”

“Did I? Well, I should say so. I’ve got it in my pocketbook now. That’s likely to mean dollars and cents to us later on.”

“That’s so. Now then, you go and tell the crew what we are going to do. They won’t cut up rough about it, especially if they think there is money in it.”

“All right. I’m off. But see here, how are you going to do it? Those kids look pretty husky.”

“Bah! What can they do against eight of us? If they get too obstreperous, a tap on the head with a marlin-spike will soon quiet them.”

While the two worthies of the schooner were cold-bloodedly discussing their plans to save themselves from the consequences of their cowardly act and at the same time enrich themselves, Nat and Joe, blissfully ignorant of any such proceedings, had hoisted the water keg on board.

This done, they started aft toward the cabin to join the professor and Mr. Tubbs. They found the two companions below, busily packing up their possessions. But at the instant they entered, the professor looked up from his desk, where he was sorting papers, with a troubled expression.

“Somebody has been tampering with my papers!” he exclaimed. “I had them arranged in a peculiar manner. And see, this lock has been forced. Oh, that rascal of a captain! If we were in a civilized port, I’d——”

The professor’s angry tirade was interrupted in a startling manner. The door at the head of the companionway stairs was slammed abruptly to.

Warned by some intuition which he could not have analyzed, Nat bounded to the stairway and strove to reopen the door. But it resisted his stoutest efforts.

CHAPTER IX.

The first effect of a sudden and utterly unexpected disaster is, usually, to produce incredulity in its victims. It was so in this case.

“Nonsense,” spoke the professor, more sharply than was his wont, “I guess, after all, I am mistaken; it must be an accident.”

“If so, it’s a remarkable one,” said Nat grimly. “The bolt has been slid into a hasp on the outside.”

“Woof!” ejaculated Mr. Tubbs. “Then we are in the position of the mouse that wandered into a nice snug trap.”

“That’s the way it looks to me,” was Nat’s rejoinder. “What do you make of it, Joe?”

The stout lad had, by this time, joined Nat on the stairway. But their combined efforts failed to budge the door.

“So did I. That means there is some one out there listening to see how we are taking it. Let’s give the door a good pounding. Maybe we can make them give some explanation.”

The idea was voted a good one. The two lads shook and banged on the door with all the vigor they possessed.

“Ain’t a bit of use your shaking that door. It’ll hold till we get good and ready to open it.”

“Now, perfusser, don’t get hot in the collar,” was the rough advice hurled back at him. “I knows what I’m doin’. You don’t think that I’m goin’ to stand trial before a maritime court just on your account, do you?”

“You precious rascal!” hailed Mr. Tubbs. “I’d like to have my hands on you for about five minutes.”

No rejoinder came this time. Evidently the skipper was not in a mood to bandy words. As a matter of fact, he was half beginning to regret his action in imprisoning the adventurers. To use the vernacular, he was rather apprehensive that he had “bitten off more than he could chew.”

It was fifteen minutes later, after an interval devoted to a discussion of their situation, that the professor spoke.

“Agreed,” struck in Mr. Tubbs, “but how in the name of the immortal Abe Lincoln are we going to do it?”

“I’ve got an idea,” said Nat suddenly. “See that old lounge in the corner there?”

“It’s old and rickety, but it’s made of stout timbers. What’s the matter with using that for a battering ram?”

“Excellent!” exclaimed the professor, catching his meaning. “But what are we going to do if we get out of here?”

“That’s a logical inquiry,” said Mr. Tubbs. “We haven’t got any weapons, and those rascals may be well armed. I know that the captain and the mate always carry revolvers. I’m not sure about the others, though.”

“Humph!” murmured Nat. “I hadn’t thought of that. Tell you what we can do, though. Let’s make a search of the cabin. Maybe we can find some pistols or other weapons in one of them.”

“A good idea,” agreed the professor; “we’ll start by examining the captain’s boudoir.”

They had hardly commenced their search of that worthy’s room, before a shout from Joe announced that he had made a discovery. It was nothing more nor less than a pistol in a case. On the wall, too, apparently as an ornament, hung an aged and rusty looking blunderbuss.

“Hurray!” cried Nat; “that’s something, anyhow. Professor, you take the pistol and I’ll——”

“If it’s all the same to you,” interrupted the man of science, “I had a good deal rather you boys took the weapons. I am short-sighted, and I know that my friend Tubbs is not over familiar with firearms——”

“Except in a shooting gallery at Coney Island,” put in Mr. Tubbs apologetically.

“Very well, sir,” said Nat. “Joe will take the blunderbuss and I’ll carry the pistol. Wonder if that old blunderbore is loaded, anyhow?”

“Look here, why wouldn’t it be a good idea to place the muzzle of this ferocious weapon to the door at the point where we think the lock is located? If it is loaded, it’s pretty sure to have enough slugs in it to carry away the lock, and the rest we’ll have to chance to luck.”

“That’s a good suggestion, too. At any rate, it won’t do any harm to try it. We can’t be worse off, unless that rascally captain makes us walk the plank or something, and he wouldn’t dare to do that, I guess.”

“Let’s see if there aren’t some more shooting-irons lying round loose,” suggested Mr. Tubbs; “seems to me that mate always had some in his room.”

But a visit to the mate’s room resulted in the discovery of nothing more formidable than a pair of ancient cutlasses, hung crosswise on the wall. The professor and Mr. Tubbs helped themselves to these, the latter flourishing his in a truly awe-inspiring manner.

“How do you like the weapon?” asked Nat, who, despite the seriousness of their position, could not forbear smiling at the moving-picture man’s antics.

“Man alive!” rejoined Mr. Tubbs, “I only wish that it was possible to get a moving picture of ourselves going into action.”

“Now then, Joe,” said Nat, when they had scoured the cabin unsuccessfully for any more weapons, “it’s time for you to try your stunt.”

Joe ascended the stairs and carefully placed the muzzle of the blunderbuss in position under the spot where he was certain the lock was situated.

But before Joe could press the bit of steel which he hoped would discharge the gun, there came a startling interruption.

“That’s the Nomad’s gun. They are attacking her and trying to make Ding-dong a prisoner!” cried Nat.

The rusty throat of the old blunderbuss roared, and Joe was knocked clean off his feet by the accompanying “kick.”

At the same instant the door was blown into fragments, and a stentorian voice could be heard roaring out:

“Reckon somebody was taking a siesta on that door and old Mister Blunderbuss disturbed him,” grinned Nat, as he caught Joe in his arms.

“Forward!” yelled Mr. Tubbs, brandishing his cutlass in the manner made familiar by the heroes of naval pictures of the olden time.

“Forward!” cried Nat, and, shoulder to shoulder, they plunged up the companionway, burst through the shattered doorway, and rushed pell-mell out upon the deck of the schooner.

CHAPTER X.

All this time Ding-dong Bell had been making history in a fashion all his own. The lad had been below, pottering about his beloved engines, at the time that the others had gone aboard the schooner, and consequently was quite unaware of what had occurred till he emerged on deck and found that the Motor Rangers’ craft was deserted.

“Guess they’ve gone aboard the schooner,” thought the lad, and was preparing to follow, when a sailor, stationed at the latter vessel’s main shrouds, to which the Motor Rangers’ boat was made fast, stopped him.

It was at this moment that Ding-dong’s sharp eyes noticed a little group, consisting of the captain, the mate, and several of the sailors, standing aft by the cabin companionway.

“I want to join my friends,” exclaimed Ding-dong, forgetting to stutter in his righteous indignation at the fellow’s tone and manner.

“Guess your friends ain’t receiving company, except by permission of Captain Lawless,” was the reply given, with an impudent grin.

As the man spoke, he made a motion as if to grab Ding-dong, who was standing with one leg on board the Nomad and the other on the schooner’s bulwarks.

But Ding-dong was quite as quick in his actions as were his two chums. Moreover, he was a muscular lad, and his thews and sinews had been toughened to a steel-like fineness by his many adventures.

Consequently, as the sailor rushed at him, the lad merely caught the man’s outstretched arm, and, by a trick that he had learned from Nat, gave it a sudden twist.

“Ouch!” grunted the fellow, and, without making any more fuss, he writhed almost double and fell in a heap. But as he did so, Captain Lawless spied what was going forward. In the haste with which the plans to capture the Motor Rangers and their friends had been made, the fact of Ding-dong Bell’s existence had been temporarily forgotten by the rascally skipper and his mate. This sudden appearance, then, of one of the Motor Rangers, alive and intensely active, was very disconcerting to them.

“Confound you, boy; where did you spring from?” roared Lawless, as he dashed at Ding-dong like an angry bull.

“Fer-fer-f-from under a go-go-gooseberry bush,” sputtered Ding-dong, giving an agile backward jump, which brought him upon the deck of the Motor Rangers’ vessel.

At the same instant came a thunderous sound from the cabin door beneath, which, as we know, the imprisoned party were pounding and rapping.

The sound told Ding-dong the whole story as plainly as if it had been put into words.

“Never you mind. Just throw up your hands and come on board this schooner or it will be the worse for you.”

“No, thank you,” parried Ding-dong, his speech quite distinct in his indignation and excitement, “I guess I know when I’m well off.”

“You brat, I don’t propose to be thwarted by such a whipper-snapper as you. Come on board at once, I say!”

As he spoke, the lad rapidly made his way forward over the turtle back of the Nomad.

A sudden idea had come to him. On this turtle back was situated the rapid-firing gun which was a part of the craft’s equipment. Joe had been polishing it that morning, the cover was off and it looked ready for instant action.

With cat-like activity and swiftness, Ding-dong made for the implement of destruction. Reaching it, he took his stand on the small platform on which it stood.

Before the astonished Captain Lawless could scramble after the lad, Ding-dong had swung the gun on its swivel, and the captain found himself gazing straight into its formidable looking muzzle.

Ding-dong had his hand on the firing lever, and the rascally skipper went white as ashes as for an instant he thought the lad was going to discharge it.

Just then he noticed that several of the crew of the schooner were about to follow their captain on board.

“You fellows, too,” ordered the boy in a sharp, shrill voice, which nevertheless rang with determination.

“I’m ver-ver-very nervous,” he went on, “and at any mum-mum-moment I’m likely to give this lever a twist.”

“I’ll get even with you for this, my hearty,” muttered the nonplussed Captain Lawless, but nevertheless he scrambled back after his crew as Ding-dong gave his crisp command.

“Now, then,” cried the boy in a determined tone, “you let my friends out of that cabin, or I’ll have to indulge in some target practice with your schooner as the bull’s-eye.”

The lad depressed the breech of the gun and gave the lever a twist. Instantly a sputter of bullets flew forth. They lodged in the schooner’s spars and rigging, sending a shower of splinters all about.

At the same instant, the roar of the blunderbuss sounded from the cabin, and a fat sailor, who had been sitting on the door, bounded into the air. He was not hurt, but imagined that a mine had exploded beneath him.

As the adventurers rushed out of the cabin, they came face to face with a scene in which Ding-dong Bell was the dominating factor. The moral effect of the machine gun’s discharge had been tremendous. Palefaced and demoralized, Captain Lawless and his crew fled forward, where they huddled in a mass like so many frightened sheep.

“Say, professor!” hailed Lawless, “call that young gad-fly off. He’s done a hundred dollars’ worth of harm to my ship already. Call him off, do you hear?”

“It would serve you right if your schooner was sunk,” retorted the professor. “What did you mean by imprisoning us in that cabin?”

“It was just a joke,” pleaded Lawless, whose face was pallid. He paid no attention to the promptings of his mate, who was urging him, in an undertone, to “stand up to the lubbers.”

“We’ll give in, professor,” he went on in a shaky tone. “You’re welcome to take all your baggage and go, without us making any more trouble.

“Tell you what,” spoke Nat; “let’s make him lock all his sailors up in the forecastle. We can guard them, and then, in case of treachery, we’ll only have two to deal with.”

The professor delivered this ultimatum. Captain Lawless readily agreed to comply with it. The crew, sullen and muttering, was ordered below, and the forecastle hatch battened down. Joe was set to guard it, while the others helped in the work of transporting the baggage on board the Motor Rangers’ craft.

Of course Ding-dong Bell, who had really displayed the qualities of a capable general, came in for much warm congratulation. He took his honors modestly.

“I dud-dud-didn’t know it was lur-lur-loaded,” he protested, and, as a matter of fact, the lad had been as much astonished as any one at the tremendous fusillade that followed his manipulation of the machine-gun’s firing lever.

At length all the baggage was on board. During its transportation, Captain Lawless and his mate had looked sullenly on, but offered no aid or interference. They were beaten men, and they knew it. Once the professor’s report of their conduct was circulated, there was not a civilized port into which they could take the schooner without being arrested and brought to book for their misdeeds.

But they watched the Motor Rangers board their own craft and cast off the lines without show of any emotion on their stolid countenances.

“You can release your crew now,” said Nat, when Joe had clambered on board. As he spoke he rang the bell for the “Go ahead.”

The Nomad began to forge through the water. By the time Captain Lawless had reassembled his crew, the schooner was not more than a speck to those on the Nomad.

“Well, that was a queer adventure,” said Nat, as they talked it over that evening. “What a foolish man that skipper was to ruin his career for the sake of spite!”

“Yes, he will be a marked man now,” spoke the professor. “In these days of wireless telegraphy and other improved means of communication, there is not a spot in the Seven Seas where he can hide his head without being overtaken by the consequences of his folly and cowardice. I think he was led into this thing by that mate of his, Durkee. He is a very bad man.”

“Well, I guess they won’t bother us any more,” struck in Joe; “in fact, my thoughts from now on are centered on the lost city and that cloud cruiser of yours, professor.”

“I reckon you folks have forgotten something,” he said. “That chap Lawless has overhauled the professor’s papers. Don’t you think it’s likely he may try to locate the lost city, too? It’s a stake worth playing for.”

CHAPTER XI.

It was Mate Durkee, of the Tropic Bird, who asked the question of Captain Lawless, as the two stood leaning on the schooner’s rail, watching the fast-diminishing form of the Motor Rangers’ capable craft.

The wind had fallen, and the schooner was dipping and rolling on the swells, with her canvas flapping idly. The crew, grouped in a mass forward, were watching their superior officers with some curiosity. Plainly they were anxious to see how the situation was to be met.

“I’ve got a plan, but it involves a good deal of risk,” was the reply. “Are you willing to take a chance?”

“I’m willing to do almost anything to get even on that outfit,” was the response, in a vicious tone.

“Then listen to me. I happen to know that we are not far from an island where I’m pretty sure we can sell the schooner to the old chief for a good price. When that is done, we can get a canoe from him and have some of his men paddle us out into the track of that line of Dutch steamers that run from Manila to Callao. If we spin a good enough yarn, we can get passage all right.”

“Why, can’t you see? We’ll get from Callao to that Chilean port for which that outfit is bound in very little time. Once there, we can use our own judgment as to how to proceed. But I must admit, that I, for one, mean to get a chance at the treasures of the lost city.”

“Suppose we did make that island you are talking of,” said Captain Lawless, in tones that showed that the mate’s plan had made a deep impression on him, “how soon would that Dutch steamer be going by?”

“I used to run on the line, so I know their schedule pretty well,” he said. “She should be going by by to-morrow night, at latest.”

“Humph! But you don’t seem to have taken the crew into consideration. What are we going to do with them?”

“Oh, give them some sort of song and dance and abandon them. They can live very well on the island till some vessel takes them off.”

This cold-blooded proposal seemed to banish Captain Lawless’ last lingering trace of hesitation.

“It’s a good plan,” he said, “but a daring one. Suppose it ever leaks out how we sold the schooner? There’ll be a clear case of barratry against us.”

“So far as that is concerned,” urged Durkee, “we can’t be much worse off than we are now, can we? That professor means to make things hot for us in the States. I saw that in his eye. We must take refuge somewhere, and Chile looks about as good to me as any place I can think of right now.”

“I don’t know but what you’re right,” agreed Lawless. “Let’s go below and look at the chart. How long ought it to be before we reach this island, if we get a good breeze?”

“Not more than eight hours. If the wind picks up, we should make a landfall before midnight.”

Some two hours later a spanking breeze arose out of the northwest. The schooner’s sails bellied to it, and a spirit of joy was abroad among the crew. Their officers had promised them a quick run to a fine island, and then unlimited shore leave. Little dreaming of the trap that was being laid for them, the crew went about their tasks of trimming sails with songs and glad shouts.

When twilight fell the schooner was bowling along at a twelve-knot gait, bound for the island of which Mate Durkee had spoken. It was known to him as Brigantine Island, although the charts called it Cook’s Land.

As the mate had foretold, it was not long after midnight when a cry of “Land ho!” rang out from the forward lookout. It was bright moonlight, and in the silvery radiance those on board the schooner had no difficulty in making out a long, low elbow of land right ahead. Close at hand they could hear the thunder of the surf as it broke on the reef.

“I could run it blindfold,” was the response. “Close haul on those head-sheets!” he called out. “Lively, now! Bring her about! That’s the way! Here, I’ll take the wheel myself!” he cried the next instant, springing to the helm.

Under his skillful guidance, for there was no denying that the rascal was an able seaman, the Tropic Bird was swung through the narrow passage-way in the reef, and shot into the calm waters of the lagoon beyond.

“Don’t seem to be much life ashore,” said Captain Lawless, scanning the moonlit island.

“Fire a rocket, and you’ll see the dingoes come running out of their holes,” laughed the mate.

As it burst in a cloud of blue flame, and the “bang” which accompanied its bursting resounded loudly, lights began to flash on shore, and they could see scores of dark figures scuttling about the white beach.

“What did I tell you?” said the mate, with a grin. “We’ll get a great reception, all right.”

“They don’t happen to be cannibals, do they?” inquired Captain Lawless timidly, his habitual caution asserting itself.

“What a one you are to get scared, Lawless!” he said. “Your name don’t fit you a bit. Cannibals, is it? I should say not. Those chaps are mission natives—some of them—and as smart a bunch as you’d want to see.”

As there was no time to be lost, if they wished to carry out their audacious plan, the captain ordered a boat lowered and he and his mate went ashore immediately. The chief was soon found. In fact, he was down on the beach. He recognized Durkee, who seemed to have some sort of a hold over him, and negotiations for the sale of the schooner were at once begun. Like most dealings with savage folk, it required a lot of diplomacy to accomplish the desired end. The trading was carried on under a palm-thatched roof, while natives with torches stood all about.

If the two white men had not been so engrossed with their own affairs, they might have been inclined to admire the savage picturesqueness of the scene. But, as it was, they devoted their attention strictly to business.

The chief, who rejoiced in the name of Billy Bowlegs—an appellation of which he seemed quite proud—proved an adroit old bargainer. He spoke English well, and was to the full as shrewd as any Caucasian trader.

But at last they managed to “make a deal,” as the saying is. Billy Bowlegs was in need of a good schooner, and had long coveted the Tropic Bird, which was well known in those waters before Captain Lawless acquired her. The chief was willing to give three hundred dollars in cash and two valuable pearls, worth fully the same amount each, for the craft.

As this was the best they could do, the two rascally white men agreed on this figure, and Billy Bowlegs agreed to give them transportation in a war canoe as far as the path of the Dutch liners, which passed to seaward of the island by fifty miles or so.

The crew, carousing and enjoying themselves in their own rough fashion, knew nothing of the departure of their captain and mate that morning, nor did those two worthies wish that they should. By the time the abandoned men awoke to the true state of affairs, Lawless and Durkee were on board the Dutch steamer Prinz Joachim of the Imperial Peru and Manila Line, bound for Callao. They were regarded with much interest on board the craft as two luckless mariners—rough but honest—who had lost their vessel in the great magnetic storm.

And so, while the Motor Rangers were gleefully heading for the land of the lost city, their two malignant foes were likewise speeding toward South America on a fast, well-equipped vessel.

CHAPTER XII.

The professor put the question, as he stood beside the young leader of the Motor Rangers on the bridge of the Nomad.

“I’ve noticed a sort of purplish mass, like a low-lying reach of clouds, in the distance for some time,” was the rejoinder. “Do you think that it can be the coast of Chile?”

“I think it is highly probable; we should be picking up the land by this time. I think—heaven bless us!”

The professor clutched wildly at his head. But he was too late. His latest “top-piece,” a cap that had belonged to Ding-dong Bell, was whirled from his head into the sea.

“It’s an extraordinary thing,” he said with a kind of patient resignation. “But I don’t seem able to keep a hat on my head at all.”

“So I’ve noticed,” rejoined Nat, with a sort of dry humor, “and that’s the last spare one on board. You’ve had six since we left the volcanic islands, and there are no others left.”

“Well, I suppose I must go bareheaded, then, till we reach land. It is most annoying, though, really. I cannot account for it.”

Nat had a hard task to keep from laughing, but he managed to maintain a straight face by dint of heroic resolution. Moreover, as the bridge was protected by awnings of red and white striped material, he did not fear that the man of science would suffer greatly from the sun.

It speedily became evident that what Nat had seen was indeed the coast of Chile. By late afternoon they could make out the great mountain masses which hang above the rather low lying coast.

“Gives one a kind of a thrill to think that if all goes well we’ll be flying over those before long,” remarked Joe Hartley, as they all stood grouped on the bridge, watching the distant land with interest.

It was three weeks since they had parted company with the schooner, and the Nomad had been somewhat delayed by bad weather. But, all things considered, she had made a good run and all on board were in high good humor as they foresaw the end of the voyage.

By nightfall they were entering a landlocked bay that forms the harbor of Santa Rosa. It seemed to be a tiny place, as well as they could judge. Above the huddle of houses there rose the inevitable twin towers of the cathedral, however, and through the glasses they could make out, with a thrill, that Old Glory was flying over one of the buildings, no doubt the American consulate.

“I tell you, that old flag never looks so good as when you see it flying in a foreign port,” observed Mr. Tubbs, a sentiment which they all echoed.

As soon as they had anchored, their craft was surrounded by a fleet of boats from the shore. It was dark, and in the blackness the tiny lights carried by the swarming craft made them resemble a fleet of fire-flies, as Nat poetically remarked.

“I am going to take a boat ashore,” said Professor Grigg, as soon as everything had been made snug. “As we wish to start on the expedition as soon as possible it is important that I should see Mr. Stowe, the American consular agent, without delay. I am anxious, too, to know if the sections of the dirigible arrived in good shape.”

“Why, bless my soul, I hadn’t thought of that,” remarked the man of science, “she ought to have one, too. What would you suggest?”

In the scuffle that ensued, the lively young engineer of the Nomad was almost toppled overboard.

When quiet was restored, the professor said that he thought that Discoverer was a very good name. And so it was decided upon.

“If I like,” echoed that lad; “of course I’d be delighted to,” he added.

Accordingly, a few minutes later they set out in one of the shore boats for the city, leaving behind them two youths with rather long faces. Ding-dong and Joe would have dearly loved to share in the expedition, but their presence on board was necessary, as the Nomad, after her long, rough cruise, was badly in need of a “general housecleaning.”

“I guess the consul will be astonished when he learns of the manner in which I have traveled here,” remarked the professor; “naturally he was expecting me on the schooner.”

“Speaking of the schooner,” said Nat as the native rowers propelled the long, narrow boat swiftly through the water, “you don’t anticipate any trouble from Lawless or Durkee?”

“No, I do not,” was the rejoinder; “in the first place, the schooner could not arrive here for many days, even if they had made up their minds to follow us. By that time we shall be, I hope, far advanced into the upper regions of Chile.”

As the professor spoke one of the boatmen gave a shout. Nat looked up and saw that a sailboat was bearing right down on them at tremendous speed. The outlines of two men could be seen, but it was too dark to distinguish their features.

“Good gracious, if that man doesn’t tack he’ll run us down!” cried the professor.

“He will indeed,” exclaimed Nat. “Hi there! Look out where you’re coming!” he yelled, adding his voice to the outcries of the boatmen.

But the occupants of the sailing craft paid no attention. At a terrific speed the larger craft bore straight down on the little boat.

The boatmen stood paralyzed with fear. They did nothing. Suddenly one of them dropped on his knees, and began imploring the protection of the saints.

Nat sprang toward him, almost upsetting the frail boat as he did so. With a quick movement he seized one of the paddle-like oars, and by exerting all his strength as he thrust it into the water, he managed to send the boat spinning out of harm’s way.

The next instant the sailing craft flashed by, almost grazing the bow of the small craft.

“You’re a nice pair of irresponsible idiots,” yelled the indignant Nat. “Do you know you almost ran us down?”

A yell of derision came from the other boat, and at the same instant something heavy whizzed past Nat’s head, almost striking him. It fell in to the water with a splash.

“They threw something at me, an iron weight, or a rock, or something,” exclaimed Nat as the sailboat, still going at the same rapid rate, vanished in the darkness. “What do you make of such conduct?”

“I don’t know what to think,” rejoined the professor. “I was inclined to believe at first that the sailors of that craft were merely careless. But the throwing of that weight puts a different complexion on the matter. It looks as if they deliberately tried to wreck us.”

“It does,” agreed Nat; “the whole thing is very mysterious. I’m sure I don’t know why any inhabitant of Santa Rosa should wish us harm.”

But further discussion of the matter was cut short by the necessity of arousing the boatmen, who were still stupid from fright. This was accomplished at last, and the boat was sent whizzing through the water again.

They were landed at a tumble-down wharf, and as the tide was out they got the full benefit of the odors inseparable from a South American town. Both, however, were too intent on the work in hand to waste much thought on this.

The professor, who spoke Spanish, as did Nat after a fashion, inquired the way to the consulate, and a ragged mestizo volunteered to escort him thither. But to their disappointment, when they reached the building, which served both as a dwelling and an office, the consul’s assistant informed them that he was not expected for an hour or more. They were invited to wait, however.

Professor Grigg, who was tired, gladly accepted the invitation, and sank into a comfortable chair. But sitting still didn’t much appeal to Nat.

“I guess I’ll stroll about the town a little and meet you here later,” he said to the professor after a few moments.

“Oh, I’ll be very cautious,” laughed Nat; “at any rate, I can’t get run down by a boat ashore here.”

Nat again promised to be careful and hurried out. He wished to mail some letters home, as well as do a bit of sight seeing. He found the post office without difficulty and, having mailed his missives, was leaving it, when a native, in a long serape, or cloak, glided up to him.

“Because if the señor wishes to see the town I am very good guide. I can show him where they sell veree fine ’Merican ice cream soda.”

“By ginger! You’re on,” cried Nat, who had a weakness for ice cream sodas; “lead on, Macduff. You don’t look very presentable, but I guess that isn’t your fault.”

“Thees way, señor,” said the man, and he walked off slightly in advance of Nat.

Suddenly he turned into a dark alley. Now, although Nat had nothing to dread, yet he began to be fearful that the fellow might mean to rob him. So he stopped short for an instant. But the next moment his suspicions were disarmed by a look at the ragged, pitiable fellow. Nat would have been a match for six of him.

“Where are you going?” he demanded, however, as they plunged into the narrow thoroughfare, which was ill-paved and black as a tunnel.

“A short cut, señor. A short cut to the Gran’ Plaza. We be there soon now.”

“Well, let’s hurry up and get out of this, quick,” said Nat; “I don’t much like——”

Something struck the young Motor Ranger on the back of the head. He extended his arms helplessly, and plunged dizzily forward, collapsing in a heap on the pavement.

At the same instant two figures glided from a doorway and joined a third, the one who had struck Nat the blow that felled him.

“Good work, Manuello,” said the voice of Captain Lawless. “Pick him up and help us carry him in.”

CHAPTER XIII.

Aided by the rascally guide, who had been employed for the express purpose of decoying Nat, the three men carried the lad’s limp form into the doorway. Inside they ascended a steep flight of stairs, and at length arrived in a room on the upper story.

A lamp was smoking and flaring on a table, which, besides one chair, appeared to be all the furniture there was in the place.

“Fling him on the floor,” ordered Captain Lawless brutally, and poor Nat was chucked into a corner with as scant ceremony as if he had been a sack of potatoes.

The appearance of both Lawless and his rascally mate was materially changed since we last saw them leaving their crew marooned on the tropic island. Both had shaved off their beards, and wore the South American style of dress, so that it would not have been an easy matter to recognize them.

The two rascals had arrived in Callao a week before, and at Lima had exchanged their pearls for substantial sums, so that they were well provided with money. They made no long stay at Lima, but hastened to Santa Rosa, where Durkee fell in with two old acquaintances, to wit, the two South Americans who were now leagued with them.

As soon as the news of the approach of the Motor Rangers’ craft spread along the water front, Lawless and Durkee engaged a sailboat. They wanted to look the craft over, and ascertain the lay of the land, as it were. But, as we know, darkness fell before the Nomad was anchored, and they were chagrined to find no easy way of getting close to the vessel. But they saw the professor and Nat leave her for the shore, and made the cowardly attempt to run them down that we have related.

When this scheme failed, they hastened back to the port, landing at a wharf not far distant from the one at which Nat and his companion had disembarked. Having found their satellites, they deputed one of them to track Nat and lure him into the alley where they lay in wait for him. How easily and unsuspectingly the lad had walked into the trap, we know.

“What are we going to do with this cub, now that we have him?” asked Lawless, as Nat was thrown into the corner.

“Better put him in Manuello’s pit downstairs,” said Durkee. “He’ll come to in a minute or so and may make us a lot of trouble.”

“You must have hit him a terrible crack, Manuello,” he said to one of the South Americans, who stood by, impassive and indifferent, while this dialogue was carried on.

“What would you?” he said. “You told me to knock him senseless, and I did so.”

“Well, if we are going to keep him in the pit over night, we had better put him there now,” remarked Durkee.

“All right. Bear a hand in packing him down stairs again, then. Confound it, I wish we hadn’t brought him up here. He’s a heavy youngster.”

“He is that,” agreed Durkee. “And he’s got muscles like iron. He’d be an ugly customer in a rough-and-tumble fight, all right.”

“No danger of such a thing as that occurring,” said Lawless, as he lifted Nat’s feet, while Durkee took his head.

Followed by the South Americans, one of whom held the lamp, they descended the stairs, and opening a trap-door in the passage, they clambered down another flight leading into a damp, earthy-smelling cellar. In the centre of this cellar, the light revealed a deepish pit. Into this pit Nat was lowered. All this time he had given no sign of consciousness and was as limp as a rag-doll.

In obedience to his commands, the South American approached a small door at the rear of the cellar and opened it. He whistled softly, and two ferocious, half famished looking blood-hounds came leaping out. Their dripping fangs were drawn back, exposing sharp, white teeth.

They seemed to comprehend him instantly. They uttered a low growl and crouched close to the edge of the pit. Their red-rimmed eyes were fixed on the boyish form lying at the bottom.

The creatures were vicious to a degree; in fact, Manuello used them in fighting, the scene of the brutal sport being the pit in which Nat now lay.

“Humph!” said Captain Lawless, as he regarded the two dogs, “those fellows are better than human guards. If that boy ever escapes from them, he’ll be——”

An astonishing thing had happened. Nat’s limp form had suddenly galvanized into aggressive, fighting life.

He sprang erect like a flash, and in one bound was out of the pit. Another instant, and his fist was crashing into Lawless’s face. The man, taken utterly off his guard, reeled backward, waving his arms wildly.

Before Durkee could recover from his amazement, he, too, had joined him. There remained only the two Spanish-Americans for Nat to face. But they had had more time to prepare themselves. Both brandished wicked-looking knives as the boy came at them.

Moreover, the dogs had now awakened to the situation. With frantic yaps and snarls, they sprang at Nat.

The lamp which had lighted their progress to these lower regions stood on the ground. Nat saw in it a weapon of necessity. Snatching it up, he swung it round his head and then sent it crashing at the brutes as they leaped for his throat.

As the crash of splintering glass resounded, the place was plunged in darkness, but the howls of the two savage brutes showed that the burning oil had singed their skins.

Without waiting an instant, Nat plunged off through the darkness, in the direction in which he judged the door lay. As he dashed forward, he collided with a body, no doubt one of the South Americans. Down went the fellow before Nat’s onrush, just as if he had opposed him on the football field.

But in the meantime, Durkee had recovered his wits and scrambled out of the dog-pit. His rough voice came bawling through the darkness with appalling ferocity.

Fear of this ruffian lent Nat winged feet. He found the door, darted through it and then down the passage and out into the dark street. At the far end of it he could see lights gleaming. He made for these at top speed and found himself in a well-lighted plaza opposite the cathedral.

He knew that the ruffians would not dare to pursue him there, and, spying an alguzil, or native policeman, he made his way to him. In Spanish Nat explained the outrage that had been perpetrated on him, and demanded that the police investigate instantly.

To his astonishment, the man merely shrugged his shoulders, and twisted his little black moustache. He said that nothing could be done that night.

“To-morrow, perhaps, but not to-night, señor,” he replied, and turned away to strut off on his beat once more.

“Gee whiz!” muttered Nat, as he watched this competent conserver of law and order, “what wouldn’t I give for a good American cop with a big nightstick, right now. However, it’s no good trying to wake that chap up, and those rascals must have decamped by this time, anyhow. Wonder if they meant to rob me, or what? Funny thing that two of the voices sounded so familiar. If it hadn’t been for the impossibility of their being here, I could almost have sworn that they were the voices of Lawless and Durkee.”

As it was past the hour at which he had promised to return to the consulate, Nat set off at a brisk pace. Once he had to ask his way. The man he inquired of, a woe-begone looking personage in a long cloak and a cone-shaped hat, replied with great volubility.

“I guess not,” rejoined Nat, with such vigor that the fellow fell back a pace, “I’ve had all I want of guides in this place.”

As Nat walked along, he felt the back of his neck, where he had been struck, for it was becoming quite painful.

“Good thing the force of that blow was mostly wasted on my shoulder,” he said to himself, “or I might have been knocked unconscious in good earnest. As it was, it was a lucky thing I shammed insensibility, or I might have got another tap.”

CHAPTER XIV.

It was morning in the large compound, or garden, adjoining the consul’s house, and our adventurers were grouped about an odd collection of articles that had formed the contents of several big packing cases.

“By the way,” put in Mr. Stowe, who had been an interested spectator of the unpacking of the cases, “I have news for you, Master Trevor.”

“What is it?” inquired Nat, whose shoulders still felt a bit stiff and sore, but was otherwise in fine fettle.

“I thought so,” said Nat, with a laugh, as he caught a twinkle in the consul’s eyes; “I guess it will be one of those to-morrows that never come.”

“I’m afraid so,” said the consul. “There is little law in this country, and it’s a case of every one looking out for himself.”

After some more talk, in which all freely expressed their indignation against the rascals who had decoyed Nat, work on the erection of the dirigible was begun. It proceeded rapidly. By afternoon the lower framework of the craft was in position and bolted firmly in place. This part of the craft merits a somewhat detailed description. It was of an aluminum alloy, of great strength and lightness.

Amidships of the structure, which was shaped not unlike a long sleigh, was a canvas-enclosed cabin. The front part of this was fitted with round windows for the helmsman to see out of, and contained the wheel by which the great rudder was controlled. The various levers and handles for the management of the engine were also manipulated, like the rudder, from this “pilot-house,” as it may be called.

Just aft of the pilot-house the canvas-enclosed framework did duty as a dining, living and sleeping room, being fitted with swinging bunks, which, when not in use, folded up against the ceiling. A collapsible table and other furniture of the same character were also to be found in this chamber, as well as a denatured alcohol stove for cooking, and a complete outfit of plates, knives, forks, etc.

Behind the pilot-house came the heavy frames and stringers, destined to support the engine. This was a six-cylinder motor of one hundred horse power, which drove a big suction propeller attached to the front of the framework. Thus the dirigible was drawn, and not pushed, through the air. The propeller was ten feet from tip to tip, and formed of laminated wood covered with canvas stretched tightly upon the timber.

A sort of gangway, or path, extended from bow to stern of this framework, enabling the aerial navigators to walk to any part of the structure at will.

The entire frame was secured to the vast gas bag by numbered ropes, with steel cores to insure their stoutness. Relief valve-cords and gas controls all ran to the pilot-house, under which structure a steel tank, capable of holding two hundred gallons of gasolene, was suspended. A reserve supply of fuel was also carried, as well as lubricating oil, and what Joe Hartley called “a machine shop full of tools.”

There were other features of the craft, which will be described as occasion arises; but when we say that the Discoverer was, roughly, a hundred and fifty feet from stem to stern, one of the largest airships of her type, constructed in America, had a capacity of 150,000 cubic feet of gas and could lift 6,000 pounds, we have covered the main features of her construction. It may be added that the motor was of the four-cycle type, and, despite its high horse power, weighed but a trifle over 250 pounds. Aluminum alloy had been used freely in its construction.

By nightfall the engine was in place and firmly bolted to its foundation plates. A test showed it to be working perfectly. The cabin provision lockers were then stored with canned goods of all descriptions, and staples, such as flour, beans, bacon, corned beef and preserved butter. Tea was also carried, but no coffee. One feature of the cabin was the “armory.” This was a chest containing rifles and shotguns of the latest automatic type. It was an important feature of the Discoverer’s equipment, inasmuch as the adventurers expected to “live on the country” to a great extent, for Bolivia abounds in game.

All that remained to do then, was to inflate the great gas bag. The adjustment of this to the frame proved tedious work. But at last it was done, and the folds all carefully straightened out, in itself an arduous job. The whole party was pretty well tired out by this time, and work was discontinued for the day.

“In the morning,” said the professor, “we will inflate the bag, and then there will be nothing more to detain us.”

The boys gave a cheer. It seemed almost too good to be true—the idea that before many hours had passed they would be flying high above old Mother Earth in a cloud cruiser, that for completeness and effectiveness surpassed their wildest dreams.

Between four and five o’clock the next morning the lads were astir. After early coffee and some fruit and rolls, the task of inflating the great bag was begun. Huge wooden tanks full of iron filings and metal scrap had already been erected. Acid was now added to the filings and the tops clamped on. Then the inflation pipes, purifier and nozzles were adjusted.

A cheer broke from the boys as they saw the huge bag begin to swell like a live thing as the gas poured into it. By noon the professor announced the inflation as being sufficient. At that time, the great yellow bag was as tight as a drum almost, and the heat of the sun served to swell it still further. While the bag had been filling, the under frame of the dirigible had been weighted down by bags of sand. Otherwise it would have risen of its own volition.

The last things loaded on the framework were several cylinders of hydrogen gas at tremendous pressure. This was the reserve supply of the adventurers, and the tanks contained enough almost to refill the bag in case of necessity. A hasty lunch was consumed at the consul’s table, and Nat gave final instructions to the man who had been employed to take care of the Nomad during their absence.

This done, there was nothing else to wait for, and at one-thirty sharp, the professor gave a final look over things. Then he turned to Ding-dong Bell.

“You can take your place at the motor,” he said. “Mr. Tubbs, you will attend to the handling of the craft as we rise.”

The versatile Mr. Tubbs, whose moving picture apparatus was in readiness, paused to take a few pictures, and then mounted to his place in the pilot-house.

Nat and his chums bade good-bye to the consul, and then took their places. It was Nat and Joe’s task to attend to the throwing off of ballast as they arose.

“Good-bye and good fortune to you,” said the consul, as the great airship quivered and strained, as if anxious to be up.

The bags had been thrown off so rapidly that now the weight of only a few held her down. The professor took his place beside Mr. Tubbs. The consul’s wife waved a dainty handkerchief.

The departure had been kept a secret, but the sight of the great yellow bag’s outlines rising above the compound walls had attracted a crowd outside. A cheer arose as the Discoverer’s electric siren sounded a prolonged blast.

It was the signal for throwing off the remaining bags. Nat and Joe worked with a will. Suddenly the craft bounded upward, almost throwing them off. Hastily they cast off the final sacks, while Ding-dong, his face pale with excitement, stood by his engines.

The lad’s hand shoved over the starting lever that gave the engines their first impulse by means of compressed air. Then he manipulated the sparking and gas controls.

The mighty propeller began to beat the air as the Discoverer soared buoyantly, and yet in stately fashion, high above the houses and tree-tops.

“Hurray! We’re off!” cried Nat, clambering along the runway as nimbly as a sailor.

Faster and faster the propeller revolved. The wind was blowing lightly out of the west, aiding the Discoverer on her flight toward the mountains.

Suddenly Ding-dong felt something fan the air past his ear. It was a bullet. At the same instant a report came from below. Somebody was shooting at the craft of the clouds. The others rushed out excitedly. They were just in time to see two figures struggling in the hands of several native policemen.

“It’s that rascal Lawless and his mate Durkee!” cried Nat. “Now I know why those voices seemed so familiar. It was those two ruffians who captured me the other night.”

It was many days before that mystery was solved for the Motor Rangers, but in the meantime they at least had the satisfaction of seeing that the cowardly endeavor to injure the airship had resulted in their arrest.

But they gave little time to thinking of Lawless and his fellow ruffian. The land of mystery, of the lost city, of the unknown, lay before them.

With a fair wind and with perfectly working engines, the Discoverer drove forward at forty miles an hour, carrying the Motor Rangers on the strangest cruise of their eventful lives.

CHAPTER XV.

Spinning along at a height the barograph showed to be 1,500 feet, was an exhilarating experience. The slight feeling of apprehension which the Motor Rangers had felt when they set out on their novel cruise, soon wore off, and was replaced by a buoyant sensation.

“Well, Master Nat, what do you think of it?” inquired the professor, emerging from the cabin and coming “aft” to where Nat was standing by the smoothly running motor.

“It’s glorious,” replied Nat enthusiastically. “I had no idea, though, that it was possible to get used to it so soon.”

“Well, a craft of this kind is vastly different from an aeroplane,” commented the man of science. “It is my belief that the aerial trans-Atlantic liner of the future will be a dirigible.”

“I wouldn’t mind undertaking the trip in the Discoverer,” declared Nat, with glowing eyes and cheeks.

“About forty miles an hour,” said the professor; “but you can tell the exact speed by stepping into the pilot-house and examining the instruments.”

The lads followed his advice, and found that the speed recorder registered a shade more than the professor had assumed. Mr. Tubbs had the wheel, and was gazing straight ahead, like a steamboat pilot.

The pilot-house of the Discoverer, in fact, was not unlike that of a steamer, although much smaller, of course. The registers and indicators, too, that were fastened to the walls, or rather the framework of the Discoverer’s “hull,” were totally unlike any that the lads had seen before.

Joe Hartley, who had been appointed chief cook and bottle washer, soon left, to begin his preparations for lunch. But Nat lingered on, fascinated. Joe’s meal proved an excellent one, and the fact that they were so high above the earth did not affect the boys’ appetites in the least. In fact, Ding-dong Bell observed that he had never felt so hungry in all his life before.

After the meal was concluded, the motors of the craft were slowed down a bit, so as to economize on gasolene as much as possible. The fact that the westerly wind had increased made it possible to slow the engine down and still make good progress.

“I wonder what they think of us down below there?” said Joe, as he stood by Nat’s side, leaning over the forward deck-rail and watching the dwarfed figures of the inhabitants of a village above which they were passing, scurrying to and fro like ants.

“I guess they must think we are some sort of demoniacal bird,” grinned Nat. “Hark!”

Faintly, very faintly, borne to their ears, came the sound of church bells ringing furiously.

“More likely they are going to pray that we don’t harm them,” responded Nat. “According to the professor, the people of this country are a very ignorant lot.”

By afternoon the Discoverer was flying above rugged country. The foothills of the great Andean range had been reached, and they were in Bolivia. It gave the boys a thrill to think that they were actually at last in the hoped-for vicinity of the lost city of the mysterious old Incas.

As the sun grew lower, the great altitude to which they had attained struck them with a sharp sense of chilliness.

“This part of the world ought to be called Chile,” observed Joe, as he and the professor and Nat stood on the forward deck just below the pilot-house.

“If you will come into the cabin and see what I have in that big chest, we can possibly get over that difficulty,” said the professor, with a smile.

The lads accompanied him within and found that the chest referred to contained a variety of warm clothing.

“I knew that the late afternoons and nights on the Andean heights were bitterly cold,” said the professor, as the boys selected some garments, not forgetting a coat-sweater for Ding-dong. “I therefore took the precaution to be prepared to meet them.”

It was not long after this that the professor addressed a few words to Mr. Tubbs, and the Discoverer began to drop. Then came a sudden signal to Ding-dong to slow up his engines. This being done, the lateral planes of the dirigible, which have not yet been mentioned, were inclined at an angle that brought her to earth with an easy, gliding motion.

“Are you going to land for the night?” asked Nat, who had watched the maneuvers with interest.

“Such is my intention,” said the professor. “It is too late in the day to get any observations now, and I don’t fancy traveling at night in this region. We might blunder miles off our course.”

The boys agreed that this was so, and then gave their full attention to what was going forward. Immediately beneath them was a charming, park-like savannah, set in the midst of dense forests of gigantic trees, from whose branches hung great twisted creepers, looking not unlike big snakes.

It formed an ideal landing spot for the big dirigible, which, in a few moments after the descending planes had been set, grazed the ground and then settled. Instantly the professor shouted an order for the anchoring process to begin.

The boys had been drilled in this before the voyage was started, and fell to work with a will on their task. By running the propeller slowly, with the descending planes set at a sharp angle, the Discoverer’s body was naturally held against the ground.

Nat and Joe leaped off on opposite sides, both armed with sledges. With these heavy hammers they drove sharp, barbed steel stakes into the ground till they were almost as firm as rocks. Each stake had a ring at its top through which ropes were rapidly looped. The ends were then led back on board and secured. This was done so that in case of a sudden attack the great aircraft could be released by those on board. Of course, in such an event, the stakes would have to be left behind, but as an extra supply was carried, this would not be such a serious matter.

Ten minutes after she nestled to the ground, the Discoverer was secured as snugly as a vessel at her wharf. The engine was shut off and the various necessary adjustments of the controls and apparatus of the pilot-house made. This done, the entire party stepped “ashore” for the first time in many hours.

This plan just suited the boys, and they scattered in all directions to obtain firewood for the encampment. While they were doing this, Mr. Tubbs set about the task of getting the needed utensils from on board the cloud cruiser. He had been busily engaged on it for some time when the professor looked up from some calculations he was making on the back of an old envelope.

“It appears to me those boys are a long time gone,” he said. “I hope they are all right.”

“Oh, they are all right,” spoke the moving-picture artist easily. “They took the rifles with them, and agreed that in case of any danger or difficulty befalling them, they would fire three times.”

But he halted with an abrupt exclamation of consternation. Mr. Tubbs’s face likewise took on a perturbed look at the interruption.

From the forest, to their right, three shots, fired in rapid succession, had resounded.

CHAPTER XVI.

“What can be the matter?” was the exclamation that burst from the professor’s lips.

“Something serious,” declared Mr. Tubbs. “Take a rifle and we’ll find out.”

Hastily selecting a weapon each, the two friends plunged into the forest in the direction from whence the shots had come.

“It’s ahead there, somewhere!” panted the professor, as the sound of a mighty threshing and struggling amidst the undergrowth came to their ears.

Neither the professor nor Mr. Tubbs was in the least faint-hearted, but they crept through the forest with some caution. If the boys had been attacked by enemies, they reasoned the best thing to do would be to give their foes no opportunity of observing the approach of re-enforcements.

But, as the noise grew louder, they hesitated no longer, but pressed right on. Suddenly, on emerging into an open space where the growth had been flattened out in every direction, they came on a scene that, for an instant, almost deprived them of their breath.

In the midst of the open space, Nat and Joe were bending over the form of Ding-dong, who was stretched on the ground, seemingly unconscious. Not far off, an immense snake, which must have been fully fifteen feet long, was lashing wildly about in its death agonies.

“Oh, professor!” cried Nat, as he saw the newcomers, “we’re so glad you have come. Ding-dong was attacked by that serpent and badly crushed. It was only by firing at the creature that we managed to save his life.”

“Merely shock, and possibly a sudden weakening of the heart,” he said. Taking a small vial from a pocket medicine-case, the professor forced some of its contents between Ding-dong’s lips. In a few moments the boy was able to sit up and take notice of things about him.

By this time the convulsive dying movements of the snake had ceased, and it lay still.

“Ugh! What a monster!” shuddered Ding-dong. “I can feel his terrible folds around me yet.”

As usual, when under the stress of emotion, Ding-dong’s hesitating manner of speech had left him, and he enunciated quite plainly.

“I was looking for wood,” explained Ding-dong, “and thought I had found a f-f-f-fi-fine c-c-chunk of timber. But w-w-when I pu-pu-put my hand on it, the ber-ber-blessed thing turned out to be a snake. I yelled at the top of my voice, and started to run, but before I had gone far I tripped and fell. The n-n-n-n-next instant the snake had me.”

“Joe and I were a short distance off,” chimed in Nat, taking up the story, “and heard Ding-dong’s yell. We hurried to him, and you can imagine how horrified we were to see him struggling with that serpent. Joe raised his rifle, but then lowered it again. He was scared to shoot at the snake for fear of hitting Ding-dong. But at last we saw a chance. I fired once and Joe twice.”

“And all three bullets penetrated the brute in and about the head,” struck in Mr. Tubbs, who had been examining the snake.

“So they did,” declared the professor, as he and the boys joined the ruddy-headed one; “good shooting, boys. This snake is of the boa variety. They are common all along this coast, but usually they are thickest near rivers. As a rule, they will not attack human beings, although cases have been recorded of their doing so. I imagine that it was Master Bell’s having grabbed him that angered his snakeship. Shall we take the skin for a souvenir?”

“N-n-n-no, thank you,” stuttered Ding-dong, “it will be no trouble to re-re-remember that f-f-f-fellow without having to l-l-l-look at his skin.”

“I agree with you,” said Mr. Tubbs. “I guess we’ll leave him here for a while. It won’t be long before some animal or other makes away with it.”

Leaving the repulsive looking carcass on the ground, they set out to return to the Discoverer.

“Well, all is well that ends well,” said the professor, as they tramped along; “at first I had a dreadful fear that you lads had been attacked by Indians.”

“I am sorry to say that they are. In other parts some of the natives have been converted to Christianity, but the natives of this section are fierce and warlike. I hope we shall manage to steer clear of them.”

“They are known as the Caripunas,” was the rejoinder. “The early Jesuits had much trouble with them, and they have ever since remained in a more or less wild and hostile state. They are very much averse to having any one enter their country, and that was one of the minor reasons why this trip was made by means of the dirigible.”

“Their country!” echoed Joe. “I should think the Bolivian government would send a regiment up here and subdue the rascals.”

“Several such expeditions have been despatched,” was the response, “but the fate of all has been the same. Several months after their departure the remainder of the force has come straggling home, more dead than alive, to tell a tale of death and defeat.”

“For one thing, they are inured to the hardships of the forest,” rejoined the professor; “for another, these Bolivian Indians wage war with poisoned arrows shot from long blow guns. A man usually dies in a few minutes after such an arrow has struck him, unless medical attention is at hand. Armed with these weapons, the Indians creep up on their foes and noiselessly decimate an entire force. It is in this way that the Indians have managed to reserve this part of the country for themselves and keep the hated white man out of it.”

The boys looked rather grave as they continued their tramp back to the Discoverer.

“Looks to me as if we were in for a more exciting time than we bargained for,” observed Nat to Joe.

“I guess you are right,” rejoined Joe. “A battle with Indians who employ such deadly weapons does not appeal to me.”

“Oh, I guess we’ll get through without trouble,” exclaimed Nat. “At any rate, if we are attacked, we can climb aboard the good old Discoverer and soon be out of range.”

“That’s so,” agreed Joe, and the lads dismissed the matter from their minds; but whether Nat’s surmise was correct or not, we shall see in due time.

CHAPTER XVII.

With the wood gathered by the young Motor Rangers, Mr. Tubbs soon had a roaring fire going. By sundown it was so cold that they were glad to huddle close to the cheerful blaze, which was for purposes of warmth only, the cooking being done on the denatured alcohol stove belonging to the galley of the Discoverer.

It was an odd meal, but one the boys enjoyed thoroughly. Mr. Tubbs was as good a hand at cooking as he was at anything else, and as a supply of fresh meat had been brought along, they had a capital meal, helped out with choice canned vegetables and even, to celebrate their first night in the land of their search, a generous portion each of plum pudding. It was canned, of course, but quite palatable, or so the boys appeared to find it.

After supper the professor gave the lads an interesting sketch of the country they were in, and finished up with an account of the old Incas, one of whose lost cities they had come to find.

Among other things of interest he told them concerning the lost race, was that they are believed to have been sun worshippers. At any rate, in one of the ruined cities which has been located in Peru, circular temples with the walls embellished with pictures of the sun have been found. Other facts concerning the vanished civilization of the Incas must ever remain a mystery, said the man of science.

For instance, at the remains discovered in Peru, a huge rock, shaped like a gigantic dome, was found. Traces of gold were discernible on its surface, and it is believed that at one time the whole great, monolithic mass was completely plated with this costly metal.

“Other strange features of these ruins,” went on the professor, “are dungeon-like chambers which are believed to have been used in cereomonies of initiation, and great baths fed by subterranean rivers, which are still flowing as they did in the days of the Incas.”

“Do you think we shall find such things?” asked Nat, his eyes aglow at the prospect.

“You mean, do I think we shall find the lost city?” corrected the professor, with a smile. “Well, Master Nat, I don’t doubt that if we find the city we shall also find such things. It is rumored that the lost city we are in search of is in even better preservation than the famous ruins of Peru itself.”

“I wish you would tell us some more about that sacred dome with all the gold on it,” said Joe.

“I’ll tell you all I know,” said the professor. “It is believed then, that the sacred dome was the place where Manco Capac, an Inca deity, descended to the earth. To this day the natives approach the spot with the utmost awe and reverence.

“According to their ideas, no bird would alight up, or animal approach it. All but priests were forbidden to come even within sight of the rock, although it is hard to know how this could be prevented, as it is of immense size. At ordinary times its gold plating was covered by a veil of the finest and most costly materials, and this was never removed, except on great religious festivals.”

“It must have been a fine sight to see that great golden rock glittering in the sun,” said Nat thoughtfully.

“It must, indeed,” agreed the professor. “There was also a Temple of the Moon, and a vast Temple of the Sun, as well as other buildings whose purposes are veiled in mystery, and must ever be. One thing is certain, though, human life must have been as cheap as water, for it is estimated that many thousands of slaves’ lives were sacrificed in building the city of which only ruins now remain.”

“So travelers have observed,” rejoined the professor; “after all, the history of civilization repeats itself.”

“Quite a good deal, yes,” was the reply; “but the Spaniards took an immense quantity of it, and to-day there is little left. However, from time to time a valuable find is made, I am informed.”

“And the city we are in search of—do the same conditions exist there?” inquired Nat.

“Very probably. According to tradition, the fierce and warlike Indians kept the Spaniards away from the spot,” was the reply.

“I hope so,” spoke Joe, in whose mind visions of vast treasures and strange, massive buildings were already rising. As for the others, perhaps they, too, even the professor, were also weaving castles in cloudland. At any rate, they were silent for a time, brooding over the great mystery to whose heart they hoped to penetrate ere long.

But the period of silence was not of lengthy duration. Mr. Tubbs, who possessed a good tenor voice, volunteered to sing a song.

The song he chose was “Old Kentucky Home.” When he came to the chorus the boys’ voices blended with his in the plaintive cadences of the music. It was a strange sound to be ringing out in that primeval place, where perchance the foot of civilized man had never trod before.

But the singing was due to terminate abruptly. Nat, who had been gazing outside the circle of firelight, caused the breaking off of the concert.

He sprang to his feet and seized up a rifle, calling on the others to do the same.

“No—that is, I don’t think so,” rejoined the boy, whose face was rather pale. “I’m almost certain that what I saw was the figure of a man crouching over yonder and watching us.”

“It may have been nothing but a jaguar or a prowling puma,” said the professor. “Are you sure your eyes didn’t deceive you?” he inquired of Nat.

“As I said, there’s a bare chance I might have been mistaken,” rejoined the lad, “but I don’t think so. However, the instant that I looked, the figure vanished.”

“It’s very strange,” mused the professor, “and yet it may have been an Indian, little as I like to think of such a contingency. However, we will keep a sharp watch to-night, and be prepared to ‘slip our moorings’ at an instant’s notice.”

All agreed that this would be an excellent plan, and forthwith the knots on the mooring ropes were retied, so that one tug from those on board the Discoverer would release the craft and allow her to shoot upwards. Preparations for what all felt was not likely to prove a restful night, were then begun.

The first watch was assigned to Mr. Tubbs and Joe, and would last till midnight. The next one would be assumed by Nat and the professor. Ding-dong Bell, who was still nervous and rather pale from his experience of the afternoon, was to be allowed to slumber all through the night.

He protested loudly against this, demanding to take his share with the rest; but was obliged to be content with the promise that if any trouble occurred he would be routed out to assume charge of the engine. In spite of their apprehensions, Nat and the professor slept as soundly as Ding-dong. In fact, it did not seem to Nat that he had been asleep more than a few minutes when Mr. Tubbs aroused him to take his watch.

“All quiet,” was the rubicund-headed one’s response to the professor’s inquiry.

Hardly were the words out of his mouth before the silence of the night was broken by an almost unearthly yell.

“Nothing but a screaming monkey,” said Mr. Tubbs. “I’ve heard them in Brazil often.”

“But they don’t cry out at night unless they are disturbed,” said the professor decidedly.

“I don’t know about a human being. But the fact that you are almost certain that you saw a man prowling about last night, makes it look suspicious.”

“Possibly. Let us hope that is the case, but in the meantime prepare for trouble; then, if it comes, we can meet it. Master Joe, rouse out Master Bell. Nat, I wish you’d bring me that peculiar-looking gun you were asking me about yesterday when you saw me place it on board.”

The gun referred to was a queer-looking weapon, with a mouth shaped like an old-fashioned blunderbuss. It had an immense barrel, and altogether was a very odd-looking weapon. Nat knew where it stood in the gun-rack and soon fetched it. The professor examined the lock and appeared to find everything satisfactory.

“I don’t want to say much about it till I see how it works,” said the professor. “It is the invention of a friend of mine. If we are attacked it will be a fine opportunity to test it.”

Nat would like to have asked more questions, but at that instant a chorus of cries and shrieks arose from the woods on every side. The cries were uttered by roosting birds and monkeys, which had been disturbed by some cause. What that cause was, the professor soon guessed.

“It’s the Caripunas,” he whispered; “almost beyond a doubt. Master Bell, stand by your engines. Tubbs, take up your position at the wheel and be ready to manipulate the searchlight. Master Nat and Master Joe will stand ready to slip the tie-ropes when the word is given.”

CHAPTER XVIII.

The moments that followed were filled with a tenser excitement than any of the lads had ever known before. After the first frightened flurry of the alarmed creatures of the forest, a deep silence prevailed. It lasted for possibly fifteen minutes, and then the professor decided not to test their nerves to the breaking point.

A sharp click followed, as the light, which was supplied by current from the storage battery, was switched on.

A dazzling white pencil of light swept all about the Discoverer. Its brilliancy pierced the night like a saber, and illumined the solemn trees and the open savannah all about.

At almost precisely the same instant, a chorus of ferocious yells and cries broke out, and from all sides there rushed on the aerial adventurers a horde of short-statured Indians. The searchlight showed them to be wild-looking men, clothed in a single garment, their heads covered with straight black hair. Through their lower lips most of them had thrust a triangular bit of white stone with a sharp point. This added to their fantastic appearance.

Nat noted that one of them, larger in stature than the rest, seemed to be the leader. He also saw, with an unpleasant thrill, that they carried long blow pipes. It was through these pipes, the professor had said, that the poisoned arrows were discharged.

Rope in hand, ready to slip at the word of command, Nat stood his ground. On the opposite side of the framework Joe was likewise waiting. Neither boy budged an inch, and Ding-dong stood steady as a rock at his engines.

So suddenly had it all happened, in fact, that neither boy could regard it for an instant as more than a dream.

Suddenly something struck the metal framework by Nat’s head with a sharp ping!

It was an arrow, and so close had it come to the lad that he had caught its whistling sound as it sped past his ear.

“Keep the searchlight in their eyes. It dazzles them!” called the professor.

“Don’t fire!” cried the professor sharply. “We don’t want to injure them if we can help it.”

The bell for “full speed ahead” rang sharply out. At the same instant the propeller began to whir.

As it did so, several Indians, who, in their onrush on the dirigible, had clambered upon it, were thrown off in all directions. They rolled over and over, like so many footballs. This made the others pause an instant, and in that instant the dirigible rose from the ground.

But the chill night air had condensed the gas, and she rose slowly. Before more than five feet had been gained in her upward rise, the Indians recovered from their amazement and charged like a pack of furies.

“Flat on your faces!” shouted the professor, as a shower of arrows pinged and pattered in the framework of the craft.

They obeyed the command, and then Nat saw the queer gun brought into use. The professor raised it to his shoulder and pulled the trigger.

Instantly a stream of colored balls, like those that issue from a Roman candle, poured from the bell-like muzzle. But almost simultaneously with their discharge, they burst with sharp reports, and the whole air became impregnated with a black, all-obscuring smoke as thick as a London fog.

The dense clouds spread on every side, completely obscuring the dirigible from the view of the Indians below. Higher and higher she rose, while below her the dense smoke veiled everything like a curtain. Nat caught a whiff of the vapor, and it made him cough and choke.

“I’ll bet those Indians aren’t enjoying it,” he thought to himself. “So that was what that queer gun was.”

In a few moments they were high above the tree-tops, and the professor ordered the lights turned on. A switch was pushed over by Mr. Tubbs in the pilot-house, and the Discoverer blazed out with incandescents like an illuminated battleship. For a few seconds nothing much was done but to exchange congratulations. No one was hurt, and not an arrow had pierced the gas bag. This was accounted for by the fact that the Indians, not understanding how vulnerable that part of the craft was, had confined their volleys to the occupants of the lower structure.

“A most fortunate escape,” declared the professor, but suddenly he clapped his hand to his head.

He held it up, transfixed by an arrow. The missile had penetrated it and whisked it from the professor’s head without touching him.

“I wouldn’t have lost that for worlds,” said the professor, thanking Joe, and removing the arrow very gingerly.

“One scratch from that arrow would result in death,” he said, in explanation of his extreme care.

He held it out for the boys’ inspection. It had a stone head, discolored by some whitish matter at the tip. The shank of it was about two feet long, with some sort of cloth wrapped around the end to make it fit the blowpipe tightly.

“An infusion of the St. Ignatius plant, from the beans of which strychnine, our deadliest narcotic, is obtained,” was the response.

“I think so,” agreed the professor; “they are not the sort of things to have lying about.”

A search of the Discoverer’s lower structure resulted in the finding of a dozen or more of the deadly missiles. These were all thrown off into the air at once.

“And now,” said the professor, planting his hat firmly on his head, “I suppose you are anxious to know something about that queer gun I used.”

“Well, it’s a weapon called the Fog-maker, and was invented by a friend of mine especially for use in aerial warfare, or for protecting a small vessel from hostile aeroplanes,” said the professor. “As you saw, it works perfectly, throwing out a thick cloud of dark, acrid smoke, which is heavier than the atmosphere. While it has no permanent bad results, yet it renders those who breathe it insensible for a time.”

“It is indeed an effective weapon,” declared Nat; “can we see one of the projectiles?”

The professor took up the gun and slid open a small space in the stock. Then, pressing a metal button, he caused two round black objects, about the size of small oranges, to roll out into his hand.

“The magazine holds ten of these,” he said. “They are made of glass and filled with chemicals.”

“Ah! That is the secret of the inventor,” was the reply, “nobody but he himself knows what they contain; but that they are effective, you must admit. He told me that the old ‘stink-pots’ that Chinese pirates used to use gave him the idea. If ever there is a war in the air, I think that the nation equipped with this invention will have a powerful implement of havoc.”

“I should think so,” said Nat; “one whiff of it was quite enough for me.”

All this time, by the professor’s directions, the dirigible had been swung in wide circles at an altitude of about fifteen hundred feet. So interested had they all been in the professor’s description of the novel aeroplane gun, and in the other matters that had occupied their attention, that the big air cruiser had not yet been “tidied up.”

This was the next task to demand their attention. Joe set to work to hoist up and coil the rope which had been cast loose when the hasty ascent was made. But he hadn’t given it more than a couple of tugs before he uttered a shout that brought the others, except Mr. Tubbs, who was at the helm, running along the substructure to his side.

“Why, either this rope has caught in something below, or there’s something heavy attached to it,” was the astonishing response.

“Impossible for it to have caught,” declared the professor, “we are now fifteen hundred feet or more above the surface of the earth, and the rope is not more than a hundred feet long, at the most.”

Nat gave the rope a tug. As Joe had said, there was clearly something heavy attached to the end of it. But what could it be?

“We’ll soon see,” said the professor. “Master Joe, attach another length of rope to it, and then have Master Bell switch power on the electric winch.”

This was done, and the powerful winch began to revolve, winding the rope on its barrel. As the rope began to grow shorter, the boys peered over the edge of the substructure in an effort to make out what could be at the end of it. The glow of light spread by the illuminated craft soon showed them.

“It’s a man!” shouted Nat in a thunderstruck voice, as the figure of a human being, clinging desperately to the rope, was brought into view.

CHAPTER XIX.

“A man!” exclaimed the amazed professor. “Why, how in the world did he come here?”

“He must have caught the rope when the Discoverer shot upward,” suggested Joe. “Maybe he thought he could stop us.”

“He’s all wer-wer-wound up in the rope,” announced Ding-dong, who had been peering over the side during this dialogue. “His eyes are closed, and he seems half-dead from fright.”

The boys lay flat, while the winch was started up until the man’s head was on a level with the under part of the substructure. Then three pairs of strong young arms reached down and dragged their involuntary passenger over the side.

“He’s an Indian!” cried Joe, as the man being dragged into safety from his precarious position proved to be a squat, black-haired little brown man, clad in a garment of rough fibre, and with one of the peculiar ornaments Nat had already noticed, thrust through his under lip.

All this time the Indian had kept his eyes tight closed, and had not uttered a word. Now, however, he opened his eyes, and threw himself down flat on his face on the Discoverer’s deck. There he groveled in an attitude of the most complete humility.

“He thinks we are sky gods, or demons of some sort,” declared the professor, reading the man’s consternation aright.

“I don’t much blame him,” said Nat, with a smile, “that ride through the air at the end of the rope must have been the most terrifying experience of his young life.”

“Well, that is young sometimes,” said the professor, who owned to that age himself, although he was as active as most men half his age.

Suddenly the Indian began to speak, but without raising his head. He poured out a flood of words. For an instant, they thought he was speaking his native dialect, but all at once the professor understood.

“He’s talking Spanish,” he said, “and imploring us to spare his life. Just as I thought, he thinks we are beings from another world.”

“Well, if I were in his fix I’d be inclined to think so myself,” said Joe.

But the professor began putting rapid questions, at the same time raising the man’s head and showing him by signs that they meant no harm to him. Little by little the Indian seemed to recover his courage. But he was sorely shaken by his adventure, and explained that when the ropes began to drag over the ground he had seized them to stop the dirigible, and had become entangled in them.

“We thought you were human beings,” was the response. “But now we know otherwise.”

He would have cast himself on his face again, but the professor raised him and spoke encouragingly to him.

“Maybe if you’d give him something to eat he’d feel better,” suggested Joe, practically.

“That might be a good idea, and it will show him that we mean him no harm,” said the professor.

The Indian, who said his name was Matco, was taken to the cabin, the sight of which, with its comfortable furnishings and strange scientific instruments, filled him with fresh terror. But little by little he regained his self-possession to a degree, and ate what he was given with zest.

The crew of the Discoverer joined him at the meal, of which they stood in need, Joe relieving Mr. Tubbs at the helm. The stout lad had taken a few lessons in steering before from Mr. Tubbs, and found that it was not as difficult as he had supposed it would be. But then, Joe had had plenty of experience at the wheels of both automobiles and boats.

But after all, the selection of a green hand at the wheel proved somewhat disastrous. The sun arose while they were still talking to the Indian, and Mr. Tubbs was hearing details of the strange manner in which the man had boarded the airship.

In that rarefied air the rays of the luminary of day soon warm the air, and, as a consequence, the gas within the Discoverer’s bag began to expand very rapidly. Those in the cabin, of course, did not notice that the craft was rising rapidly, and Joe did not give a glance at the barograph, it not occurring to him to do so.

All at once he gazed over the front of the pilot-house and looked down below. What he saw almost made him utter a cry. The Discoverer was at a tremendous height, and appeared to be rising more and more rapidly.

Joe, in a sudden panic, twitched a lever, and the next instant the craft shot skyward at breathtaking speed. The boy had set the wrong lever and had adjusted the planes to a rising angle.

Before the professor, who had felt the craft rear upward, could reach the pilot-house, the dirigible had shot up five hundred feet or more. Behind the professor came the others, except Matco, who was sent into a fresh paroxysm of fright by the strange and sudden upward leap of the airship.

“Good heavens!” cried the professor, as he jerked over the descending lever, “we have risen to a height of more than eight thousand feet.”

“Just like Joe to make a break like that,” said Nat, with a good-natured laugh that took the sting out of his speech; “we’d better get down to earth once more as quickly as possible. It’s too cold to be comfortable up here.”

“Have you got the descending planes set at their sharpest angle?” demanded the professor.

“Yes,” was the response, “but they seem to have no effect on her at all.”

“We shall have to pull the escape valve and let out some gas,” he said. “The rising sun has warmed the air till the expansion of gas has made the bag too buoyant for the planes to have any effect on it.”

“Yes, but we will have to do it. Mr. Tubbs, pull the escape valve, please,” said the professor, whose nose was red and whose teeth were beginning to chatter.

The air was filled with flying flakes, and the Discoverer seemed to be soaring through a wonderful white void. But it was no time for admiring such effects.

Reaching above his head, Mr. Tubbs gave the cord that worked the escape valve situated on the top of the big bag, a sharp tug.

“It’s stuck fast!” he said, the words coming out shrilly from his blue, frozen lips.

Suddenly, and without the least warning, the cord broke off short in their hands, and they fell sprawling on the floor. To his astonishment, when Nat tried to rise, he found the task difficult. Breathing seemed to be a labor, and his limbs felt like lead. The professor had actually to be helped to his feet, and then staggered, with one hand over his heart, to the helmsman’s settee, on which he sank, breathing with a queer, whistling sound.

“What on earth has happened?” demanded Joe, who like the others, felt strangely oppressed and heavy. His head ached as if it would burst.

“The—the cord must have frozen to the sides of the bag,” gasped out the professor. “The change to this awful altitude turned the night moisture accumulated on the gas bag’s sides to ice. I fear we are doomed, unless——”

“Then we must drift higher and higher till we perish of cold, or the bag explodes and we are precipitated to the earth.”

CHAPTER XX.

Nat staggered toward the door of the pilot-house. Mr. Tubbs, at the wheel, the least affected of the adventurers, turned his head.

“Maybe, but I’m going to make a try for it, anyhow. All our lives depend upon it.”

“By hooky, if it’s to be done, you’ll do it, and if not, why then, I guess we’ll have to meet death as bravely as we can,” was Mr. Tubbs’ muttered remark, as Nat plunged out of the door.

In the cabin Ding-dong, breathing hard, lay on a narrow bunk. Matco was stretched on the floor, apparently unconscious. Nat gazed at them half stupidly.

“Pretty far gone,” was the thought that came into his dazed mind. Then he plunged on again, reeling as he went, his mind concentrated with bitter intensity on the task that lay before him. Gaining the deck, he found the cold almost too much for him, and he turned back for an instant and donned warmer clothing from the professor’s chest.

Then he doggedly proceeded with his self-imposed task. He noticed that the engine had stopped. The bitter cold had condensed the moisture within it and frozen the lubricating oil.

But Nat wasted no time on these observations. What he had to do must be done quickly if at all.

Gazing upward at the huge bulging curve of the under side of the gas bag, he saw the broken ends of the valve cord fluttering from the bag. They were far above his reach, even if the securing of them would have done him any good.

It was only for an instant that he paused. Then, summoning up every ounce of resolution in his determined mind, he seized hold of the starboard rigging and began clambering up and outward.

He did not dare to look down into the awful void beneath him—vast and empty as eternity itself. Keeping his eyes steadily fixed on the bulging bag, Nat climbed by sheer force of will power till he was up to the network that encased the bag.

Right here began the most difficult and terrifying part of his task. Hanging desperately above the immensity beneath him, he had to make his way to the upper part of the bag. He did not dare to think of what he was doing. The very notion of it made him feel sick and dizzy. The lad just climbed, fixing his mind on the thought of reaching and opening the valve.

Somehow—to this day Nat couldn’t tell you how—he clambered round under the bulge of the bag and began the easier task of making his way up the tightly rounded sides to the top of the great cylindrical gas container. As the professor had surmised, ice had formed on the outside of the bag, and made Nat’s endeavor ten times more hazardous and difficult. This ice had clogged the valve ropes, and Nat saw that the only thing to do was, as he had made up his mind, to climb on till he reached the top of the bag.

The possibilities of a slip were awful, and Nat no more dared think about them than he had about the chances of his slipping when he was hanging between earth and sky under the lower part of the bag. He resolutely dismissed them from his mind.

But the physical difficulties of the lad’s self-imposed task were almost overwhelming. There was a sharp pain in his chest, and his limbs felt as if they had leaden weights attached to them. Suddenly a warm stream of something Nat knew to be blood, gushed from his nose; but still he worked his way upward, climbing amidst the network meshes like a sailor on ratlines.

Once or twice he was compelled to pause from sheer exhaustion, and, clinging on with might and main, to spread himself flat on the surface of the gas bag to rest.

If Nat had not been a clean-lived lad all his life, and had not been a hater of smoking and bad company, he would never have been able to endure this ordeal; but somehow, his young vitality won out, and at last he could reach out a hand and touch the valve.

Bracing himself against the rigging, he tugged with all his might. But the condensed moisture had formed ice on the valve, and it stuck.

Nat felt a childish rage take possession of him. Raising his fists, he beat and tore at the valve, while tears of physical weakness and exhaustion streamed down his cheeks.

But even his frame gave way at last, and suddenly his eyes grew dim and he felt as if a sword had been plunged through and through him.

As everything grew black, Nat, with a last effort of consciousness, clutched at something to save himself from being plunged backward into space.

He caught it, or thought he did, and then his senses went out from him with a vivid flash and a terrible roaring in his ears like the sound of a hundred waterfalls.

Half an hour later, or at ten o’clock, Joe Hartley opened his eyes. At first he hardly knew what had befallen him; but in a few seconds his recollection came back with a rush. He remembered that the Discoverer had seemed doomed, recalled Nat’s plunge through the door and how he had tried to follow his chum, but had fallen, overcome by exhaustion, at the door.

But now all the chill was out of the air, bright sunlight streamed through the pilot-house ports, and the professor and Mr. Tubbs, both of whom had collapsed on the floor, were sitting up looking about them rather bewilderedly. The professor was the first to speak.

“A miracle has happened,” he declared. “The Discoverer is out of danger.”

“The barograph shows twenty-five hundred feet,” announced Joe, who had been studying that instrument.

As if in answer to his question, Ding-dong Bell appeared in the doorway between the pilot-house and the main cabin.

“No. The only person out there is Matco. He’s so scared that he’s under the ber-ber-bunk.”

“Where is the lad?” demanded the professor earnestly, with a note of anxiety in his voice.

Mr. Tubbs, who had been struggling with his dim memory of events preceding his collapse, spoke:

“I recall it now,” he said. “Nat said he was going to get that valve open”—he paused—“somehow.”

“I—I didn’t mean to,” stammered the repentant Mr. Tubbs, “but I was so nearly on the verge of caving in, that I couldn’t carry out my resolve.”

“Search the craft thoroughly,” ordered the professor, lines of anxiety showing in his face, “there was only one way to open that valve.”

“He must have, and succeeded, too,” said the professor in a curiously tense voice, “the opening of that valve was the only thing that would result in our having dropped to a supportable region of the air.”

“No. The automatic cut-off arrangement would have closed the valve when we had reached a warmer belt of atmosphere,” explained the professor, “but don’t let us lose time talking here. Scatter through the Discoverer and make a thorough search. He may have dropped unconscious somewhere.”

The anxiety with which the search was conducted may be imagined. The Discoverer was allowed to drift lazily along while they sought some trace of the missing lad, but the search resulted in nothing.

“There is only one conclusion to be reached,” said the professor in a solemn voice, “poor Nat paid the penalty of his bravery with his life. He——”

The man of science broke off, unable to command his voice, and at the same instant came a cry from above them—a hail from out of the air, it seemed:

“Good heavens! It’s Nat!” fairly shouted the professor, as Nat, whose feet were alone visible round the bulge of the gas bag, clambered nimbly down and dropped from the rigging, beside them.

In his excess of joy, the professor flung his arms around Nat’s neck, much to the lad’s embarrassment, while the rest fairly fought for a chance to grasp his hand. In intervals of joy making, Nat told his story, part of which we are familiar with.

It seemed that when he swooned on the swaying balloon top he instinctively clutched at the first thing his hand encountered, which was one of the valve ropes. The valve, already loosened by his pounding on it, yielded to the sudden pressure upon it and jerked open. At least, this was the only explanation Nat could furnish of the fortunate occurrence.

When he came to himself he said he saw that the Discoverer was at a reasonable height, and manipulating the cords he again closed the valve. He was too weak to attempt the descent at once, but lay outstretched on the top of the gas bag, regaining his strength. All this time he suffered with a dreadful fear that his friends below might have succumbed to the awful rigors of the upper air. With an apprehensive heart he at last began the climb down and he concluded:

“You may imagine how delighted I was to hear your voices, even if the professor was preaching my funeral sermon.”

“Three cheers for Nat Trevor, the bravest boy on earth!” shouted Joe Hartley.

The shouts rang out oddly in the thin atmosphere of mid-air, but they relieved the boys’ feelings. As they died out, Matco appeared at the door of the cabin, and gazed at the scene a moment. Then seeing that Nat was the idol of the moment the Indian ran nimbly along the swaying deck and throwing himself on his knees, placed Nat’s foot on his head.

“Say, fellows!” cried Nat with a red face, “that’s about all of this hero business. Let’s have some breakfast and get the engine going.”

And so, what might have been a tragedy, ended in one of the merriest meals ever enjoyed by aerial travelers.

By noon the Discoverer, none the worse for her involuntary flight into the icy realms of space, was able to resume her voyage over the desolate peaks and abysses of unknown depths, above which the adventurers were now soaring.

CHAPTER XXI.

The professor’s observations that day showed that they were within two hundred miles of where the fabled city ought to lie, always supposing that it really had an existence. But you may be sure that not one of the Motor Rangers doubted that fact.

The course was altered, and the Discoverer’s bow turned toward some ragged-looking peaks that cut the sky line to the northwest. The country over which they were now passing was, as has been said, desolate in the extreme. It appeared to have been devastated by earthquakes or forest fires, and the vegetation was scanty, while the surface of the ground was split, and scarred and hillocked like a crumpled bit of parchment. But toward afternoon the character of the scenery changed. The mountains grew in gloomy grandeur and were clothed with dense tropical growth. Between the great masses and lofty elevations lay dark and unfathomable chasms, at whose depth only a guess could be made. It was wild and dismal scenery, and, viewed even from above, oppressed the travelers with its sense of lonely vastness.

The Discoverer was not making as good time as usual, owing to a stiff headwind. Then, too, the engine had not developed its full power since its freezing up in the upper aerial regions. But the professor announced himself as well satisfied with their progress. Matco gradually got over his first fear of the air travelers and talked to the professor in his rough Spanish, which Nat could hardly understand, so besprinkled was it with mispronunciations and Indian words.

The old Indian was much interested in trying to find out what the white men,—for he no longer thought them gods,—were doing in that part of the country. But the professor deemed it wisest not to tell him. Ultimately they would have to set him free, and if he knew too much of their expedition he might make trouble for them with the other Indians.

It was the middle of the afternoon, and Nat was seated in the cabin reading a book on the Incas, when a hail from the pilot house brought him to his feet. Joe, who was at the wheel, was calling him.

Nat lost no time in obeying. As he joined Joe the latter excitedly pointed ahead of the Discoverer’s bow.

“Look at those birds, Nat; they are the largest I have ever seen. I wonder what they can be?”

The birds referred to were flying and wheeling in great circles above a ravine some distance off, but far off as they were, it was easy to see that they were of immense size.

“They are bigger than the biggest turkey buzzard I ever saw in California,” said Nat, gazing at them. “Let’s have a look through the field glasses.”

He took the instruments out of their box near the helmsman’s wheel and applied them to his eyes.

“Why, they look like small aeroplanes!” he exclaimed in astonishment. “Their wing spread must be ten or twelve feet, judging from here.”

“Easily fifty, I should say. Maybe more. It would be impossible to count them accurately.”

“They are right on our course,” said Joe, glancing at the compass, “so that we shall soon have a close view of them.”

“I’ll go and rouse the professor. He’s taking a nap; but I know he’d like to see such a sight.”

By the time he returned with the professor, the Discoverer was much closer to the giant birds. The man of science scrutinized them through the glasses.

“Condors,” he announced. “This is most interesting. These birds are the largest birds of prey in existence. Humboldt, the famous traveler, said that Indians told him that they had been found measuring eighteen feet from wing tip to wing tip.”

“Well, I should say they are aeroplanes,” exclaimed Nat. “Do they ever attack men?”

“Cases of it are not unknown,” said the professor, “and almost every Andean village has a story about a condor flying off with a baby. As a matter of fact, though, I guess they confine their attentions mostly to young sheep or calves light enough for them to carry.”

As they drew closer to the soaring mass of birds, they could see that if they were interested in the birds, the birds were quite as much interested in them. One or two began making long, wheeling arcs that brought them closer to the Discoverer.

“I guess they are wondering what sort of a bird we are, anyhow,” laughed Nat.

Indeed, it seemed so. Almost imperceptibly the birds gathered about the Discoverer, wheeling and screaming all about the craft. It could now be seen that they had sharp, large, hooked beaks, and a ruffle of dark flesh at the bottom of a flabby neck. Their wings were of a dull gray color, with black tip feathers, and were of a sweep and size undreamed of hitherto by the boys.

“They do, indeed,” said the professor. “One could readily imagine such creatures tearing unfortunate human beings to pieces.”

“They don’t seem afraid of us, anyhow,” said Nat suddenly, as one of the great condors swept by quite close to the Discoverer and uttered a wild scream that sounded like a cry of defiance.

“No, they don’t. I—— Bless my soul, they are attacking us!” cried the professor as two or three of the birds flew at the gas bag with beak and claw.

“Get out the rifles, quick!” cried Nat. “They’ll tear the bag open if they keep that up.”

But he might as well have said “Shoo!” to a tiger as to the giant birds of prey that now surrounded the Discoverer on every side. Angry screams and the rushing noise of huge wings filled the air.

Nat returned with the rifles, and with Ding-dong Bell, who had already, from his post at the engines, observed the great birds.

“Now, boys,” spoke the professor, “we must use our best marksmanship on these creatures. They are a real menace to the ship.”

Nat took up his position at one side of the pilot house, Ding-dong Bell at the other, while the professor aimed from the centre window.

At the word “fire!” from the professor, all three rifles began to pump lead into the wheeling, circling, screaming flight of condors.

Several stopped abruptly in their soaring circles and fell to the earth, stricken to death. But others, that were only wounded, fought with more fury than ever. The attack by the adventurers appeared to enrage them. They flew furiously at the Discoverer, and one or two even dashed themselves at the pilot house.

But after ten minutes or more of steady firing their numbers diminished. The ones that were left began to sheer off, and finally took flight away from the invaders of their realm. The noise of the firing brought Mr. Tubbs and Matco out of the cabin, and both watched with interest the effects of the fusillade.

When it was over, and the Discoverer had left the last of the great birds behind, old Matco spoke excitedly in Spanish to the professor.

“What does he say?” asked Nat, when the old man had finished what appeared to be a tirade against something or somebody.

“He says,” rejoined the professor, “that what we have done is very good. That when he was a youngster he was carried off by one of these birds. His mother, who rushed out to save him, was attacked by the condor’s mate and so seriously maimed and torn that she died.”

“His father shot the bird that was carrying him off, with one of the poison arrow tubes,” rejoined the professor, “both the bird and the infant fell to the earth, and Matco says that is the reason his leg is so twisted and that he walks with a limp.”

The boys found this very interesting. It explained, too, something that they had noticed before, and that was that old Matco walked with a decided limp.

“As I think I said,” rejoined the professor, “it is one of the vulture family, and is found from the Isthmus of Panama clear down to the Straits of Magellan. They usually live in the mountains, but sometimes they come down to the seashore to pick the flesh of dead whales. In fact, they have a preference for dead or decaying flesh.”

“They are a first cousin of that bird,” said the professor. “A friend of mine, who had been a great traveler in South America, told me once that the Indians will catch them for two dollars each, and that sometimes they do quite a lively trade.”

“I shouldn’t much care to have one for a pet,” spoke Joe; “but how do they manage to get hold of such immense birds?”

“By a very simple and ingenious method. They build a pen around the carcass of the first dead steer they can find on some cattle estancia, and then await the arrival of the condors to feast on the flesh.

“That is true,” said the professor. “Well, as I was saying, the bird cannot rise without this preliminary run, and, of course, the picket fence interferes with this. That is the condor catcher’s opportunity. He throws a lasso around the bird he has selected and lets the condor fight till he is exhausted. Then he throws another and another till Mr. Condor is tired out. That done, the bird is placed in a rough cage and conveyed to the customer.”

“That’s a lo-lo-lot of work for t-t-t-two d-d-d-dollars,” stuttered Ding-dong Bell.

“Any kind of work would be hard for you,” grinned Joe, which almost precipitated a fight. Nat checked it.

“Don’t roll overboard on this craft,” he said, “even if there aren’t any sharks about.”

“Humph! I don’t know that they are much worse than those condors,” was Joe’s comment.

“If only I’d got a moving picture of that fight with the condors,” he said regretfully.

CHAPTER XXII.

Shortly after the battle with the condors, the professor announced that, inasmuch as they were passing above a favorable landing place, he intended to make a landing. The spot selected was an open space beside a fairly large river, the glint of which could be plainly seen like a glittering ribbon beneath them.

Preparations for a landing were at once begun, and the Discoverer commenced nestling down toward the earth. The professor announced that the first task of the evening would be to replenish the supply of gas in the bag from the hydrogen tanks.

The anchorage was made without a hitch, and the Discoverer moored as securely as before; but in view of their experience of the night before, the travelers decided to have everything ready to “slip and run” in case the unpleasant experience was repeated.

As soon as the dirigible was secured, the task of adding to her depleted gas supply was begun. Two of the cylinders were dragged from their resting place and deposited on the ground, while the filling tube was made ready.

The Discoverer was anchored almost on the banks of the stream, a rapid one, with a rocky bottom and steep banks. While the others were working about the Discoverer, Ding-dong Bell set himself to examining the gas cylinders.

They were about ten feet long and very slender in proportion to their length. They were heavy, too, as the tremendous pressure within them made it necessary to construct them of the thickest and strongest steel,—the very finest grade obtainable, in fact.

Ding-dong, with his natural curiosity, started lifting one, and found that to raise one end was all he could manage, and that only by dint of puffing and blowing.

Joe Hartley, looking around from his work on the filling tube at which he was assisting Nat and the professor, noticed what his chum was up to.

“Say, put that down! You’re not strong enough to lift it,” he jeered. “Those things aren’t for kids to monkey with.”

“They’re not, eh?” puffed Ding-dong valiantly, “I’ll soon show you.”

With a supreme effort he managed to raise the cylinder and move it a short distance.

“Here, stop that!” shouted the professor as he espied what the boy was doing. “Don’t you know those things are dangerous unless handled carefully? They’ll go off like a bomb under a sudden shock.”

“That one must have got a sudden shock when it saw Ding-dong,” scoffed Joe. “Most people do.”

It was too much for Ding-dong. He set down the cylinder and made a jump toward his tormentor. In doing so, his foot struck the cylinder which, as it happened, was only just balanced on the steepish slope leading down to the precipitous river bank.

Before he could complete the sentence, Ding-dong was valiantly off after the rolling cylinder. He grasped it, but its weight and the velocity it had attained, caused it to evade him, and while he fell sprawling in an effort to regain his balance, the cylinder bounded on toward the brink of the steep river bank.

“Down on your faces! Down on your faces! Everybody!” fairly roared the professor.

They all obeyed blindly, not sensing the utility of the order, but realizing its urgency in the tones of the professor’s voice.

The cylinder gave a leap as it struck a stone, and then bounded over the edge of the river bank.

An explosion that shook the ground followed almost instantly. From the bed of the river a geyser of mud and water and rocks spouted up, showering everything for a radius of several yards. The explosion the professor had dreaded had taken place; but, by a miracle, no one was hurt. No doubt the fact that the detonation took place below the river bank accounted for this fact.

“If you ever catch me mo-mo-monkeying with that h-h-high-diddle-diddle g-g-g-gas again you can ber-ber-ber-blow me up with it,” he declared.

“That ‘high-diddle-diddle gas,’ as you call it, is much too precious for that,” said the professor with a laugh he could not restrain, “but I shall adopt other measures.”

The boys had a good opportunity then to see the destructive force stored in one of those innocent-looking cylinders. Peering over the river bank they could see that a great hole had been blown in its bed, and rocks riven and split in every direction.

“It is, indeed,” said the professor. “The condition of that river bed gives mute evidence of that.”

“Just think what would happen if a spark should ever enter that gas bag of ours,” said Nat, with a slight shudder.

“Come, let us get back to work,” suggested the professor, “roll that gas cylinder closer to the filler tube and we will make the connections.”

Gingerly enough, as you may imagine, the lads rolled the cylinder toward the end of the filler tube, which now lay extended on the ground. The end of the tube was fitted with a union, which, in turn, was screwed on to the nozzle of the gas cylinder. Then the professor turned on the vapor, of whose power they had just had such a striking example.

With a hiss and a roar the gas poured through the filler tube into the bag, and several small wrinkles, which had developed in its upper surface, began to fill out. Two cylinders were emptied before the professor and Mr. Tubbs announced that the bag was full enough.

The evening passed off quietly. As before, the evening meal was eaten on the ground, and the adventurers utilized the cabin of the Discoverer for sleeping quarters. Old Matco, the Indian, shared the meal, but refused to sleep within the cabin. Instead, he rolled himself up outside, on the substructure, like an animal of some sort. He had the true aborigine’s dislike of sleeping under a roof. It savored to him of a trap possibly.

The old fellow, now that he had become used to aerial navigation, did not seem to object to it in the slightest. He rather appeared to like it, in fact, and took a childish delight in watching the various operations that went on on board. It appeared that he had no intention of detaching himself from the party as yet, and indeed, seemed to have the liveliest gratitude to them for rescuing him from his unpleasant position at the end of the swinging rope.

The professor was of the opinion that Mateo might prove useful to them, so no move was made to urge him to return to his tribe. Indeed, they were now in the country of another tribe of Indians altogether,—so Matco informed them,—a tribe as warlike and resentful of the intrusion of white men as his own. This was not encouraging news, but the adventurers resolved to make the best of it, and guard against surprises by keeping a good watch.

Nothing occurred during the first part of the night, and when Ding-dong and Joe came on duty at midnight the professor and Nat had nothing to report.

“Don’t forget that time you shot at the mule,” warned Nat, addressing himself to Ding-dong.

“Oh, no danger of my doing that again,” Ding-dong assured him; “b-b-b-b-besides, they d-d-don’t have mules in this p-p-part of the country.”

“That’s good logic, at all events,” laughed the professor, who had heard the story of how Ding-dong shot at a mule in mistake for an Indian the night the Motor Rangers camped in the petrified forest in the Sierras.

Ding-dong and Joe marched up and down for some time, without anything occurring to mar the quiet of the night. But on what was, perhaps, the stuttering lad’s twentieth parade around the dirigible, he heard a queer, inexplicable sort of noise coming from the river.

“That sounds like somebody snoring, and Indians who were coming to attack us wouldn’t announce their presence like that,” thought Ding-dong.

The snoring noise continued. Joe was on the other side of the dirigible, while Ding-dong was on the river end of it.

“It’s a good chance to distinguish myself,” thought the lad, “after the mess I made of that gas cylinder this afternoon. I’ll just creep down there and see what on earth that racket is.”

He began tiptoeing softly toward the river bank, while the grunting, snoring sound still continued.

“I do believe it’s some one asleep down there,” exclaimed the lad to himself. “Maybe I’ll make a prisoner and get even on Joe for laughing at me.”

His mind full of these visions of glory, Ding-dong at last reached the river bank. Behind him he could hear Joe softly calling, but he made no answer.

Lying flat on his stomach Ding-dong peered cautiously over the bank. He could see the gleam of the water about ten feet below him and—what was that? Two dark figures, that appeared to have bulk of considerable size, moving about in the water? One was larger than the other, and it didn’t take the boy long to make out that whatever the mysterious objects were, they were not human beings.

“Wonder if they’re panthers?” thought the boy with a sudden chill. But then he recollected that panthers are not in the habit of prowling about in the river bottom.

“And I never heard of a panther grunting,” considered Ding-dong, “I guess I’ll just——”

But what Ding-dong had “just” made up his mind to do was never revealed. The bank at the point where he had been leaning over, was cut out beneath by the action of the river, and in scrutinizing the dark objects he had leaned rather far over.

Suddenly the bank caved in, and amidst a shower of gravel, rocks and small bushes, Ding-dong went rolling down into the river.

He landed in a deep pool, which, luckily for him, was of sufficient depth for him to avoid injuring himself. Still clutching his rifle he rose to the surface, puffing and blowing, and scrambled out.

“Well, here’s a fix,” thought Ding-dong, “just like my luck. I’m always getting in bad.”

All this time he had quite forgotten about the two dark, moving objects, to whom he owed his present predicament. But their existence was rudely recalled to him as, out of the darkness, something rushed at him, snorting loudly and angrily, and advancing like an express locomotive.

CHAPTER XXIII.

The adventure might have had a serious termination for the lad if Joe, who had heard the collapse of the bank and the subsequent roar of the avalanche, of which the luckless Ding-dong was the centre, had not rushed to the river bank. Ding-dong, far too much astonished to raise his rifle, was standing stupidly gazing at the animal that was rushing toward him when Joe fired.

The creature gave a leap into the air, a queer kind of squeal, “like a stuck pig,” Ding-dong said afterward, and fell dead.

The shot aroused every one on the Discoverer, and they came crowding down to the river, to find Joe and Ding-dong examining, by their electric pocket lights, the carcass of a large animal with a peculiarly shaped snout. Explanations ensued, and the professor announced that it was a tapir, a species of water animal common in South America.

Matco assured them that the meat of the creature was very good eating, and much esteemed by his people, and he was permitted to cut some steaks from Joe’s prize.

“If I hadn’t ter-ter-tumbled into that pool, though, he’d have been mer-mer-mine,” declared Ding-dong positively.

“I guess you’d have been his,” laughed Joe, “that is, if you didn’t move any quicker than you were when I saw you.”

“You watch me. I’ll do something great yet,” declared Ding-dong, with a positiveness that deprived him of his stammer.

“It must have been great the way you went over that bank,” laughed Joe unfeelingly.

The professor made Ding-Dong put on dry clothes, and then the interrupted rest of the travelers was resumed. The remainder of the night passed without incident, and a breakfast that took place soon after dawn was eaten amidst much rallying of Ding-dong on his adventure of the night before.

“I’d like to have seen any of the re-re-rest of you ber-ber-brave enough to have gone near that snor-snor-snoring,” sputtered the lad, valiantly helping himself to some more tapir steak, which was found to be as good as the old Indian had declared was the case.

At eight o’clock the Discoverer was ready to resume her flight. She took the air without any accident, and under her replenished supply of gas rose with tremendous buoyancy. In fact, the descending plane had to be adjusted to keep her from shooting up too rapidly. No one on board had any desire to repeat that flight to the chilly regions of the upper air. As Ding-dong put it, “N-n-n-no more on my per-per-plate, thank you.”

“Do you think we shall sight the city to-day?” inquired Nat, as he and the professor stood on deck, just below, and in front of, the pilot house.

“Impossible to say, my lad,” was the rejoinder. “As I told you, the directions to reach it are vague in the extreme. We may have to cruise about for several days before we satisfy ourselves of its existence or non-existence.”

Nat looked disappointed. The boys, at a consultation among themselves, had about decided that that day ought to find them at their long-sought goal. Their expectation had been keyed up to such a height that delay was exasperating.

At noon the professor took his observations, and declared that, if the city existed in that part of the country, they ought to be within striking distance of it.

Excitement ran at fever heat. The boys could hardly leave the deck to eat a hasty meal. The field glasses were in constant demand. The professor announced that he would donate a handsome rifle to the first lad to spy a sign of the mystery of which they were in search.

If the boys had been eager before, this offer doubled their alertness. Ding-dong even climbed into the rigging till he was sternly ordered down by the professor.

“I thought if I got higher that I c-c-c-c-could see it s-s-s-sooner,” he explained.

“As we are now at a height of two thousand feet,” observed the professor, “I don’t think that a foot or two more of elevation would give you a very much extended view.”

It was about one-thirty when Mr. Tubbs, who was at the wheel, called the professor’s attention to something odd on the horizon. “It’s glittering,” he said, “and may be a ledge of quartz or something.”

“No,” was the rejoinder. “It just flashed up for an instant,—like a mirror in the sunlight,—and then vanished.”

“Keep a sharp lookout for its reappearance,” said the professor, with a hint of suppressed excitement in his voice.

“Shall I steer in the direction in which I last saw it?” asked the navigator of the Discoverer.

“Yes. If the old documents are correct we are so near to the location of the lost city now that any clue is worth following.”

“I cannot say,” rejoined the professor. “It may have been that, or it may have been the sunlight flashing, for an instant, on a hidden lake.”

“But wouldn’t a lake up here come pretty near to proving the existence of the city we are in search of?” asked Nat.

“How do you draw such a conclusion?” inquired the professor, with scientific exactitude.

“I thought you said the old documents said that the lost city was on an island in a lake.”

“Ah, yes; but there may be many lakes of the kind described in these regions,” was the reply. “Any more unusual signs yet, Mr. Tubbs?” he asked presently.

“No,” was the rejoinder; but the moving picture man’s keen eyes scanned the distance like those of a hawk.

It was an hour later that Nat, who had the glasses, set them down with an excited face.

“I can see a lake!” he cried. “At least, I’m almost certain it is one.”

“Off there—in the same direction that Mr. Tubbs saw a glitter. I only caught a glimpse of it, but it looked as if there was the glint of water in among those queer, sharp-pointed peaks off there.”

“Speed up the engine if you can, Master Bell,” said the professor, with an expression in his voice that the boys had never heard there before.

“We must investigate this at once and lose no time,” he went on. “The old documents say that the lost city is on an island in a lake set in the midst of mountains, over which there is no way of climbing but by the lost and secret roads of the Incas.”

“I guess you get the rifle, Nat,” said Joe, without a trace of envy in his voice, though.

“I w-w-w-wish I’d s-s-seen it f-f-first,” sputtered Ding-dong, who was leaning far out over the rail.

The abrupt conclusion of the stuttering boy’s speech had been caused by the fact that, as he made it, he half turned, and losing his balance plunged over the rail.

The Discoverer was then nineteen hundred and fifty feet above the surface of the earth!

CHAPTER XXIV.

But even in that instant of deadly peril, Ding-dong did not lose his presence of mind, or, perhaps, instinct of self-preservation would be a better phrase.

As he felt himself lose his balance, he clung to the network of the rail, and hung there head downward between the sky and the earth for one instant. But that brief molecule of time was enough for Joe and Nat to secure his feet, as they flashed over the rail, and drag him back on board.

“Go to the cabin, sir,” ordered the professor, who was white and shaky, as, indeed, were the others.

There was no gainsaying his words, but Ding-dong, as usual, had to say something. He was the most unperturbed person on board, in fact.

“I d-d-d-d-didn’t do it on p-p-purpose, you know,” he remarked, as he walked off.

“Good heavens!” exclaimed the professor, leaning against the rail, “what trouble is that boy going to get into next?”

The stuttering lad’s narrow escape had so unnerved them all that there was no answer.

“Well?” said the professor at length, as if seeking a reply to his question.

“Don’t ask me, sir,” gasped out Nat. “I haven’t got my breath back yet.”

It was, perhaps, half an hour later when the entire craft was electrified by a cry from Joe.

No need to ask to what he referred. The professor ordered the Discoverer sent higher, so as to give them a larger horizon, or, rather, a bird’s-eye view.

As the craft rose upward in obedience to her planes, they saw beneath them, but still at some little distance, what Nat has since declared was the most wonderful sight he has ever seen or hopes to see.

Rimmed by bare, gaunt mountains, inhospitable and bleak, lay a small lake, set like a turquoise in dull gold. In the midst of this lake was an island, and on this island, even at that height, they could perceive, were buildings rising in terraced formation. At the extreme summit of the island, which rose to a peak, was something that flashed and glowed in the sunlight almost blindingly.

“Say, Nat,” said Joe in rather a shaky voice, laying one hand on Nat’s arm.

“What is it, Joe?” asked Nat, without taking his eyes off the wonderful sight before him.

“Nothing; only—only I feel a bit scared,” was Joe’s quavering confession.

“You may well feel awe-stricken,” said the professor, whose eyes were gleaming, “ours are the first eyes to behold that island since the mysterious catastrophe that wiped out the race that inhabited it, occurred.”

It was the incorrigible Ding-dong, who had taken advantage of the excitement to slip out of his place of involuntary confinement.

But, in the general interest in all that was occurring, no attention was paid to him. In the midst of the eager talk, and still more eager scrutiny of the island, old Matco, who had come out upon the deck and had stood silently gazing at the lost city, uttered a sharp cry.

Then, raising his hands above his head and fixing his eyes upon the sun, he began muttering what seemed to be a prayer.

This done, he turned to the professor and poured out a rapid flood of eager, emphatic words in his corrupt Spanish. So fast did he speak that the professor had difficulty in following him. But by paying close attention he managed to make out the old man’s meaning.

“What does he say?” asked Mr. Tubbs, as the old Indian ceased his torrent of words, and leaned back, looking quite exhausted.

“Why, it’s like fiction,” said the professor. “The old man says that we are fulfilling a tradition of his race which says that one day winged men from the sky would discover the city.”

“W-w-w-whatever that may be,” sputtered Ding-dong. “Guess you mean n-n-no men.”

But the professor paid no attention to the irrepressible youth. Instead, he assumed rather a grave look.

“Why, I’m not quite so sure that it is a good augury,” he said slowly. “The old man says that the prophecy or tradition goes on to say that the wrath of the long-dead Incas shall be visited on the violators of their hidden city, and that a terrible end will overtake the sky men who invade it.”

As the professor talked the old Indian fixed his eyes on him as if he realized what he was saying. As the man of science concluded, he nodded solemnly, as if indorsing all that had been told.

“Oh, well,” said Nat, “we are not going to turn back for the sake of an old Indian ghost story.”

“Of course not,” said the professor; “but I thought if any of you are superstitiously inclined, I would warn you.”

“I guess it would take more than talk like that to turn us back now,” said Joe. “I’d face a legion of spooks to investigate that place.”

The others agreed with him. Indeed, as the Discoverer grew nearer, the marvels of the lost city grew more and more awe-inspiring.

What had appeared in the distance to be a mere huddle of terraced buildings, were now seen to be stately palaces, some of them with trees still growing amidst them. The buildings rose in this form till they reached their climax at the great gold-plated dome that capped the summit of the wonderful isle.

The walls, so far as could be seen, were white, but profusely ornamented with barbaric magnificence.

Not a little of the mystic effect of the island was gained from the precipitous and rugged cliffs of the mountains that walled the lake.

“However do you suppose a lake came to be in such a situation?” wondered Nat, addressing the professor.

“In my opinion,” said the scientist, “that lake is what was once the crater of a volcano, more enormous than any yet known.”

“And what we thought were separate mountains were once only part of the summit of that volcano?” asked Nat wonderingly.

“I think we would be correct in assuming so. In many parts of the world the craters of extinct volcanoes are found to be filled with water, just as this one is.”

“In some cases it has been impossible to touch bottom, even with the longest lines and the most perfect sounding apparatus,” was the astonishing reply.

“But how does an island come to be in the middle of such a deep lake?” was what Mr. Tubbs wanted to know.

“What we call an island is probably the summit of another peak of the crater,” said the professor, “or it may have been formed, like those volcanic islands of which we have such a keen recollection, by the action of earth’s internal fires.”

The dirigible dropped lower. It was now almost directly above the lost city. It could be seen that surrounding the golden dome was a vast, semi-circular platform or courtyard of stone, with other stones set up perpendicularly around it.

“It is precisely like the arrangement of the Temple of the Sun in Peru,” said the professor.

“Doesn’t it seem almost like a sacrilege to bring a modern dirigible to earth in the very courtyard where the rites of ancient religion were practiced?” spoke Nat, who was an imaginative lad.

“Not at all,” said the professor, “and as for that ancient religion, if we had lived in the days when it flourished, I fancy we wouldn’t have liked it much. Like most ancient religions, it was a creed of bloodshed and violence. Human sacrifices may have been indulged in on those very stones we see beneath us.”

The boys agreed that this put quite another light on the matter, and the descent was made without further comment. The dirigible came to rest in the lost city of the Bolivian Andes at three o’clock in the afternoon. Mr. Tubbs was left to guard the Discoverer with old Matco, who refused to move one step through the silent, long-deserted streets. But the boys and the professor set out on a tour of exploration.

The streets, they found, were like those of mountainous cities in Europe, and consisted mostly of steps. It was one of the most uncanny feelings that any of them had ever experienced, this walking through a city of the dead. For, although the ancient places were mostly in ruins, from earthquakes the professor judged, the city yet seemed lifelike enough for some of the vanished race to turn a corner at any instant.

For some reason, the boys kept very close to each other and to the professor, showing no disposition to wander. They found that, as they approached the lake, the buildings grew poorer in character and were not carved or decorated like those closer to the temple. The remains of a splendid wharf remained, however, which set the boys to wondering what had become of the boats that must have once plied between the city and the shore.

This, in turn, suggested ruminations upon the means employed by the vanished race of reaching the lake, for to climb over the mountains was obviously impossible. The professor opined that, at some time, a tunnel must have existed. This set the boys crazy to try to find it, but the man of science declared that, in all probability, the tunnel, if it had ever existed, had been ruined by earthquakes long since.

They stood by the lake side for a time looking into its dark blue depths, and then began a return up the street, climbing the steps cut in the rock.

“Where’s all the treasure we were going to find?” asked Joe, as they climbed the steep causeway worn by the feet of a race long since passed out of existence.

“I don’t imagine we are likely to find much that is valuable,” said the professor. “My belief now is, that when the Spaniards came the inhabitants of this city concealed everything valuable in it in some place known only to themselves.”

“That is not improbable. At any rate, I think we shall have to content ourselves with the glory of having discovered this wonderful place. It is far more perfect than the ruins of Peru are described as being.”

“What about taking that gold plating off the sacred dome?” said the practical-minded Joe.

“Not with my consent,” said the professor. “I would wish this city to be the Mecca of antiquarians from all over the world.”

“I agree with you,” said Nat. “It would be vandalism of the worst sort to strip that rock.”

“Here’s a peculiar-looking building,” went on Joe, a few moments later, as they passed a tower-like structure, higher than the other buildings, and without windows.

“Let us survey it,” said the professor. “See, here is a door. It has fallen in, it is true, but I imagine we can squeeze through.”

By dint of getting on their hands and knees they managed to crawl under the richly carved and broken portal, Nat pausing to notice that the carvings seemed to be of various astronomical bodies.

Within the tower they found themselves standing at the bottom of a tall, narrow, perpendicular shaft. It was, in fact, like looking up a circular chimney. At the top was something which at first sight seemed to be a big glass lens; but the professor pronounced it to be pure crystal.

“This is the most amazing find yet!” he exclaimed with enthusiasm. “I believe that this tower formed a sort of rude telescope, through which different observations were carried on.”

He clasped his hands in scientific fervor. Indeed, they had seen enough that afternoon to turn the brain of the least imaginative man of science!

“That settles the matter,” said the professor enthusiastically. “Good heavens, what a find! It has long been a controversy between various scientific men as to whether or no the ancient races understood astronomy in the true sense. The finding of this rude telescope will go far toward—— Gracious! what was that?”

Before the professor could conclude his sentence the boys saw a small brown paw project from a ledge above him and whisk his unlucky hat from his head.

“T-t-t-there they go,” cried Ding-dong, as a dozen or more apes of the prehensile tailed type rushed off amidst the ruins, chattering and squealing and tearing and clawing at the professor’s unlucky headgear.

“Just to think,” sighed the man of science with resignation, “that I came all this way, and we have made all these discoveries, and yet my ill-fortune with hats pursues me still.”

“I’d give several dozen hats to have seen what we’ve seen,” Nat reminded him.

The professor leaped back just as an ugly flat head, with a pair of malicious leaden eyes, protruded itself at his elbow from between the crevices. It was the head of an immense snake.

“Exploring is certainly strenuous work,” commented Joe as they gained the open air.

CHAPTER XXV.

Early the next day the explorers, boys and adults, resumed their investigation of the Lost City. The professor estimated that it would take some time before they had completed their work and collected relics, records and films of the various features of absorbing scientific interest to be found there.

Joe and Nat struck out in one direction, while the Professor, Ding-dong and Mr. Tubbs assumed another line of investigation. The path taken by the two boys led them down one of the crumbling streets to the lake front of the Lost City. On the way they entered several of the houses and collected some small relics and Joe, who had some talent that way, busied himself in making rough sketches of the buildings they examined.

At last, thoroughly tired out, the two lads sat themselves down on a raised pile of carefully fitted stones in the courtyard of a splendid white building with a pyramid-like cupola. They had brought some sandwiches and a flask of water with them and made a light meal while they rested.

“Seems like a sort of sacrilege to be eating corned beef sandwiches in what may have been a temple,” said Nat as he ate.

“From what we know of the folks that used to live here they used to make corned beef out of anyone they didn’t like, so don’t worry about that end of it, old fellow.”

“That’s so,” agreed Nat. “I wonder, for instance, if this business we’re sitting on at this moment isn’t an old altar of some kind. Looks as if it might have been.”

“It does that,” agreed Joe, “and see here, Nat, here’s a metal ring right here in this slab of stone. I wonder if they used to tie their poor victims to it?”

He indicated a big ring of dull, greenish metal which they had not noticed before. It was countersunk in one of the slabs of stone that formed the top of the altar.

“I guess more likely it was used to raise this stone,” he said. “Maybe the altar is hollow inside and contains relics of some sort.”

“Cracky! I’d like to raise it,” declared Joe; but, although he tugged and pulled till his ruddy face was redder than usual, Joe could make no impression on the stone.

With what idea, he could not exactly say, the boy gave the ring a gentle twisting motion instead of tugging at it. Then an astonishing thing happened. The entire top of the altar tipped downward and the boys were shot, scrambling and struggling, into the interior of the altar, if such it had been. Before they knew just what had occurred they found themselves in total darkness, for, having tipped them off, the stone had swung into place again.

A thrill of fear crept icily through Nat’s veins as he realized that they were prisoners. But he put all the heart he could into his reply when Joe in a frightened voice gasped out:

“Why, just this,” was the reply. “That altar top was counterbalanced. Our weight was on one end of it. In some way, when I twisted that ring, a spring or catch must have been loosened and—and—we’re in the interior of the altar.”

“That’s just what we’ve got to find out, and quickly, too, Joe,” was the response. “Got any matches?”

“Yes; luckily I brought some. I’ve got a pocket lantern here, too, with a candle in it. Shall I light up?”

The next minute the interior of the altar was illumined by a yellow light. But so perfectly had the swinging top of the altar been fitted that not a crevice appeared and as for any lever or handle by which it might have been opened, none was revealed by the light.

But it was some minutes before the boys found out this fact. When they did, however, it came with a sense of stunning bitterness. If they could not find a means of egress from the altar, they were, in all human probability, doomed to die in that gloomy prison.

Although they both realized their situation, neither lad voiced his fears. There still remained one end of the altar to be examined, and Nat lost no time in proceeding to investigate the hitherto neglected portion of their prison. But its masonry appeared to be as solidly constructed as was the case in every other part of the altar. Nat, almost in despair, was turning away when Joe, who had been at his side, gave a sudden cry.

“Nat! Nat! There’s a stone loose here. I can move it with my foot. When I press down on it—Great-jumping-horned-toads!”

Joe’s exclamation was caused by the fact that as he pressed down on the loose stone a small door opened out before them in the end of the altar. It was impossible to say, however, whither it led, as beyond lay total darkness.

“What do you say, shall we try it?” asked Joe in a rather tremulous voice, for the darkness looked singularly mysterious and forbidding.

“We’ve got to try it,” said Nat gloomily. “It’s our only alternative, unless we want to stay here and starve to death.”

Joe had to agree that this was a true statement of the facts of the case, and not without quickened pulses the two lads made the plunge into the darkness beyond the door. The portal was square and so low that they had to bend to get through it. The rays of Joe’s candle-lantern showed the two youths that they were in a low-roofed passage, or tunnel, just wide enough for them to proceed in single file.

“You go first,” said Joe in a rather quivery tone, which showed better than anything else that the adventure was having its effect upon him, the usually unperturbed.

“Maybe I don’t, too. If we ever get out of this place, I’ll leave all such devices severely to themselves in future.”

“On the other hand, it may have been designed as a means of executing their criminals or enemies. I’ve heard of such things.”

No more was said for a time. The circumstances didn’t make the boys feel much inclined for conversation.

All at once they emerged into a vaulted chamber, seemingly cut out of the living rock. At the top of its arched roof was set a huge crystal, very like the one they had seen in the “telescope tower,” only much larger. Through this lens light was streaming into the place, the walls of which were painted and carved with all manner of strange-looking inscriptions and designs. Nat was so intent on gazing at these that he did not look as carefully where he was going as he had in his progress down the passage.

Suddenly his feet slipped from under him and he found himself falling downward. Joe uttered a cry as he saw his comrade vanish. He leaped forward, checking himself just in time to avoid sharing Nat’s plight. He found himself on the brink of a sort of well about ten feet deep. At the bottom of this was Nat. Joe uttered a cry of relief as Nat hailed him and assured him that, by a miracle, he was not hurt.

How, indeed? The question certainly was a poser. The walls of the well were as smooth as glass almost and Joe noticed a peculiar feature. From its “curb” radiated long lines extending over the floor of the rocky chamber. These lines were cut in the rock and reminded Joe of lines he had seen cut on a sun dial.

But he gave little thought to this at the moment. His mind was centered on finding a means to get Nat out of his predicament. But, though he thought and thought, no solution of the problem occurred to him.

Joe was still wrapped in thought at the edge of the well when he felt a sudden blast of fearful heat on his back. He looked hastily round. His first thought was that some hidden fire must suddenly have burst into life behind him.

But, no, what he had felt had been the rays of the sun pouring through the crystal at the top of the cavern and striking down with tremendously magnified force upon him.

It was a moment later that he observed something that filled him with a vague sense of alarm, which swiftly crystallized into a sharp, livid pang of fear.

The sun was now striking down into the well. Like a thunderbolt the purpose of the pit and the reason of the crystal lens burst upon Joe.

The ancient dwellers of the Lost City had been Sun Worshippers. This chamber was a sacrificial one and the priests of the vanished race had offered up their victims’ lives by literally dedicating them to the Sun gods. As this alarming truth broke upon Joe a faint cry came from Nat, down in the pit.

“Joe, for gracious sake, do something to get me out of here! The sun is striking down into the pit. It is fearfully hot. If you don’t get me out soon I’ll be baked alive.”

Poor Joe cast his eyes about him despairingly. The sun was streaming through the lens at an angle now. What would happen when its direct rays poured down into the narrow well he could not bear to think.

CHAPTER XXVI.

Suddenly a thought struck him. Perhaps by joining his belt and Nat’s together and then leaning over the edge of the pit he could haul his unfortunate chum up to safety. It was worth trying, anyway.

Going to the edge of the pit and leaning over, Joe communicated his idea to Nat. By this time the sun was streaming dazzlingly into the pit and only by crouching in one corner could Nat escape its ardent rays. Acting on Joe’s instructions, Nat took off his belt and threw it upward. After one or two trials Joe managed to catch it. Then, taking off his own, he joined the two together. Then he extended himself at the edge of the well, and, reaching out his arm to the utmost, lowered the two joined belts down to Nat. They were about a foot too short for Nat to reach them even with the utmost endeavor of which Joe was capable!

Things began to look black, indeed. Momentarily the sun was nearing the zenith, and the place into which Nat had fallen was so designed that when the luminary reached its highest point in the skies the excavation would be filled with its rays, magnified many times by the crystal lens. The lens, in fact, was nothing more nor less than an immense burning-glass designed to shrivel up the victims of the ancient priesthood. How little those who invented such a cruelly ingenious device could have imagined that a boy of the twentieth century would ever be in danger of losing his life by it! Yet such was the case and neither Nat nor Joe could conceal the fact from themselves an instant longer.

“Can’t you think of anything? Don’t you think you could climb up just a foot or two?” asked Joe, despairingly.

“The walls are smooth as glass. I don’t believe a fly could get a hold on them,” was the rejoinder. “Joe, the heat is getting awful!” gasped out poor Nat in conclusion.

“Gracious! What am I to do?” cried Joe to himself. He rose to his feet and gazed about him. Suddenly a thought struck him. If the priests, as seemed only too probable, really roasted people to death in that well, they must have had some means of getting the bodies out. How did they do it? It must have been by a chain or rope, or something of the sort, was the thought that struck Joe after a minute’s reflection. In that case the chain, or whatever they used for the purpose of extricating their victims, must be somewhere in the chamber.

Then he hailed Nat in as cheerful a voice as he could muster. He told him what he was going to do and begged him to keep up his courage. Nat replied bravely that he could hold out a while longer; but the weakness of his voice made it painfully evident that if help was to be furnished him it would have to come quickly or be too late.

Joe noticed, now that his sight was quickened by the need of hasty action, that off at one side of the chamber was a recess cut in the rocks. He hastened over to it and found that within it was an ancient chest of some sort of sweet-smelling wood. This was so dry-rotted with the ages that a vigorous kick of the lad’s foot smashed the moldering lock off and Joe hastily threw the lid open.

He could not refrain from uttering a cry of joy as his eyes noted its contents, some spears, axes, of stone or flint—whose former purpose seemed only too evident—and, best of all, a coil of chain, forged of the same peculiar greenish metal as the ring had been.

“Hurray!” shouted Joe as he dragged out the chain, “this is what we wanted. Now I’ll have Nat out in no time.”

Hastening back to the lip of the well with the chain, he dangled its end, which terminated in a hook, over the edge. As he did so he gasped at the hot fumes which arose from the cylindrical pit. Joe was only just in time. Nat had barely strength enough to fasten the chain under his armpits and begin scrambling up as Joe hauled with all his might.

But if the hole had not been small enough in circumference for Nat to brace his legs against one side of it and help work himself up in this way, Joe would never have got him out. As it was, the task almost exhausted the strength of both boys, and when it was completed they lay gasping at the edge of the well for some moments, utterly unable to command their limbs.

Joe was the first to recover. The sun had now reached the zenith, and through the mammoth burning-glass was pouring hotly into the well. A sudden idea struck Joe. He tore a bit of paper off an old envelope he happened to have in his pocket and let it flutter into the pit.

As it dropped waveringly the paper turned brown, then black, and as it struck the bottom of the sun-heated pit it dissolved altogether into shrivelled cinder.

Joe turned away from the pit with a shudder. The thought of the fearfully narrow escape Nat had had almost unnerved him. But for Nat’s sake he did not let the other lad see how shaken he was. Shortly after Nat, though still weak, was sufficiently recovered to get shakily to his feet. Then the two lads set about to find a way out of the sacrificial cave. First, however, they armed themselves with a stone-axe apiece.

The arched entrance of another passage than the one by which they came opened off on one side of the cavern, and as they peered into it they could feel a sharp puff of delightfully cool air. “That means that this passage leads out into the open,” cried Nat gleefully. “Come on, Joe, we’ll soon be out of this mess.”

Joe, rejoicing as much as Nat, followed the young leader of the Motor Rangers. As they advanced the air blew upon them cleaner and sweeter every instant. Both lads inhaled it in great lungfuls. It seemed as if they could never get enough of it after that oven-like chamber of the sun.

“Near the camp, I hope. How astonished the others will be when we tell them of what has happened to us! I’ll bet they’ve had a tame time compared to ours.”

“I hope so for their sakes,” said Nat with a laugh, “but I guess we are out of the woods now.”

But were they? It seemed to the two young Motor Rangers, a moment later, that they were not by any means “out of the woods,” as Nat had phrased it.

Instead, they soon found themselves at the mouth of the passage; but as far from finding their friends as ever. For the tunnel emerged in the face of a precipitous cliff, below which glittered the waters of the lake. It was a cruel disappointment.

While they still stood there, almost crushed by the sense that after all they were still prisoners—and apparently hopeless ones—a startling thing happened.

Human voices they were beyond a doubt. They were borne to the ears of our two young friends with the booming sound produced by the tunnel, which formed, as it were, a giant speaking-tube.

The boys exchanged alarmed glances. Who could these denizens of the subterranean world of the island be? Survivors of the cruel race of whose practices they had just had a terrible revelation? Robbers, or worse, who had made the Lost City their rendezvous? Or was it, after all, a trick of the imagination?

Determined to test this last idea, Nat slipped a short distance into the tunnel and listened intently.

A few seconds satisfied him that their imaginations had played them no pranks. Voices, far off, but apparently coming nearer, could be distinctly heard. Nat turned faint and sick for an instant, and a glance at Joe’s face showed him that his companion, too, was badly shaken. Nat did not blame him. The knowledge that mysterious beings of some sort were within the tunnel and coming toward them—perhaps on their track—gave him a most uncomfortable thrill.

He glanced down from the ledge on which they stood. The cliff face was smooth, although some metal rings showed that a ladder must once have existed by which the lake might be reached. Above the mouth of the tunnel the precipice was sheer also.

They were fairly trapped. As they realized this each lad instinctively grasped his stone-axe tighter. Nat crouched behind a boulder and Joe squeezed in close beside him.

“Who do you think they are?” he quivered, “survivors of the Lost Race, or—or——”

“I don’t know,” rejoined Nat, with what composure he could summon, “but this I do know, that they are not likely to be friendly if they find us.”

“Yes, a chance that they may not come as far as this, or may not see us. They may be crossing some intersecting passage from a higher level.”

But a few minutes later the voices grew louder. The perspiration broke out on Joe’s forehead. He gripped his axe more tightly, but the sense of the mystery surrounding the beings who were approaching made him catch his breath in agitation. He felt as if he were in some nightmare.

“Mind! Don’t make a hostile move unless they attack us first,” warned Nat in an impressive whisper.

“Jumping hop-toads! That’s Ding-dong Bell!” cried Joe, dashing down his hammer.

With wild whoops of joy the two boys who an instant before had been expecting to face, they knew not what, peril, rushed to meet their friends. They were in such a hurry that they narrowly escaped being shot, the other party being as much alarmed at their approach as they had been at the advance of the professor and his companions.

Matters were soon explained. The professor and his comrades had found the mouth of a tunnel in an old temple. Entering this, it had brought them underground. Some distance above the lake end of the tunnel which the boys had traversed, the passage by which the professor had travelled joined it. The hurry of Nat and Joe to reach the fresh air explained why they had not noticed the branch passage. Had they done so and followed it they would have come out not far from camp.

CHAPTER XVII.

The search of the ruins was prosecuted with vigor for several days more before they stumbled upon anything in the way of “te-ter-treasure,” as Ding-dong Bell called it. But during that time the boys’ eyes had been so satiated with wonders of ancient architecture and carvings, that they had almost forgotten about the more material part of their quest.

One afternoon Nat and Joe had set forth to explore a temple which, hitherto, had not been entered. The professor would have accompanied them, but he was busy working up his field notes into his journal, and compiling in systematic form descriptions of the wonders of the island. Mr. Tubbs and Ding-dong had gone off making photographs, of which a goodly number had been taken, not forgetting several motion pictures, showing the explorers at work.

“Suppose we take a look over that queer, oblong building,” said Joe, as they set out, indicating a smaller building than the others, not so very far removed from the grand circle of structures fronting on the circular Sun Temple, which formed the “hub” of the island.

“Very well,” said Nat; “but I don’t suppose it contains anything but a replica of what we’ve seen already.”

“Well, inasmuch as the professor has made up his mind not to leave the island till everything has been explored and recorded, we might as well see what we can see in there,” went on Joe.

So the two lads set forth on their tour of exploration. The door of the temple they had elected to investigate was in fairly good preservation, the lintel post not having cracked, as was the case with most of the other buildings. The usual condition was an evidence of the severity of the earthquakes that must, from time to time, have shaken the island.

Passing through the entrance they found themselves in pitchy darkness. But, as they had long since found electric flashlights needful articles in searching the ruins, they soon had drawn out a couple of these and illuminated the gloom.

“This is a queer sort of place,” remarked Nat, looking about him as they flashed the lights hither and thither, “I wonder if the same peculiar feature about it has struck you as it has me.”

“Why, in every other one of these old temples and ruins we have seen, there was every provision for the admittance of light; in fact, the old Incas were sun worshippers.”

“I see what you mean now,” cried Joe eagerly. “This place hasn’t a window in it.”

“No; that’s odd, isn’t it? I wonder if, by any chance, this can be the Temple of the Moon that the professor was anxious to discover.”

“We’ve seen enough of them in the last few days to make you get accustomed to them.”

“That is true; but just the same, the more I see of them the less I like them. These ruins all seem to be alive with them.”

“Ugh! I can never think of that one that almost got poor Ding-dong without a shudder.”

“Well, let’s push on. This place seems to have a sort of dome for a roof.”

As he spoke, Nat flashed his light up till its beam of radiance showed a finely modeled but low dome above them. As the light fell on the concave structure, the lad gave a cry.

“That’s what it is. There is almost as much silver there as there is gold on the sacred dome. Those old fellows were not sparing with precious metals.”

“I should say not. But what’s that over there, Nat? Surely it’s a door.”

The two lads crossed the stone floor, upon which the dust of the ages lay thick and rose in choking clouds, and reached the portal which Joe had pointed out. The great ring affixed to one side of it was of some peculiar sort of metal, not unlike bronze, and was untarnished.

Not without a faster beating of his heart, Nat turned the ring. It moved easily, and as it did so the door swung outward. It was of stone, and massive as the living rock itself.

Within they made out a flight of stairs that led steeply upward into the darkness.

But the stairs proved solid. They wound upward steeply, worming their way around a central pillar covered with carvings. At last the boys emerged on a kind of platform at the top, which was roofed in by an irregularly shaped covering. Right in front of them were two round holes placed at some distance apart, and at their elbows were some curious-looking bits of apparatus. One of these looked like a gigantic bellows, and another was not unlike a megaphone in form.

“I don’t know, but light is coming in through these holes. Let’s look out and see.”

The boys each took one of the circular windows and peered out. To their astonishment they looked into a vast cavernous chamber, lighted from the summit which admitted sunshine, the roof of which was supported by pillars. It was so vast that it took the breath away almost, to gaze into its great distances and heights.

The floor of this place was marked with a circle, about which were inscribed signs at regular intervals.

“Must have been their equivalent for the signs of the zodiac,” breathed Nat, awestruck at the enormous spaces before him.

“Then this was a temple,” said Joe looking down from his window at the great floor, which was fully twenty feet below where the boys stood peering.

“It must have been,” gasped out Nat, “and—and—Joe, we are in the very holy of holies of this island.”

“Can’t you see? Look below you. We are peering out of the eyes of a huge idol made out of the rock. That stuff at the head of the stairs must have been the apparatus the priests used to make the idol speak and utter terrifying noises.”

There was no question but that Nat was right. Both boys could now make out beneath them, the rounded outlines of a huge squatting figure. In the head of this monstrous figure—its eyes, in fact—were the two circular holes through which they were looking.

“Gracious, what a sight it must have been when that temple was full of people of the vanished race, adoring this great idol,” murmured Nat, in awestruck tones.

“And what a job the priests must have had fooling them through that megaphone and that big bellows,” said Joe, the practical.

“That wouldn’t have detracted from the grandeur of the scene. It must have all been very real to them. Why, this place must be as vast as the hugest cathedral.”

“It gives me the shivers,” said Joe. “Hark, how your voice goes echoing off there among the pillars.”

“I wish there was some way of climbing down through these eyes. I’d like to explore that temple. I wonder where the entrance is.”

“Must be on the other side of the island. In the meantime, let’s look at the head of the stairs there, and see if we can discover anything else.”

The boys flashed their lights about among the pile of mouldering relics and machinery of the ancient priests. Suddenly Nat gave a shout of triumph.

“This” was a huge chest, the lid of which, bound and embossed with dully glittering metal, was open. It was full of various articles, some of which gleamed and flashed with gems. Nat plunged in his hand and drew out a golden breastplate. Joe followed this discovery by drawing forth a cup of what seemed to be pure turquoise. Various head-dresses of precious metal, more cups and vessels of gold, all jewel studded, followed.

“Well, we’ve found it,” breathed Nat; “we’ve found it, Joe, old boy.”

“Yes, and now we have, let’s take what we can of this stuff and get out of here,” said Joe. “We’ll come back with more lights and company. It’s getting kind of creepy and lonesome in the dark here.”

The boys loaded themselves with all they could carry, including the turquoise cup, and stumbled down the stairway. It did not take them long to retrace their steps and dump down their prizes in front of the astonished professor. He declared that the value of the turquoise cup alone was inestimable, while the jewels in some of the breastplates and vessels were worth more than he dared to name.

“I should say that what you have here would fetch two hundred and fifty thousand dollars in the value of the jewels alone,” he said. “As to what they are worth as relics of a vanished race, I am not prepared to say.”

Half an hour later, while they still sat awed and silent about the pile of wonderful relics, Ding-dong Bell appeared lugging an armful of photographic plates.

“We got some dandy pictures,” he began, “we—— Wer-wer-well, I’ll be jer-jer-jer-jig-gered!”

For the first time in his life Ding-dong Bell was fairly taken aback and bereft of all speech. He could only stand and blink in owl-like fashion at the marvelous display laid out before him.

The voice sounded in the ear of the leader of the Motor Rangers, and was accompanied by a violent shaking of his shoulder.

“I’m not shaking your bed, Nat. It’s the whole island that’s shaking! Quick, help me arouse the others!”

Nat was awake in a flash. As he hastily drew on some clothes a strange moaning noise filled the air. It was followed by a rushing sound overhead.

“It’s an earthquake!” exclaimed the professor, as soon as he was awakened.

As he spoke the whole structure of the Discoverer was shaken as if by a giant hand beneath her.

At the same instant the voice of old Matco was heard calling out as if in prayer.

“Get her loose, for heaven’s sake!” cried Mr. Tubbs, “or we’ll be destroyed!”

“It is the vengeance! The vengeance!” cried old Matco in Spanish, bursting into the cabin.

Joe sprang into the pilot house and threw the switch. A blaze of light illumined the aircraft. It showed a strange scene in her cabin. Half-dressed, and wholly bewildered, the adventurers were being thrown about like so many ninepins. The substructure of the Discoverer shook like an ague-stricken human being, as the earth beneath her rocked and rumbled.

Nat and Joe, the most self-possessed of any on board, sprang out upon the decks. The ropes had been tied, it not having been anticipated that they would want to leave in a hurry.

The sky was being ripped and seared by livid lightning, while the flashes of light showed the lake to be a mass of white foam. The air was filled with a strange, roaring sound.

As the boys’ knives fell on the ropes, the Discoverer shot upward. Up and up into the lightning-riven sky she arose, while beneath them the earth shook and rocked and rumbled.

“Great Scott!” cried a voice,—it was Nat’s,—“if ever we get struck by a flash of that lightning,—good-bye!”

The words sounded flippant, but the danger was real. The boy recalled reading of the fatal disaster to the great Zeppelin dirigible in a thunder-storm. But still they could not seek a refuge on the earth, at any rate not on the island. The air was the only place for them to seek safety.

The noise all about was nothing less than terrific. Voices could not be heard unless raised to a shout. The rigging of the dirigible creaked and groaned as the great bag swayed, and added to the distracting turmoil.

Paralyzed by the very suddenness and utter unexpectedness of it all, the adventurers for a time merely clung to the rails of their swaying, madly careening craft. How that night passed, none on board was exactly able to tell in after days.

They got the engine going, and held the big cloud cruiser as close to the earth as they dared, using the descending planes to steady her under the wild swaying of the great gas bag. A furious wind accompanied the earthquake, and when the lightning died away it seemed as if there was to be fresh and even more deadly peril, from the possibility of the great gas container being ripped bodily from the substructure.

But the rigging held tightly, and dawn found the disturbance almost at an end. It was a shaken, white-faced crew that regarded one another in the gray light. The night had been one to try the nerves of a man of iron, and the Motor Rangers were only youths.

However, the storm died out almost as swiftly as it had come, and breakfast and hot coffee heartened them wonderfully. Even old Matco plucked up his spirits, although, during the night, he was certain that they were bound to perish in the anger of the old gods of his country.

After the morning meal they began to look about them. They found that, during the night, they had been blown far to the southward of the site of the lost city, but they could still make out the ragged peaks that marked its locality.

The professor called a meeting, and it was unanimously decided to wing back and find out how the island of the dead had fared. They reached the spot by noon, and sailed over the peaks and gazed down into the place where the island should have been.

It had vanished as completely as if it had been a dream. Only the waters of the lake rippled as placidly as of yore, hiding forever under their azure surface the city that had been and now was not.

Silent and stunned the adventurers turned the Discoverer’s prow toward the westward once more.

“If it wasn’t for those relics in the cabin,” said Nat pensively, “I should think that we’d dreamed it all.”

As he spoke he looked back toward the far horizon. Already the ragged peaks were fading on the sky and soon would be out of sight.

“After all,” said the professor at length, “perhaps it is better so than if that noble city of a vanished race had become the resort of gossiping tourists.”

And in after days they agreed with him; but with Nat and Joe it was long a bitter thought that they had left in the Temple of the Moon some of the most marvelous remains of an ancient civilization ever discovered.

The untimely ending of the existence of the wonderful island put an end also to the Motor Rangers’ aerial adventures, for the professor decided to abandon all attempts at relocating it and employing divers, as had been his first intention.

The voyage north was made on the staunch old Nomad, and Mr. Tubbs and the professor accompanied the boys. Old Matco received a substantial reward, and decided to spend his last days in the shelter of Bolivian cities rather than to take once more to the life of the forest.

As for Captain Lawless and his rascally mate, they were last heard of roaming about Bolivia, still seeking for the lost city, of whose destruction they were not aware. They had engineered an expedition with their remaining money for this purpose, but not, of course, till after their release from prison for firing at the airship. But as this was only a brief incarceration, it did not delay their plans much. The present chronicler is not in a position to state their ultimate fate.

It may be of interest to state here, that the crew they had so basely deserted, managed to regain their schooner from the rascally old island chief and sail her home, where they collected salvage from the owners.

The Motor Rangers enjoyed a long rest at home and then visited New York to aid in classifying and arranging the pictures and relics of the lost city. The cloud cruiser was sold to a syndicate, which long used her as a passenger craft at fairs and exhibitions, and it is safe to say that not one of her passengers ever dreamed of what the airship that carried him had passed through.

Their exciting adventures above the earth will ever remain to the trio of boys among their most thrilling recollections, says Nat; but in a recent letter to a friend he hints that tiring of inactivity he and his two chums have already started out in search of fresh incident and adventure.

From what Nat says the tale of their experiences should form a suitable sequel to the other volumes of this series, and it will be called: The Motor Rangers’ Wireless Station.

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This is an absorbing story of the continuous adventures of a motor car in the hands of Nat Trevor and his friends. It does seemingly impossible “stunts,” and yet everything happens “in the nick of time.”

Enemies in ambush, the peril of fire, and the guarding of treasure make exciting times for the Motor Rangers—yet there is a strong flavor of fun and freedom, with a typical Western mountaineer for spice.

The strange adventures of the sturdy craft “Nomad” and the stranger experiences of the Rangers themselves with Morello’s schooner and a mysterious derelict form the basis of this well-spun yarn of the sea.

From the “Nomad” to the “Discoverer,” from the sea to the sky, the scene changes in which the Motor Rangers figure. They have experiences “that never were on land or sea,” in heat and cold and storm, over mountain peak and lost city, with savages and reptiles; their ship of the air is attacked by huge birds of the air; they survive explosion and earthquake; they even live to tell the tale!

Blest with natural curiosity,—sometimes called the instinct of investigation,—favored with golden opportunity, and gifted with creative ability, the Boy Inventors meet emergencies and contrive mechanical wonders that interest and convince the reader because they always “work” when put to the test.

A thought, a belief, an experiment; discouragement, hope, effort and final success—this is the history of many an invention; a history in which excitement, competition, danger, despair and persistence figure. This merely suggests the circumstances which draw the daring Boy Inventors into strange experiences and startling adventures, and which demonstrate the practical use of their vanishing gun.

As in the previous stories of the Boy Inventors, new and interesting triumphs of mechanism are produced which become immediately valuable, and the stage for their proving and testing is again the water. On the surface and below it, the boys have jolly, contagious fun, and the story of their serious, purposeful inventions challenge the reader’s deepest attention.

What it meant to make an enemy of Black Ramon De Barios—that is the problem that Jack Merrill and his friends, including Coyote Pete, face in this exciting tale.

Read of the Haunted Mesa and its mysteries, of the Subterranean River and its strange uses, of the value of gasolene and steam “in running the gauntlet,” and you will feel that not even the ancient splendors of the Old World can furnish a better setting for romantic action than the Border of the New.

As every day is making history—faster, it is said, than ever before—so books that keep pace with the changes are full of rapid action and accurate facts. This book deals with lively times on the Mexican border.

The Border Boys have already had much excitement and adventure in their lives, but all this has served to prepare them for the experiences related in this volume. They are stronger, braver and more resourceful than ever, and the exigencies of their life in connection with the Texas Rangers demand all their trained ability.

How Frank’s summer experience with his boy friends make him into a sturdy young athlete through swimming, boating, and baseball contests, and a tramp through the Everglades, is the subject of this splendid story.

We find among the jolly boys at Queen’s School, Frank, the student-athlete, Jimmy, the baseball enthusiast, and Lewis, the unconsciously-funny youth who furnishes comedy for every page that bears his name. Fall and winter sports between intensely rival school teams are expertly described.

The gymnasium, the track and the field make the background for the stirring events of this volume, in which David, Jimmy, Lewis, the “Wee One” and the “Codfish” figure, while Frank “saves the day.”

With the same persistent determination that won him success in swimming, running and baseball playing, Frank Armstrong acquired the art of “drop kicking,” and the Queen’s football team profits thereby.

Under peculiarly trying circumstances Ben Stone wins his way at Oakdale Academy, and at the same time enlists our sympathy, interest and respect. Through the enmity of Bern Hayden, the loyalty of Roger Eliot and the clever work of the “Sleuth,” Ben is falsely accused, championed and vindicated.

“One thing I will claim, and that is that all Grants fight open and square and there never was a sneak among them.” It was Rodney Grant, of Texas, who made the claim to his friend, Ben Stone, and this story shows how he proved the truth of this statement in the face of apparent evidence to the contrary.

Baseball is the main theme of this interesting narrative, and that means not only clear and clever descriptions of thrilling games, but an intimate acquaintance with the members of the teams who played them. The Oakdale Boys were ambitious and loyal, and some were even disgruntled and jealous, but earnest, persistent work won out.

The typical vacation is the one that means much freedom, little restriction, and immediate contact with “all outdoors.” These conditions prevailed in the summer camp of the Oakdale Boys and made it a scene of lively interest.

The “Sleuth” scents a mystery! He “follows his nose.” The plot thickens! He makes deductions. There are surprises for the reader—and for the “Sleuth,” as well.

A new element creeps into Oakdale with another year’s registration of students. The old and the new standards of conduct in and out of school meet, battle, and cause sweeping changes in the lives of several of the boys.

Especially interesting and timely is this book which introduces the reader with its heroes, Ned and Herc, to the great ships of modern warfare and to the intimate life and surprising adventures of Uncle Sam’s sailors.

In this story real dangers threaten and the boys’ patriotism is tested in a peculiar international tangle. The scene is laid on the South American coast.

To the inventive genius—trade-school boy or mechanic—this story has special charm, perhaps, but to every reader its mystery and clever action are fascinating.

Among the volunteers accepted for Aero Service are Ned and Herc. Their perilous adventures are not confined to the air, however, although they make daring and notable flights in the name of the Government; nor are they always able to fly beyond the reach of their old “enemies,” who are also airmen.

How the Bungalow Boys received their title and how they retained the right to it in spite of much opposition makes a lively narrative for lively boys.

A real treasure hunt of the most thrilling kind, with a sunken Spanish galleon as its object, makes a subject of intense interest at any time, but add to that a band of desperate men, a dark plot and a devil fish, and you have the combination that brings strange adventures into the lives of the Bungalow Boys.

The clever assistance of a young detective saves the boys from the clutches of Chinese smugglers, of whose nefarious trade they know too much. How the Professor’s invention relieves a critical situation is also an exciting incident of this book.

The Bungalow Boys start out for a quiet cruise on the Great Lakes and a visit to an island. A storm and a band of wreckers interfere with the serenity of their trip, and a submarine adds zest and adventure to it.

Billie Campbell was just the type of a straightforward, athletic girl to be successful as a practical Motor Maid. She took her car, as she did her class-mates, to her heart, and many a grand good time did they have all together. The road over which she ran her red machine had many an unexpected turning,—now it led her into peculiar danger; now into contact with strange travelers; and again into experiences by fire and water. But, best of all, “The Comet” never failed its brave girl owner.

Wherever the Motor Maids went there were lively times, for these were companionable girls who looked upon the world as a vastly interesting place full of unique adventures—and so, of course, they found them.

It is always interesting to travel, and it is wonderfully entertaining to see old scenes through fresh eyes. It is that privilege, therefore, that makes it worth while to join the Motor Maids in their first ’cross-country run.

South and West had the Motor Maids motored, nor could their education by travel have been more wisely begun. But now a speaking acquaintance with their own country enriched their anticipation of an introduction to the British Isles. How they made their polite American bow and how they were received on the other side is a tale of interest and inspiration.

Would you like to admit to your circle of friends the most charming of college girls—the typical college girl for whom we are always looking but not always finding; the type that contains so many delightful characteristics, yet without unpleasant perfection in any; the natural, unaffected, sweet-tempered girl, loved because she is lovable? Then seek an introduction to Molly Brown. You will find the baggage-master, the cook, the Professor of English Literature, and the College President in the same company.

What is more delightful than a re-union of college girls after the summer vacation? Certainly nothing that precedes it in their experience—at least, if all class-mates are as happy together as the Wellington girls of this story. Among Molly’s interesting friends of the second year is a young Japanese girl, who ingratiates her “humbly” self into everybody’s affections speedily and permanently.

Financial stumbling blocks are not the only things that hinder the ease and increase the strength of college girls. Their troubles and their triumphs are their own, often peculiar to their environment. How Wellington students meet the experiences outside the class-rooms is worth the doing, the telling and the reading.

Roy Prescott was fortunate in having a sister so clever and devoted to him and his interests that they could share work and play with mutual pleasure and to mutual advantage. This proved especially true in relation to the manufacture and manipulation of their aeroplane, and Peggy won well deserved fame for her skill and good sense as an aviator. There were many stumbling-blocks in their terrestrial path, but they soared above them all to ultimate success.

That there is a peculiar fascination about aviation that wins and holds girl enthusiasts as well as boys is proved by this tale. On golden wings the girl aviators rose for many an exciting flight, and met strange and unexpected experiences.

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The delicacy of flight suggested by the word “butterfly,” the mechanical power implied by “motor,” the ability to control assured in the title “aviator,” all combined with the personality and enthusiasm of girls themselves, make this story one for any girl or other reader “to go crazy over.”

How the Bungalow Boys received their title and how they retained the right to it in spite of much opposition makes a lively narrative for lively boys.

The Bungalow Boys start out for a quiet cruise on the Great Lakes and a visit to an island. A storm and a band of wreckers interfere, with the serenity of their trip, and a submarine adds zest and adventure to it.

What it meant to make an enemy of Black Ramon De Barios—that is the problem that Jack Merrill and his friends, including Coyote Pete, face in this exciting tale.

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No author has achieved a greater national reputation for books of genuine humor and mirth than George W. Peck, author of “Peck’s Bad Boy and His Pa.”

We are fortunate to be able to offer, within everyone’s reach, three of his latest books. The titles are

By failing to procure any one of these books you lose an opportunity to “laugh and grow fat.” When you get one you will order the others.

A famous series of books, formerly sold at $2.00 per copy, are now popularized by reducing the price less than half. The lives of these famous Americans are worthy of a place in any library. A new book by Edward S. Ellis—“From Ranch to White House”—is a life of Theodore Roosevelt, while the author of the others, William M. Thayer, is a celebrated biographer.

An author whose writings are famous and whose stories are brim-full of adventure. Boys delight in reading them.

Charles Carleton Coffin’s specialty is books pertaining to the War. His celebrated writings with reference to the Great Rebellion have been read by thousands. We have popularized him by publishing his best works at reduced prices.

A limited line comprising subjects pertaining to the careers of men who have helped to mould the world’s history. A library is incomplete without the entire set.

One of the most popular writers of boys’ stories in America to-day. This author has the happy faculty of pleasing the boys with writings which are noted for their animation and excitement. A select list is named below:

Few boys are alive to-day who have not read some of the writings of this famous author, whose books are scattered broadcast and eagerly sought for. Oliver Optic has the faculty of writing books full of dash and energy, such as healthy boys want and need.

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CHAPTER		PAGE
I.	The Magnetic Island	5
II.	Nat to the Rescue	17
III.	The Islands Vanish	27
IV.	Professor Grigg and Mr. Tubbs	37
V.	Trouble with a Hat	47
VI.	“What Would You Say to a Voyage in the Air?”	55
VII.	A Strange Sail Appears	63
VIII.	Trapped by Two Rascals	71
IX.	Some Strategy	80
X.	“Ding-Dong” and a Gun	88
XI.	Captain Lawless Tries Trickery	99
XII.	“Good Work, Manuello!”	108
XIII.	South American Justice	120
XIV.	Off on Their Strange Voyage	130
XV.	A Signal that Meant “Danger”	140
XVI.	Indians?	148
XVII.	A Queer Sort of Gun	156
XVIII.	What It Did	166
XIX.	An Involuntary Passenger	177
XX.	“All Our Lives Depend on It”	187
XXI.	“Feathered Aeroplanes”	199
XXII.	A Serious Accident	211
XXIII.	Overboard!—1950 Feet Up!	223
XXIV.	The City of a Vanished Race	231
XXV.	A Strange Adventure	246
XXVI.	Saved from the Sun Gods	257
XXVII.	“Did We Dream It All?”	268