Even from the distance at which the boys viewed them they conveyed an almost sinister impression in their rugged shapes. Their harsh outlines cut the sky in a serrated line like the teeth of a huge saw.

"Look, look, Frank!" shouted Harry suddenly as they were passing high over a small clearing.

Both Frank and Ben peered over the side in answer to the boy's excited hail.

Far below them was a strange sight.

In the center of the clearing were four huge African elephants solemnly conducting a sort of Brobdingnaggian game of tag. One of the great beasts would tap the other with its trunk and then would scamper away till it in turn was "tapped" by a blow that would have swept a small regiment off its feet.

Frank pushed over a lever and swung the ship in a circle so that they might watch the great animals to better advantage. Suddenly the boys saw one of the elephants, evidently seized by sudden rage, start goring one of its companions with its huge tusks. The attacked animal had no chance, and but for the boys would speedily have been killed.

"I'm going to give that big bully a shot," exclaimed Harry, and he got out one of the heavy rifles from the rack under the starboard transom.

"Wait, I'll drop a bit," said Frank.

In response to his manipulation the aeroplane dropped till she hovered not more than two hundred feet above the great animals. Then a strange thing happened. The shadow of the craft fell upon the center of the clearing in front of the dueling beasts and the on-looking pachyderms, and as it did so the bully stopped goring its mate and gave a snort of astonishment.

Its note of surprise quickly changed to a loud trumpet of terror as the great pachyderm saw swooping above it what must have appeared to it an aerial inhabitant even larger than itself. Its note of fright was echoed in a chorus that sounded like an assemblage of cracked trumpets as the others also sensed the impending danger.

"Now let him have it," shouted Frank.

Harry's rifle cracked and the big bully staggered. Twice more the boy fired and the huge creature staggered on to its knees and then with a mighty groan rolled over on its side. The others, even the wounded one, had made off as soon as they had caught sight of the hovering Golden Eagle.

Even from the height at which they were the boys could see that the dead animal had an enormous pair of tusks, no doubt extremely valuable.

"We ought to have them there figure-heads," commented Ben Stubbs. "What do you say if we drop down and get them?"

Frank looked at his watch. It was half-past nine.

"We cannot be more than a hundred miles now from the foot of the range," he said, "and I suppose we have plenty of time. We might as well drop and get them as let some native tribe have the find and then get skinned out of them by an Arab trader."

As he spoke the boy set the planes for descending and the Golden Eagle settled down—after a few minutes rapid falling—fairly in the center of the clearing. It was almost a fairylike spot. On every side it was hedged in by the densest jungle vegetation, the solid walls being broken here and there by elephant paths leading off into the green tangle.

The little glade in which the Golden Eagle had settled was covered with short, yellow grass and had been trampled almost bare of vegetation, apparently by the gambols of countless generations of elephants.

"This must be one of the elephant playgrounds I have read about," exclaimed Harry, looking about him.

"No doubt it is," replied Frank. "But look at those tusks, why there's ivory enough there alone to give us all a nice wad of pocket money."

Ben Stubbs, with one of the small axes, at once set about hacking out the dead elephant's huge tusks and a long job it was. Finally, however, he managed to cut them free and clear and the boys loaded them into the aeroplane.

"Now we are all ready for a fresh start," said Frank as they clambered in after him and settled down in their places; but a startling interruption occurred.

With a wild yell, that struck a sudden chill to the heart of every one of the little group, a band of beings that at first sight looked like nothing so much as huge gorillas, burst from the forest on every side.

Their heads were misshapen and flat and their protruding lips were daubed with white and red clay which gave them a ghastly unearthly look. From their ears hung huge ivory pendants. They carried elephant skin shields and were armed with spears and bow and arrows. As if they did not consider themselves sufficiently hideous, several of the tribe had cut their faces in long stripes and the hardly healed scars of these wounds rendered their already sinister faces terrifying indeed.

Desperately Harry threw over the wheel and the engines started faithfully to respond but not before half a dozen of the savages had thrown themselves on to the aeroplane.

Their weight held her down although she scudded over the ground; and in the meantime the other natives started pouring a shower of arrows and spears into her. Fortunately none of these struck the boys although Frank felt an arrow whiz through the loose sleeve of his shirt.

"Get those fellows off or I can't get the ship up," he yelled.

Harry and Ben Stubbs fired their automatics into the clinging mass of savages.

Two dropped and the aeroplane began to rise but the others desperately clung on.

"Get 'em off," shouted Frank, as he desperately strove to raise the air-craft.

As he spoke he fell back with a cry of pain.

An arrow had struck him on the shoulder inflicting a painful wound.

Like a flash Harry took in the situation and leaped to the steering wheel. As he did so the savage with whom he had been contending clambered clear into the chassis. At the same instant Ben Stubbs' revolver dispatched the last of the men clinging to the planes and the Golden Eagle began to rise.

As she shot upward the savage who had climbed into the chassis gave a wild shriek of real terror. But his outburst didn't come before he had made a savage lunge at Ben Stubbs with a short heavy knife. The solo adventurer dived under the black's arm and struck it upward as he lunged and the weapon went whirling groundward out of the air-ship.

With a cry of despair the savage rushed to the edge of the car and was about to throw himself into empty air when Ben leaped forward to try to restrain him.

But it was too late.

As the boys' sturdy companion gallantly attempted to save the savage's life a flight of arrows whizzed up from below.

With a groan the man on the edge of the car pitched forward into open space, pierced to the heart with an arrow sped by one of his own tribesmen. Down he shot like a stone to the earth below, while the Golden Eagle—as if rejoicing in her escape, shot upward and onward.



CHAPTER IX

THE VOICE OF THE MOUNTAIN

Frank's wound fortunately turned out to be nothing very serious— though painful enough—and after it had been treated with antiseptics from the medicine chest he declared that, aside from the stiffness and soreness, he felt no ill effect.

"Those fellows certainly gave us a sample of what we may expect," remarked Harry, examining the hole in his shirt where the arrow had ripped through.

"It was quite as narrow an escape as I care to experience," agreed Frank. "How about you, Ben?"

"Wall," said the old adventurer, "I don't know as how I think that kind of excitement is as beneficial fer the health as the rest cure."

Meanwhile the Golden Eagle, plowing through the clear African air at fifty miles an hour, rapidly drew nearer and nearer to the mysterious Moon Mountains.

As they neared the range the extraordinary character of it was revealed more and more clearly. Seamed with deep gloomy abysses and almost bare of vegetation, except a few scanty groves of palms and the hardier tropical trees, they seemed indeed fitted to be the theater of dark mysteries and the haunt of savage tribes.

"Well," exclaimed Harry, as be scrutinized the strange mountain mass through the glasses, "I should say that if those Winged Men are to be found anywhere, here is where they'd reside."

"I should think they'd use their wings to get out—a nastier looking lot of mountains I never saw," was Ben's reply.

Frank made no comment, but the sinister character of the mountains they were so rapidly approaching impressed itself on his mind nevertheless. Eagerly he scanned the range for the first sign of "The Upturned Face." Harry and Ben, too, gave quite as eager scrutiny toward the discovery of this striking mark of the ivory's hiding-place.

All at once it shot into view with a suddenness that made the boys' beads swim.

It was as clear as daylight. The line of the mountain for which Frank had the Golden Eagle II now directly headed was unmistakably the outline also of a hawk-nosed facet.

If the mountains themselves had an evil, menacing look, the stone face possessed this same quality in an infinitely greater degree.

"Well, if we've got to go looking for ivory right under that face the sooner we find it the better," exclaimed Ben. "I'd hate to be shipmates with the fellow who sat for that portrait."

"No human being ever sat for it, Ben," laughed Frank; "it's a mere freak of nature which has so disposed the mountain mass at this point as to give the semblance of what the map-maker terms The Upturned Face."

"Well, if I had a mug like that I'd turn it down instead of up before some one did it for me," was Ben's comment.

The Golden Eagle landed on a plateau about halfway up the mountain, beneath the upturned face. It made an almost ideal camping-place, considering the rugged nature of their surroundings. In one part of it a small grove of bananas and palms had taken root, and their smiling greenery offered a refreshing contrast to the dark oppressive gloom of the giant rock masses piled all about. From the center of this oasis in the rocky range bubbled a tiny spring of water as clear and cold as if it had been filtered and iced. Frank's first act was to send out a wireless to the River Camp, telling of their arrival.

"Well, thank goodness, we've got something green and pleasant to look at," remarked Ben, as they set about transforming the chassis of the Golden Eagle into a comfortable tent by means of running up the canvas curtains on the aluminum frames provided for that purpose. Thus equipped, the chassis served the uses of an improved tent, as the floor was well above the ground and out of all danger of the unwholesome, vapors rising from the ground and also the scorpions and other reptiles.

But if the oasis itself was a pretty spot, it was made doubly so by the contrast it afforded to the scenery surrounding it. On all sides shot up frowning walls of rugged black rock which seemed to have been torn and ripped in some remote period by a terrific convulsion of nature. In places, too, the rock masses seemed to have been seared by subterranean fires. Frank gazed upward at the terrific character of the scenery about them.

"We shall need the rope-ladder," he announced suddenly after a long silence.

"The rope-ladder?" inquired Harry, "what for?"

Frank laughed.

"I mean the rope-ladder we use in the Golden Eagle. As you know, the only way to locate the cache is to strike a direct line down from the nose of the upturned face. That will bring us to the small cairn or pile of rocks that marks the Arab's hiding-place."

"He could hardly have chosen a better," remarked Harry. "Who would ever guess, unless they had the key to the mystery, that these mountains held such a fortune in tusks."

The rest of that day was spent in overhauling the outfit which they would need to use on their expedition of the morrow. Luckily the boots they wore had been fitted with "hob-nails" so that they were ideal for the tough climb that they had ahead of them. Each member of the three was to carry a pick and of course they all were to be armed, carrying several rounds of ammunition each in their cartridge-belts.

That night after a supper of fried ham, canned corn and pancakes—all cooked by the skilful Ben over a fire of wood collected from the little grove—Frank sent out a wireless to the members of the camp on the river bank and felt much reassured when Lathrop's "All well—good luck," came back through the air. It was delightfully cool on the mountain-side after the oppressive fetid air of the river and its neighborhood, and as Ben had remarked before they turned in:

"Fine weather for sleeping."

But sleep would not come to Frank. He tossed and turned on his transom bed and several times gazed out into the night through the canvas curtains. An unaccountable feeling of unrest possessed him. Could they get the ivory out of the cache before Muley-Hassan and his band arrived by land?

Fast as they had traveled through the air Frank realized that the Arab, who doubtless by this time had been informed by the treacherous Diego of the boys' bold dash, would push on at furious speed in order to head them off. That he would come accompanied by a well-armed band Frank could not doubt. He and Harry and Ben could only put up a feeble resistance against such an attack. There was only one chance to secure the ivory and that was to get at it before the Arab arrived. It all depended then on how quickly they could find the cache. Frank lit the lantern and shielding it so that it would not strike in the eyes of his sleeping brother, drew out the map and scanned it attentively.

Yes, here were the directions written in the queer hand of Muley-Hassan's follower.

"A line from the nose straight down to the cairn of stones."

It seemed simple enough and certainly the nose of the Upturned Face was as clearly to be made out as a ship at sea. But Frank had been too long trained in the hard school of adventure to underestimate the difficulties of any piece of work. They faced a hard job and none realized the fact better than the young leader.

At last he blew the lantern out and once more composed himself to sleep. He was just dozing off when a sufficiently startling interruption occurred. One which drove all further thoughts of rest from his head.

It was an extraordinary sound that brought the boy out of his bed with a bound and caused him to clutch his revolver with a heart that beat loud and thick in spite of himself.

Clutching his weapon the boy rushed to the door of the chassis tent and gazed out.

There was a bright moon which threw into inky blackness the depressions of the rugged mountains and threw up their projections into a blue glare. It was almost as light as day under that wonderful African moon. Had there been any one near the boy must have been able to see them.

But look as he would there was not a soul in sight. All about him stretched the barren frowning mountains sleeping under the moon.

But the sound that he had heard?

There was no mistaking it. It had been too like the low humming of a human voice for him to have been misled. Perhaps he had been dreaming?

But as if to give the lie to any such supposition the strange sound that had so alarmed him at that moment made itself manifest once more:

"A-hooo-A-AH-HOOO-00-a-ho-ho-ho-o-!"

It started softly and gradually ran up the scale till it reached a crescendo shout and then died out in a soft sound like a woman's wail. Heard anywhere the sound would have been alarming enough, but coming as it did in the midst of these unknown, mysterious Mountains of the Moon it struck a chill to the boy's heart and caused his scalp to tighten in a manner that even the bravest man or boy in the world would have had no reason to feel shame over.

A human enemy, a foe he could see, Frank would have faced with iron nerve; but this strange wailing noise coming from what quarter of the compass he could not judge—was so uncanny that he was really disturbed. He bounded into the chassis and roused Ben and Harry. He had hardly whispered to them the extraordinary intelligence when again the voice arose.

"A-ho-ho-h-o-o-o-A-h-hoo-ho-AH-HO-HO-O-O-O-AH-ho-h-o-o-o-o-o-o!"

"Well, who?" roared Ben angrily, "come out and show yourself, you human hyena, and I'll put so much lead in your system you'll be worth a nickel a pound. Come, you old Ah-Hoo, and I'll show you who I am quick enough—shiver my topsails!"

But the only reply to Ben's tirade was the dismal echo of his voice among the rocky chasms.

"Shiver my topsails!" roared the echo and then the hills bandied the cry about from ridge to ridge till it died out in a whisper:

"My topsails!"

"Hum," remarked Ben, "I don't think I'll talk so loud around here. There seem to be a lot of folks listening. Such a dreary hole as this I never—"

"Never," sighed the echoes, "—never."

"Here, I can't stand this," cried Harry. "I'm going to send a bullet up there the next time that fellow starts 'Ah-hooing."'

But as the strange mournful cry rang out once more the boys paused in bewilderment.

There was no locating the sound.

It seemed to fill the air. To come from every quarter of the compass at once.



CHAPTER X

THE ARAB'S CACHE

The mysterious cries were not repeated that night although the boys laid awake till daylight listening for any repetition. No theory they could advance, although these ranged all the way from cannibals and gorillas to ghosts, had any effect on the solution of the mystery. They finally agreed to trust to solving it in some chance way, and like sensible boys did not continue to worry themselves over the unsolvable.

Frank's first action was to send out a wireless to the river camp and to his great relief he found that events there were still proceeding with the same regularity as before. Nothing had occurred to mar the even life of the young adventurers left behind. This was the tenor of the message, but there was something about it that worried Frank. Lathrop, he knew, was an expert wireless operator, but the sending that he performed that morning was so jerky and irregular that the rankest amateur might have done better.

"What is the matter?" asked Frank sharply after the sending had become even more unskilled and shaky.

There was no answer; which caused Frank a vague feeling of apprehension. He speedily drove this impression from his mind, however, with:

"Pshaw! the sleepless night I passed has made me nervous."

After breakfast there was so much to be done that there was no more time to waste on gloomy forebodings and the boys started, as soon as the camp had been put in order, on their expedition up the mountain-side to the Upturned Face—which was to be the starting point for the uncovering of the secret ivory hoard.

The climb was quite as stiff as Frank had anticipated and, laden as they were with the rope-ladder and the other equipment, it was rendered even tougher. All three carried water-canteens covered with wet felt, containing half-a-gallon each. Frank had insisted on this as it was doubtful if they could find water at the summit of the mountain.

As the sun rose higher in the sky and beat down on the bare rock ridges over which the adventurers were making their way, it became as uncomfortable as any expedition on which the boys had ever beer engaged.

"Talk about New Mexico or Death Valley," exclaimed Harry, "I feel like a piece of butter rolled up in a paper and I've melted."

"I feel like a Welsh rarebit myself," laughed Frank, "how about you, Ben?"

"I feel like a pot of boiling tar with a fire lighted under me," growled the veteran angrily; "consarn these rocks, I'd give a whole lot for a bit of that shade we left behind us."

Despite the discomfort and the heat, however, they struggled on up the mountain-side, frequently using the rope-ladder to get over rough places, and at about noon they stood beneath the steep rock cliff that formed the nose of the upturned face.

It was easy enough then to reach a spot below the tip and Frank, with a long cord he had brought for the purpose, laid out a straight line from the point down the southern slope of the mountain-side. While they were busy about this they were startled by a repetition of the same strange cry, half-warning, half-savage, that they had been so alarmed by the night before.

"A-ho-o-o-o-AH-H-O-O-O-a-h-o-o-hoo-o-o-o-o!"

"Great Scott," yelled Harry, "what on earth do you think of that?"

Frank—considerably startled himself—had, however, made a determined effort to ascertain the source of the sound as it rose and fell in its strange cadence.

"I've got it!" he shouted; now with a cry of triumph.

"Got what?" cried Harry, as if he feared his brother had suddenly become infected with some strange complaint—"rabies or the pip?"

"The noise—I mean I know where it comes from," cried the excited boy.

"Where?" chorused Ben and Harry.

"From somewhere about the Upturned Face," cried Frank triumphantly, "Hark!"

The strange wailing cry rang out once more. They all listened intently.

Sure enough it seemed to proceed from the sinister countenance carved in the living rock above them.

"Well, here's where we end this mystery for all time," shouted Frank, drawing his revolver, "who is game to follow me?"

Of course Harry and Ben rushed to his side, and while the echo of the mysterious cry was still sobbing and sighing among the crags they dashed back up the mountain-side utterly oblivious now to the heat or anything but their determination to discover who or what had uttered the extraordinary cry. The side of the nose—or the nostril so to speak—was formed of a wall of rock fully twelve feet in height.

"You fellows give me a boost up there and I'll travel right along the face till I find out where the racket comes from."

On Ben's strong shoulders Frank was soon hoisted up to a height where he could lay hold of a projecting bit of rock and shin himself up on to the top of the nose.

"Look out he doesn't think you are a fly and try to brush you off," laughed Harry from below.

"No danger of that," shouted back Frank, "unless I lit on him in the Golden Eagle."

The surface of the face was as remarkable as its profile.

Apparently some forgotten tribe had at some time or other been struck by the facial outline of the rocks and had cut into the flat surface, which was upturned to the sky, eyes and a mouth, the latter well provided with teeth, in each of which was drilled a tiny triangular hole.

While Frank was puzzling over the meaning of these apertures there came a repetition of the weird cry, but this time the lad was so startled that he almost lost his balance and fell backward.

The call seemed to proceed from his very feet. Then, all at once, he realized what it was.

The strange sounds proceeded from the mouth of the stone face.

Frank ran to the edge of the steep declivity that formed the nose.

"Say, Harry, and you too, Ben, examine the surface below there very carefully for any holes. They will probably be small ones and in a row."

"None this side," announced the searchers after a lengthy quest.

"Try the other," ordered Frank.

They did so and after a few minutes of careful scrutiny Harry shouted that they had found a row of small holes pierced in the rock just below where Frank stood.

"Then we have solved the mystery of the voice," exclaimed Frank.

"What do you mean?" demanded Harry.

"That it is nothing more or less than an arrangement of holes through which, when the wind blows in a stiff puff, air is forced with violence enough to cause the cry that disturbed us so much last night," was the reply.

This indeed was the solution, and had the boys known it there are many such rocks in Africa, carved out by some forgotten race, and the weird cries that the vent-holes give out in the wind doubtless acted as a powerful "fetish" to keep away troublesome enemies.

"No wonder the niggers down below don't come near the Moon Mountains," said Harry, as they all buckled over the simple explanation of the phenomenon that had caused them so much alarm. "I wouldn't care to, myself, unless I knew just what made that cry."

"It certainly was as depressing as anything I ever heard," said Frank, "and now having solved the great mystery—let's get back to work."

The three adventurers went at the job with a will. The line was about a hundred feet long and the method of procedure was this: Frank tested the straightness of the line, as accurately as possible with his eye, while Ben and Harry carried it stretched between them. The end of each hundred feet was signalized by a stone, and Harry, who was at the end of the line, carried his end to this mark before they laid out a fresh hundred feet. In this way they must have measured off very nearly half-a-mile of the mountain-side when Frank gave a sudden sharp cry and pointed to a depression in the dark range immediately below them. As the others looked they echoed his cry and gave a dash forward.

Directly beneath them, about in the center of the little dip, was a cairn of rough stones perhaps four feet in height. In a few bounds they had reached the pile, which they knew meant the discovery of the ivory cache and the end of the most difficult part of their expedition. Little did they imagine the amazing things that were yet to happen to them and of which they were but on the threshold.

"Good Lord, look at that, boys!" exclaimed Frank, as they stood at the foot of the cairn.

There was a good reason for the boy's exclamation.

Distributed around the base of the pile were a dozen or, more human skulls.

"Are they those of white men?" asked Harry in an awed tone. Frank shook his head.

"No, they are those of negroes I believe," he replied after a careful examination, "and I imagine that Muley-Hassan killed them after they erected the cache so that they would not be able to spread the knowledge of its whereabouts to any of the marauding tribes who might even brave the ghostly voice when such a great treasure of ivory tempted."

A shout from Ben, who had been walking round the pile examining it from every view-point interrupted them. They looked up and saw the old adventurer pointing to the mountain summit where it cut the sky. Outlined against the deep azure was the object that had caused his exclamation. It was the figure of a man that had apparently been watching them intently.

But as they gazed the strange, crouched form suddenly vanished.



CHAPTER XI

THE AGE OF SIKASO

It was late afternoon of the day that Frank, Harry and Ben had left the River Camp. Lathrop, Billy, Barnes and old Sikaso had wandered into the jungle with their rifles, intent on bringing down some sort of game to replenish the camp larder. For hours they tramped about in the thick jungle and a fair measure of success had fallen to their rifles. Shortly before sundown the trio met in a glade not more than a mile from the camp and compared notes. To Billy's gun had fallen a plump young deer and Lathrop had brought down, not without a feeling of considerable pride, a species of wild hog which Sikaso proclaimed with a grunt was "heap good."

Flushed with triumph and carrying their own bag, the young hunters set out for the camp, arriving there at dusk. As has been told, it was not long after that that Frank's wireless from the Moon Mountains winged its way through the air and Lathrop was able to flash back in response an "all-well" message. The boys turned in early, Billy and Lathrop to their tent and old Sikaso to the rough shelter he had contrived for himself and which he declared was far more comfortable than any tent. Like a wild beast the savage old warrior disliked to have anything approaching a roof over him. It appeared to savor too much of a trap of some kind.

Billy might have been asleep five hours or so and it was approaching midnight when he heard a noise outside the tent door and a second later old Sikaso announced his presence by a whispered:

"Awake, Four-eyes, there is danger."

"What do you mean, Sikaso," demanded the half asleep reporter, "danger to our friends?"

"No; to us, and here and soon," was the disquieting response, "arouse your friend. We have no time to lose."

Billy was wide awake now and made a motion as if he would light the lantern.

Sikaso stopped him with a quick gesture.

"Do not light the lamp, my white brother," he whispered in the same tense tones, "to do so would be to reveal to those who are now approaching that we are awake and expect them. Rather let us pretend that we are unaware that they come and spring upon them like the leopard when she is least expected."

"Yes, but—" exclaimed Billy in a bewildered tone, "what do you mean, Sikaso, what enemies are coming? How do you know that they are approaching?"

"I have seen it in the smoke," was the somber reply; "the smoke never lies. After I lay down on my skins I could not sleep, I felt there was danger approaching us. From where I knew not. So I made the "fetish" fire. In it I saw a band of men coming toward us down the river and at the head of them was a dark man—a man you know well, my white brother with the four eyes."

"Diego!" exclaimed Billy divining the other's thought.

"Yes, Diego; cursed be the day that my war-axe did not cleave his ugly skull; but beside Diego there is another. Hearken to the words of Sikaso, the elephant in his rage is not more merciless, the serpent not more cunning, the crocodile not more savage in onslaught than this other. He is Muley-Hassan, the Arab, and the deeds he has done, my brother, when recounted turn strong men's blood to water."

Small wonder that Billy, as he hastily roused Lathrop, felt a shudder run through him. He had heard enough from Frank of the ways of Muley-Hassan to know that they could not well fall into the hands of a more pitiless foe and that now, with the Golden Eagle gone and the Boy Aviators already at the ivory cache, it was probable that the slave-dealer's rage would render him even more savage than was his wont.

In a few rapidly whispered words Billy apprised Lathrop of the situation. Like Billy, the other boy had no lack of pluck but his heart sank, as had his companion's, as he sensed the full meaning of Sikaso's warning.

"But perhaps the smoke was mistaken," he said eagerly, willing to grasp even at that straw of hope; but the old warrior's answer dashed his aspirations to the ground.

"The smoke is never mistaken," he said simply; but with such calm conviction that the boys, despite themselves, realized that the old Krooman had really the knowledge of grave peril approaching.

"Had we not better arm the other Kroomen?" asked Billy anxiously.

"It would be useless," was Sikaso's reply, "they are cowards. At the first sight of blood they would run to the forest like the sons of weaklings that they are."

"We must rouse Professor Wiseman at once," cried Billy.

"It is well," muttered Sikaso, "we shall need every man who can hold a rifle to-night but the professor is old, my brothers, and his heart is as a woman's."

"Well, he'll have to fight," said Billy with bloodthirsty determination. "I for one am not going to stand calmly by and have my throat cut, or worse still be taken prisoner by this old Muley-Hassan."

Old Sikaso glanced approvingly at him.

"Well spoken, Four-eyes," said he; "spoken like a son of a warrior."

Billy's ears tingled at the compliment, which was really in the old African's opinion the highest that could be paid to a man or a boy, and hurried off to wake "the bugologist" as be disrespectfully termed the professor. To his surprise, for he more than half expected an outbreak, Professor Wiseman did not appear particularly concerned at the news that Diego, and Muley-Hassan were—as the boys had every reason to believe—at that moment advancing on the camp.

"I will dress myself with all alacrity," he said, "and join you in your tent, but I must say I don't believe in all this witchcraft."

"Will this Muley-Hassan be well armed?" asked Billy, in a voice which was rather shaky, of their black friend.

"Plenty rifles," was Sikaso's brief reply.

"Don't you want a rifle or at least a heavy caliber shotgun?" asked Billy.

The old warrior laughed and swung his mighty axe round his head till the blade flashed like a continuous band of steel and the air whistled at the cleavage of the sharp edge. Then he began to sing softly a war-song which may be roughly rendered in English thus:

"At dawn I went out with my axe into the red fight; Like the grass before the fire, like the clouds before the wind, I drove them. I, Sikaso, I drove them. There were rivers that day; but the rivers were red. They were the rivers of the blood of my enemies; With my war-axe I killed them. This is the song of mighty Sikaso, and his terrible axe of death."

Although the boys of course did not understand the words, the fierce voice in which the old warrior intoned the chant made them realize what a terrible foe he was likely to prove in battle. But now as Sikaso brought his song to a conclusion and rested his axe on the ground, leaning on its hilt, he suddenly stiffened into an attitude of close attention.

"Hark, my white brothers!" he cried, "the war-eagles are gathering for the slaughter."

But the slight sound the keen ears of the savage had caught without difficulty was longer in making itself manifest to the two white boys. After a few minutes of listening, so intense as to be painful, they likewise, however, distinctly heard the regular, rhythmic dip of paddles coming down the river.

"There are six war canoes full of them," announced, Sikaso, with almost a groan, after he had given close attention to the sounds. "Alas, my white brothers, there is little use of our giving battle."

"Well, I for one am not going to give up without dropping a few of the cowardly wretches," cried Billy.

"Nor I," echoed Lathrop, enthused by Billy's brave example.

The old warrior's eyes kindled as he gazed at the two brave young Americans, each clutching his rifle and waiting for the moment to arrive when they could use them.

"If we only had had time to throw up a stockade, my brothers, we might have driven them off yet," he cried.

"Well, we'll give as good an account of ourselves as possible," declared Lathrop.

And now began what has been acknowledged to be the most trying part of any engagement, from a duel to a battle—the waiting for hostilities to begin. It seemed that an interminable time had elapsed from the moment that they heard the first "dip-dip" of the paddles to the sharp crack of a twig sounded in the jungle directly ahead of them. The snapped branch told them that the enemy's outposts were reconnoitering to see that the camp was actually, as it seemed to be, wrapped in sleep.

Apparently the scout, whoever he was, was soon convinced of the fact that the adventurers were slumbering, for he advanced boldly from the dark sheltering shadows of the jungle and emerged into the bright moonlight which flooded the clearing in which the camp stood.

Billy raised his rifle to his shoulder and the next minute would have been the savage scout's last had not old Sikaso sternly seized and lowered the weapon, saying in a tense whisper:

"The time is not yet ripe, my brother. To fire now would be unnecessarily to give the alarm. Wait until they are massed thick and then fire into the bodies of the Arab dogs."

The scout didn't waste much time in reconnoitering. After a short time spent in peering about he dived once more into the forest and Billy whispered to Lathrop:

"Now it's coming, old man."

And come it did.

Five minutes after the scout had dived back into the forest a dozen dark forms crept from the bush and stealthily advanced toward the tent.

The leader had reached the door and Billy was frantically imploring old Sikaso to let him shoot when an appalling shriek rent the air.

The old Krooman's axe flashed once in the moonlight and the leader of the attacking party lay dead at the tent door, severed almost to the chest.

There was not a second's time, however, to take in what had happened. In a flash the whole horde was upon them, and Billy and Lathrop began firing desperately into the mass of foemen who appeared to spring from every side of the clearing at once.

Even in this extremity a strange thought flashed across Billy's, mind:

"Where was Professor Wiseman?"



CHAPTER XII

IN THE HANDS OF SLAVE-TRADERS

The ebon form of the Krooman giant seemed everywhere at once.

In the moonlight his terrible axe flashed incessantly and every time it fell a shriek or a muffled groan showed that it had found its fatal mark. The huge form of the warrior black seemed, however, to bear a charmed life. Again and again one of the attacking force would fire at him, but the bullets seemed to be warded off by some supernatural force. He was immune alike to bullets and arrows—with which latter the natives attached to Muley-Hassan's force battled.

Billy and Lathrop fought with unflinching courage, pouring out a leaden hail into the onslaught that again and again seemed as if it must drive the attacking force back. But fighting at such desperately uneven odds could not in the nature of things last long. There came a minute when Billy, turning to reload, found that before he could snatch up a handful of cartridges a huge Arab was on top of him.

Lathrop's clubbed rifle struck the fellow helpless the next minute and sent his long, cruel knife with a ringing crash to the floor.

Before Billy's half breathed "Thanks, old man," had left his lips, however, another of Muley-Hassan's followers had rushed in and the moment would have been Lathrop's last but that Billy drove his fist into the fellow's face with a crashing blow that knocked him on the top of his fallen comrade. It was hand-to-hand fighting then with a vengeance. Billy seized hold of the muzzle of an Arab's revolver as it was thrust into his very face, and twisted it upward as it was discharged. Seizing up a camp chair Lathrop swung it round his head like a club and scattered the brains of a native follower of Muley-Hassan.

But strategy was to put an abrupt end to the fight even if it could have continued much longer.

Billy was bleeding from a cut over the forehead which blinded him, and Lathrop had got two nasty knife thrusts, one in the arm and the other in the fleshy part of the calf of his leg, when they were suddenly attacked from the rear by half-a-dozen slavers. The next minute, wounded and bound, they were as helpless as two captured puppies.

The fight was over, but the Arabs had come out of it with a badly crippled force.

Of the twenty-five men who had attacked the adventurers' camp ten had been killed outright and half a dozen others so badly wounded that they could not move. Hardly one of them had not received some minor injury, and the very fact that they had made such a poor showing against two American boys and a Krooman armed only with an axe, filled Muley-Hassan with savage rage.

Furiously the slave-dealer ordered the two boys brought before him. A huge fire had been lighted by his followers and in the glare cast by this he received them. It was a wild scene and the two boys hardly knew whether they were awake or dreaming, as they were roughly hustled into the presence of their captor.

Diego de Barros, his cruel, thin lips curled in a sneer that showed his yellow teeth, stood by the side of Muley-Hassan, the latter a tall determined-looking man with a crisp, curly black beard and a sinister cast of features. A long burnoose of white, worn after the Arab style, hung from his head and framed his dark features, which were just then overspread by a frown as black as thunder.

Outside the circle of firelight lay the bodies of the victims of the Krooman's axe and the boys' bullets. All who could do so of Muley-Hassan's followers were gathered about him, as the two young Americans were brought face to face with the man they had such good reason to fear.

"So these are the young Americans?" he asked as Billy and Lathrop returned his hawk-like gaze unflinchingly.

"No, sir," spoke up Diego, "they are not. Wiseman has just told me that the Chester boys have flown in their air-ship and these are the cubs left behind to guard the camp."

At Wiseman's name mentioned in such a connection both the boys started.

"What! they have gone?" thundered the Arab chief.

"Yes, sir," stammered Diego, his coward nature aroused at the sight of his superior's fury.

"And by this time they are rifling the ivory cache. That fool Wiseman shall pay dearly for this. Bring him to me," shouted the Arab.

Desperate as was the boys' position they could not restrain a start of amazement as Professor Wiseman, his face pale as ashes to his very lips, came tremblingly forward.

"You were attached to this boys' camp to prevent by all means their sailing till I attacked the camp and made them prisoners, were you not?" demanded Muley-Hassan angrily.

Wiseman stammered something in reply.

"You are a coward as well as a fool," went on the slave-dealer, a cruel sneer breaking over his face; "but you have blundered for the last time. Take this fool away and kill him!" he ordered, turning away as if there was an end of the business.

Pitiful cries broke from the lips of the unhappy professor as he heard his death-warrant thus pronounced. He threw himself on his knees and begged and pleaded in a loud screeching tone for a little more time. But the chief was obdurate.

"Take him away," was all he said, and his men, not daring to disobey his orders any longer, fairly dragged the unfortunate prisoner toward the river bank. There was a short, sharp scream that chilled every drop of blood in the boys' bodies and then a splash. Professor Wiseman had paid the price of his treachery.

It was not till long after that the boys heard the full measure of his villainy. How posing as a naturalist he had wandered up and down the Ivory Coast for years acting as the secret agent of Muley-Hassan and making arrangements for the smuggling of slaves and illicitly procured ivory out of the country. He was too accomplished a rascal to be suspected and his learned appearance made it still more improbable that he should be engaged in any illegal trafficking. It was small wonder, too, that he had started when Frank mentioned the name of Luther Barr, for it was Luther Barr whom he had betrayed to Muley-Hassan and advised him of the whereabouts of the wily old New Yorker's ivory cache. As soon as he heard Frank mention the name he had of course surmised that the pretended hunting expedition was merely a blind to cover a bold dash to recover the ivory, though how they were to discover its whereabouts he could not imagine till, by prying and listening, he learned that they had a map of the locality of the stolen stuff.

He had then dispatched native canoe-men to Muley-Hassan and apprised him of the coming of the boys, and Diego had been at once sent out by the Arab to secure possession of the map if possible and, failing that, to destroy the boys' canoes. That the aeroplane would also have been put out of commission there is little doubt, if Diego or Wiseman could have found an opportunity. The brutal Arab could then have disposed of the expedition at his leisure. But the Golden Eagle II was too closely guarded for the two spies to be able to harm it.

The Kroomen porters attached to the camp had, as old Sikaso had forecast, fled into the jungle at the first attack of the Arab's followers and they did not put in an appearance till long after the marauders had left the camp.

But what puzzled the boys, as they stood facing the Arab with Professor Wiseman's scream still ringing in their ears, was "What had become of the old warrior."

He could not have turned traitor. His valiant behavior in the skirmish made that impossible to consider a minute. But it was equally certain that he was nowhere to be seen. What could have become of him? A dread that he was dead oppressed both boys as they stood there waiting for the Arab to speak.

Muley-Hassan seemed to be considering.

He twisted the ends of his jet-black mustaches like a man lost in thought, and the firelight playing on his bold reckless features showed there an expression of deep perplexity. But it was no question of mercy that was agitating his mind.

It was whether he would kill the boys right there or sell them into slavery.

To his money-making mind the latter idea commended itself. Two strong youths such as they were would fetch a good price anywhere, and so it came about that Billy and Lathrop—who had fully expected to share the Professor's fate—were flung by no gentle hands into their bullet-riddled tent and left to pass the night as best they could. Two men were posted to watch them and a rough cuff on the head rewarded Billy's single attempt to speak to Lathrop.

The next day at dawn the camp was the scene of great activity. The dead were carried into the forest a short distance and buried, while the wounded were attended to with such rough surgery as Muley-Hassan knew. In this work Diego, his lieutenant, who seemed to be a sort of Jack-of-all-trades-outside of his regular occupation of scoundrel-aided him; bandaging the, cuts and extracting the bullets of his companions with some skill.

The boys were then given to eat some sort of stew in a big wooden basin and being just healthy American boys and not heroes of romance they ate heartily of the compound and felt better. Muley-Hassan himself examined the cut on Billy's forehead and Lathrop's two wounds and pronounced them mere scratches.

Just as it appeared that a start was about to be made the signal bell of the wireless rang. As our readers know it was Frank signaling from the Moon Mountains.

A sudden idea seemed to strike Diego at this. He called Muley-Hassan aside and talked earnestly with him for a few seconds, then he came up to the boy and demanded fiercely which one of them it was that understood wireless.

Lathrop replied that he did, and the next minute wished that he had bitten out his tongue before he had admitted it; for Diego, in a rough tone, ordered him to sit down at the instrument and reply that all was well at the River Camp.

"And, mind you, youngster—no tricks," he said savagely, "or I'll kill you as dead as mutton. I understand the Morse code myself and can tell what you are sending; and send slow so that I can get every letter."

Lathrop was in a quandary. To refuse to sit down at the instrument meant instant death.

He could tell that by the look in Diego's eyes and from what he had seen of him he knew he would not stop at a little thing like a murder to drive home a point.

The question was, did the man really understand telegraphy? If he didn't and was only, bluffing Lathrop determined to inform Frank of the true state of affairs. Otherwise it would do neither himself nor the others any good to try to trick Diego.

With a prayer on his lips that the Portuguese might not have been stating the truth about his knowledge of wireless the boy started to send. He had in his mind the message he would try to get through:

"We have been attacked. Get help and follow us."

But he had hardly tapped out with a hesitating finger the first word of his message when he felt a bullet whiz by his ear and the report flashed so close to him that it deafened him and scorched his skin.

"Thought I was bluffing did you, eh?" sneered the Portuguese, "come now, no tricks; send out what I tell you or the next bullet will come closer."

And so it came about that the queer hesitating message that Frank received at Moon Mountains was sent out.

Immediately it was dispatched Muley-Hassan gave the order to advance and his ragged followers, carrying the worst wounded in improvised litters, set out toward the northwest.

"We are going to the Moon Mountains," whispered Billy to Lathrop, "at least it looks that way. I overheard Muley-Hassan say to Diego that we'd have to hurry to get the ivory—"

Lathrop's reply was cut short by a scene that sent the angry blood to both boys' faces.

Before the camp was abandoned for good and the plunge into the forest began, Muley-Hassan gave a sharp order and directed several of his men set about demolishing the camp. Diego himself smashed the field wireless of which Frank and Harry had been so proud. He hacked it to atoms with one of the heavy axes. The tents and provision boxes were next piled in a heap and set in a blaze.

As the column of dark smoke rose from the ruins of the once happy camp into the clear sky the order to advance was given and the train once more moved forward.

They had hardly deserted the clearing before, from the river bank, half a hundred wild figures appeared.

They were similar in appearance—only even more wild-looking than the savages fought off by Frank, Harry and Ben the previous day. Like the others their slashed and scarred faces and clay-daubed lips showed them to belong to one of the fierce cannibal tribes of the Bambara region.

Their leader, a tall, thin savage of exceptionally repulsive appearance, motioned with his fingers to his thick lips for absolute silence among his followers.

Clutching their great broad-headed war-spears the next moment the savages slipped into the forest in the direction the Arab and his band had gone. Steadily they advanced with the quiet stealthy tread of panthers on the track of their prey.



CHAPTER XIII

GORILLAS—AND AN AERIAL TOW-LINE

The mystery of the man on the hill bade fair to be an unsolved one, for although the boys watched for some time with considerable anxiety he did not reappear. This feature of the incident set them to comparing notes and they found that their impression of the apparition differed considerably. Both Frank and Harry were ready to swear that he was a black man, while Ben Stubbs was equally convinced that his skin was of a reddish hue. All three, however, agreed that he was weaponless so far as could be seen, and his attitude appeared to be more one of interested curiosity than of actual hostility.

"Well, there's no use wasting time in speculation," said Frank at last, "more especially as it does not look as if we can get any nearer to solving the problem in that way. The thing to do now is to get at the ivory and that as quickly as possible. If that man is the forerunner of a band that means to attack us, it is all the more reason that we should get a move on."

"Right you are, Captain," assented Ben, "and here goes!"

With a mighty swing of his pick the former prospector dislodged a pile of the rough stones of which the cairn was composed and the boys, too, laid on with a will. In an hour or so all that was left of the once lofty cairn was a few big rocks.

Excitement ran fairly to fever heat as the last obstruction that lay between the adventurers and the ivory hoard was cast aside.

In a few minutes now, if all went well, they would be in possession of the treasure. More than once as they worked, Frank drew his field-glasses out of their case and scanned the surrounding wilderness of rocky chasms and swept the green jungle that lay stretched like an emerald ocean far below, but each time he replaced them with a sigh of relief. So far there was no sign of any rivals' approach, although Frank well knew that by this time Muley-Hassan must be upon his way to contest the boys' claim to the ivory.

As the last stone was chucked aside with a mighty heave by the combined forces the perspiring adventurers broke into a hearty cheer.

Beneath it was a wooden trap-door which had a ring placed in the middle evidently for the purpose of lifting it. Frank gave it a heft, but the weight was too much for even his wiry muscles; but when Ben and, Harry assisted him the door gave with a jump that threw them all to their feet.

Scrambling up in a second they rushed to the edge of the hole revealed by the uplifting of the wooden cover. What they saw showed them instantly that their wildest hopes had not been overdrawn. There, at their feet, lay a king's ransom in yellow ivory.

From the hole rose a fetid, sickening odor that at first was almost overpowering. It came from the rotting flesh that still adhered to the roots of many of the huge trunks.

With a cheer Harry was about to spring down into the aperture when Frank, with a quick exclamation, drew him back.

"Jump back for your life!" he shouted.

Harry was accustomed to obeying his brother in everything, and jump backward he did with an agility that would have done credit to a gymnast. Before he could ask a question Frank's revolver cracked and a little spit of dust shot up almost at his very feet.

There lay a tiny snake viciously wiggling about in its death agony, pierced through by Frank's bullet.

It was a rock adder—one of the deadliest of African snakes. Barely more than three inches in length, and a dull gray in color, it was small wonder that Harry in his excitement had not seen it as he was about to jump almost upon it.

"We shall have to be careful," said Frank, as he kicked aside the still writhing body of the disgusting looking reptile. "There is just a chance that Muley-Hassan, with the cunning of an Arab, may have put several more of those customers in here to guard his ivory."

It was therefore cautiously that the boys proceeded to work at getting the ivory out of the hole and although they killed three more of the venomous reptiles it seemed more probable that they had got in by accident than that the Arab slave-dealer had deliberately placed them there. By mid afternoon a big pile of ivory lay ready for transportation to the Golden Eagle Il and only a few more tusks remained in the hole.

"How are we ever going to get the tusks down the hill to the Golden Eagle II?" asked Harry as he gazed at the formidable pile.

"I have a better plan than that," replied Frank, "we will bring the Golden Eagle II here."

"What?" gasped both his listeners.

"Why not? It will be a ticklish job to land her on this spot, but I think I can do it. I mean to try anyhow."

"You are risking breaking up the ship," objected Harry.

"On the other hand, if we don't get this ivory out of here in jig time Muley-Hassan will be here with a big force and we shall assuredly all have our throats cut."

This argument proved insurmountable, and while Ben was left by the ivory Harry and Frank hurried down the steeps to the plateau on which they had left the Golden Eagle II. It was the work of a few minutes to tune her up. In a brief time from the moment they had left the ivory cache, considering the clamber they had had, the boys were in the air and headed for the spot where they had left the hoard.

But as they rose into the air they were startled by the sound of a shout and then another and another, then carne a volley of shots.

What could be the matter?

The shooting evidently was taking place at the spot where they had left Ben to guard the ivory.

Muley-Hassan! was the first thought that shot through Frank's brain.

The next minute, however, he dismissed the idea as absurd. The Arab, even by the swiftest marching, could not have reached the Moon Mountains in such record time unless he also had an air-ship, which Frank knew was impossible.

As the ship soared higher and rushed straight as an arrow through the air to the ivory cache a strange sight was revealed to the two young voyagers. High up on the mountain-side they could see Ben struggling with what appeared to be dozens of naked savages. The boys could see his gallant resistance as he swung his clubbed rifle again and again at his savage opponents. Several of them lay dead on the ground about him, but those that remained were attacking him with what seemed demoniacal fury.

"Good Lord," gasped Frank, "what on earth can have happened?"

"They're cannibals!" gasped Harry.

"No—no," exclaimed Frank hastily, "they're—give me the glasses quick, Harry—that's right—I thought so. They're not savages, but worse almost."

"What do you mean?"

"That they are gorillas!"

At her utmost speed the big aeroplane bore down on the scene of the unequal combat between Ben Stubbs and the savage beasts.

The boys could see that one of the brutes had seized their stalwart companion's rifle from him and with incredible strength had broken it in half as if it had been a wooden toy. The next minute Harry's rifle spoke and the gorilla that had just performed the miraculous feat of strength fell dead. With a shriek of rage the others turned to see whence came this new enemy.

At the sight of the great aeroplane bearing down upon them they at first started to flee with howls of terror, but the next minute they rallied and with low growls of rage, that bared their cruel fangs, they deliberately waited to see what this strange object might be.

This gave Ben a brief respite and he occupied it by reloading his revolver. The boys were delighted to see by this that their brave comrade was not seriously injured.

But now the Golden Eagle II was ready to settle and Frank, guiding his aerial steed with one hand, grasped his revolver with the other, for it was evident that the rush would come as they struck the ground. And come it did. As the wheels of the aeroplane struck the earth and Frank threw in the brakes sharply crashing into a rocky wall, with a howl of defiance the whole horde of man-like brutes rushed down on the air-craft with wicked rage in their spiteful little red eyes.

The leader of them, a huge "old man" gorilla, brandished an immense stone which he hurled with vicious energy at the new arrivals. Luckily it fell short of the air-ship or it would have crashed through the plane covers and have seriously crippled, if not ruined, the air-ship.

The boys' rifles cracked simultaneously and two of the attackers rolled over, with horrible human-like cries, but the leader, the bad "old man," was still in the field. As he saw his fellows fall he gave a mighty yell of rage and hatred that seemed to come from the depths of his hairy chest, and beating rapidly on it, as if it were a war-drum he rushed straight at the aeroplane.

"Don't let 'em get near the engines," was all Frank had time to shout before the avalanche of hairy, ill-smelling brutes was upon them. Some of them had armed themselves with rocks which they hurled with ferocious force. Others used nothing but their bare hands. Some of them, wounded as they were, fought with added fierceness. Desperately the boys fought them off and when the magazines of the rifles and revolvers were emptied they fell back on their hunting knives.

Frank had made a furious lunge at the "old man" and missed him by a hair's-breadth when he felt two great hairy arms encircle him from behind and the hot breath of one of his horrible opponents whistling savagely in his ear. He tried to lunge backwards at the creature, but toppled over and fell sprawling. In a flash the "old-man" gorilla was on him when Ben's revolver cracked and the "old-man," badly wounded, sprang high into the air and rolled over and over, clutching his head with both his huge hands and screaming in an agonized manner.

The fall of their leader seemed to discourage the others. They fought on for a while but it was half-heartedly. The boys had had time in the brief pause that followed the killing of the "old-man" to reload, and with their rifles newly charged they were in position to make terrible reprisals on the gorilla band for the mischief they had wrought. The monsters evidently were about to quit the battle when suddenly a cry rang through the air that ended the fight more abruptly than even the boys' bullets could have done.

"Ah-o-o-o-o-AH-O-O-O-O-o-o-o-o-o-o-o-o-o-o-o!"

It was the voice of the mountain once more.

With yells of dismay and terror the remainder of the gorilla band instantly dashed up the rocky mountain-side dragging with them, in grotesquely human fashion some of their wounded. Several of these, however, still lay on the ground and the boys put them out of their misery with a few well-directed shots. A pathetically human look lingered in the eyes of some of the injured gorillas and Harry burst out with:

"This is awful work. I'd rather fight a dozen bands of cannibals than have to do this."

"And yet," replied Frank, "if we hadn't killed them they'd have killed us."

At last the unpleasant work was over and the ivory was rapidly loaded into the aeroplane. But here an unanticipated difficulty manifested itself. Obviously the aeroplane would be too heavily laden if she attempted to carry all or even a good part of the ivory.

"Now we are stuck," cried Harry.

"Hold on," exclaimed Frank with a smile, "I anticipated this. We are going to turn the Golden Eagle into a tow-boat."

"A tow-boat?"

"That's what I said."

"What do you mean?"

Frank, in reply, bent over the stem-locker of the aeroplane and drew out what Harry instantly recognized as the silk envelope of an experimental dirigible they had built the year before.

"Now then," said Frank, "give a hand here."

They all three pulled and hauled till the envelope was spread level on the ground, all folds and creases having been carefully shaken out.

"Well," said Harry, "this would carry an awful weight of ivory, but how are you going to inflate it?"

"With these cylinders," was the answer as Frank opened the store-room below the floor of the Golden Eagle and pointed to a dozen cylindrical steel receptacles. "They contain more than enough pure hydrogen gas at a high pressure," he explained, "to inflate the bag."

In his enthusiasm Harry waved his helmet and Ben did the same.

"An aerial express, hurray!"

The inflation hose was soon connected to the first of the cylinders and with a hiss the gas rushed into the bag when a turn of the wrench set free the precious stuff. Slowly the big yellow envelope swelled and assumed shape until by the time the last cylinder was empty it was tugging and straining to rise. But the boys had weighted it down with rocks and pegged its net ropes to the ground.

The ivory was loaded into a sort of rope basket, like those used to hoist cargo aboard a ship, and in a short time, so quickly did they work, they were ready for the air, so far as what Harry called "the airbarge" was concerned.

"We shall have to strip the Eagle," decided Frank, when the inflation job was finished.

"Of everything that we can spare," added Harry, setting to work at once to rip the transoms and detach the bolts that held the heavy wireless apparatus in place. As he did so, Frank was moved by a sudden thought.

"Hold on a second, Harry," he shouted, "I'll call up the river camp before we cut off all communication."

Rapidly he sent out the call. Again and again his nervous finger agitated the key—but there was no response.

"They—they don't answer," gasped Frank at last—heavy anxiety in his tones.

"Oh, Frank, do you think anything serious is the matter?" cried Harry.

"It may only be that the apparatus is out of order," replied the elder brother seriously; "but it looks bad. That field wireless was in prime condition and it would be next to impossible for them to fail to receive our call."

"Well, there is only one thing to be done," remarked the practical Ben Stubbs.

"And that is—?" queried Harry.

"To get back there as soon as possible, for if they need us they need us dern bad," was the energetic reply.

Half an hour later the Golden Eagle, stripped of all her heavy gear and only carrying just enough gasoline to get her to the river camp, where the adventurers expected to find a reserve supply, rose slowly into the air with her queer tow tugging behind on the wireless ground rope. The boys had cached the wireless apparatus and the other gear, to be called for at some more opportune time. To their great regret, also, they had had to leave some of the ivory behind them. But the majority of what they did not dare trust to the gas-bag they carried in the chassis. Luckily for them there was hardly a breath of wind and the novel carrier towed well.

As the occupants of the great aeroplane gazed back at the sinister Moon Mountains as they fast faded out—they saw silhouetted against the evening sky a dark figure.

It was recognized at once as one of the beaten gorillas scouting to see if the terrible white men had really gone.

"There's the man we saw this afternoon," laughed, Frank, as with rapidly beating propellers the Golden Eagle II winged her way with the convoy toward the River Camp.



CHAPTER XIV

AN ESCAPE—AND WHAT CAME OF IT

From the pace at which Muley-Hassan's band traversed the jungle paths it was evident to the two young captives that there was imperative need in Muley-Hassan's mind of arriving somewhere at a set time. The usual noonday rest, which even the avaricious slave-trader was in the habit of taking, was not observed and the travelers pressed straight on. Lathrop and Billy were almost ready to drop with fatigue when that evening, just at dusk, they arrived at the bank of a muddy river which Muley-Hassan, impatient as he was to proceed, decided it would be unwise to ford till daylight—when they could look for a good crossing place. At the spot which they had halted, the stream—swollen apparently by rains in the mountains—roared between its banks, in a dark chocolate-colored flood.

Muley-Hassan himself was the only one of his band provided with a tent, or anything resembling one, and the boys shared the common bed of the rest of the party—which was the ground. A more unwholesome resting-place in Africa, particularly on the steamy, swampy banks of a river, could hardly be imagined. So indeed Muley-Hassan seemed to think, for after a short time, during which the boys vainly tried to secure some sleep, he ordered Diego to provide them with blankets to place between themselves and the bare earth.

"I expect to get a good price for them eventually," he said, "and I don't want to lose them unless I have to."

As the boys' wrists and ankles were bound with tough grass while there was no particular attempt made to watch them, and soon the snores of the camp bespoke that it was at rest. Then it was that Billy whispered to Lathrop.

"Now's our time to try for it!"

"Try for what?" whispered back Lathrop in an inert tone.

"To get away."

"What!"

"I mean it. I found a sharp stone imbedded in the ground near to me and I have nearly sawed through my wrist-bands."

After a few seconds' more vigorous scraping against the stone, Billy whispered:

"My hands are free. Wait till I wiggle my fingers and get up some circulation and then we'll make our attempt—"

When he had once more got full control of his cramped fingers Billy stooped cautiously over and loosened the thongs about his ankles. So tightly had they been drawn, though, that it took some little time to get the cramps out of them. At last, however, the boy succeeded in restoring the circulation and then he was ready for the most daring step of his attempt. Cautiously he fell on his hands and knees and began to crawl toward the nearest of the sleeping slave-traders.

"What are you going to do, Billy?" asked Lathrop, in an agony of fear lest the man should awaken.

"Watch me," was the young reporter's reply, as on his stomach he wiggled painfully across the few yards separating him from the sleeping man. In reality it took only a few minutes, but to both the boys the period of time occupied seemed interminable.

But it was no time to hurry things. One false step night cost them their lives and Billy realized this.

With the slow deliberate movement of a snake he, reached out his hand when he got near enough and took from the sleeping man's side his long curved Arab scimitar. Then he glided back to Lathrop as silently as he had left.

He had just reached his resting-place when there was a stir from the further side of the camp. Like a rabbit ducking into its hole Billy was under his blanket and apparently fast asleep in a second. But his heart beat so loudly that it felt to him that anyone who was not deaf could hear it a hundred yards away.

The man who had moved was Diego and the boys could hear his cat-like footfalls as he neared their sleeping-places. Once he stumbled over one of the sleeping men and the aroused one rose with a start and called wildly:

"What is it?"

"Hush, Adab," cautioned Diego, "it is I—Diego. I'm going to give an eye to those two American brats."

"They're tied up hard and fast enough," chuckled the other.

"If they were of any other nationality—yes;" was Diego's reply, "but these Yankees are brave and clever enough to escape from almost any trap."

"You bet we are," thought Billy to himself, giving a realistic snore.

Although he did not dare to open his eyes, the young reporter could feel Diego standing over them in the moonlight and gazing down at them to ascertain if they were still "hard and fast," as the other had expressed it.

For an instant a terrible thought flashed across Billy's brain.

"Suppose Diego should take an idea to examine their thongs?"

But the lieutenant of Muley-Hassan apparently was satisfied, for after a few minutes' scrutiny he turned to go Billy could hear his feet scrape as he swung around.

At almost the same instant the night was filled with savage cries and the camp was thrown into confusion by an onrush of wild figures before whose spears the half-awakened Arabs were slaughtered like sheep.

Not realizing in the least what was happening, Billy yet conjectured that the Arabs were just then too busy to pay any attention to himself and Lathrop. With two slashes of the stolen scimitar he severed Lathrop's bonds and dragging him to his feet dived into the forest.

As they entered its recesses a fleeing Arab, still clutching his rifle, dashed by them and an instant later fell dead. He had been speared through the back.

Billy, with a quick inspiration, seized the dead man's long rifle and his ammunition pouch and, followed by the bewildered Lathrop, plowed desperately forward into the screen of the jungle.

Behind them they heard cries for mercy and fierce shouts from the attacking savages. At first the cries and imprecations of the slave-traders predominated and then, by the altered sounds that came from the scene of the fighting and the crashing of the Arabs' volleys, the boys realized that the tide of battle had changed and that the Arabs were driving back the attacking force.

"What do you suppose happened, Billy?" asked Lathrop, only half awake, as the boys, with the fleetness and endurance that desperate need lends, plunged deeper and deeper into the forest.

"Why, that some cannibal tribe that Muley-Hassan pillaged for slaves at some time has trailed him and attacked him," hazarded the reporter.

How near he came to the truth our readers know. The band that had made the midnight attack was the same that had painstakingly trailed Muley-Hassan since he destroyed the boys' camp on the river bank.

"But the Arabs have beaten them off?" queried Lathrop.

"Evidently," replied Billy, as the volleys died out and victorious Arab shouts were beard. "Hark at that! It's really too bad. I'd like to have seen old Muley and his precious band driven into the river. But if they have driven off the savages they'll be thinking about chasing us."

As he spoke there came a low, growling sound that seemed to proceed from some distance, but nevertheless filled the air. It rumbled and rolled above them like—

"Thunder!" exclaimed both boys in the same breath.

"We've got to find shelter of some kind, quick," exclaimed Billy; "these tropical storms are unlike our little disturbances, and if we get caught among these trees in one, of them we stand a good chance of being killed. It looks like we've jumped out of the frying-pan into the fire."

Without the least idea in which direction they were proceeding, the two chums struggled bravely on, Billy encouraging the flagging Lathrop from time to time with a joke, though these latter were, as Billy admitted to himself:

"Pretty dismal!"

At length, just as dawn was beginning to break, they found themselves facing a steepish cliff of rough rocks.

"Well, here's where we turn back," remarked Billy, bitterly discouraged nevertheless.

If they were lost in this equatorial forest, what chance did they stand of ever seeing their home and friends again?

As for Lathrop he sat down on a rock overgrown with a kind of monstrous lichen and gave way to tears. But not for long. Lathrop was a plucky enough lad, and as Billy truthfully remarked:

"We are going to have enough water before long without our turning on the weeps."

So Lathrop braced up and the boys looked about them. To their intense joy they soon spied in the rocks, a short distance from where they then were, a dark hole partly overgrown by creepers, which was evidently the entrance to a cavern. At the same instant there began a mighty pattering on the leaves of the dense tropic growth all about them, and a louder growl of thunder announced that the storm that had been heralded a few hours before was about to break.

"Well, me for that African Waldorf-Astoria," cried Billy, grasping his rifle and making a dive for the hole. Lathrop followed him and as soon as they were inside the cave he lit a match from his waterproof box.

"Looks to me like there might be snakes in here," he whispered, awed by the darkness and silence of the place.

"Rats," laughed Billy, although he himself felt by no means sure that at any moment some scaly monster might not descend from the roof; "but I'll tell you what we'll do. Light a fire."

"How are we to get wood?" asked the practical Lathrop.

"There's plenty of it right at the mouth of the cave. I'll get a few armfuls and in a minute we'll have things snug."

The young reporter hastened to the cave mouth and in a few trips had gathered up several huge armfuls of wood-drift of all kinds from under the great trees all about. He was just re-entering the cave when there came a flash of blinding light so brilliant that it seemed as if the sky itself had split wide open. A bluish glare enveloped the forest and the lightning flash was instantly followed by a crash of thunder that shook the ground under the boys' feet.

"Well, they don't do things by halves in this country," remarked Billy as he re-entered the cave after a second of being temporarily stunned by the terrific flash.

It didn't take the boys long to have their wood in a blaze and as the smoke did not, as they had feared, fill the cavern, they assumed that there must be some opening above through which it escaped. This fact they verified shortly when, after the storm had been waxing in fury for half-an-hour, a perfect torrent of water came tumbling in from the rear of the rocky cavern.

"Hark!" exclaimed Billy as the boys busied themselves trying to scrape out a water-course that would divert the flood from their fire. From far in the rear of the cave came a plaintive sound of "Mi-ou, Mi-ou."

"Cats!" cried Lathrop.

"Cats nothing," was Billy's scornful reply; "here, let's have a look."

He seized a blazing brand out of the fire and hastened to the place from which the sounds emanated.

"Come here, quick, Lathrop," he cried. The younger lad scurried back and found Billy bending over a roughly constructed nest or bed. On it lay four tiny, fuzzy yellow things. They were "meowing" at the tops of their voices as the torrent of water that had annoyed the boys dripped into their snug nesting-place. At the same instant the boys became aware of a sickening odor of decaying flesh.

"Come on! we've got to get out of here quick as quick as we can," exclaimed Billy as they hastened towards the fresh air.

"Why, what is it, Billy?" asked Lathrop.

"I don't know; but I think that those are lion cubs—they look like the ones I've seen in the Bronx Zoo," was the young reporter's reply, "and if they are, this is no place for us. Come on—the storm is letting up. Let's get out quick before the old ones get back."

The storm, with the suddenness with which these furious tropical disturbances arise and vanish, had indeed gone and the sun was shining down once more on the drenched jungle, which glittered with diamond like spangles as the rays struck the dripping fronds and branches. But the boys had no eyes for the scene about them, beautiful as it was, for as they emerged from the cave a low growl greeted them.

Crouched on the ground—her tail lashing the earth like a cat's when it is about to spring—was a huge tawny lioness—her cruel green eyes fixed full upon them.



CHAPTER XV

THE FLYING MEN

For a breath the boys stood petrified and then Billy hastily slipped a cartridge into the rifle he had taken from the dead slave-trader. But even as he did so the lioness curved her lithe body, as if her backbone had been a steel spring, and launched her great form through the air.

That minute would have been Billy's last—for in his excitement he pulled the trigger before he had brought the rifle to his shoulder and the bullet whistled harmlessly into the air—but for a strange thing that now occurred.

While the tawny brute was in mid-spring, her cruel claws outspread to maul the unhappy reporter, a great spear whizzed straight at her and buried itself in her heart just behind the left shoulder. With a howl of pain the brute fell short in her spring and, before she could make another attack, Billy had reloaded and sent a bullet crashing between her eyes. As the lioness rolled over dead, the tall form of a. savage sprung out of the jungle and stood for a second gazing at the boys, as much astonished, it seemed, at them as they were at him.

Billy, seeing that the best plan was to be pacific, threw down his rifle and cried:

"Seesenab," (peace); the word be recollected hearing the big Krooman use the day that he attempted to take his unlucky photographs.

"Seesenah—white boys," replied the other, the latter words in fair English and in a deep guttural tone, coming forward with the head of his other spear held downward in token of peace. "From where come the white boys—what do they in our land?" was his next question.

"We are lost," explained Billy, "and we are also, blamed hungry," he added, in a burst of confidence.

The savage smiled and rubbed his stomach.

"That's the idea," cried the irrepressible reporter. "Heap—empty— savee?"

The man leant over the dead lioness and, using his spear-point as a skinning knife, rapidly stripped her of her hide. Then, swinging the pelt over his shoulder he motioned to the boys to follow him.

"I don't know where the dickens he means to take us," confided Billy to Lathrop as they obediently trailed along behind, "but so long as we get something to eat I'm so hungry that I don't care if we get eaten the next minute."

"That's just the way I feel," agreed Lathrop, "and anyhow he seems to be a pretty decent sort. He saved your life, that's one thing sure."

"I guess I'll never make a mighty hunter," said Billy dolefully, "there was a chance to make real Bwana Tumbo shot and I missed it."

The savage stalked along in front of them for some distance till they suddenly emerged on a small clearing by a river bank, in which a rough native camp had been pitched. The tents of grass occupied by the hunters being of a peculiar conical shape, like the pointed caps that used to be labeled "Dunce."

Much excitement was created by the arrival of the two boys and their companion, and the hunters crowded round the chums while their guide explained with a wealth of gesture the incident of the killing of the lioness, and also the fact that the boys were very hungry.

Several of the men instantly filled wooden bowls with something from a pot that simmered over the fires and the bowls were thrust before the two ravenous boys. As there were no forks of course the boys used their fingers. But this did not interfere with their appetite and after they had put away two bowls apiece the savages' opinion of them evidently rose considerably. Among the West African natives a big eater is esteemed as a mighty man. Lathrop was considerably embarrassed, however, while he satisfied his hunger by the attention the hunters bestowed on his red hair. Several of them came up behind him and rubbed their hands in it as if they imagined it possessed some sort of medicinal value. Had any one at home dared to take such liberties with the boy's rubicund locks there would have been a fight right away, but Lathrop felt that the best policy to assume in the present situation was silence, and as the old ship captain said to his mate, "dem little of that."

"I say, Billy," whispered Lathrop suddenly, as, after eating the stew, they watched the hunters piling their belongings into their canoes, "you don't suppose they mean to fatten us up to eat us, do you?"

"Well, we can't starve even if that is the reason," replied the practical Billy, "but so far they seem friendly enough. They have not even taken my rifle away."

"That looks encouraging, certainly," replied Lathrop; "if only we knew where Frank and Harry and good old Ben were we might find this all very interesting, as it is though—"

"We've got to make the best of it," chimed in Billy, "come on. See old job-lots is signing to us to come down and get in a canoe."

"Whatever they mean to do with us they seem determined to make us comfortable," remarked Billy, as the boys took their seats in a canoe in which skins had been piled to make an easy seat.

For most of that afternoon they paddled steadily up the brown river, the savages singing from time to time an unending sort of chant, that sounded like nothing so much as a continuous repetition of:

"I-told-you-so. I-told-you-so. I—told-YOU-SO."

"Hum," commented Billy, "if anyone had told me so I'd have stayed in New York."

At length after what seemed endless hours of paddling and chanting the river took an abrupt turn and the boys found themselves at the foot of a steep cliff that towered up, it seemed, for six hundred feet at least. It was formed of black basalt and was crowned with a fringe of contrasting vegetation, but the most remarkable thing about it was that its surface was literally honeycombed with small holes from which, as the canoe cortege drew up, innumerable heads were poked.

An astonishing thing, however, about the men who scrutinized the lads from their lofty watch-towers, was that they were several degrees lighter in complexion than the boatmen and almost as white as the boys in fact. Their features, too, were different. As the boys looked in wonderment at this extraordinary dwelling-place and its equally strange inhabitants, Billy gave an excited shout:

"Great jumping horn-toads, look at that!"

One of the light-colored men had emerged from his, hole and with as little concern as if he were taking a walk had suddenly launched himself into space. But instead of falling to the ground or into the river, as the boys had fully expected to see him do, he floated gracefully to the opposite bank of the river with as little effort as a settling bird.

"Good land of hot-cakes, Lathrop, do you realize where we are?" almost shrieked the excited Billy.

"In the village of the Flying Men," stammered Lathrop, as, one after another, the inhabitants of the rock holes dropped from their aeries and floated groundwards. As the boys watched they saw distinctly that each man, from his wrist to his side, was possessed of a sort of leathery fiber like that of bat's swing, and that as their arms were of unusual length this fiber supported them in their downward flights like a parachute.

"I'll never call any one a liar again as long as I live," choked out Billy, as one after another these strange beings gathered in a chattering group on the river bank.

"But they can't fly upward," exclaimed Lathrop, pointing eagerly to where some of the gliders, having swum the river, were nimbly clambering up a grass rope-ladder to their homes.

"Oh, gee! if I only had a camera," groaned Billy.

"It will be no use telling anyone about this even if we do get out of here, they'll say that we have had a rarebit dream."

"That's so," assented Lathrop, "and honestly, Billy, are you sure we are awake?"

"Sure," replied the reporter giving himself a vicious pinch, and exclaiming "Ouch!"

But there was no time to talk further. Their guide now came up to them and jumping into their canoe paddled them to where the end of the rope-ladder dangled in the stream. He pointed upward for them to ascend. But Billy's curiosity would not let him mount before he had asked a question.

"Who are these people?" he asked in, for him, an awed tone.

"Very old-time people," rejoined their guide. "We hunt for them, work for them. They the same as fetish."'

The boys mounted the ladder slowly.

Unused as they were to such a contrivance it required all their nerve to keep on going up, as they swung at a higher and higher altitude above the river. Neither of them dared to look down, as they were certain that they would be overcome by dizziness.

With their eyes glued to the rock in front of them, they mounted what seemed to be endless rungs till at last they found themselves at the top of the ladder and facing a large opening cut in the rock.

As they found out later, this was the main entrance to the dwelling of this strange community and from it various galleries and passages branched off to their separate dwelling-places. Each family lived in a rock house exactly adapted to the size of the circle. There were six stories, so to speak, of these dwelling-places, but they all communicated, either by means of stair-ways cut in the rock or inclined galleries, with the main passage at the entrance of which the chums now stood.

Their guide, who was immediately behind them on the swaying ladder, took the lead as soon as the three stood side by side on the summit, and escorted them down the long passage. Before they started he took from a bracket in the wall a kind of torch, made of some resinous wood unfamiliar to the boys. Striking piece of flint against his spear blade he soon produced light and holding the torch high above his head, so that its light shone on the walls, rendered glossy by the rub of uncounted ages of greasy elbows and bodies, he led the way down the passage. The boys could feel that after walking a short distance it took a sudden rise and yet further a cool wind began to blow in their faces.

About a hundred yards from the spot where they first noticed the air stirring in their hair the boys and their guide emerged on a scene whose beauty at first shock almost took the lads' breath away.

Before them stretched a fertile valley neatly divided into patches—each hedged off in squares in which flourished all sorts of vegetables, including sweet corn and potatoes and several other less familiar varieties. In pastures, fenced in with mathematical regularity by hedges of the African cactus thorn, herds of humped cattle were feeding contentedly in the mellow glow of the setting sun, occasionally lowing softly, which latter made Billy, as he expressed it, "long for the old farm."

The Winged Men likewise cultivated, it seemed, fruits of many kinds and had also stockades in which poultry, of breeds strange to the boys, but undoubtedly sprung from the aboriginal African fowl, were abundant.

It seemed as if they had struck a land in which the inhabitants lived an ideal life, surrounded as they were by every comfort and necessity that one could imagine; but that even they were distressed by the raids of enemies transpired when the boys' guide, whose name they had learned by this time was Umbashi, pointed to the west in which the setting sun was now kindling a ruddy glow and said:

"Sometime elephant come—then much trouble."

Of the full significance of those words, however, neither boy dreamed as, after a supper of fresh corn, bitter melon, stewed deer meat and a dessert formed of some sort of custard they sank to sleep on their couches of skins, spread for them by Umbashi's direction in a vacant dwelling in the cliff face.

Their slumber senses carried them back to New York and Billy was in the midst of escorting Umbashi in full war paint through the office of the New York Planet, followed by hordes of joshing reporters and inquisitive office boys, who wanted to know whether he'd match his dusky friend to fight Jim Jeffries, when he was awakened by Umbashi himself, who in a few words told him it was morning and time to get up and dress swiftly, as the King of the Flying Men wanted to see him and his young companion at once.



CHAPTER XVI

FOOLING AN ARAB CHIEF

"Frank, what do you make of it?"

"Harry, I don't know what to think."

"Ain't nuffin fer it but ter keep on hopin' fer the best, as the feller said when they had a rope around his neck fer horse-stealing and was about to string him up."

The three—Frank and Harry Chester and Ben Stubbs—were standing round the charred remains of their once lively, well-equipped camp—where they had arrived that morning at daybreak after a tiresome night spent circling about in the moonlight trying to locate it—and now the reason why they had failed to see the white tents was fully apparent by their blackened sites.

"Billy and Lathrop have been carried off!" It was Harry who spoke.

"Beyond a doubt. I thought at first that the raid must have been made by cannibals, but cannibals do not carry rifles, as a rule, and look here." Frank stooped and picked up half-a-dozen cartridges of the kind used by the Arab slave-traders.

"You know there were no shells like that in our party," he went on, "but I can see by the collection of empty shells in the place where the tent stood that Billy and Lathrop must have put up a hot defense."

"Frank, do you—you don't think, do you—" Harry burst out.

"That they have been killed?" Frank finished for him. "No, I do not. Unless they fell in the fight and then we should have seen their bodies down with the others by the river. No, it is my idea that they have been carried off to be sold as slaves. They would have a high market value you know."

Harry groaned.

"But don't you think there is a chance of our getting them back?"

Frank's face grew grave.

"Of course we are going to try every means in our power, but once in the hands of that scoundrel Muley-Hassan it is doubtful if we ever see them again. There is only one thing for us to do."

"And that is—?"

"To get back to the Moon Mountains at once. But we have no gasoline."

This was a stunning blow; in the excitement their of fuel had not occurred even to the farseeing Frank. They had had, as our readers know, to leave most of their gasoline at the Moon Mountains in order to lighten the aeroplane. Without it they could not move an inch in their air-craft. Harry tested the tank. Only a few paltry gallons remained—not enough to drive the aeroplane ten miles.

As the boys stood, struck dumb by the realization of the disaster that had overtaken them, Ben Stubbs, who had been down to the river bank, reappeared.

"Look here!" he exclaimed, holding out at arms length a long white cloak. One glance at the garment was enough—it was an Arab article of dress. There was no further doubt about it, then. Muley-Hassan and his men had carried off Billy and Lathrop.

"But that's not the most extraordinary part of it," went on Ben; "while there are half a dozen of the Arabs' canoes down there, there are a lot of others, that must have belonged to a bunch of natives from their shiftless look—and I could see the bare imprint of the savages' feet in the mud, coming after the Arabs had trod around there."

This was a new mystery. Apparently, then, a tribe of cannibals had been on the trail of the Arabs who had carried off their two young companions. This could only mean one thing, that they meant to punish the Arab slave-dealers for some outrage and, while this would have been quite satisfactory to the boys under other conditions, as things were it meant that there would be a fight in which both Lathrop and Billy would probably be seriously wounded, if not killed. How wrong this surmise was we know, and it serves to show how very wide of the mark it is possible for the constructors of a theory to steer.

And here for a time we will leave our despairing friends while we go back to the Moon Mountains.

The outline of the Golden Eagle II, in her flight to the river camp, had not faded out on the twilight sky, before, through the jungle at the foot of the Moon Mountains, a strange figure pushed its way. It was Sikaso, but a changed Sikaso from the agile muscular black who had wielded his axe with such terrible effect at the fight of the evening before. His ebony body was cut and scarred with the signs of his battle with the thorns and saw-bladed grasses of the dense forest, across which he had cut in desperate haste, scorning all paths in order to warn the Boy Aviators and their chum Ben of the rapid approach of Muley-Hassan. With that strange instinct that white men in Africa recognize in certain of the natives as a sixth sense, the giant black had read in a fire kindled after the battle, that the boys were at that moment in the Moon Mountains, and had at once set out—exhausted as he was—at top speed on the long journey. Only a man of his adamantine strength could have endured the hardships and it had fatigued even his iron frame, as was evident by his stumbling footsteps as he made his way up the side of the mountain—pausing from time to time as if to listen to the whisperings of his mysterious instinct.

Billy and Lathrop, half inclined to accuse the old black in their minds of base desertion, did him a gross injustice. After he had seen the two boys taken prisoners, the old warrior had realized that he could be of far more use to them at liberty than he would be if made captive by Muley-Hassan. Indeed there was no doubt in his own mind that the Arab would put him to death instantly if he ever got his hands on him. He had therefore built a fetish fire and in it had made out distinctly Frank and Harry and Ben in their air-ship, encamped on the mountain-side, and had set out without delay at the peculiar jog-trot by which the native bush-runners can cover daily as much ground, and more, than a horse.