The motion of the air-ship, too, seemed strange.

When they had gone to sleep it seemed as if they were sleeping in a room ashore, so perfectly evenly did the ship rush ahead through the night; but now every portion of her frame seemed to be complaining in its own particular voice, and she groaned and strained like a ship in a storm.

Frank aroused Harry, and a few minutes later Ben Stubbs, too, was awakened by the peculiar motion of the ship.

"What's happening?" he demanded, as one of the air sailors ran heavily along the deck overhead.

"I don't know," rejoined Frank; "but it seems to me that we are in a storm of some kind.—Hark!"

As he spoke there was a blue glare of lightning outside, in which the ropes and stays of the ship, seen through the closed port, stood out as in an etching. Simultaneously there came a terrific crash of thunder. They were evidently in a bad storm.

"I wish we were outside instead of cooped up in here," exclaimed Ben. "I like to be out on deck in bad weather and not penned up in a cubby hole."

"Let's try the door," suggested Frank, "we might be able to force the lock."

But the lock was evidently put on to stay, and tug and strain as they would, they could not budge it an inch.

The motion of the ship by this time was so violent as to make them feel quite seasick. She swayed from side to side and now and then took long dips.

"I know what they are doing," exclaimed Frank as the ship executed the latest of these diving maneuvers; "they are setting their aeroplanes low so as to try and find a smooth current of air."

"They've got a fine chance to, if it's blowing as hard as it seems to be," was Harry's comment.

The uproar on deck grew louder.

They could now hear Malvoise's voice, directing the crew to strengthen this stay or lend a hand on that rudder brace.

The ship was evidently passing through a crisis.

It was hard for the boys to remain cooped up in their pen, but deliverance was near at hand.

The door was suddenly flung open, and Malvoise himself stood framed in the square of light from the illuminated saloon behind him.

"You had better come out of there," he said briefly, "we are in a bad storm."

"Are we in danger?" asked Harry.

"I don't know yet. If it doesn't blow any harder we may be able to weather it."

"And if not?"

"If not, we may go to the bottom."

"Is anything wrong with the ship?" was Frank's next question.

"Yes, the engine is not working right. It is not developing enough power to keep us driving against the storm. I am afraid it may strike us broadside on and tear the cabin and decks loose from the gas-bag," replied the Frenchman.

As the boys and Ben gained the deck, the storm struck them in its full fury. It was not cold, they were too far south for that, but the wind fairly drove their breath back down their throats.

"Say, let's grab on to a stay or something," gasped Harry, "I don't want to get blown overboard."

They fairly fought their way to the edge of the navigating deck, which was swaying in a sickening fashion, and clung to one of the stout mainstays of the stressed and storm-driven gas bag above them.

Far below, the sea roared and its wave crests gleamed with phosphorescent light, as the furious wind ripped off their tops and sent them scurrying over the heaving waters.

But, bad as the wind was, a far graver peril menaced the dirigible, and the boys knew it. The lightning was zipping and ripping across the sky in every direction, and, in the event of a bolt striking the craft to which they clung, the boys knew that they might as well be sitting on a keg of exploding dynamite. There would a blinding crash as the gas exploded, and then oblivion.

As they hung on for dear life, Malvoise, his face gleaming white in the glare cast from one of the cabin ports, came up to them.

"Do you think you can take the wheel for a while?" he asked Frank. "What with fear and exhaustion Constantio is almost unable to stand up."

Frank agreed, and, followed by the others he entered the pilot-house. With the exception of the binnacle light above the compass and a small shaded incandescent that shed a glow on the height indicator, the place was as black as a well.

"How is she doing now?" the boys heard Malvoise ask the inventor.

"Ah, senor, poor thing, she is torn and strained in every direction. My heart bleeds for her!" exclaimed the Spaniard.

"Yes—yes," broke in Malvoise impatiently; "but can she last out?"

"I do not know," came the reply of the other. "It is much to ask of any dirigible to last out such a storm. See," he turned the light on to the wind-gauge—it showed a pressure of sixty miles an hour, "it is a wonder to me she has not been torn apart," he declared.

"Well, you'd better go and get some sleep now," said Malvoise abruptly, "one of these boys here will take care of the ship while you nap."

"Very well," said the Spaniard, "do not drive her too hard against the wind, senor, but rather let the wind drive her. Good-night."

He staggered out on to the swaying, plunging deck and vanished. Frank had taken the wheel as the Spaniard relinquished it and he was astonished to find how, in spite of its gears, the wind-stressed rudder tore and tugged at the spokes.

"The strain on the rudder must be terrific," he thought to himself; "it's a wonder it has held out as long as it has."

Taking a casual glance at the height indicator, Frank gave a start. It indicated twelve thousand feet. It was higher than the boy had ever been before.

For several minutes he was too busy easing the dirigible through a blast that seemed as if it would rip her apart to notice the gauge again. When he had an opportunity to do so, he gave a whistle of surprise.

The dirigible had now climbed on the wings of the storm to an altitude of fourteen thousand feet.

Glancing through the pilot-house window the young helmsman saw tattered shreds of storm clouds driven by at a terrific speed; but fast as they went, the dirigible was hurried along with them at an equal speed. The rapid motion had a tendency first to exhilarate and then to turn dizzy those who participated in it.

All at once a sharp whistle sounded from a tube placed so that it was close to the helmsman's ear.

"A signal from the engine-room," cried Malvoise, "answer it."

"Hullo!" called Frank, turning back the whistler at the mouth of the tube. Then he placed his ear to it.

"Two cylinders are missing fire," came the hail, "to make repairs we shall have to stop the engine."

"Keep on with what power you have," shouted back Frank. "We've got to keep going."

There was no need to explain to the others what the bad news from the engine-room was. They had guessed from his reply.

And still the dirigible rose.

She was now at an altitude of fifteen thousand feet, and even as Frank gazed at the indicator she soared higher.

It grew bitterly cold.

"Something will have to be done," he shouted to Malvoise, "if we keep on going higher the air will soon be so rarefied that we shall be unable to breathe."

"Set your dropping planes," shouted Malvoise, above the turmoil.

"I have tried to," yelled back Frank, "but she won't drop unless the engine forces her ahead faster. The wind is stronger than we are."

"Let out the gas," suggested Harry.

Frank shook his head.

"I don't want to do that except in case of actual necessity," he said. "We may need all we have before long."

"I can feel an awful pressure on my ear drums!" suddenly exclaimed Harry.

"No wonder," was Frank's rejoinder; "look at that."

He pointed to the gauge.

The dirigible had now been driven to a height of eighteen thousand five hundred feet, and breathing was really becoming painful.

Desperately Frank struggled to get the sinking planes to act, but the wind pressure on the bag counteracted all his efforts in this direction. So fast was the hurricane now driving the gas-bag ahead that the sub-structure lagged behind, straining at its confining stays and braces.

All at once Harry gave a cry and sank to the floor of the pilot-house. Malvoise, the next instant, hastened to the deck and cried:

"Air, air!"

Frank felt a warm liquid streaming from his nose and ears. He put up his hand. It came away stained red. Even tough old Ben Stubbs felt the baleful effect of the high altitude.

"I'll be hornswoggled if I can stand this much longer," he gasped out to Frank.

"Can you take the wheel?" replied the young aviator. Ben nodded.

"Then take it. I'm going to get this ship down."

Frank reeled from the pilot-house on to the deck. He almost stumbled over the body of Malvoise as he did so. It lay as inanimate as in death where it had been thrown against the railing by the impact of the ship's wild swaying.

"You'll go overboard if you're not careful," Frank found himself saying in a voice he hardly recognized as his own.

Making his way aft the lad encountered the red-headed sailor, Wells.

"Oh, sir, what is happening?" gasped the poor fellow.

"We've gone too high," replied Frank, every word cutting his chest as if a knife had been plunged into it. "Where's the valve cord?"

"Aft there, sir, it's belayed to the starboard rail."

As he spoke the man pitched forward as if he had been shot and lay inanimate on his face.



CHAPTER XXIV.

THE INVENTOR'S TREACHERY.

Weak almost as a baby, Frank made his way to the stern of the navigating deck, and with what seemed the last ounce of strength in his body he gave the cord a feeble yank.

It resisted and the boy tugged once more.

Still it stuck.

Mustering his strength to keep on his feet a minute longer, the boy tied the cord to his wrist. Then, as he fell forward in the swoon that he knew must ensue, the cord tightened under the weight of his body and yielded.

The dirigible with an unconscious crew aboard plunged on through the night, but every moment exhausted more gas from her bags and the craft gradually dropped till she had reached an altitude where the air was breathable.

Frank was the first to stir. He discovered at once that the air-ship's drop must have been considerable and hastened to close the valve which connected by a tube with each one of the gas partitions. The dirigible's fall was checked in this way and the lad made his way forward.

By this time a sickly dawn had arisen and although it was still blowing hard the full fury of the hurricane had distinctly moderated. The dirigible, however, was clearly beyond all control and Frank, after a glance into the engine-room, where the engineer lay insensible beside his machines, started for the pilot-house.

At its threshold he stopped with a cry of surprise.

The railing, against which he had left Malvoise lying, gaped open raggedly for a space of several feet, as if a heavy body had plunged through it. A brief examination showed the boy some bits of cloth still clinging to the rough ends of the shattered rail, indicating plainly enough that the doomed Frenchman had been hurled into empty space while the storm was at its height and they all lay senseless.

Undoubtedly his body had been rolled by a lurch of the ship in toward the cabin and then been cast outward again by a reverse swing. The railing, none too strong at best, had evidently not been capable of withstanding the impact and the Frenchman's body had been hurled through into the void.

Shuddering at the thought of such an end, Frank aroused his brother and Ben and then went aft to inspect the engine-room. He found that of the eight cylinders only five were doing their work, and a brief examination showed why. The insulation on three of the spark plugs had cracked and it was not before he had done a lot of rummaging around that the boy found spare ones stored in a locker.

By this time the engineer, who seemed a decent enough fellow, and told Frank his name was Dick Richards, had recovered and helped the boy fit the new sparkers to the motor. First, however, Frank had hailed Harry through the tube leading to the pilot-house.

"How high are we?" he asked.

"A thousand feet," came back the reply.

"All right," shouted Frank back. "I guess the wind has moderated enough now for us to drift for a while. I am going to stop the engine."

The machinery accordingly was brought to a standstill and Frank and the engineer set busily to work placing the new sparkplugs and wiring them up.

This completed, Frank hailed Harry once more.

"I'm going to start up."

"All right. I'm looking out," came the reply.

The compressed air apparatus that started the engines was put in operation and the engine was soon working as if nothing had happened.

"Say, you are an all right mechanic," was Dick Richards' admiring tribute to Frank's skill.

By noon the last traces of the hurricane had died out and the dirigible was driving forward over a sparkling sea with a cloudless sky overhead. After breakfast, in which the now resuscitated members of the crew and Constantio took part, Frank called them forward and told them of the fate of Malvoise. None of them seemed particularly grieved, as the man had undoubtedly been a hard taskmaster.

"You are captain of this ship now," said Constantio to Frank. "I am only her inventor and have already received from Luther Barr the full purchase price. I have deposited it in a bank in New York. In this treasure they are hunting I have no interest. All I want to do is to invent air-ships."

Constantio had recognized Ben Stubbs as soon as he set eyes on him, and laughed with apparent good nature at the recollection of their meeting in Boston. He had recovered the watch the little gamin got away with, he told them, and had never mentioned to Luther Barr the fact that Ben had inspected the air-ship and then escaped, for fear of the grim old millionaire's wrath.

"When he is mad he is like one volcano," he declared volubly.

Breakfast over, they skimmed along through the air till noon, when Frank took an observation with the ill-fated Malvoise's instruments.

"We ought to be falling in soon with one of the Bahama group of islands," he announced. "We were not driven so far as I thought, and if we can make a landing we ought to be able to effect repairs and then fly for land. We certainly cannot go much further on the supply of gas we now have, the ship is getting lower all the time."

This was indeed the fact. With her heavy load and reduced supply of gas the air-ship was rapidly decreasing the space between herself and the sea.

During the afternoon the water tanks were emptied, which lightened the ship considerably, but left the voyagers only a small supply of the fluid, which was likely to prove serious if they did not find land soon. By supper time it became necessary also to tear out some of the heavy cabin fittings and cast them away.

By early the next day, after a restless night, the ship had settled so much, despite the lightening process, that she rode soggily along at not more than fifty feet above the level of the sea. The situation was indeed a serious one.

Suddenly there came a hail from Ben, who was standing at the bow of the craft.

"Land ho!"

The adventurers crowded forward.

There, sure enough, dead ahead of them, was what looked like a tiny blue cloud on the horizon, but which Ben's practiced eye had told him was land. With new heart the voyagers drove on and by mid-afternoon were in sight of the island, which on closer view proved to be one of those small palm-crowned atolls that are common enough in these waters.

The dirigible had by this time settled so badly that she was barely twenty feet above the wave-tops.

Some sacks of ballast still remained, kept by Frank for an emergency. He now was compelled reluctantly to give the order to cut these away and one by one they dropped overboard; but as they did so, the ship rose and an hour later they landed on a smooth beach.

The island did not seem to be of great extent, but to the delight of the adventurers, from the midst of the cocoanut grove that crowned the islet there flowed a tiny stream of clear water. This was indeed a godsend, as they did not know how long they might have to remain there. With a spade, which formed part of the dirigible's outfit—"I suppose they figured on shoveling out the treasure," laughed Harry—a small basin was soon dug out for the water to settle in and make a sort of small well, from which it could be dipped out for cooking and drinking purposes.

Fortunately the larder of the dirigible was well stocked, and as they were two mouths short they were not in any immediate fear of hunger. That evening, when arrangements for sleeping and keeping watch for any passing steamer or vessel had been made, Constantio beckoned to Frank and asked him to join him in a walk along the beach. The lad, nothing loath of a chance for exploration, started off with the Spanish inventor, who seemed to be anxious to confide something to him.

"You are worried about getting away from the island?" he said.

"I am—yes," rejoined Frank, "you see our gas is exhausted and I for one can't figure out but we shall stay here till some one comes along and picks us up. Unless we can build a raft out of the remains of the dirigible."

"Oh, make yourself easy about that, my dear young friend," exclaimed the inventor. "I can refill the gas-bag and that without delay, but—but—well, to be frank with you, how much is it worth to you if I do so?"

Frank was amazed at the sudden proposal and no less astonished at the Spaniard's boast that he could inflate the dirigible.

"What do you mean?" he asked. "I confess I don't altogether understand you."

"I thought I had made myself clear," was the reply. "I have changed my mind since I spoke to you last about the treasure, and now I feel that I am entitled to some of it if I can refill the dirigible."

"Why, yes," said Frank, with a laugh; "of course you are IF you really can."

"Would five thousand dollars' worth of ornaments or doubloons seem too much?" ventured the Spaniard.

Frank broke into a loud laugh.

"Why, no; you shall have that, and gladly, if you think you can help us to get out of this place."

"Thank you," said the inventor, quite seriously, "I don't want more than my just dues, but I certainly am entitled to that."

"Oh, certainly," laughed Frank, much amused at the man's deprecatory manner. "What is your plan?"

"Well, senor," said the Spaniard, "I have a certain amount of my gas-producing powder left in my cabin. There is none too much, but enough, I think, to inflate the dirigible with—at any rate, to fit her for flight to the mainland, which cannot be so very far off."

Frank nodded.

"There are some empty cylinders on board," went on the inventor. "All that is necessary to do is to put equal parts of sand, water and my powder into the cylinders and then screw on the caps to produce almost pure hydrogen gas at tremendous pressure. You follow me?"

"Yes," said Frank, "when can we do this?"

"Why, to-morrow morning," was the reply. "The actual inflation will take but little time."

As they returned to their camp they found it in a state of great excitement. Two of the men, in strolling about the island, had found lying up in a small cove, where it seemed to have drifted, a ship's boat.

There was no clue as to how it had come there, but on its stern were painted the words "Falcon, New York."

"I'll bet a lemon that it's one of the ship's boats of the Falcon that I read about been missing this year," exclaimed Ben; "it's got oars in it, too, they say. They are lashed under the seats, so that it must have broken loose from the ship when she went down and been washed ashore here. We can get away in the boat if nothing better offers."

Frank drew him aside and explained to him Constantio's plan for reinflating the gas-bag.

"We will try that, and if that plan fails then we can take to the boat," said the boy.

Ben agreed that if the air-ship could be inflated it would be much better to fly to land in her than to set out under the tropical sun in an open boat, not knowing where they might land.

The camp was so arranged that night that the treasure was placed near to the boys and Ben, while the three members of the dirigible's crew, her engineer and Constantio slept at some little distance.

Had the boys seen the gleam that had come into the inventor's eyes at the discovery of the boat they would not have been so trustful of him when he volunteered to take the middle watch of the night. As it was, however, they little imagined the plot that had formed in the fellow's head. While the boys and Ben slumbered, however, he drew aside the engineer and Wells, the red-headed sailor, and the three rapidly stocked up the boat with water from the spring in kegs and jars taken from the dirigible and laid in a supply of provisions. Then they awakened the other two men and explained to them in low whispers the plan to escape from the island they had formed.

"We will get all the treasure and divide it," whispered the cunning inventor. "If the boys wake while we are getting it to the boat, don't hesitate to attack them. We are stronger in numbers and can beat them off."

The other two readily agreed, more particularly as the inventor told them that it was the boys' intention to keep all the treasure for themselves in the event of their getting ashore in the dirigible. Before the boat had been found the inventor had been willing enough to aid the boys, but with the discovery of that means of escape his plans had undergone a change. He saw a way to appropriate the entire mass of treasure.



CHAPTER XXV.

THE FIGHT ON THE ISLAND.

Silently as cats the plotters approached the pile of treasure sacks when they judged that the time was ripe for their raid on the valuables. Constantio, who was a coward at heart, had taken his station by the boat so as to be the furthest away from danger should the boys be aroused.

With a beating heart he waited the appearance of the first heavy bag of treasure. At last the engineer and one of the sailors came in sight dragging it over the top of a sand dune.

"Phew, that's heavy," exclaimed the sailor, who was our red-headed friend, Wells, setting the bag down with a sigh. "How far is it from the camp to this boat, Mister Concertina?"

"Not more than a few hundred yards," replied Constantio; "I don't see what a big strapping fellow like you is making so much fuss over packing a fortune that little distance."

"It's a wonder you wouldn't tackle the job yourself," said Wells indignantly, as he and the engineer heaved the sack into the boat. "I guess you are scared though. I always knew that Spaniards were cowards."

Infuriated as much by the truth of the insult as stung by the stigma it conveyed, Constantio, pale with fury, sprang at the sailor with his knife drawn. He sprang back again with the same agility and crouched on his haunches like a tiger-cat, as the sailor whipped out a revolver and leveled it at him.

"Now you be careful what you are doing, Concertina," he said, "or I'll have to send you where you won't make no more trouble."

As he spoke there came a loud report from the direction of the camp.

It was followed by another and another.

"They have discovered us!" cried Constantio, seizing hold of the boat and trying to drag it off.

At the same instant the two sailors, who had been left behind to bring a second sack of the treasure, appeared, racing over the top of the sand dune.

"They heard us as we were moving the sack," cried one of them; "something jangled, I guess, and—"

"They awakened and fired at us,—see here," he held up a bleeding arm, "broke my elbow I guess."

"Come on," shouted Wells, "we are playing for too big a stake to let two boys and an old man beat us off. Who is for coming back and driving them off?"

Constantio turned white, fighting was not in his line, but the sailor stepped to his side and whispered something, at the same time pressing his revolver to the Spaniard's head, and the wretch, trembling in every limb, followed the others back. But the attacking party was doomed not to get any more treasure that night. As they approached the camp Frank called out in a clear voice:

"We don't want to do you any harm, but don't come any closer or we shall fire."

For reply Wells let fly a bullet at the boy's head, which, if the sailor had not been an indifferent shot, would have inflicted a serious wound. As it was, it flew wide and went whistling out to sea.

Before Frank could check him, old Ben in a furious rage stood up and fired straight at Wells. He shattered the man's wrist and with a howl of pain he dropped his revolver.

"Come on, men," shouted Constantio, as he saw the mainstay of the attackers rendered helpless; "we've got enough loot in that one sack to secure us all a good sum when we get ashore. Come on—I'm for the boat!"

So saying he turned and ran at top speed for the boat, the others after him. The shore gained, they leaped to the sides of the craft, having first thrown in the wounded sailor Wells, and then shoved the boat off till they were waist-deep in water.

The boys and Ben reached the spot just as they were clambering in and getting out the oars.

"Shall I tell 'em to come back, or have a hole shot in their boat?" asked Ben.

"No," decided Frank, "let them go. We are cheaply rid of the rascals at the cost of only one sack of valuables."

The men fell to the oars with a will, and were soon out of sight in the darkness. Nothing more was ever heard of them by the boys, but as some time ago a sailor was arrested on the Bowery trying to pawn a candlestick of solid gold marked Buena Ventura, it is reasonable to suppose the men eventually got ashore. The prisoner gave the name of Jones, but as he had red hair it is not unreasonable to assume that he was none other than Wells. As nobody claimed the candlestick and the police had received no word of such an article being stolen, it was given back to the man and he was released.



CHAPTER XXVI.

THE BOYS WIN OUT.

"Now," said Frank briskly the next morning, "as that scoundrel Constantio tried to steal a march on us we shall have to try to discover his powder and make the gas by ourselves."

"What," exclaimed Harry, "do you mean to say that you think it would be possible to do it?"

"If he can, I don't see why we can't," rejoined the other. "The first thing to do is to find his powder. Then to mix it with equal parts of water and sand in the cylinders and screw the caps on."

"Sounds easy," commented Harry.

"I guess the hardest part will be to find the powder," put in Ben. "How are we to tell whether it's hydrogen gas powder or Seidlitz powder, I'd like to know."

After a hasty breakfast a thorough rummaging of the cabin occupied by Constantio was begun.

"Say, Frank," suddenly cried Ben, who was bending over a locker, "is this the stuff?"

Frank hastened to his side and saw, ranged side by side, a number of wooden boxes about a foot square labeled "Dangerous."

"I guess that's the stuff all right, Ben," he said, "bear a hand and we'll drag it out. Only be very careful of it. It is probably a high explosive if not handled delicately."

One by one the boxes were transferred until two dozen of them stood on the beach, set in soft sand. Then a sudden difficulty flashed into Frank's mind. Constantio had said "equal parts of sand, water and the powder," but he had not said how much these equal parts were to be. The only thing to do was to experiment.

Fortunately the massive steel cylinders, in which the gas was to be generated, were provided with gauges to register the pressure. One thousand pounds were marked as top measure, so Frank assumed that somewhere about 800 pounds would be enough.

The first mixture they tried only registered three hundred pounds, but by gradually increasing the amount of powder they at last hit upon the required strength, and were ready to start on the work of inflation.

They had six cylinders full of the gas. Not enough to fully inflate the bag, but enough, Frank calculated, to render it sufficiently buoyant to carry the reduced weight it would be called upon to convey now that the crew was gone.

The inflation nozzle was connected with cylinder after cylinder, till the bag became so buoyant that it was necessary to weight the machine down with heavy stones. At last the cylinders were emptied and the great bag, expanded by the warm sun, swelled up till it seemed it must burst. The expansion of gas by the sun was one of the things Frank had counted on when filling the bag, and he was glad to see his theories work out right. The treasure bags were hastily laden on to the craft and then the boys, standing on the lower framework, one on each side, while Ben stood in the pilot-house, started to kick off the weights that restrained the ship from rising.

They had not cast off more than half a dozen before the ship gave a mighty bound upward that threatened to throw them off her frames and before they could catch their breath they had shot up 1,200 feet or more. Hastily clambering aboard and laughing at the sudden jump, the boys got the engine going and shaped a course that would bring them over the spot where they had left the Bolo.

They held steadily on their course that day and the next. Early in the morning of the second they encountered a surprising incident. Frank, who was on lookout, hailed "Air-ship ahead."

And there, sure enough, heading northward, was a big red dirigible coming toward them like the wind.

As they drew near, a man with a megaphone appeared on her bridge and signaled that he wanted to hail them. Frank shut down the engine and the two air-ships drew alongside.

"What ship is that?" hailed the man on the bridge of the red air-ship, who wore yachting flannels as did his three companions.

"The Luther Barr of New York," responded Frank for lack of a better name.

"We are the Dos Hermanos, five days out from Cuba, bound for Jacksonville, Florida," was the response, "can you spare us any bread?"

"Come alongside," responded Frank in a hearty tone, "and we'll give you some tins of pilot bread."

"Bully for you," responded the red air-ship man.

The two dirigibles drifted together and the boys handed over some tins of pilot bread or ship biscuit with which the larder of the Luther Barr, as Frank had called her, was well provided.

"Thank-you," shouted the men on the red dirigible, as the lines were cast off, "good-bye and good luck."

"Same to you," hailed the boys, as the engines were started. An hour later the red dirigible had vanished on its voyage to the north.

"Well," said Frank, "that's the first time I've ever heard of 'ships that pass in air and speak to each other in passing.' I'm glad we were able to help a fellow voyager out."

Frank's observations that day showed that they could not be far from the spot from where the Bolo had been left, but eager scrutiny failed to reveal her till almost sundown, when Ben's sharp eyes spied her—little more than a tiny black object on the horizon.

"There she is," he hailed.

Frank's binoculars soon confirmed the good tidings.

But as they neared the Bolo an astonishing thing happened.

Through the glasses they saw a form they recognized as Bluewater Bill's come out on the deck and gaze at them in amazement, to judge from the way he threw his arms about.

Presently he was joined by two other figures that the boys recognized as Billy Barnes and Lathrop.

Harry impetuously rushed to the rail, oblivious of the fact that at that distance the boys could not hear him, and shouted at the top of his voice.

"Hullo, Billy, hullo, Lathrop, hullo, Bill!"

It was then that the surprise was sprung. Frank through the glasses saw Bluewater Bill raise a rifle to his shoulder, and take deliberate aim at the dirigible. The bullet sang by the pilot-house chipping off a bit of molding.

"What on earth is the matter with them, have they gone crazy?" exclaimed Harry.

Frank was as puzzled as his brother for a minute, but suddenly the meaning of this inexplicable conduct burst upon him.

"They think we are Luther Barr! The sight of the dirigible has deceived them," he cried.

"I'll bet that's the right explanation," cried Harry, "how are we to undeceive them without getting our heads shot off?"

"I have it," cried Frank, diving into his pocket and bringing out a rumpled bit of silk, "that's the old Golden Eagle flag. I saved it when we had to abandon her."

Ben seized it from the boy's hand and ran to the rail with it, waving the bit of silk furiously. Evidently the occupants of the Bolo saw and recognized it, for they stopped their threatening demonstrations and began waving furiously.

As they hovered above the Bolo, Frank shouted as much explanation as he could through the megaphone, and then told the Boloites to be ready to make fast a line. This done a tackle was rigged and one by one, amid great cheering on Billy Barnes' part, the sacks of treasure were lowered.

This task accomplished, there remained but one thing for the boys on board the dirigible to do—namely to get on board the Bolo. The gas-bag was deflated by means of the escape valve till the big dirigible was but a few feet above the Bolo, and then the adventurers slid down the rope on to the smaller vessel's deck. There being no way of transporting the dirigible, she was allowed to drift away.

What greetings, handshakings, dances and yarn spinning took place then, we will leave our readers to imagine. Early next day, after it had been agreed that two-thirds of the treasure was to be divided among Bluewater Bill, Frank and Harry, and the remainder in even parts to Billy Lathrop and Ben Stubbs, anchor was got up and the Bolo headed for the Florida coast. The young adventurers meant to head for St. Augustine and then take train to New York, sending the Bolo back to Galveston with a hired crew.

They had but one regret—the loss of the gallant Golden Eagle. How she was recovered will be related in another volume, but restored to them she was.

"I'm glad we came through with such flying colors," said Harry to Frank one evening, while the boys were all seated on the foredeck, "but I hate to think our adventures are all over."

"I don't suppose we shall have any more for awhile," sighed Billy Barnes, "it seems to me we've done about all that's possible."

Frank laughed.

"With the money we can make from the sale of the treasure, we can build another aeroplane and have lots of good times," he said, "we might even try a transcontinental flight."

"From New York to Frisco—bully," exclaimed Billy Barnes.

"Do you think that you really could make such a flight, Frank?" asked Lathrop.

To satisfy the curiosity of others like Lathrop, we will say that not only could the boys make the flight but that they did, and had a series of surprising adventures in connection with it.

It now only remains to tell of the conclusion of Luther Barr's vain quest for the treasure. Perhaps an item from a New York newspaper best covers the ground. The clipping we have selected reads as follows:

"Luther Barr's yacht, Brigand, returned to-day and thus cleared up some of the mystery connected with her long sojourn in Southern waters. Seen on board her, Mr. Barr declined to be interviewed or to tell anything about his absence, which has created some stir on Wall Street. Asked if he were still interested in aeronautics, he became furiously angry and threatened to have the reporter thrown overboard. Mr. Barr said he had not heard anything about the remarkable discoveries on a derelict Spanish galleon made by Frank and Harry Chester, the Boy Aviators, and a party of adventurers who accompanied them, and of which a full account was printed in these columns some days ago, on the safe arrival of the boys from St. Augustine, Fla. Frank Chester said yesterday that there was nothing to add to our article as printed, except that the valuables recovered had realized more than $500,000."

And here for the present we will leave our young friends to renew our acquaintance with them in the next volume of this series, which will be called:

THE BOY AVIATORS IN RECORD FLIGHT; OR, THE RIVAL AEROPLANE.

THE END.