Five Thousand Miles Underground

 Or

The Mystery of the Centre of the Earth

by Roy Rockwood, 1908

 CHAPTER I

 WASHINGTON BACKS OUT

"WASHINGTON! I say Washington!"

Throughout a big shed, filled for the most part with huge pieces ofmachinery, echoed the voice of Professor Amos Henderson. He did notlook up from a small engine over which he was bending. 

"Washington! Where are you? Why don't you answer me?"

From somewhere underneath an immense pile of iron, steel and aluminumcame the voice of a colored man. 

"Yas sir, Perfesser, I'se goin' t' saggasiate my bodily presence inyo' contiguous proximity an' attend t' yo' immediate conglomeratedprescriptions at th' predistined period. Yas, sir!"

"Well, Washington, if you had started when you began that long speechyou would have been at least half way here by this time. Hurry up!Never mind tightning those bolts now. Find the boys. I need them tohelp me with this engine. They must be around somewhere. "

"I seen 'em goin' fishin' down by th' brook a little while ago, "answered the negro, crawling out from under what seemed to be acombined airship and watercraft. "Jack says as how yo' gived himpermission t' occupy his indisputatious period of levity inendeavorin' t' extract from th' liquid element some specimens ofswimmin' creatures. "

"If you mean I said he and Mark could go fishing in the brook, you'reright, Washington, " replied the professor with a smile. "But you wastea lot of time and breath trying to say it. Why, don't you give upusing big words?"

"I reckon I was brought up t' it, " replied the colored man grinningfrom ear to ear. He did not always use big words but when he did theywere generally the wrong ones. Sometimes, he spoke quite correctly. 

"Well, I suppose you can't help it, " resumed Mr. Henderson. "However, never mind that. Find the boys and send them to me. "

"With th' least appreciatableness amount of postponement, " answeredthe messenger, and he went out. 

Washington White, who in color was just the opposite to his name, ageneral helper and companion to Professor Henderson, found MarkSampson and Jack Darrow about a quarter of a mile from the big shed, which was in the center of a wooded island off the coast of Maine. Thelads were seated on the bank of a small brook, fishing. 

"Perfesser wants yo' immediate, " said Washington. 

"But we haven't caught a single fish, " objected Mark. 

"Them's the orders from headquarters, " replied the colored man. "Yo'both got t' project yo'selves in th' vicinity of th' machine shop. Ireckon th' new fangled contraption that th' perfesser is goin' t'navigate th' air an' sail th' angry seas in, am about done. He want'st' try th' engine. "

"Come on then, " said Jack. "We probably would not catch any fish, anyhow, Mark. "

Accompanied by Washington, the youths, each of whom was about eighteenyears old, started toward the big shed. 

While they are on their way opportunity may be taken to tell a littleabout them, as well as about Washington and the professor, and thecurious craft on which the scientist was working. 

A few years before this story opens Mr. Henderson had invented awonderful electric airship. He had it about completed when, one day, he and the two boys became unexpectedly acquainted, and, as itdeveloped, friends. 

Mark and Jack were orphans. After having rather a hard time knockingabout the world trying to make a living, they chanced to meet, andresolved to cast their lots together. They boarded a freight train, and, as told in the first volume of this series, entitled, "Throughthe Air to the North Pole; or the Wonderful Cruise of the ElectricMonarch, " the cars were wrecked near where Professor Henderson wasbuilding his strange craft. 

The boys were cared for by the scientist, and, after their recoveryfrom hurts received in the collision, they accepted his invitation tomake the trip through the upper regions in the airship, to search forthe north pole. With them went Andy Sudds, an old hunter, and TomSmith and Bill Jones, two farmers, but who were hired as helpers onthe voyage. The party had many adventures on the trip, having battleswith savage animals and more savage Esquimaux, and were tossed aboutin terrible storms. After making some scientific observations, whichthe professor was much interested in, they started back home. 

Having found he could successfully sail in the air, Mr. Hendersonresolved to try what it might be like under water. 

He moved his machine shop to a lonely spot on the Maine coast, andthere, with the help of the boys, Washington, Andy and two machinistsconstructed a submarine boat, called the Porpoise. 

In this the professor resolved to seek the south pole, he having atheory that it was surrounded by an open sea. After much hard work thePorpoise was made ready for the voyage. 

What occurred on this great trip is described in the second book ofthis series, called "Under the Ocean to the South Pole, or the StrangeCruise of the Submarine Wonder. " In that is told how once more Tom andBill, with Andy, the boys and Washington, accompanying ProfessorHenderson, had many thrilling experiences. 

They were caught in the grip of the grass of the terrible SargassoSea. Monstrous suckers grasped the boat in their powerful arms, andhad to be fought off. They were caught in a sea of boiling water andimprisoned between big fields of ice. 

By means of strong diving suits they were able to leave the ship andwalk about on the bottom of the sea. They visited a graveyard ofsunken ships, saw many strange monsters as well as many beautiful fishin the great depths to which they sunk. Many times they were in direperil but the resources of the professor, the bravery and daring ofthe boys, no less than the help Washington and Andy Sudds, the hunter, rendered at times, brought them through. 

Those of you who read of their adventures will recall the strangeisland which they came upon in the Atlantic Ocean, far from the coastof South America. 

When they first drew near this island they were almost sucked into thedepths of a great whirlpool, caused by water pouring down a big holethat seemed to lead far into the earth. They reversed their ship justin time. 

But, on going to another side of the island they were able to approachsafely, as at this point the great hole was farther from the shore. Then they landed and investigated. 

They found the island was almost circular, and the hole was alsoround, but not in the center of the land. It was an immense cavity, sowide they could not see across, and as for the depth they could onlyguess at it. Looking down they could only see rolling masses of vaporand clouds caused by the water which poured down from the ocean withthe force of a Niagara. 

Gazing down into the big hole Mark suggested it might lead to thecentre of the earth, which some scientists claim is hollow. Theprofessor admitted that the cavity looked as though it led to China. 

They had no means of investigating further the mystery of the openingand returned to their submarine, completing the voyage to the southpole. 

It was now about two years since they had come back from that eventfultrip. One of the first things the professor did, after docking thePorpoise, was to shut himself up in his study and begin to draw plans. To the questions of the boys he returned no answer for several days. Then he announced he was working on a craft which could both sail ontop of the water and navigate the air. 

In time the plans were done, and, in order to keep the work secret, the shop was moved to an island which the professor owned. 

Parts of the Monarch and the Porpoise were used in constructing thenew craft, so there was no need to get other help than that which theboys, Washington and Bill and Tom could give, since the two latteraccepted an offer of the professor to remain and work for him. Theboys, of course, would not leave their friend. 

The professor realized that he had a more difficult task in his newventure than he had set himself on other occasions. For a ship to belight enough to rise in the air, and, at another time, and with nochange, to be strong enough to navigate the ocean, was indeedsomething to tax Mr. Henderson's ingenuity. 

However, in the course of a little over a year the larger part of thework was done. Inside the big shed was the huge affair which, it washoped, would enable its owner to be master of both air and water. 

"Did the professor say anything special?" asked Mark of Washington. 

"Nope. I reckon he were too busy problamatin' the exact altitudeprojected in an inverse direction by th' square root of th' new enginewhen operated at a million times inside of a few seconds, but hedidn't say nothin' t' me. I were busy underneath th' ship, fixin'bolts when he tole me t' find yo'. I wouldn't be s'prised if he hadth' thing goin' soon. "

"Do you think he'll be generating the new gas to-day?" asked Jackeagerly. "That's the most troublesome part; to get that gas right. "

"He didn't say nothin' t' me 'bout it, " Washington stated, as hewalked along beside the two boys. "He jest seemed anxious like. "

"We'd better hurry, " advised Mark. "He may be at an important part inhis experiments and probably needs us. I hope it will work. He hasspent many days on it, and we all have worked hard. It ought to be asuccess. "

"Perfesser allers makes things work, " declared Washington stoutly. 

"That's a good way to feel about it, anyway, " observed Mark. "Well, we'll soon know. "

The three hurried to the shed which they could see as they rounded aturn of the path through the wood. They noticed an elderly manapproaching with a gun on his shoulder. On one arm he carried a gamebag. 

"Guess Andy got something for dinner, " remarked Jack. 

"I hopes so, honey, " put in Washington. "I'se got a sort of gonefeelin' in my stomach!"

"Any luck, Andy?" called Mark, when he came within hailing distance. 

"Fine, " replied Andy Sudds. "Rabbits and quail. We'll have a gooddinner to-morrow. "

While Andy entered the living part of the big shed to put away his gunand game, the boys and Washington kept on to the engine room. Theyfound the professor, with Bill and Tom, busy fitting pipes to thesmall engine which was set up at one side of the structure. 

"Come, boys, I need your aid, " remarked Mr. Henderson as they entered. "Take off your coats and pitch in. Tighten up these bolts, Jack. Mark, you mix up those chemicals the way I taught you, and see that thedynamo is in working order for Washington to attend to. "

In a little while the shop was a veritable hive of industry, and itresounded to the sound of hammers, wrenches and machinery. In thebackground was the big ship, which seemed like two immense cigars, oneabove the other, the lower one the larger. 

"Where was you calalatin' t' take this here ship when it gits done, Perfesser?" asked Washington, during a lull in the operations. 

"Do you remember that big hole in the island we visited on our trip tothe south pole?"

"I suah does, " answered the colored man. 

"We are going to explore that, " went on the scientist. "We are goingto make a voyage to the interior of the earth in our Flying Mermaid. "

"Go down into th' earth!" exclaimed Washington, his eyes big withfright. 

"Certainly; why not?"

"Not for mine!" cried the colored man, dropping the wrench he washolding. "No sire I'm not goin' t' project myself int' a grave whileI'se alive. Time enough when I kicks th' bucket. No sir! If yo' an'the boys wants t' risk yo' se'ves goin' down int' th' interior of th'earth, where th' Bible says there's fiery furnaces, yo' kin go, butWashington White stays on terra cotta! That's where he stays; He ain'tready t' be buried, not jest yet!" and the frightened colored manstarted to leave the shed. 

 CHAPTER II

 THE FLYING MERMAID

"HERE! Stop him!" cried Professor Henderson. "Don't let him get away. We still need his help to get the ship in shape. He needn't befrightened. We're not going to start at once. "

Mark and Jack ran after Washington, whose progress was somewhatimpeded because he kept looking back as if he feared the new ship waschasing him. 

"Come on back!" said Mark. "There's no danger, and if there was we'renot going to start to-day. "

"Ain't yo' foolin' me?" asked Washington, pausing and lookingdoubtfully at the boys. 

"Of course not, " answered Mark. "You know Professor Henderson wouldnot make you do anything you didn't want to do, Wash. He wishes you tostay and help him get ready, that's all. "

"Well, Washington, " observed the aged scientist. "I didn't think you'dgo back on me. "

"I'd do mos' anything fer yo', Perfesser, " said the colored man, "butI got t' beg off this time, " and he looked at the Flying Mermaid as ifhe thought the metal sides would open and devour him. 

Then help me get things in shape to generate the gas, " the scientistsaid. "I want to give the new vapor the first real test in liftingpower to-day. On the success of it depends the future of the ship. "

Seeing there was no immediate danger of being carried to the centre ofthe earth, Washington resumed his labors. The professor, the boys, Bill and Tom were also hurrying matters to enable a test to be madebefore night. 

As will readily be seen, even by those not familiar with theconstruction of airships and submarines, the chief problem was to findsome agent strong enough to lift from the earth a weight heavier thanhad ever before been put into an apparatus that was destined totraverse the clouds. For the Flying Mermaid was not only an airshipbut an ocean voyager as well. It had to be made light enough to belifted far above the earth, yet the very nature of it, necessitatingit being made heavy enough to stand the buffeting of the waves and thepressure of water, was against its flying abilities. 

Professor Henderson realized this and knew that the chief concernwould be to discover a gas or vapor with five times the lifting powerof hydrogen, one of the lightest gases known, and one sometimes usedto inflate balloons. 

After long study he had been partially successful, but he knew fromexperiments made that the gas he had so far been able to manufacturewould not answer. What he wanted was some element that could be mixedwith the gas, to neutralize the attraction of gravitation, or downwardpull of the earth. 

While he was seeking this, and experimenting on many lines, theconstruction of the air-water ship went on. In general the outwardconstruction was two cigar shaped hulls, one above the other. Aluminum, being the lightest and strongest metal that could be usedfor the purpose, formed the main part of both bodies. 

The upper hull was one hundred feet long and twenty feet in diameterat the widest part. It tapered to points at either end. It wasattached to the lower hull by strong braces, at either end, while fromthe center there extended a pipe which connected with the lowersection. This pipe was intended to convey the lifting gas to the partwhich corresponded to the bag of the balloon, save that it was ofmetal instead of silk, or rubber as is usual. 

There were two reasons for this. One was that it would not be liableto puncture, particularly in the proposed underground trip, and theother was that it did not have to be so large as a cloth bag wouldhave had to be. It was also a permanent part of the ship, and on avoyage where part of the time the travelers would be in the air andpart on the water, and when the change from one to the other wouldhave to be made quickly, this was necessary. It would have taken toolong to raise the ship in the air had a cloth bag been used to containthe gas. 

The lower hull or main part of the craft was one hundred and fiftyfeet long, and forty feet through at the largest part, in the centre. 

It was divided into four sections. The forward one contained thesleeping quarters of Professor Henderson and his crew. There was asmall stateroom for each one. Above was a conning or observationtower, reached by a small flight of steps. From this tower the shipcould be steered, stopped and started, as could also be done from theengine room, which was in the after part of the hull. 

As in the Porpoise and Monarch, electricity formed the motive powerand was also used for many other purposes on board. Engines operatedby gas produced the current which heated, lighted and moved the ship, as well as played a part in producing the wonderful gas. 

The ship moved forward or backward by means of a novel arrangement. This was by the power of compressed air. From either end of the lowerhull there projected a short pipe working in a ball and socket joint, so it could be turned in any direction. By means of strong pumps acurrent of compressed air could be sent out from either pipe. Thuswhen floating above the earth the ship was forced forward by the blastof air rushing from the pipe at the stern. It was the same principleas that on which a sky rocket is shot heavenward, save that gasesproduced by the burning of powder in the pasteboard rocket form itsmoving impulse. 

In the case of the Flying Mermaid, it could be made to move backwardby sending the air out of the forward tube. Thus, when in the water, the compressed air rushing from the pipe struck the fluid and forcedthe ship forward or backward as was desired. It floated on thesurface, the deck being about three feet out of water, while thealuminum gas bag was overhead. 

The engine room was a marvel of machine construction. It containedpumps for air and water, motors, dynamos, gas engines, and a maze ofwheels and levers. Yet everything was very compact and no room waswasted. 

The use of the air method of propulsion did away with the necessity ofa large propellor such as most airships have to use, a propellor whichmust of necessity be very light and which is easily broken. 

Next to the engine room was the kitchen. It contained an electricrange and all necessary appliances and utensils for preparing meals. There were lockers and a large reserve storeroom which when the timecame would be well stocked with food. Forward of the kitchen was theliving and dining room. It contained comfortable seats, folding tablesand a small library. Here, also were many instruments designed to showhow the various machines were working. There were gages, pointers anddials, which told the direction the ship was traveling, the speed andthe distance above the earth or below the surface. Similar indicatorswere in the conning tower, which had a powerful search light. 

The ship was lighted throughout by incandescent lamps, and there waseven a small automatic piano worked by the electric current, on whichpopular airs could be played. 

If the gas and the gravity neutralizer worked as Professor Hendersonhoped they would, as soon as the ship was completed, all that would benecessary to start on the voyage would be to fill the aluminum bag andset the air compressor in motion. 

The gas was made from common air, chemically treated and with a secretmaterial added which by means of a complicated machine in a measuredid away with the downward pull of the earth. Thus all that wasnecessary to carry on a long voyage was a quantity of gasolene tooperate the engine which worked the electric machines, and some ofthis secret compound. 

The professor and his helpers had been working to good advantage. Atlast all was in readiness for the gas test. 

It was proposed to try it on an experimental scale. Some of the fluidwas to be generated and forced into an aluminum cylinder under thesame pressure it would be used in the air ship. To this cylinder wereattached weights in proportion to the weight of the Flying Mermaidwith its load of human freight, engines and equipment. 

"This cylinder is just one one-hundredth the size of the cylinder ofthe ship, " said the professor. "I am going to fasten to it a hundredpound weight. If it lifts that our latest contrivance will be asuccess. "

"You mean if the little cylinder pulls a hundred pounds up the bigship will take us and the machinery up?" asked Mark. 

"Certainly, " answered the professor. "If this cylinder lifts a hundredpounds, one a hundred times as big (as that of the Mermaid is), willlift a hundred times as much, or ten thousand pounds. That is fivetons, or more than a ton over what I figure to be the weight of ourship and contents. The latest war balloon can lift one ton with ease, and if my machine can not do five times as well I shall bedisappointed. "

The last adjustments were made, pipes were run from the gas generatorto the cylinder, and the hundred pound weight was attached. 

"Everybody look out now, " said Mr. Henderson. "I am going to start themachine and let the gas enter the cylinder. It is a very powerful gasand may break the cylinder. If it does you must all duck. "

The scientist gave a last look at everything. The boys got behind someboards whence they could see without being in danger. Washington, whohad little fear so long as there was no danger of going under ground, took his place at the dynamo. Andy Sudds, with Bill and Tom, stationedthemselves in safe places. 

"All ready!" called the professor. 

He pulled a lever toward him, turned a wheel and signalled toWashington to start the dynamo. There was a sound of buzzingmachinery, which was followed by a hiss as the gas began to enter thecylinder under pressure. Would it stand the strain? That question wasuppermost in every one's mind save the professor's. He only cared tosee the cylinder leave the ground, carrying the weight with it. Thatwould prove his long labors were crowned with success. 

Faster and faster whirred the dynamo. The gas was being generated fromthe air. The secret chemical made a hissing which could be heard forsome distance. The gage registered a heavy pressure. Anxiously theprofessor watched the cylinder. 

"There!" he exclaimed at length. "It has all the gas it can hold. Nowto see if it works!"

He disconnected the pipe leading from the generator. This left thecylinder free. It seemed to tremble slightly. There appeared to be amovement to the hundred pound weight which rested on the ground. Itwas as if it was tugging to get loose. 

"There it goes! There it goes!" cried Mark, joyfully. 

"Hurrah!" shouted Jack. "There she rises!"

"It suttinly am projectin' itself skyward!" yelled Washington, comingfrom the dynamo. 

Sure enough the cylinder was slowly rising in the air, bearing theweight with it. It had lifted it clear from the ground and wasapproaching the roof of the big shed. 

"It will work! It will work!" exclaimed the professor, strangelyexcited. 

The next instant the cylinder, carrying the weight, sailed right outof an open skylight, and began drifting outside the shop, and acrossthe fields. 

"Quick! We must get it back!" cried Mr. Henderson. "If it gets away mysecret may be discovered and I will lose all! We must secure it!"

But the cylinder was now two hundred feet in the air and being blownto the east, the weight dangling below it, making it look like aminiature airship. 

"We can never catch that!" cried Mark. 

 CHAPTER III

 WASHINGTON DECIDES

"WE must catch that cylinder!" the professor exclaimed. "Some one mayfind it when it comes down and analyze the gas. Then he would discoverhow to make it. The cylinder must come down!"

"Don't see how we can proximate ourselves inter th' vicinity of itlessen we delegate th' imperial functions of orinthological specimenst' some member of this here party, " observed Washington. 

"If you mean we can't catch that there contraption unless we turn intobirds I'll show you that you're mistaken!" cried Andy Sudds. "I guessI have a trick or two up my sleeve, " and the old hunter quickly threwopen the breech of his gun and inserted a couple of cartridges. 

He raised the piece to his shoulder and took quick aim. There was asliver of flame, a puff of smoke and a sharp report. The professor andthe boys who were watching the cylinder saw it vibrate up in the air. Then there came a whistling sound. An instant later the metal bodybegan to descend, and it and the weight fell to the earth. 

"I'm sorry I had to put a bullet through it, Professor, " said old Andywith a queer smile, "but it was the only way I saw of bringing itdown. Hope it isn't damaged much. "

"It doesn't matter if it is, " the scientist answered. "I can make morecylinders, but I don't want that secret of the gas to become known. Your bullet served a good turn, Andy, for it let the compressed vaporout just in time. "

"Then we may consider the experiment a success, " said Mark, asWashington went to where the cylinder had fallen, to detach it fromthe weight and bring both to the shed. 

"It seems so, " Mr. Henderson answered. "True, it was only anexperiment. We have yet to test the ship itself. "

"When can we do that?" asked Jack. 

"I hope by Monday, " the scientist answered. 

"Will you try it in the water or air first?" asked Mark. 

"I'm almost certain it will float in the water, " the aged inventorsaid. "It does not require much work to make a ship which will dothat. But the air proposition is another matter. However, since thecylinder rose, I am pretty sure the Flying Mermaid will. 

"But we have done enough work to-day. Let's rest and have something toeat. Then, with Sunday to sit around and talk matters over, we will beready for Monday's test. "

Some of the game Andy had killed was soon on the table, forWashington, in addition to his other accomplishments, was an expertcook. During the evening the boys and their friends sat in the livingroom of the big shed and talked over the events of the day. 

Sunday was spent in discussing what adventures might lie before themshould they be able to descend into the big hole. Washington did notsay, much, but it was easy to see he had no notion of going. He evenbegan to pack his few belongings in readiness to leave the service ofMr. Henderson, for whom he had worked a good many years. 

No one remained long abed Monday morning. Even Washington was up earlyin spite of the interest he had lost in the professor's voyage. 

"I jest wants t' see yo' start fer that place where they buries livefolks, " he said. 

In order to properly test the Flying Mermaid it was necessary to movethe craft from the shed from which place it had never been taken sinceit's construction was started. It had been built on big rollers inanticipation of this need, so that all which was now necessary was toopen the doors at the end, and roll the craft out. 

This was accomplished with no small amount of labor, and it was nearlynoon before the big ship was moved into the open. It was shoved alongto a little clearing in front of the shed, where no trees wouldinterfere with its possible upward movement. 

Everyone was bustling about. The professor was busiest of all. He wentfrom one machine to another; from this apparatus to that, testinghere, turning wheels there, adjusting valves and seeing that all wasin readiness for the generating of the powerful gas. 

As the airship was half round on the bottom and as it rested in a sortof semi-circular cradle; it brought the entrance some distance abovethe ground. To make it easier to get in and out while preparations forthe trial were going on, Bill and Tom had made an improvised pair ofsteps, which were tied to the side of the ship with ropes. 

Up and down these the professor, the boys and Andy went, taking intools and materials, and removing considerable refuse which hadaccumulated during the building of the craft. 

Finally all was in readiness for starting the making of the gas. Theship was not wholly complete and no supplies or provisions for thelong voyage had been taken aboard. The Flying Mermaid was about a tonlighter than it would be when fully fitted out, but to make up forthis the professor had left in the ship a lot of tools and surplusmachinery so that the craft held as much weight as it would undernormal conditions. If the gas lifted it now it would at any othertime. 

"Start the generator, " said Mr. Henderson, to Mark. "We'll soon seewhether we are going to succeed or fail. "

The boy turned a number of levers and wheels. The machine which madethe powerful vapor was soon in operation. The professor had alreadyadded enough of the secret compound to the tank containing the otheringredients, and the big pump was sucking in air to be transformedinto the lifting gas. 

The boys and the professor were in the engine room. Andy Sudds, withBill and Tom, had taken their places in the living room, to moreevenly balance the ship, since the things in it were not yet all intheir proper places. As for Washington he was busy running from theshed to the ship with various tools and bits of machinery theprofessor desired. 

The gas was being generated rapidly. Throughout the ship thereresounded a hissing noise that told it was being forced through thepipe into the aluminum shell above the ship proper. 

"I wonder how soon it will begin to lift us, " said Mark. 

"It will take about half an hour, " replied Mr. Henderson. "You see wehave first to fill the holder completely, since there is no gas in it. After this we will keep some on hand, so that it will only need theaddition of a small quantity to enable the ship to rise. "

He was busy watching the pointer on a dial which indicated thepressure of the gas, and the lifting force. The boys were kept busymaking adjustments to the machinery and oiling bearings. 

Suddenly, throughout the length of the craft there was felt a curioustrembling. It was as though the screw of a powerful steamer wasrevolving in the water. 

"What is it?" asked Jack. 

"I hope it is the lifting power of the gas making itself felt, " theprofessor answered. "Perhaps the Flying Mermaid is getting ready totry her wings. "

The trembling became more pronounced. The gas was being generatedfaster than ever. The whole ship was trembling. Tom and Bill came fromthe room, where they were stationed, to inquire the meaning, but werereassured by the professor. 

"Don't be alarmed if you find yourselves up in the air pretty soon, "he remarked with a smile. "Remember the Electric Monarch, and theflights she took. We may not go as high as we did in her, but it willanswer the same purpose. "

The gas was hissing through the big tube as it rushed into theoverhead holder. The gage indicated a heavy pressure. The ship beganto tremble more violently and to sway slightly from side to side. 

"I think we shall rise presently, " said Mr. Henderson. His voiceshowed the pride he felt at the seeming success with which hisinvention was about to meet. 

Suddenly, with a little jerk, as though some one with a giant hand hadplucked the Flying Mermaid from the earth, the ship gave a littlebound into the air, and was floating free. 

"Here we go!" cried Mr. Henderson. "The ship is a success. Now we'reoff for the hole in the earth!"

The Flying Mermaid was indeed rising in the air. True it did not go upso swiftly as had the Monarch, but then it was a much heavier andstronger vessel, and flying was only one of its accomplishments. 

"It's a success! It's a success!" shouted Mark, capering about in hisexcitement. 

"Now we'll see what the centre of the earth looks like, " went on Jack. "I can hardly wait for the time to come when we are to start on thevoyage. "

At that instant, when the ship was but a few feet from the ground, butslowly rising, the boys and the professor heard a shouting below them. 

"What's that?" asked the scientist. "Is any one hurt?"

Mark ran to a small window, something like a port hole in an oceansteamer, and looked out. 

"Quick!" he shouted. "Stop the ship! Washington will be killed!"

In fact from the agonized yells which proceeded from somewhere underthe craft it seemed that the accident was in process of happening. 

"Save me! Save me!" cried the colored man. "I'm goin' to fall! Catchme, some one!"

"What is it?" asked the professor, making ready to shut off the powerand let the ship settle back to earth, from which it had moved aboutfifty feet. 

"It's Washington, " explained Mark. "He evidently tried to walk up thesteps just as the boat mounted skyward. He rolled down and managed tograb the end of the rope which was left over after the steps weretied. Now he's swinging down there. "

"Are you going to lower the ship?" asked Jack. 

"Of course!" exclaimed the professor. "I only hope he hangs on untilhis feet touch the earth. "

"Keep a tight hold!" shouted Mark, from out of the small window. 

"That's th' truest thing yo' ever said!" exclaimed Washington. "Youbet I'm goin' to hold on, and I'm comin' up too, " which he proceededto do, hand over hand, like a sailor. 

The boys and the professor watched the colored man's upward progress. The ship had hardly begun to settle as, in the excitement, not enoughgas had been let out. Closer and closer came Washington, until he wasable to grasp the edge of the opening, to which the steps werefastened. 

"I thought you weren't coming with us, " observed the professor, whenhe saw that his helper was safe. 

"I changed my mind, " said the colored man. "It's jest luck. Seems liketh' ship done wanted me t' go 'long, an' I'm goin'. I'll take mychances on bein' buried alive. I ain't never seen th' centre of th'earth, an' I want's to 'fore I die. I'm goin' 'long, Perfessor!"

 CHAPTER IV

 WHAT DID MARK SEE?

"WELL, I'm glad you've decided at last, " the professor remarked. "Nowcome inside and we'll see how the ship works. "

Once over his fright, Washington made himself at home on the craft hehad helped build. He went from one room to another and observed theengine. 

"She certainly am workin'" he observed with pride. "Are we still goin'up, Perfessor?"

"Still mounting, " replied Mr. Henderson, "We are now three hundredfeet above the earth, " he added as he glanced at a registering gage. 

The great air pump was set going and soon from the after tube, a bigstream of the compressed vapor rushed. It acted on the ship instantlyand sent the craft ahead at a rapid rate. By elevating or depressingthe tube the craft could be sent obliquely up or down. Then, byforcing the air from the forward tube, the Mermaid was reversed andscudded backward. 

But it was more with the ship's ability to rise and descend thatProfessor Henderson was concerned, since on that depended theirsafety. So various tests were made, in generating the gas and usingthe negative gravity apparatus. 

All worked to perfection. Obeying the slightest turn of the wheels andlevers the Mermaid rose or fell. She stood still, suspended herself inthe air, or rushed backward and forward. 

Of course the machinery was new and did not operate as smoothly as itwould later, but the professor and his friends were very wellsatisfied. 

"Now we'll try something new, " said the scientist to the two boys asthey stood beside him in the tower. "I only hope this part succeeds, and we shall soon be off on our voyage. "

He turned several levers. There was a hissing sound as the gas rushedfrom the container, and the ship began to settle down. 

"What's th' matter? Are we goin' t' hit th' earth?" yelled Washington, rushing from the engine room. 

"Keep quiet, " ordered the professor. "We are only going down, that'sall. "

"But good land! Perfesser!" exclaimed the colored man. "The ocean'sright under us! You forgot you sailed sway from the island! We'll bedrowned suah!"

"Leave it to me, " said Mr. Henderson. "The Flying Mermaid is going totake a bath!"

"As long as it swims it will be all right, " observed Mark in a lowtone to Jack. "I'm glad I can take care of myself in the water. "

Before Jack could reply the Mermaid seemed to take a sudden divethrough the air. The next instant she struck the water with a splashthat sent the waves rolling all about. The craft rocked violently toand fro on the surface of the sea. For a while there were anxioushearts aboard, for there was no certainty but that the ship might notsink to the bottom. 

But the old professor had not calculated and builded in vain. Afterrocking about like a vessel newly launched, the strange craft rodesafely and upright on the water. It set down far enough to bring thepropelling tubes well under, but not so far but that the conning towerwas well out and there was a small deck available. 

"Now to see if we can conquer the water as we did the air!" cried theprofessor. "Mark, start the air pump. Jack, you steer, for I want towatch the machinery under the additional strain. "

From the rear tube rushed such a volume of air that the ocean near itbubbled and foamed. The ship trembled from stem to stern, and then, after hanging for an instant as if undecided what to do, it began tomove forward as easily as though it had never sailed any other elementthan the sea. 

"She fits her name!" the professor cried. "She is indeed the FlyingMermaid, for she sails the ocean as easily as she navigates in theclouds!"

For a mile or two the craft was sent ahead over the waves. Then it wasreversed and run backwards. Satisfied that his long months of work hadnot gone for naught, the professor after trying several experiments, decided to try and raise the ship while in motion. 

With Jack and Mark to look after the air pumps, while Washington, Tomand Bill busied themselves in the engine room, Mr. Henderson began togenerate the gas and start the negative gravity apparatus. All thewhile the craft was forging ahead. 

There was again the hissing sound that told of the aluminum holderbeing filled. For a few minutes there seemed to be no change, theMermaid plowing forward. 

Then like a bird rising from the waves, or like a flying fish leapingfrom the sea to escape some pursuing monster of the deep, the new shipshot up diagonally from the surface and winged its way into the upperregions of the air. 

"Success! Success!" cried the professor. "This proves all I wanted toknow. Now. We are ready for our great trip!"

Great were the rejoicings in the camp that night. It was like livingover again the days when they were aboard the diving Porpoise or theflying Monarch. To the recollections were added the anticipations ofwhat was before them in the trip to the interior of the earth. 

Busy days followed, for there was still much to be done to the FlyingMermaid. The machinery, which was only partly completed, had to befinished. Besides this the professor was working on some apparatus, the use of which he did not disclose to any one. It was stored aboardthe ship at the last minute. 

Plenty of provisions had to be taken aboard, and many supplies neededto work the Mermaid and insure that it would go to the end of thevoyage. The materials for generating the gas and negative gravity, spare parts, records for the automatic piano and other things werestored away. 

Some guns and ammunition were taken along as were a few revolvers, since old Andy had said it was best to prepare for any thing in theshape of enemies or wild beasts that might be met with in the interiorregions. 

It was decided to make the start by sailing along the surface of thesea for several days, as in the event of any weakness in the machinerybeing discovered there would be less danger. If, at the end of fourdays, no trouble developed, the professor said he would send theMermaid into the air and make the rest of the voyage through the sky. 

The night before the start was to be made the professor, with theboys, Washington and the other helpers, went about through the variousshops and buildings, locking them up securely. For they could not tellhow long they would be away, and they had to leave behind muchvaluable material. 

As there were several things that needed attention they divided thework up. Mark had finished his share and was walking back toward theliving cabin where they were all quartered, when, down at the shore, near where the boat was moored, he fancied he saw, in the gatheringdarkness, a moving figure. 

"I wonder who that can be, " he thought. "All the others are near themachine shop, for I just left them there. Perhaps it's some one tryingto spy out how the Mermaid is built. "

Knowing the professor wanted his secret well guarded, Mark walkedsoftly toward the little dock that served as a place whence theMermaid could be easily boarded. As he approached he saw the figuremoving. Something struck the boy as peculiar. 

Though the object had some of the characteristics of a man it did notwalk like a human being, but shuffled along more like a huge ape ormonkey. It seemed bent over, as if it stooped toward the ground. 

"Who are you?" called Mark suddenly. 

For an instant the figure halted and then hurried on faster thanbefore, with a curious, shuffling walk. It was approaching the ship. 

Somehow it struck Mark as if it was an uncanny being; an inhabitant ofsome other world. Then he laughed at his half-fear, and started on arun toward the dock. 

"If it's some tramp trying to find a place to sleep he'd better not goaboard the ship, he might do some damage, " the boy thought. 

He could hardly see the figure now as it had passed into the shadowcast by the boat. He was about to summon the professor to make aninvestigation, when Washington started going the search light whichwas placed just over the door of the living cabin. It was kept thereas a sort of beacon light, as, near the island was a dangerous ledgeof rocks. 

Then, in the blinding white glare from the big lantern as Washingtonaccidentally swung it toward the Mermaid, Mark beheld a strange sight. 

The figure he had been watching stood out in bold relief. Though itwas shaped like a human being it was not like any person the boy hadever seen. It seemed covered with a skin twice too large for it; askin, which, in spite of the clothes that concealed it, hung in foldsabout the arms and legs, dropping pendent like from the neck like abig garment, and flapping in the wind. 

For an instant Mark was so startled he cried out, and the professorand the others ran to see what was the matter. 

"There-- by the ship! A horrible creature!" exclaimed Mark. 

Shouting to Washington to keep the light steady in the direction ofthe dock, Mr. Henderson ran toward the moored Mermaid. Jack, Andy, Bill and Tom, with Mark in the rear followed him. 

"Nothing here, " said the scientist, after a careful search about. "Areyou sure you saw something, Mark?"

"Positively, " replied the lad with a shudder. He described the visionof the darkness. 

"I guess it was a big otter, or maybe an enormous turtle, " theprofessor said. 

 CHAPTER V

 ATTACKED BY A WHALE

BUT Mark was certain it was nothing like that, though a careful searchfailed to reveal anything or any person near the ship. It was too darkto examine for footprints, and even Mark, after taking a look allabout, felt he might have been deceived by shadows. Still he was alittle nervous, and could hardly sleep for imagining what the thing hesaw could have been. 

The next day every one was so busy that no one, not even Mark, recalled the little excitement of the night before. Shortly afternoon, final preparations having been made, they all got aboard theMermaid and started off. 

It was a bright sunshiny day, and the craft, speeding away from theisland where it had been constructed, over the dancing blue waves, must have presented a strange sight had there been any spectators. Forsurely no such ship had ever before sailed those waters. 

However, there was no other vessel in sight, and the island, as far asthe professor and his friends knew, had never been inhabited. 

"We will not try for any great speed, " Mr. Henderson remarked as he, with Mark and Jack, stood in the conning tower managing the Mermaid. "We don't want to strain any joints at the start or heat any enginebearings. There will be time enough for speed later. "

"Yes, and we may need it more when we get into the centre of the earththan we do now, " observed Mark. 

"Why so?" asked Jack. 

"No telling what we may run up against underneath the ground, " went onMark. "We may have to fight strange animals and stranger beings. Besides, the atmosphere and water there can't be the same as up here;do you think so, Professor?"

For a few minutes the scientist was silent. He seemed to be thinkingdeeply. 

"I will tell you what I believe, " he said at length. "I have neverspoken of it before, but now that we are fairly started and mayeventually have a chance to prove my theory, I will say that I thinkthe centre of this earth on which we live is hollow. Inside of it, forming a core, so to speak, I believe there is another earth, similarto ours in some respects which revolves inside this larger sphere. "

They were well out to sea now, as they could observe when they emergedon the little deck. Above their heads was the aluminum gas holder, which served as a sort of protection from the sun that was quite warm. The Mermaid rode with an easy motion, being submerged just enough tomake her steady, yet not deep enough to encounter much resistance fromthe water. In fact it could not have been arranged better for speed orcomfort. 

"I think we will sail well to the eastward before making our coursesouth, " Mr. Henderson said. "I do not care to meet too many ships, asthose aboard will be very curious and I do not want too much news ofthis venture to get out. We will take an unfrequented route and avoiddelays by being hailed by every passing vessel whose captain willwonder what queer craft he had met with. "

The boys enjoyed the sail, for the weather could not have been better. Even old Andy, who seldom said much, seemed delighted with theprospect of having strange adventures. He had his rifle with him, and, indeed, he seldom went anywhere that he did not carry it. 

"For there's no telling when you may see something you want to shootor that ought to be shot, " he used to say, "and it's always the manwithout a gun who needs it most. So I'm taking no chances. "

They sailed all that afternoon without meeting with a craft of anykind. Straight to the east they went, and when night began to settledown Washington got supper. It was decided to run slowly after darkuntil all hands were more familiar with the ship. 

Morning found the Mermaid about a hundred miles from the island whereshe had been launched. The night had been uneventful, except that Marktold Jack he heard some strange noise near his bunk several times. Hewas nearest the storeroom where spare parts, and the curious cylinderthe professor had brought aboard, were kept. 

"I guess it was rats, " said Jack. "They are always in ships. "

"Old wooden ships, yes, " admitted Mark. "But I'll bet there's not arat aboard the Mermaid. "

"Then you were dreaming, " said Jack, as if that settled it. 

Mark did not speak further of the noise, but he did considerablethinking. However, the next night there was no further disturbance. 

The fourth day out, when everything had passed off well, the enginesdoing their best, the professor decided to speed them up a bit, sincehe was satisfied they had "found" themselves as mechanics term it. 

"We'll see how fast we can go through the water, " said Mr. Henderson, "and then I think we can safely turn our course south. We are wellbeyond the ordinary lines of travel now. "

Having oiled the bearings well, and seen that everything was in placeand properly adjusted, the professor and the boys took their places inthe conning tower, while Washington, Tom and Bill remained in theengine room. Andy stayed on deck with his gun. 

"I might see a big fish, and we could vary our bill of fare, " he saidwith a laugh. 

"Here we go!" exclaimed the professor as he shifted the levers andturned some wheels and valves. "Now we'll see how fast we can travel. "

As he spoke the Mermaid responded to the added impulse of thecompressed air and shot through the water at a terrific speed. Thesudden increase in momentum almost threw the boys from their feet, andthey would have fallen had they not grasped some projecting levers. 

"I guess that will do, " Said the scientist. "I think we have speedenough for almost any emergency. I'll let her run at this rate for awhile, and then we'll slack up. "

Looking ahead, the boys could see the green waters parting in front ofthe bow of the Mermaid, as if to make room for her. Two huge waveswere thrown upon either side. 

Suddenly, dead ahead, there loomed up a big black object. 

"Look out you'll hit the rock!" cried Mark to the professor, who wassteering. 

With a turn of his wrist Mr. Henderson moved the wheel whichcontrolled the tube. It was deflected and sent the boat to larboard. 

At that instant from the rock two small fountains of water rose in theair, falling back in a shower of spray through which the sun gleamed. 

"That's not a rock! It's a big whale!" cried Jack. "And we're going tohit him!"

The professor had miscalculated the speed of the craft, or else hadnot thrown her far enough to larboard, for, a second later, theMermaid was almost upon the big leviathan. 

With a desperate twirling of the steering wheel the professor veeredthe craft as far as possible. But all he could do did not suffice, forthe craft hit the whale a glancing blow on the side, and the shipcareened as if she would turn turtle. 

At the same time there rang out from upon deck the sound of a rifleshot. Old Andy had taken a chance at the enormous creature of thedeep. 

"Hurrah!" the bays heard him shout. "I give him one plumb in the eye!A fine shot! And we hit him besides with the boat. I guess he's agoner!"

"I'm afraid not, " muttered the professor. "That was a bad blow westruck him, but I think it will only ruffle his temper. We'll have tolook sharp now, boys. "

By this time the ship had rushed past the whale, but the boys, lookingthrough a window in the rear of the tower could see the huge body. Nowthe fountains of water which the whale spouted were tinged with red. 

"He's bleeding!" exclaimed the professor. "I guess Andy hit him in avital spot. "

"But not vital enough!" cried Mark. "See! He's coming after us!"

And so it proved. The whale, angered, and, probably half crazed by thepain of the bullet and the blow, was coursing after the ship, comingon with the speed of an express train. Straight at the Mermaid helunged his huge bulk. 

"We must escape him!" cried Mr. Henderson. "If he hits us he'll sendus to the bottom!"

He had made ready to slow up the Mermaid to see if it had sustainedany damage from the impact with the whale, but when he saw the monstercoming after the boat he knew the only safety lay in flight. 

"Let us go up into the air and so escape him!" cried Jack, with suddeninspiration. 

For an instant neither Mark nor the professor grasped what Jack meant. Then, with an exclamation, the professor pulled forward the lever thatgenerated the gas and set working the gravity neutralizer, which wouldenable the ship to rise. 

Faster through the water went the Mermaid, and faster after her camethe whale. Above the hum of the engines was heard the hiss of thepowerful gas. The ship trembled more violently. 

"We are rising!" exclaimed the professor, as he looked at a gage. 

The boys could feel the craft lifting from the waves which clung toher as if they hated to lose her. The boys knew the gas was beginningto operate. 

"If it is not too late!" whispered Mark, half to himself. 

For the monster of the seas was coming on, lashing the water to foamwith his terrible flukes, and sending aloft a bloody spray. His speedwas awful. 

Now he was but ten feet away from the fleeing craft-- now but eight--now five! Ten seconds more and the big head, like the blunt stern of abattle ship, forced forward by the tons of blubber, flesh, bone andfat behind it would strike the Mermaid and crush it like an egg shell. 

Now if ever was the need for the Flying Mermaid to prove herselfworthy of the name. Now, if ever, was the time for her to leave thewatery element and take to the lighter one. 

And she did. With a last tremble, as if to free herself from the holdof the waves, the gallant craft soared up into the air, leaving thewater, which dripped from her keel like a fountain's spray, andshooting aloft like a bird, escaped her terrible enemy which passedunder her, so close that the lower part of the Flying Mermaid scrapedthe whale's back. 

"Saved!" exclaimed the professor. 

 CHAPTER VI

 THE CYCLONE

IT was only in the nick of time, for a second later and the big mammalof the ocean would have struck the ship and split it from stem tostern. 

Higher and higher into the air mounted the Flying Mermaid, while inthe water below, the whale, incensed by missing his prey, was lashingthe waves to foam. 

"Well, that was a narrow squeak; as close as I ever care to come toit!" exclaimed Andy as he let go of the steel rail to which he wasclinging and entered the conning tower. "I had no idea of hitting thebig fish. "

"I guess he would have taken after us whether you had fired at him ornot, " said Mr. Henderson. "He was probably looking for trouble, andtook the first thing that came in his way, which happened to be us. Some whales are like that, so I have read; big bull creatures, exiledfrom the school to which they once belonged, they get like madcreatures and know neither friend nor foe. Something like rogueelephants, I imagine. "

Now, having thus unexpectedly risen into the air, the professordecided to continue travel in that style for a while at least. Itwould require less force to propel the ship, and the going would bemore comfortable, since in the upper regions the Mermaid rode on aneven keel, while in the water there was more or less rolling, due tothe action of the waves. 

Once recovered from their fright caused by the whale, and having lostsight of the enormous creature, for they were now far above the ocean, the adventurers began to think of something to eat. 

Washington lost little time in preparing a meal, and it was eaten witha relish. The electric cooking stove worked to perfection, for thecolored man had learned how to use that aboard the Porpoise andMonarch, and could be depended on to turn out appetizing dishes. 

"What do you say to traveling through the air at night?" asked Mr. Henderson, as he arose from the table. 

"Suits me, " replied Mark. "There's less danger than in the water, Ithink, "

Bill, Tom and Washington arranged to stand the night watch, and, whenthe professor had examined the engines and given orders about keepingthe ship on her course through the air, he retired to his bunk. Jackand Mark soon followed. 

It must have been about midnight when Mark was awakened by a movementthat seemed to come from the storeroom next to where his sleepingplace was located. At first he thought he had been dreaming, but, ashe found he was wide awake, he knew it was no imagination that hadaffected him. 

"I certainly heard something, " he said to himself. "It sounded just asit did the other night. I wonder if I ought to investigate. "

He thought over the matter carefully as he sat upright in his bunk inthe darkness. True the noise might be a natural one, due to thevibration of the engine, or to some echo from the machinery. As Marklistened he heard it again. 

This time he realized it was the slow movement of some heavy body. Hefelt a cold shiver run over him and his hair evinced an uncomfortabletendency to stand upright. But he conquered his feelings and resolvedto keep cool and see if he could discover what had awakened him. 

He got up and moved softly about the little room that contained hisbunk. He could hear better now, and knew it was no echo or vibrationthat had come to his ears. 

Once again he heard the strange sound. It was exactly the same asbefore; as if some big creature was pulling itself over the floor. 

"Maybe it's a snake; a water snake!" thought Mark. "It may havecrawled aboard when we did not notice it. "

Then he remembered that the ship had not been open in any way thatwould enable a serpent to come on it, since it had been started on itsocean trip. Before that, he was sure no snake had entered the FlyingMermaid. Still it sounded more like a snake than anything else. 

"I'm going to make a search, " decided the boy. 

He took a small portable electric light, run by a storage battery, and, slipping on a pair of shoes and a bath robe, he left hisstateroom. 

He had decided that the noise came from the storage compartment and somade for that. The door he knew was not locked, since he had seen Mr. Henderson go in late that afternoon, and the professor had used nokey. 

Moving softly, Mark left his room and soon found himself in acorridor, on either side of which were located the sleeping quartersof the others. He did not want to awaken them, and, perhaps, belaughed at for his curiosity. 

To get to the storeroom Mark had to go first from the corridor intothe dining room. He soon reached the door that guarded what he thoughtmight be a strange secret. Trying the knob softly he found it givingunder his fingers. 

"I wonder if I had better go in, " he thought. "Perhaps, after all, itwas only rats, as Jack said. "

But, even as he listened he again heard the odd sound coming from theroom. This determined him. He would solve the mystery if possible. 

Cautiously he turned the knob. The door was slowly swinging open whenMark was startled by a noise from behind him. He turned suddenly tosee Professor Henderson confronting him. 

"What is it, Mark? Is the ship on fire? What's the matter? Is any onehurt?"

"I was just going in this room to----" began Mark. 

"Don't do it! Don't do it!" exclaimed the professor in an excitedwhisper. "No one must go in that room. I forgot to tell you and Jackabout it. No one must enter. It contains a secret!"

"I heard a strange noise and----" Mark began again. 

"It could make no noise! It would be impossible for it to make anoise!" the professor exclaimed. 

"I heard something, " the boy insisted. 

"You were dreaming!" said the professor. "Now go back to bed, Mark, and don't let this happen again. Remember, no one must enter that roomunless I give permission!"

Somewhat crestfallen at the outcome of his investigations, butrealizing that the professor could do what he wanted to aboard his ownship, Mark went back to bed. But he could not sleep. All the rest ofthe night he was wondering whether Mr. Henderson had some strangecreature hidden aboard the Mermaid. He feared lest the old scientist'smind might be affected and, in his wildness he had made some infernalmachine that would, in time, blow the whole ship apart. 

But tired nature asserted itself at last, and, weary with vainimaginings, Mark fell into a slumber. The next morning he awoke with astart from a dream that he was being devoured by an immense watersnake. 

He said nothing to the others about his night's adventure, for, as ittranspired, no one else had been awakened by his investigations. Theprofessor did not refer to his conversation with Mark. 

"There's something queer going on aboard the ship this trip, " saidMark to himself. "But I guess it's none of my business. ProfessorHenderson seems to know what he is doing and I guess I can trust him. "

He resolved to think no more of the strange noises and movements, and, for several nights thereafter he was not disturbed by them. 

The weather, which, up to this time had been fair, took a sudden turnfor the worse about the fourth day after Mark's little nightexpedition. One evening the sun sank in a mass of dull lead-coloredclouds and a sharp wind sprang up. 

"We're going to have a storm, " said Mr. Henderson. "It's liable to bea bad one, too, from the way the barometer is falling. "

He looked at the glass, and scanned the various instruments that toldhow high up the Mermaid was and how fast she was traveling. 

"We're pretty high up in the air, " he said, "and scooting along atabout fifty miles an hour. We are going against the wind, too, butfortunately it is not blowing hard. "

At that moment there sounded from without a peculiar howling sound, asif a siren whistle was being blown. 

"'Pears like there's goin' t' be a tumultuous demonstration ofsub-maxiliary contortions in th' empherial regions contiguous t' th'upper atmosphere!" exclaimed Washington, entering from the engine roominto the conning tower. 

"What's the trouble?" asked Mr. Henderson. 

"Terrible big black cloud chasin' us from behind!" exclaimed thecolored man. 

Noting the alarm in Washington's voice the professor glanced from therear window. What he saw caused him to exclaim:

"It's a cyclone! We must drop down to avoid it!"

He sprang to a lever controlling the gas and yanked it toward him. There was a shrill hissing sound, and a second later the Mermaid beganto sink. The boys watching the gages on the wall of the tower, sawthat the craft was falling rapidly. 

But, with a rush and roar, the terrible wind was upon them. It caughtthe craft in its fearful grip and heeled it over as a ship careens tothe ocean blast. 

"It's a storm in the upper regions! We'll find it calm below!" criedthe professor above the howling of the gale. He opened the gas outletwider and the ship fell more rapidly. 

"Are you sure we're over the ocean?" asked Mark. 

"Positive!" the professor called back. "We have been travelingstraight south over the Atlantic for the last week. We will land inthe midst of the waters and float safely. "

Lower and lower went the Mermaid. The wind was now blowing with theforce of a tornado, and, as the craft had to slant in order todescend, it felt the power of the gale more than if it had scuddedbefore it. But, by skilful use of the directing tube, the professorwas able to keep the boat from turning over. As they came further downtoward the earth the force of the wind was felt less and less, until, as they came within two hundred feet of the water which they saw belowthem in the gathering dusk, it died out altogether. 

"Now we are free from it, " said the professor as the Mermaid came downon the waves like an immense swan. 

"Are you going ahead or going to stop here?" asked Mark

"We'll keep right on, " Mr. Henderson answered. "No telling when thestorm may strike down here. We'll go as far as we can to-night. "

 CHAPTER VII

 A QUEER SAIL

NOW that the fear and worriment was over they all began to feelhungry, and, while Mark and Jack took charge of the conning towerWashington got breakfast. The professor seemed preoccupied during themeal, and several times, when Mark spoke to him, he did not reply. 

"I wonder if he is worried about something, or is thinking ofsomething which seems to be concealed in the storeroom, " the boythought. 

But, after a while, the professor seemed to be more like himself. Hewas busy over several maps and charts, and then announced the shipwould try air-sailing again for a while. 

"We can make better time above than we can on the water, " he said, "and I am anxious to get to the mysterious island and learn what is instore for us. "

Perhaps if the professor had been able to look ahead, and see what wassoon going to happen, he would not have been so anxious for it tooccur. 

It was shortly after dinner when, the gas container having beenfilled, the ship rose in the air, and began sailing over the ocean, about a mile up. The day was a fine one, and, as they were movingsouth, it was constantly growing warmer. Down on the water, in fact, it was quite hot, but in the air it was just right. 

Like some immense bird the Mermaid went flying through the air. Theboys and the professor sat upon the deck in easy chairs. It was likebeing on the top of some tall "sky-scraper" building which, by somestrange power, was being moved forward. Below them the ocean tumbledin long, lazy swells. 

Suddenly Mark, who was looking through a telescope at the expanse ofwater stretched out under them, gave a cry. 

"There's a ship! She's on fire!"

"Where?" asked the professor, stretching out his hand for the glass. 

"Just to the port of the forward tube. See the smoke!" exclaimed Mark. 

Mr. Henderson looked. Through the lens he saw a column of black vaporrising skyward. Mingled with it were red flames. 

"Lower the Mermaid!" he cried. "We must save those on board if wecan!"

Mark ran to the conning tower, where Washington was, to give theorder. The colored man, who was looking ahead, intent on guiding theship, did not at first hear what Mark called. 

"Lower us! Send the Mermaid down!" Mark cried again. 

The sudden shout, and the excited voice of Mark so startledWashington, that, fearing some accident had happened, he pulled thelever, controlling the gas supply, with more force than necessary. 

There was a loud explosion, followed by a crackling sound, a flash oflight, and the Mermaid came to a sudden stop. 

"What's the matter?" cried Mark, feeling that something was wrong. 

"I don't know!" Washington replied, as he dashed toward the engineroom. 

The Mermaid, her forward flight checked, hung in the air, suspended, neither rising or falling. 

"Why don't we go on down?" the professor asked, hurrying to the tower. 

"There has been an explosion-- an accident!" exclaimed Mark. "I guesswe can't go down!"

"But we must!" Mr. Henderson insisted, seizing the lever which shouldhave produced a downward motion. The handle swung to and fro. It wasdisconnected from the apparatus it operated. 

The ship was now stationary in the air, moving neither forward norbackward, neither rising nor falling. Washington had stopped the airpumps as soon as he learned something was wrong. 

When Mr. Henderson saw the useless lever, which had controlled theoutlet of gas from the holder, he ran out on deck. One glance told himwhat had happened. One of the electric wires had becomeshort-circuited, -- that is, the insulation had worn off and allowedthe current to escape. This had produced a spark, which had explodedthe gas which was in the pipe leading from the generator up into thealuminum holder. Fortunately there was an automatic cut-off for thesupply of vapor, or the whole tank would have gone up. 

As it was, only a small quantity had blown up, but this was enough tobreak the machinery at the point where the lever in the conning towerjoined the pipe. If it had not been for the automatic cut-off all thegas in the holder would have poured out in a great volume, and theship would have fallen like a shot. 

"Can we do nothing to save those on the burning vessel?" asked Mark, pointing to where a cloud of smoke hung over the ocean. 

"I fear not, now, " answered the professor. "We are in a bad plightourselves. "

"Are we in any danger?" asked Jack. 

"Not specially, " Mr. Henderson replied. "But we must find a means oflowering ourselves gradually. "

"Then it will be too late to save any of those on the ship, " observedMark. 

"I'm afraid so, " the scientist made reply. 

The Mermaid rested some distance above the surface of the waters. Shemoved slightly to and fro with the wind, and rocked gently. Theprofessor was examining the broken machinery. 

"I have a plan!" suddenly cried Mark. 

"What is it?" asked Mr. Henderson. 

"Can't we bore a hole in the tank, insert a small faucet or tap, andlet the gas out that way gradually?" asked the boy. "When we get downwe can rescue those in danger of fire, and, later, can repair thebreak. "

"The very thing!" exclaimed Mr. Henderson. "I never thought of that!Here, Washington! Bring me a drill, and a small stop-cock!"

The drill was obtained from the engine room. Working rapidly Mr. Henderson bored a hole in the lower part of the holder. As soon as themetal was penetrated the gas, which was under considerable pressure, rushed from the tank with a hissing sound. At once the Mermaid beganto settle rapidly. 

But the professor was prepared for this. He thrust the end of thestop-cock into the hole. It was screwed fast and the valve turned. This stopped the flow of gas and checked the descent of the ship. Then, by opening the tap the vapor was allowed to escape gradually, bringing the Flying Mermaid gently to the water. 

As the adventurers approached they could see that the vessel was now amass of flames. The wind was driving the fire toward the forecastle, and the crew had sought refuge aft. But this expedient could not lastlong, for, already the tongues of fire were licking the sides of thecraft and coming nearer and nearer the seemingly doomed men. Thevessel was a large one, and heavily laden. 

As those in peril caught sight of the Mermaid settling down into thewater, apparently from the clouds, their fears gave place toastonishment. So great was this that they ceased their cries ofterror. Then, as they saw that the strange craft navigated the ocean, for the engines were started aboard the Mermaid, they began to callfor help. 

 CHAPTER VIII

 THE FLYING MERMAID DISABLED

"WE'LL save you!" shouted Mr. Henderson, who was on the deck, whileMark was steering the craft. "Hold on a few minutes longer and we'llbe alongside!"

"They're real! They're real!" some of those aboard the burning shipcould be heard to shout. Evidently more than one of them had taken theMermaid for a delusion of their fear-crazed brain. 

"They are real persons!" they called again and again. "They are comingto save us!"

Mr. Henderson ran his ship as near the burning craft as he dared. Thenhe called to the crew to leap into the water and swim to him. He, withWashington, Jack, Bill and Tom, stood ready to haul aboard any whowere too weak to help themselves. 

In a few minutes all of those left alive on the sailing vessel--fourteen in all-- had come safely aboard the Mermaid. The ship was nowcompletely enveloped in flames. 

"Are there any more left on her?" asked Mr. Henderson of one whoappeared to be a mate of the burning craft. 

"Not a soul!" was the answer. "The captain and ten men perished in theflames. The fire broke out a week ago in the lower hold. We fought itas well as we could but it got the best of us. Then it suddenly brokethrough the decks, almost like an explosion, a little while ago, andthe captain and others were lost, and so were our small boats. Wemanaged to get aft but were about to give up when you appeared. "

"What ship is it and where are you from?"

"The Good Hope, laden with logwood, hides, jute and other materialsfrom South America, " the mate answered. "We were bound for New York. "

"It is more like the Last Hope instead of the Good Hope, " observed Mr. Henderson in a quiet voice, as he saw the flames mount higher andhigher over the ship. A few seconds later the craft seemed rent by aninternal explosion. It appeared to break in two parts, and, amid ashower of sparks and a cloud of black smoke, the vessel sank under thewater and was seen no more. 

The rescued men turned to behold the final end of their ship. Theybetrayed no particular emotion, and some of them even laughed, whichthe professor thought, at the time, was rather strange. But there waslittle opportunity for speculation. The men were in a sad plight. Fewof them had more than the clothes they stood in, though each one woreabout his waist a belt, and all of them seemed to guard the leathercirclets jealously. 

The professor and his crew were soon busy supplying remedies forburns, since several of the men were seared by the flames. Then, as itwas learned they had eaten nothing for many hours, it having beenimpossible to use the galley, a meal was prepared and the survivors ofthe wreck were well fed. 

The hunger of the newcomers having been appeased, they showed muchcuriosity over the strange craft that had so opportunely come to theirrescue. Most of the sailors were ignorant men, and the professor hadlittle fear of them learning anything concerning his secrets. Heexplained briefly about the Mermaid, but said nothing of whither shewas bound. 

The addition of fourteen men to the rather small accommodations of theMermaid was a serious matter to consider. The ship was able to holdthem all, and even to sail through the air with them, since Mr. Henderson had provided an excess of power. But it was going to be aproblem to feed so many, and still save enough provisions, for thelong voyage which lay ahead. 

However, Mr. Henderson felt his first duty to be toward his fellowmen, even if his voyage must be delayed, or given up for a time, while hegot more provisions. There would be no sleeping quarters for thesailors, but when this was explained to them they cheerfully said theywould sleep on deck if necessary. In fact some of them had to, but asthe weather was warm and clear this was no hardship. A few foundquarters in the engine room and other apartments of the Mermaid. 

Finding, after an examination, that his ship was in good order savefor the broken gas apparatus, Mr. Henderson gave orders to proceedalong the surface of the ocean. The sailors wanted to see how it feltto mount into the air, but Mr. Henderson, refused to attempt a flightuntil he had made complete repairs, and this would take a day or more. 

At this there appeared to be some discontent among the survivors, andthey muttered to each other as they stood in a group on deck. But theprofessor and his assistants were too busy with their preparations forfixing the break to notice this. 

While the men were gathered in a knot near the after part of the smalldeck, the mate separated from them, and, coming close to where Markwas standing, unscrewing some of the broken parts of the pipe said, ina low voice. 

"Tell the captain to watch out. "

"What do you mean?" asked Mark quickly. 

"Hush! Not so loud!" the mate exclaimed. "If the men hear me talkingto you, or see me, they may kill me. Tell the captain to look out;that's all. Be on guard, and watch the engine room carefully. "

"But why-- ?" Mark began, when, turning suddenly, the mate left him. It was well he did so, for, at that instant, one of the sailors, whohad observed the two conversing, strolled in their direction. 

Much alarmed, Mark sought Mr. Henderson and told him what he hadheard. 

"I suppose the fire may have turned the poor man's head, " thescientist said. "I wonder if he thinks the men I rescued would mutinyand take possession of my ship? If they did they would not know how towork it, so what good would it do?"

"Hadn't we better look out?" asked Mark. 

"I'm not afraid, " replied the professor. "I will be too busy the nextfew days, repairing the break, to think of anything else. Besides, what would they want to harm us for? Didn't we save their lives?"

Seeing the scientist placed no faith in what the mate had said, Markwent back to his task. 

It soon became too dark to work, and it was decided, after supper, tohalt the ship until morning as it would be less risky. 

Mark did not sleep well, his dreams being disturbed by visions ofpirates and black flags. But morning came and nothing had developed. The men seemed to recover their spirits with daybreak, and mast of thecrew, after breakfast, greeted Mr. Henderson pleasantly, and asked tobe allowed to help fix the ship. 

It took the skilled labor of the professor, Washington and the boys tomend the break, and, even at that, it was four days in the repairing. But at last the final bolt was in place, and the Mermaid was able toresume her trips through the air. 

"We will rise the first thing in the morning, " said the professor toMark and Jack that night. "I am anxious to see how the ship behaveswith a big load aboard. "

 CHAPTER IX

 THE MUTINY

MARK was awakened that night by feeling some one trying to turn himover. At first he thought it was Jack, and sleepily muttered that hewanted to be let alone. 

"Sorry I can't oblige ye, my hearty!" exclaimed a rough voice in hisear, "but I got particular orders t' tie you up!"

At that Mark tried to sit up, but he found he could not. He discoveredthat he was closely bound with many turns of a rope, while in front ofhis bunk stood one of the rescued sailors. 

"There, " said the man, with a final tightening of the ropes. "I guessyou're safe. "

"What's the matter? What does it all mean?" asked Mark, muchbewildered. 

"It means that we have possession of the ship, " the sailor answered, "and, if you're wise you'll not make a fuss. It wouldn't do any good, anyhow, as all your friends are in the same condition. "

Then, picking Mark up, as if he was a baby, the man slung him over hisshoulder and carried him to the living room. There Mark saw Jack, theprofessor, Washington, and the others similarly bound. 

"Do you realize what you are doing?" asked the professor angrily ofhis captors. "You are mutinying, and are liable to severe punishment. "

"If they ever get us, " added one of the men. "We've got the ship now, and we mean to keep her. You'll have to run her or show us how. "

"Never!" cried the professor. 

"I guess he will when he feels this, " said one of the men, as hedragged from a recess two wires. "I happen to know something ofelectricity, and when he feels these perhaps he'll change his mind. I'll start the dynamo. "

The sailor showed that he was acquainted with machinery, for soon thehum of the electric apparatus was heard. 

"Now to make him tell!" the man with the wires exclaimed, advancingtoward the professor, who turned pale. 

"Stop! You must not torture the old man!" cried a voice, and the mateof the Good Hope stepped in front of the sailor with the electrifiedwires. 

"Who's going to stop me?" asked the man. 

"I will. It's not necessary, " the mate went on quickly. "If we makehim weak we may kill him, and he can not tell us what we want to know. One of the boys can tell us how to run the ship. "

The mate came quickly over to where Mark lay, and whispered:

"Consent to tell. It is the only way of saving his life. Tell 'em howto raise the craft. Then leave all to me. I will save you all and theship, too, if I can. But consent. "

Mark nodded his head, and the mate cried:

"I knew I could fetch 'em. I have hypnotic power. This boy will raisethe ship for us. Loosen his bonds, some of you. "

Satisfied that they were now on the way to experiencing a newsensation, the sailors took the ropes off Mark's arms and legs, and hewas allowed to rise. With a reassuring nod toward the professor he ledthe way to the engine room, followed by half the men. He resolved tostart the gas machine slowly, so as to make the upward trip lastlonger, thinking before it had gone far, some way of escape from themutineers might be found. 

While a crowd of the sailors stood near him, Mark operated themachinery in the engine room that started the gas generating, and setthe negative gravity apparatus working. 

"You'd better not try any tricks on us, " said one of the men in anugly tone of voice. 

"I'm not going to, " replied Mark. "If you go out on deck you will soonsee the ship leaving the water and mounting into the air. "

"Some of you go, " ordered a man with a big bushy red beard. "See ifthe ship rises. When she begins to go up sing out. I'm going to stayhere and see how the young cub does it so I can work it myself. "

Obeying the red-bearded man, who seemed to be a leader, several of thesailors went out on the deck. It was quite dark, but there was aphosphorous glow to the water which made the rolling waves visible. 

The gas was being generated, as could be told by the hissing sound. Mark watched the machinery anxiously, for he knew much depended onhim, and the professor was not at hand to guide and instruct him. Hewatched the dial of the gage which registered the gas pressure and sawit slowly moving. In a little while it would be at the point at whichthe ship ought to rise. 

Presently a quiver seemed to run through the Mermaid. Now a shout camefrom the watchers on deck. 

"She's going up!"

The ship was indeed rising. The red-bearded man, who was addressed asTony, ran from the engine room to the deck. He saw that the ship wasnow ten feet above the water. Back he came to where Mark stood by thegas machine. 

"Lucky for you that you didn't fool us, lad, " he said with a leer. "See that you mind me hereafter. Now show me how the shebang works. "

When the ship had risen as far as Tony desired he made Mark send itstraight ahead. The boy adjusted the air tube to carry the crafttoward the south, but Tony, seeing by a compass in which directionthey were headed, ordered Mark to steer due east. 

"Fix things so they will stay so, too, " added Tony. "I don't want tostop until I get a thousand miles away. Then we'll come down, sail tosome sunny island, and enjoy life. "

Mark locked the steering apparatus so as to keep the Mermaid headeddue east. 

"Now you can go back to your friends, " Tony said. "When I want youI'll send for you. "

With a heavy heart Mark rejoined the professor and others. He foundthem with their bonds removed. But to guard against their escapeseveral men were on watch outside the door. 

"What are they doing?" asked the professor eagerly as Mark entered, and the boy told him what had taken place. 

"They will ruin my ship and spoil the whole trip, " cried the oldscientist. "Oh, why did I ever go to the rescue of the scoundrels?"

"Never mind, " said Jack. "Perhaps we may yet outwit them. "

Morning came at last. The ship was still shooting forward at fastspeed, in an easterly direction. The sailors had learned, in theirshort stay aboard, where the food and stores were kept, and they lostlittle time in getting breakfast. They sent same in to their captives, including a big pot of hot coffee, and, after partaking of this theprofessor and his friends felt better. 

The mate of the Good Hope came in to help clear away the dishes. As hepassed Mark he slipped into the boy's hand a note. 

"Don't read it until you are alone, " he said in a low voice, as hehurried from the room. 

As soon as the other sailors had left, Mark glanced at the slip ofpaper. It bore these words:

 "Open when you hear three raps, then two, then three, and keep silent. "

"What is it?" asked Mr. Henderson. 

Mark showed him the paper. 

"I wonder what it means, " the boy said. 

"Do you think he is a friend of ours?" the professor asked. 

Mark told him of the mate's conversation the night previous. 

"I think we can trust him, " the scientist went on. "He must intend topay us a visit when the others are asleep. When we hear the knocks ashe specifies we must open the door and let him in. "

All that day the captives were kept in the living room. Once or twiceMark was sent for to make some adjustment to the machinery, but theapparatus, for the most part, was automatic, and needed littleattention. The professor, as well as the others, were all impatiencefor the promised visit of the mate. Still they felt he would not comeuntil night. 

In fact it was long past midnight before Mark, Jack and the professor, who were anxiously listening, heard the three raps, then two, thenthree more. Mark quickly opened the door, and the mate stepped inside, holding his finger to his lips as a sign of caution. Old Andy, Washington, Bill and Tom had fallen asleep. 

"I have only time for a few words, " the mate said. "I am closelywatched. Tony mistrusts me. I will save you if I can. "

"Why have they repaid my kindness with such actions?" asked Mr. Henderson. 

"Because they are desperate men, " replied the mate. "They are nothingmore than pirates. They mutinied on the other ship, killed the captainand those of the crew who would not join them, and started off to seektheir fortunes. I pretended to join them to save my life, but I haveonly been watching for a chance to escape. 

"Because of lax discipline the ship was sent on fire. We tried to putit out but could not. The rest you know. "

"I heard them plan to capture this airship, but could do nothing tostop them. Then I resolved to pretend to act with them. They fearpursuit for their other mutiny, and are anxious to get as far away aspossible. "

"Do you think they will abandon the ship in a little while?" asked theprofessor hopefully. 

"I'm afraid not, " answered the mate. "I think they want to get rid ofall of you, so they can sail about as they please. Tony is a smartman. He could soon learn to run this ship, he thinks. "

"I doubt it, " Mr. Henderson answered. "But how are you going to helpus?"

"I have not fully made up my plans, " the mate answered. "However Iwanted you to know I would do my best to save you. Now I must go. Beon the watch and when I can I will let you know what I have decidedon. I will hand Mark a note when I bring your meals, just as I didto-day. I think----"

"Hark! What was that?" asked the professor. 

There was a noise outside the door, as if some one was listening. 

"Put out the lights!" whispered the mate, and Jack switched off theelectric incandescents. 

A knock sounded on the door and the voice of Tony called:

"Mark! Come here! I want you to look at the gas machine. It hasstopped working, and we are falling!"

 CHAPTER X

 FOOLING THEIR ENEMIES

MARK hurried into the corridor, taking care to close the door afterhim, so Tony could get no glimpse of the mate who had risked so muchto save his friends. But he need not have been alarmed for the leaderof the mutineers was too excited over the stopping of the gasapparatus to give any heed to who was in with the captives. 

"Do you think you can fix it?" he asked the boy. 

"I guess so, " Mark replied confidently. "If I can't there is nodanger, for we will fall gradually and land in the water. "

"But I don't want to do that, " Tony objected. "I want to keep onthrough the air. "

Mark did not reply. By this time he was at the gas machine. He soonsaw nothing was the matter save that new material must be placed inthe retort where the vapor was generated. He refilled it, the gas wasmanufactured once more, and the ship began to rise. 

"I will know how to do it next time, " Tony said with a grin. Markrealized that every time he showed the leader of the mutineerssomething about the ship it was putting the professor and his friendsmore and more into the power of the scoundrels. But there was no helpfor it. 

The ship was still plunging ahead, and kept about a mile above theearth. As there was no further need of Mark, he was told he could goback to his friends. When he reached the room where they were heldprisoners, he found the mate had gone away, promising again to do allhe could for them. 

The next night, which it seemed would never come, for the day, lockedas the captives were in their room, seemed endless, finally closed in. Mark, Jack and the professor were anxious to know whether the matewould pay them another visit. As for Andy, Tom and Bill, while theywere interested in the ship, and wanted to be free from the power ofthe mutineers, they did not lose any sleep over it. 

Shortly after midnight, there came again the peculiar knock, and themate entered the room. He seemed much excited over something, and, assoon as the portal was securely closed he said to Professor Henderson:

"Is there an island any where near here where men could live for atime?"

"What do you mean?" asked the scientist. "Do you want us to desert theship and leave these scoundrels in charge?"

"Nothing of the sort, " replied the mate, who, had said his name wasJack Rodgers. "But first answer my question. A great deal may dependon it. "

Seeing Rodgers was in earnest, the professor looked over some maps andcharts, and announced that they were within a few hundred miles of agroup of islands. 

"When would we reach them?" was Rodgers's next question. 

Mr. Henderson made a few rapid calculations on a piece of paper. 

"At the present rate of sailing, " he said, "we should be there aboutten o'clock to-morrow. That is, provided the ship does not slackenspeed or increase it. "

"There is no danger of either of those two things happening, " said themate. "Tony is too afraid of the machinery to do anything to it. Soyou may safely figure that our speed will continue the same. "

"Then I can guarantee, with all reasonable certainty, " the professorsaid, "that about ten o'clock to-morrow we will be less than a milefrom the islands. They are a group where friendly natives live, andwhere many tropical fruits abound. One could scarcely select a betterplace to be shipwrecked. But I hope the plans of Tony and his friendsdo not include landing us there. "

"No, nothing like that, " the mate answered. "Quite the contrary. But Ihad better be going. I will try and see Mark some time to-morrow. Tonydoes not mind when I speak to him. "

With this Rodgers left the captives, as he heard some of the sailorsmoving about and did not want to be discovered. The professor and theboys wondered what the mate's plan might be, but they had to becontent to wait and see. 

The night passed without incident. About nine o'clock the next morningthe mate came to the door of the room where the professor and hisfriends were prisoners. He made no secret of his approach, but knockedboldly. 

"Tell Mark I want to see him, " he said, as the professor answered. "All of you keep quiet, " he added in a whisper. "There may be goodnews soon. "

Mark slipped from the room. He followed the mate to the upper deckwhich, at that time was deserted as all the sailors were in the diningroom eating, which practice they indulged in as often as they could. 

"I have a plan to get rid of these rough men, " the mate said to Mark. "It may work, and, again it may not. At any rate it is worth trying, It all depends on you with what help I can give you. "

"I'm willing to do my share, " Mark said, and for the next ten minutesthe boy and the mate were in earnest conversation. 

It was about thirty-five minutes later when there arose a suddencommotion in the ship. Mark had returned to his friends and the matehad disappeared. The confusion seemed to come from the engine roomwhere Tony had posted some of his men. 

"We're falling down! We'll all be killed!" shouted the men. "The shipis falling into the sea!"

"What is the trouble?" asked the professor as he heard the commotion. 

"It is part of the mate's plan, " said Mark. "He told me to tell you todo nothing. If Tony or any of the other men come to you just referthem to me. "

Two minutes later Tony came rushing into the apartment where thecaptives were held prisoners. 

"Here! Come quickly, Mark!" he exclaimed. "Something has gone wrongwith the gas machine again, and you must come and fix it before we areall dashed to pieces!"

With every appearance of haste Mark rushed from the apartment, following Tony. The latter led the way to the engine room. 

"Can anything be done?" he asked. 

Mark took a survey of the machinery. 

"It is too late, " he said as though much excited. "The ship is fallingdown toward the sea with terrific force. "

It needed but a glance at the height gage to show this. The pointerwas revolving rapidly about the face of the dial. 

"Will the ship stand the blow?" asked Tony. 

"Not at the rate it is falling, " replied Mark. "She will go all topieces when she strikes the water, and she may explode!"

"What are we to do then?" asked the leader of the mutineers. 

"We must save ourselves!" cried the mate, running in at this juncture. "Let our prisoners shift for themselves as best they can. Let's allleap into the sea. There we at least have a chance for our lives. Butif we stay on this ship we will all be drowned like cats in a bag. "

"What do you propose?" asked Tony, his face white with fear. 

"When the ship comes near enough the surface of the water to make itsafe we should all drop overboard!" the mate exclaimed. "We are nearsome islands, I understand, and we can thus save our lives by swimmingashore. "

This plan seemed to meet with instant favor, and a little later therewas a rush for the deck, as each one wished to be the first to escapefrom the boat they believed to be doomed. 

Lower and lower fell the Mermaid. She was like a wounded bird whichthe shot of the hunter has crippled. Down and down she fluttered. 

By this time all the sailors, save the mate were on deck. He and Markremained in the engine room. 

"Don't let her get too low, " the mate whispered. 

"I'll watch out, " Mark replied. "I want to give them a good scarewhile I'm at it. "

The ship was now within fifty feet of the water. There was a cry ofterror from the sailors. Some of them leaped over the rail and startedto swim ashore, as the ship was by this time close to a group ofislands. 

Suddenly, from the engine room the mate rushed. 

"Jump! Jump for your lives!" he exclaimed. "The ship is about to blowup!"

 CHAPTER XI

 MYSTERIOUS HAPPENINGS

THE voice of the mate echoed through the Mermaid. Those on deck heardit, as did Tony in the engine room, where he was vainly trying tounderstand the complicated machinery. 

An instant later there sounded from beneath the ship a series ofsplashes. More sailors were leaping from the deck of the craft to theocean. The distance was not great, particularly as they all landed inwater. 

"Quick!" cried the mate to a group of sailors that hesitated beforetaking the jump. "The ship may blow up any minute now. "

The men needed no second urging. As soon as they struck the water theybegan to swim ashore, as it was not far away. One after another theyjumped over the rail. Tony was the last to go. He urged the captivesto follow him, but they all refused. 

A minute later the only one of the pirate crew left on the ship wasthe mate. The others were all struggling in the sea. Eventually theyall reached shore in safety. 

The airship was now within about twenty feet of the water. It wasstill falling but not so rapidly. 

"Better send her up, now, " said the mate to Mark, and the boy turnedthe necessary levers to accomplish this. 

Dipping into the water as a sea gull does when searching for food onthe wing, for she had come quite low, the Mermaid mounted once moreinto the air, and was soon sailing along over the heads of Tony andhis gang. 

"What's it all about?" asked Mr. Henderson, who seemed in a sort ofstupor. "I thought the ship was broken. How, then, can it rise?"

"It was only a trick of mine, " Rodgers said. "The gas machine is notbroken. I had Mark fix it so that only a little vapor would begenerated. When the supply in the holder was not enough, and no morewas being made, the ship had to sink. Mark and I pretended it wasworse than it really was just to scare the scoundrels. "

"And you evidently succeeded, " observed Mr. Henderson. "They have allleft us. I am glad you stayed. "

"So am I, " said Rodgers. "I was just waiting for a chance to escapefrom that crowd. This was the plan I thought of that night. I wantedto see the men put on some island where they could manage to live, andwhich was not too far away. "

The Mermaid was now mounting upward rapidly, as Mark had adjusted themachinery properly. The craft was well rid of the pirate crew, and wasable to proceed on its way, and enable Mr. Henderson to carry out hisplans. 

When the Mermaid had reached a certain height her prow was turned theother way, and she was sent back racing over the ground she had justcovered. But now the ship was in the hands of friends. Fortunately nogreat damage had been done by the sailors, and the professor was soonable to get things in ship-shape. The engines had not been molestedand were working better than ever. 

"Now to make another attempt to reach the big hole in the earth, " theprofessor cried. "We will be careful next time, who we rescue fromships at sea. "

The island was soon left behind, becoming a mere speck on the ocean. Those aboard the Mermaid knew no harm could befall the sailors, asthere were no savage tribes on the little spot of land. Eventually thesailors were picked up by a passing vessel and taken to their homes. The story of their first mutiny leaked out and they were properlypunished. 

It required several days travel before the airship regained thedistance she had lost because of the plans of the pirates. Also, therewere a number of minor repairs to make, and the professor and hisfriends were kept busy. 

"How much longer before we come to the big hole?" asked Jack, one day. 

"I think we ought to be near it in about two weeks, " the professorreplied. "I only hope we shall not be disappointed, and will be ableto explore it. "

"'Tain't goin' t' be no fun t' be decimated an' expurgitated inter aconglomerous aggregation of elements constituting th' exterior portionof human anatomy, " said Washington in dubious tones. 

"You mean you're afraid of being boiled in the steam from the bighole?" asked Mark. 

"Jest so, " replied the colored man. 

"You don't need to worry about that, " put in the professor. "I willnot take the ship down if there is any danger, though of course therewill be some risk. "

The ship, having been fully repaired, was now able to be speeded up, and was sent scudding along toward her destination. Rodgers proved avaluable acquisition toward the crew, for he had sailed many years inthe waters over which they were flying, and was able to give theprofessor many valuable hints. He had heard vague stories of theisland with the big hole, but had never been near it. He did not makethe trip however, as, at his request, he was put off at an inhabitedisland one night. 

It was about a week after the sailors were frightened from the ship, that a curious experience befell Mark. Washington was on duty in theconning tower, attending to the apparatus as the ship flew through theair, and all the others had gone to bed. Mark had remained up, laterthan the others as he was interested in reading a book on science. 

About ten o'clock he became hungry, and going to the pantry got somebread and cold meat. He set these on a table, and then, remembering hewould need some water to drink, started after some in the cooler, which was in a little room near the tower. 

Washington heard the boy as he turned the faucet to draw the liquid, and spoke to him, as the colored man was rather lonesome at his post. Mark did not linger more than a minute or two, but when he returned towhere he had left the food he was much surprised. 

There was not a trace of it to be seen. The dishes were on the table, but every vestige of bread and meat had disappeared. 

"I wonder if a cat or dog has been here, " was Mark's first thought. Then he remembered that no such animals were aboard the Mermaid. 

Something on the floor caught his eye. He stooped and picked it up. Itwas a slice of bread, but in such shape that the boy stared at it, puzzled as to how it could have become so. 

It was flattened out quite thin, but the strangest part of it was thatit bore what seemed to be the marks of thumb and fingers from a verylarge hand. So big, in fact, was the print, that Mark's hand scarcecovered half of it, and, where the bread had been squeezed into aputty like mass (for it was quite fresh) the peculiar markings on theskin of the tips of the fingers were visible. 

"It looks as if a giant grabbed this slice of bread, " Mark observed. "There are strange happenings aboard this ship. I wish I knew whatthey meant. "

He looked all around for the food, thinking perhaps a rat had draggedit off, but there was no trace of it. 

Suddenly the boy thought he heard a sound from the big storeroom. Hewas almost sure he heard something moving in there. He started towardthe door when he was stopped by hearing the professor's voice call:

"Don't open that door, Mark. Have I not told you that place must notbe entered?"

"I thought I heard some one in there, " Mark replied. 

"There is nothing in there but some apparatus of mine, " Mr. Hendersonsaid. "I want no one to see it. What is the matter?"

Mark explained matters to the scientist, who had, as he said later, arisen on hearing the boy, moving about. 

"Oh, it was a rat that took your stuff, " Mr. Henderson said. "I guessthere are some pretty big ones on the ship. Get some more food and goto sleep. "

Mark felt it best to obey, though he was by no means satisfied withthe professor's explanation. He listened intently to see if any morenoises came from the storeroom, but none did, and he went to bed. 

Several times after that Mark tried the experiment of leaving foodabout. On each occasion it was taken. 

"It looks as if the ship was haunted, " he said. "Of course I know itisn't, but it's very queer. They must be strange rats that can getfood from shelves when there is only the smooth side of the ship toclimb up, " for on some occasions Mark had tried the experiment ofputting the food as nearly out of reach as possible. 

It took several nights to learn all this, and, as he did not want totake any one into his confidence, he had to work in secret. But, withall his efforts he learned nothing, save that there was something oddabout the ship that he could not fathom. 

At first he believed the professor had some strange animal concealedin the storeroom, but he dismissed this idea almost as soon as hethought of it. For what could the scientist want with an animal whenthey were going to the interior of the earth? That some beast hadslipped aboard was out of the question. Mark was much puzzled, butfinally, deciding the matter did not concern him a great deal, gave uptrying to solve the mystery, at least for a time. 

The ship was now in the neighborhood of the equator and the climatehad become much warmer. So hot indeed were some nights that they sleptout on deck, with the Mermaid flying through the air at a moderatepace, for it was deemed best not to go at any great speed after dark. 

One night the professor, after consulting various charts and maps, andmaking calculations which covered several sheets of paper announced:

"We should sight the mysterious island to-morrow. "

"That's good news!" exclaimed Jack. "I'm anxious to see what's belowinside of that big hole. "

"Everybody git ready for their funerals!" exclaimed Washington in adeep voice. "I ain't got many----"

"Cheer up, " interrupted Jack, poking Washington in the ribs. Thecolored man was very ticklish, and he began to laugh heartily, though, perhaps, he did not feel like it. 

Suddenly, above the sound of his shouts, there came a crashing, grinding noise from the engine room. 

 CHAPTER XII

 THE BIG HOLE

"SOMETHING has gone wrong!" exclaimed the professor as he jumped up. He reached the engine room ahead of any one else, and when the twoboys got there they found him busy twisting wheels and shiftinglevers. 

"Anything serious?" asked Jack. 

"It's the gas machine again, " Mr. Henderson replied. "It broke wherewe fixed it. However it doesn't matter. I was going to lower the shipanyhow, as I want to approach the island from the water. We will godown a little sooner than I counted on. "

The disabling of the gas machine caused the vapor to escape slowlyfrom the tank, and this made the ship sink gradually. By means of theemergency stop-cock the descent could be controlled almost as well asthough the machinery was in working order. Half an hour later theMermaid rested on the water. 

It was a little rough, as there was quite a swell on, and not sopleasant as floating in the air on an even keel, but they made thebest of it. 

On account of the little accident, and not being certain of itsextent, it was deemed best not to send the ship ahead. So they laid tountil morning. 

For the better part of two days all those on board the Mermaid hadtheir hands full mending the break and making other repairs foundnecessary. In that time they lay to, floating idly with the currents, or blown by the wind, for the professor would not start any of theengines or apparatus until the ship was in good condition. 

In this time Mark had several times recalled the curious happenings inregard to the disappearing food, and the mystery of the storeroom. Butthere were no further manifestations, and no other signs that theremight be a strange visitor aboard. 

"I couldn't have imagined it all, " said Mark, "but I guess what didhappen may have been caused by natural means, only I can't discoverthem. "

It was about two days after this, the ship having sailed scores ofmiles on the surface of the water, that Mark, who was in the conningtower exclaimed:

"That looks like a waterspout ahead of us. "

"That's what it is!" Jack agreed. "What shall we do?"

"Call the professor!" said Mark. "He'll know. "

When Mr. Henderson came, he looked for a long time at a cloud of blackvapor which hung low in the east. 

"It may be a waterspout, " he said. "We'll rise in the air and see ifwe can avoid it. "

The ship was sent up into the air. As it rose higher and higher, theprofessor, making frequent observations from his conning tower, criedout:

"That is no waterspout!"

"What is it?" asked Mark. 

"It is the steam and vapor rising from the big hole in the earth!Boys, we are almost there!"

"Are you sure that's it?" asked Mark. 

"Almost positive, " Mr. Henderson replied. "You can see how much warmerit has become of late, as we approached the equator. We are almost dueat the island, and I have no doubt we have reached it. "

As the ship flew forward the mass of dark vapor became morepronounced. Through the glasses it could be noticed to consist ofrolling masses of clouds. What lay beneath them no one knew. Theadventurers were going to try to find out. 

Now that they had arrived at the beginning of the main part of theirjourney, the travelers felt their spirits sink a little. It was onething to plan to go down into the depths of the earth, but it wasquite another to make the actual attempt. Still, they were not goingto give up the project. The professor had confidence in his ship andbelieved it could safely make the trip. Still it was with no littleapprehension that Mr. Henderson watched the nearer approach of thecraft to that strange island. 

"Perfesser, are yo' really an' truly goin' t' depress this elongatedspheroid an' its human consignment int' that conglomerous convolutedmass of gaseous vapor regardless of th' consequences?" askedWashington, as he gazed with wide opened eyes at the sight before him. 

"If you mean am I going to let the Mermaid go down into that hole youare perfectly correct, " the scientist answered, "though you could havesaid it in fewer words, Washington. "

"I-- I guess I'll get out an' walk, " the colored man made reply. 

"This isn't any trolley car, " observed Mark. "Don't lose your nerve, Wash. Stay with us, and we'll discover a gold or diamond mine, maybe. "

"Is there diamonds down there?" asked the colored man, his frightseeming to leave him. 

"There are all sorts of things inside the earth, " the professoranswered. 

"Then I'm goin' along!" Washington declared. "I always did want adiamond ring, an' I knows a little colored gal that wants one, too. I'm goin' all right! This suttenly am th' most kloslosterousconjunctivity of combativeness that I ever sagaciated!" and he beganto do a sort of impromptu cake-walk. 

 CHAPTER XIII

 DOWN INTO THE EARTH

IT was now noon, but the adventurers did not think of dinner in theexcitement of approaching the mysterious island. The speed of the shipwas increased that they might the more quickly come to it. As theyapproached they could see the masses of vapor more plainly, and itappeared that some great commotion must be going on inside the bighole, since clouds of steam arose. 

"I only hope it doesn't prove too hot for us, " observed the professor. "However, I provided a water jacket for the ship, and we may need it, as well as the vacuum chambers to keep the heat from us. "

It was about three o'clock when the flying ship reached the edge ofthe island. From there it was about a mile to the rim of the big hole, over one side of which the waters of the ocean poured with a roar thatcould be heard over half a mile off. 

"I think we had better halt and see that everything is in good shapebefore proceeding, " said Mr. Henderson. "Jack, you and Mark make athorough inspection of the engine room, and see that all the apparatusis in working order, "

The two boys prepared to do as they were told. Mark, who was walking alittle ahead of Jack, entered the apartment from which the storeroomopened. As he did so he saw, or thought he saw, the door of the placewhere the extra supplies were kept, close. Without saying anything toJack he hurried forward, and tried the knob. It would not turn. 

"That's funny, " said Mark to himself. "I could almost swear I saw someone go into that room. Yet I know the professor did not enter, for Ijust left him. And none of the others would dare to. I wonder if Iwill ever solve the mystery. "

But he had too much to do to allow him to dwell on that matter. Several of the dynamos needed adjusting and for two hours he and Jackhad all they could do. 

In the meanwhile the professor had gone over the other parts of theship, and gotten everything in readiness for the descent. The Mermaidwas lowered to within a few hundred feet of the sea, and, through ahose that was let down, the compartments, provided for this emergencywere filled with water. These compartments were between the outer andinner hulls of the lower part of the craft, and were designed toprevent the interior becoming heated in case the travelers found theyhad to pass close to fire. There were also vacuum chambers, and fromthese the air was exhausted, as of course every schoolboy knows avacuum is a non-conductor of either heat or cold. 

"Now I think we are ready, " the professor announced at length. 

"Everything's all right in the engine room, " announced Jack. 

"Yes, an' everything's all right in th' kitchen, " put in Washington. "I've got a good meal ready as soon as any one wants to eat. "

"It will have to wait a while, " Mr. Henderson remarked. "We are goingto start to make the descent before we dine. "

The hose was reeled up, and the ship was sent a few hundred feethigher into the air, as Mr. Henderson wanted to take a last goodobservation before he went down into the hole. 

But having risen some distance above the masses of rolling vapors hefound he was at no advantage, since the strongest telescope he couldbring to bear could not pierce the cloud masses. 

"We'll just have to trust to luck, " the scientist said. "I judge we'reabout over the centre of the opening. Lower away Mark!"

The boy, who, under the watchful eye of the professor, wasmanipulating the levers and wheels in the conning tower, shifted somehandles. The gas was expelled from the holder, the negative gravityapparatus ceased to work, and the Flying Mermaid sank lower and lower, toward the mysterious hole that yawned beneath her. 

The hearts of all beat strangely, if not with fear, at least withapprehension, for they did not know what they might encounter. Perhapsdeath in some terrible form awaited them. But the desire to discoversomething new and strange had gripped all of them, and not one wouldhave voted to turn back. 

Even old Andy, who seldom got excited, was in unusual spirits. He tookdown his gun and remarked:

"Maybe I can kill some new kind of animal, and write a book about itshabits, for surely we will see strange beasts in the under-world. "

Lower and lower sank the ship. Now it was amid the first thin massesof vapors, those that floated highest and were more like a light fog, than anything else. By means of a window in the bottom of the craft, which window was closed by a thick piece of plate glass, ProfessorHenderson could look down and see what was beneath them. 

"The clouds seem to be getting thicker, " he said, as he peered throughthe small casement. "If they would only clear away we could seesomething. "

But instead of doing this the vapors accumulated more thickly aboutthe ship. It was so dark inside the Mermaid now that the electriclights had to be switched on. In the room with the floor-window thelights were not used, as had they shone one could not have seen downbelow. 

The professor maintained his position. The descent was a perilous one, and he wanted to be on the watch to check it at once if the Mermaidwas liable to dash upon some pointed rock or fall into some fiery pit. His hand was on the signal levers. 

Suddenly he looked up and glanced at a gage on the wall. The hand ofit was slowly revolving. 

"We are at the earth's surface, " the scientist said. "Now we are belowit. Now we are fairly within the big hole! Boys, we may be on theverge of a great discovery!"

An instant later it seemed as if a hot wave had struck the Mermaid, oras if the craft had been plunged into boiling water. 

"It's going to be hot!" cried the professor. "Lucky I provided thewater jackets!"

Then the lights in the interior of the ship went out, leaving thewhole craft in darkness. 

"What has happened?" cried Mark. 

 CHAPTER XIV

 MANY MILES BELOW

"DON'T be alarmed, " spoke the calm voice of the professor. "I haveonly turned off the electrics. I want to switch on the search lights, to see if we can learn anything about our position. "

As he spoke he turned a switch, and, the gloom below the ship, as theboys could see by glimpses from the floor-window, was pierced by adazzling glare. In the bottom of the Mermaid were set a number ofpowerful electric arc lights with reflectors, constructed to throw thebeams downward. The professor had built them in for just thisemergency, as he thought that at some time they might want toilluminate what was below the craft. 

Not that it was of much avail on this occasion, for, though the lightswere powerful, they could not pierce the miles of gloom that lay belowthem. The beams only served to accentuate the darkness. 

"I guess we'll have to trust to luck, " the professor said, after avain attempt, by means of powerful glasses, to distinguish something. "There is too much fog and vapor. "

"What makes it so warm?" asked Mark, removing his coat. 

"Well, you must remember you are approaching the interior of theearth, " the professor answered. "It has been calculated that the heatincreases one degree for every fifty-five feet you descend. We havecome down several hundred feet and of course it is getting warmer. "

"Then if we go down very far it will get so hot we will not be able tostand it, " Jack put in. 

"I do not believe we will suffer any great inconvenience, " Mr. Henderson went on. "I believe that after we pass a certain point itwill become cooler. I think the inner fires of the earth are more orless heated gas in a sort of inner chamber between two shells. If wecan pass the second shell, we will be all right. "

"But aren't we liable to hit something, going down into the dark thisway?" asked Mark. 

"We will guard ourselves as far as possible, " the scientist answered. 

The Mermaid seemed to be going down on a side of the immense shaft agood way distant from the strange waterfall. When they had firstdropped into the hole the travelers could hear the rush of waters, butnow the noise was not audible. 

"I think the hole must widen out the farther down we go, " theprofessor said. "We are probably many miles from the fall now. "

"I'm sure I hope so, " put in Jack. "It would be no fun to have to takea shower bath in this place. "

After a meal, the boys and the professor took some more observations, but with all their efforts nothing could be seen below the ship but avast black void, into which they were steadily descending. 

"I wonder when we're going to stop, " asked Mark. "It's like playingthe game 'Going to Jerusalem, ' you keep wondering when the music willcease and you will have a chance to grab a chair. I only hope we havea chair or something else to sit on, in case we go to smash. "

"We're not liable to have any accidents with the professor in charge, "Jack answered. "Didn't he bring us safe out of some pretty tight holeswhen we went to the north pole in the airship, and again when we foundthe south pole in the submarine?"

"Yes, but this is different, " objected Mark. 

"Well, I'm not worrying, " Jack went on. "It doesn't do any good, andonly makes you lie awake nights. By the way, I wonder what time it isgetting to be. "

He looked at his watch and found it was close on to eight o'clock inthe evening. So late had dinner been served, and so varied were thehappenings of the last few hours, that time had passed quickly. 

"Why it's almost bed-time, " said Jack. "I wonder if we are to go ondropping into the depths of nowhere all night. "

At that moment the professor entered the room where the boys were. Heseemed quite pleased over something, and was smiling. 

"Everything is going along famously, " he said. "I have just tested theair and find it is rich in oxygen. We shall suffer nothing on thatscore. The heat too, seems to have decreased. On the whole, everythingfavors us. "

"Are we going on down?" asked Mark. 

"As far as we can, " Mr. Henderson answered. "Let me see how far we arebelow now. "

He went to the gage that indicated the vertical position of the ship. Because of the changed conditions, the craft now sinking below thesurface of the earth instead of rising above it, as was its wont, somecalculations were necessary. These the scientist made as quickly as hecould. 

"We are now ten miles underground!" he exclaimed. "That is doing verywell. My theories are working out. I think we shall land somewherebefore long. "

"I hopes so!" exclaimed Washington coming in at this point. "I'mmighty skeered shootin' down int' this dark hole, and no time-table t'show when we's due t' arrive. "

"We ought to land in a couple of days more, " the professor answered. "Never mind about worrying Washington, I'll take care of you. "

"I hopes so, Perfesser, " the colored man said. "I got a little girlwaitin' for me back in Georgia, an' I'd like t' see her 'fore I gitburned up. "

Accompanied by the professor, the boys made a tour of the ship to seethat all the machinery and apparatus were in working order. Owing tothe changed conditions the negative gravity engine had to be worked atfaster speed than usual, since the downward pull of the earth wasgreater the farther they descended into the interior and they did notwant to fall too swiftly. But this was easily provided for, since theprofessor had made the apparatus capable of standing a great strain. 

The ten miles had become fourteen when the professor, finding thateverything was in good shape, proposed that the boys go to bed. They, did not want to, though they were sleepy, and they feared to miss somestrange sights. 

But when the professor had promised to call them in case anythingunusual developed, they consented to turn in, and Bill and Tom assumedtheir duties, which were light enough, now that the ship was merelyfalling into the immense shaft. 

When Mark turned into his bunk he could not go to sleep at once. Itmay have been the excitement over their new position, or because hehad eaten too hearty a supper, but the fact was he remained awake forsome time. 

While thus tossing restlessly on his bed, wondering what ailed him, hethought he heard a noise in the main apartment out of which thestoreroom opened. He crawled softly from his bed, and looked from hisstateroom door. 

In the light of a shaded electric Mark saw the figure of some oneglide across the floor and take refuge in the room, which ProfessorHenderson always was so particular about. 

"I wonder what or who that was, " reasoned Mark. "There is some mysteryin this. Can the professor have concealed some one on this ship whosepresence he does not want to admit? It certainly looks so. "

Not wanting to awaken the ship's crew, and remembering what Mr. Henderson had said about any one entering the storeroom, Mark wentback to bed, to fall into an uneasy slumber. 

"Breakfast!" called Washington breaking in on a fine dream Jack washaving about being captain of a company of automobile soldiers. "Lastcall for breakfast!"

"Hello! Is it morning?" asked Jack. 

"Not so's you could notice it, " Washington went on. "It's as dark as astack of black cats and another one throwed in. But breakfast is readyjest the same. "

The boys were soon at the table, and learned that nothing ofimportance had occurred during the night. The Mermaid had been keptgoing slowly down, and about seven o'clock registered more than fiftymiles below the earth's surface. 

Still there was no change in the outward surroundings. It remained asblack as the interior of Egypt when that country was at its darkest. The powerful electrics could not pierce the gloom. The ship wasworking well, and the travelers were very comfortable. 

Down, down, down, went the Mermaid. The temperature, which had risento about ninety went back to sixty-nine, and there seemed to be nomore danger from the inner fires. 

They were now a hundred miles under the surface. But still theprofessor kept the Mermaid sinking. Every now and again he would takean observation, but only found the impenetrable darkness surroundedthem. 

"We must arrive somewhere, soon, " he muttered. 

It was about six o'clock that night that the alarm bell set up asudden ringing. The professor who was making some calculations on apiece of paper jumped to his feet, and so did a number of the others. 

"We are nearing the bottom!" he cried. "The bell has given uswarning!"

 CHAPTER XV

 IN THE STRANGE DRAUGHT

THE boys ran to attend to the engines and apparatus to which they hadbeen assigned in view of this emergency. The professor, Washington, Bill, Tom and Andy, who had kept to themselves since the descent, camerunning out of the small cabin where they usually sat, and wanted toknow what it was all about. 

"We may hit something, in spite of all precautions, " Mr. Hendersonremarked. "Slow down the ship. "

The Mermaid was, accordingly checked in her downward flight, by aliberal use of the gas and the negative gravity machine. 

The bell continued to ring, and the dials pointed to the mark thatindicated the ship was more than one hundred and fifty miles down. 

Mark, who had run to the engine room to check the descent, came back. 

"Why didn't you slow her down?" asked the professor. 

"I did, " replied the boy. "The negative gravity and the gas machinesare working at full speed. "

"Then why are we still descending?" asked the scientist. "For a whileour speed was checked, but now we are falling faster than before. "

"I attended to the apparatus, " Mark insisted. 

Just then, from without the ship, came a terrible roaring sound, asthough there was a great cyclone in progress. At the same time, thoseaboard the craft could feel themselves being pulled downward withterrific force. 

"We are caught in a draught!" Mr. Henderson cried. "We are beingsucked down into the depths of the earth!"

He ran to the engine room. With the help of the boys he set in motionan auxiliary gravity machine, designed to exert a most powerfulinfluence against the downward pull of the earth. As they watched thegreat wheels spin around, and heard the hum and whirr of the dynamos, the boys watched the pointer which indicated how low they weregetting. 

And, as they watched, they saw that the needle of the dial keptmoving, moving, moving. 

"Our efforts are useless! We can't stop!" the professor cried. 

Grave indeed was the plight of the adventurers. In their ship theywere being sucked down into unknown regions and all their efforts didnot avail to save them. It was an emergency they could not guardagainst, and which could not have been foreseen. 

"What are to do?" asked Mark. 

"We can only wait, " Mr. Henderson replied. "The terrible suction maycease, or it may carry us to some place of safety. Let us hope for thebest. "

Seeing there was no further use in running the engines in an effort tocheck the downward rush the machines were stopped. Then they waitedfor whatever might happen. 

Now that they seemed in imminent peril Washington was as cool as anyone. He went about putting his kitchen in order and getting ready forthe next meal as if they were sailing comfortably along on the surfaceof the ocean. As for old Andy he was nervous and frightened, andplainly showed it. With his gun in readiness he paced back and forthas if on the lookout for strange beasts or birds. 

Bill and Tom were so alarmed that they were of little use in doinganything, and they were not disturbed in their staterooms where theywent when it became known that the ship was unmanageable. 

The boys and the professor, while greatly frightened at the unexpectedturn of events, decided there was no use in giving way to foolishalarm. They realized they could do nothing but await developments. 

At the same time they took every precaution. They piled all thebedding on the floor of the living room, so that the pillows andmattresses might form a sort of pad in case the ship was dashed downon the bottom of the big hole. 

"Not that it would save us much, " Jack observed with a grim smile, "but somehow it sort of makes your mind easier. "

All this while the ship was being sucked down at a swift pace. Thepointer of the gage, indicating the depth, kept moving around and soonthey were several hundreds of miles below the surface of the earth. 

The professor tried, by means of several instruments, to discover inwhich direction they were headed, and whether they were going straightdown or at an angle. But some strange influence seemed to affect thegages and other pieces of apparatus, for the pointers and hands wouldswing in all directions, at one time indicating that they were goingdown, and, again, upward. 

"There must be a strong current of electricity here, " Mr. Hendersonsaid, "or else there is, as many suspect, a powerful magnet at thecenter of the earth, which we are nearing. "

"What will you do if the ship is pulled apart, or falls and issmashed?" asked Mark with much anxiety. 

"You take a cheerful view of things, " said Jack. 

"Well, it's a good thing to prepare for emergencies, " Mark added. 

"If the ship was to be separated by the magnetic pull, or if it fellon sharp rocks and was split in twain, I am afraid none of us could doanything to save ourselves, " the professor answered. "Still, if wewere given a little warning of the disaster, I have means at handwhereby we might escape with our lives. But it would be a perilous wayof----"

"I reckon yo' all better come out an' have supper, " broke inWashington. "Leastways we'll call it supper, though I don't rightlyknow whether it's night or mornin'. Anyhow I've got a meal ready. "

"I don't suppose any of us feel much like eating, " observed Mr. Henderson, "but there is no telling when we will have the chanceagain, so, perhaps, we had better take advantage of it. "

For a while they ate in silence, finding that they had betterappetites than they at first thought. Old Andy in particular did fulljustice to the food Washington had prepared. 

"I always found it a good plan to eat as much and as often as youcan, " the hunter remarked. "This is a mighty uncertain world. "

"You started to tell us a little while ago, Professor, " said Mark, "about a plan you had for saving out lives if worst came to worst, andthere was a chance to put it into operation. What is it?"

"I will tell you, " the aged inventor said. "It is something aboutwhich I have kept silent, as I did not want to frighten any of you. Itwas my latest invention, and I had only perfected it when we startedoff on this voyage. Consequently I had no chance to try it. Themachine works in theory, but whether it does in practice is anotherquestion. That is why I say there is a risk. But we may have to takethis risk. I have placed aboard this ship a----"

The professor was interrupted in what he was about to say by a curioustremor that made the whole ship shiver as though it had struck someobstruction. Yet there was no sudden jolt or jar such as would havebeen occasioned by that. 

At the same time Washington, who was out in the kitchen, came runninginto the dining room, crying:

"We're droppin' into a ragin' fire, Perfesser!"

"What do you mean?" asked Mr. Henderson. 

"I jest took a look down through th' hole in th' bottom of the ship!"cried Washington. "It's all flames an' smoke below us!"

"I wonder if it is the end, " the professor muttered in a low voice. 

Followed by the boys, the inventor hastened to the floor-window. Thelights were turned off to enable a better view to be had of what wasbelow them. 

Leaning over the glass protected aperture the boys and the professorsaw, far, far down, a bright light shining. It was as if they weremiles above a whole town of blast furnaces, the stacks of which werebelching forth flames and smoke. The rolling clouds of vapor wereilluminated by a peculiar greenish light, which, at times, turned tored, blue, purple and yellowish hues. 

The effect was weird and beautiful though it was full of terror forthe travelers. It seemed as if they were falling into some terriblepit of fire, for the reflection of what they feared were flames, couldplainly be seen. 

"I wish I'd never come on this terrible voyage!" wailed Washington. "I'd rather freeze to death than be burned up. "

"Washington, be quiet!" commanded the professor sternly. "This is notime for foolishness. We must work hard to save our lives, for we arein dire peril. 

"Mark, you and Washington, with Jack, start the engines. Turn on everybit of power you can. Fill the gas holder as full as it will hold, anduse extra heavy pressure. I will see if I can not work the negativegravity apparatus to better advantage than we did before. We mustescape if possible!"

The boys, as was also Washington, were only too glad to have somethingto do to take their mind off their troubles. All three were muchfrightened, but Mark and Jack tried not to show it. As for Washingtonhe was almost crying. 

Soon the whirr and hum of the machinery in the Mermaid was heard. Thecraft, which was rushing in some direction, either downward, ahead orbackwards within the unknown depths, shivered from the speed of thedynamos and other apparatus. Soon the boys could hear the professorstarting the negative gravity engine, and then began a strugglebetween the forces of nature and those of mankind. 

Once more the adventurers anxiously watched the gages and indicators. For a while the ship seemed to be holding out against the terribleinfluence that was sucking her down. She appeared to hesitate. Then, as the downward force triumphed over the mechanical energy in thecraft, she began to settle again, and soon was descending, if that wasthe direction, as fast as before. 

"It is of no use, " said the professor with a groan. "I must try ourlast resort!"

He started from the engine room where Mark and Jack had gone. As hedid so, he glanced at a thermometer hanging on the wall near the door. 

"Has any one turned on the heat?" he asked. 

"It's shut off, " replied Mark, looking at the electric stove. 

"Then what makes it so hot?" asked the scientist. 

He pointed to the little silvery column in the tiny tube of theinstrument. It registered close to one hundred degrees, though a fewminutes before it had been but sixty. And the starting of themachinery could not account for the rise in temperature, since most ofthe apparatus was run by electricity and developed little heat save inthe immediate proximity. The thermometer was fully ten feet away fromany machine. 

"It's the fiery furnace that's doing it!" cried Washington. "We'refalling into th' terrible pit an' we're goin' t' be roasted alive!"

"It certainly is getting warmer, " observed Mark, as he took off hiscoat. Soon he had to shed his vest, and Jack and the professorfollowed his example. The others too, also found all superfluousgarments a burden, and, in a little while they were going about inscanty attire. 

Still the heat increased, until it was almost torture to remain in theengine room. Nor was it much cooler elsewhere. In vain did theprofessor set a score of big electric fans to whirring. He even placedcakes of ice, from the small ice machine that was carried, in front ofthe revolving blades, to cool off the air. But the ice was meltedalmost as soon as it was taken from the apparatus. 

"Them flames is gittin' worser!" Washington cried a little later. "We's comin' nearer!"

From the bottom window the professor and the boys looked down. Trueenough the curious, changing, vari-colored lights seemed brighter. They could almost see the tongues of flame shooting upward inanticipation of what they were soon to devour. 

The heat was increasing every minute. The sides of the ship were hot. The heads of the travelers were getting dizzy. They could hardly talkor move about. 

"I must save our lives! I must trust to the----" The professor, whowas muttering to himself started toward the storeroom. As in a dreamMark watched him. He remembered afterward that he had speculated onwhat might be the outcome of the mystery the professor threw about theplace. "I will have to use it, " he heard the scientist say softly. 

Just as Mr. Henderson was about to open the door there came a fiercerblast of heat than any that had preceded. At the same instant theconditions in the Mermaid became so fearful that each of the travelersfelt himself fainting away. 

"Go to-- storeroom-- get cylinder-- get in----" the professormurmured, and then he fell forward in a faint. 

 CHAPTER XVI

 THE NEW LAND

"WHAT is it? Tell us!" exclaimed Jack, almost in his last breath, for, a few seconds later he too toppled over senseless. Then Washingtonwent down, while Andy, Bill and Tom succumbed to the terrible heat. 

Mark felt his head swimming. His eyes were almost bulging from theirsockets. He dimly remembered trying to force himself to go to thestoreroom and see what was there. He started toward it with thatintention, but fell half way to it. 

As he did so he saw something which impressed itself on his mind, halfunconscious as he was. 

The door of the storeroom suddenly opened, and from it came a giantshape, that seemed to expand until it filled the whole of theapartment where the stricken ones lay. It was like the form of somemonster, half human, half beast. Mark shuddered, and then, closing hiseyes, he felt himself sinking down into some terrible deep and blackpit. A second later the whole ship was jarred as though it had hitsomething. 

How long he and the others remained unconscious Mark did not know. Hewas the first to revive, and his first sensation was one as though hehad slept hard and long, and did not want to get up. He felt verycomfortable, although he was lying flat on the floor, with his headjammed against the side of a locker. It was so dark that he could notdistinguish his hand held close to his face. 

"I wonder if I'm dead, and if all the others are dead too, " he thoughtto himself. "What has happened? Let's see, the last I remember wassome horrible shape rushing from the storeroom. I wonder what it couldhave been? Surely that was not the secret the professor referred to. "

Mark shuddered as he recalled the monster that seemed to have grownmore terrible as each second passed. Then the boy raised himself upfrom his prostrate position. 

"Well, at any rate, some one has turned off the heat, " he murmured. "It's very comfortable in here now. I wish I could strike a light. "

He listened intently, to learn if any of the others were moving about. He could hear them breathing, but so faintly as to indicate they wereinsensible. Mark stretched out his hand and felt that some one waslying close to him, but who of the adventurers it was he could notdetermine. 

"If only the dynamo was working we could have light, " he said. "But itseems to have stopped, " and, indeed there was a lacking of thefamiliar purr and hum of the electrical machine. In fact none of theapparatus in the ship was working. 

"The storage battery!" exclaimed Mark. "That would give light for awhile, if I can only find the switch in the dark. "

He began crawling about on his hands and knees. It was so intenselyblack that he ran into many things and received severe bruises. Atlast he came to a doorway, and as he did so his hand came in contactwith an easy chair. It was the only one aboard, and by that he knew hehad passed into the sitting room. He had his general direction now, and knew if he kept straight on he would come to the engine room. There he was familiar enough with the apparatus and levers to be ableto turn the electric switch. 

Crawling slowly and cautiously, he reached the room where all theengines were. Then he had to feel around the sides to locate theswitch. At length he found it. There was a click, a little flash ofgreenish fire, and the copper conductors came together, and the shipwas flooded with the glow from the incandescents. 

Mark hurried back to where the others were lying. They were stillunconscious, but an uneasy, movement on the part of Jack told that hewas coming out of the stupor. Mark got some ammonia and held itbeneath his comrade's nose. The strong fumes completed the work thatnature had started and Jack opened his eyes. 

"Where am I? What has happened? Are any of them dead?" he askedquickly. 

"I hope no one is dead, " Mark replied. "As to the other question, Ican't answer. I don't know whether we are a thousand milesunderground, or floating on the ocean, though I'm more inclined to theformer theory. But never mind that now. Help me to bring the othersback to their senses. I'll work on the professor and you can begin onBill or Tom. Washington seems to be all right, " for at that moment thecolored man opened his eyes, stared about him and then got up. 

"I thought I was dead for suah!" he exclaimed. 

"Some of the others may be if we don't hurry, " said Mark. "Get towork, Wash!"

With the colored man to help them the two boys, by the use of theammonia, succeeded in reviving Bill, Tom and old Andy. But theprofessor, probably on account of his advanced age, did not respond soreadily to the treatment. The boys were getting quite alarmed, as evensome of the diluted ammonia, forced between his lips, did not causehim to open his eyes, or increase his heart action. 

"If he should die, and leave us all alone with the ship in thisterrible place, what would we do?" asked Jack. 

"He's not going to die!" exclaimed Mark. "Here I have another plan. Washington bring that medical electrical battery from the engineroom. " This was a small machine the professor had brought along forexperimental purposes. 

Quickly adjusting it, Mark placed the handles in the nerveless fingersof Mr. Henderson. Then he started the current. In about a minute theeyelids of the aged inventor began to quiver, and, in less than fiveminutes he had been revived sufficiently to enable him to sit up. Hepassed his hand across his forehead. 

"What has happened?" he asked in a faint voice. 

"I don't know; none of us knows, " Mark answered. "We all lost oursenses when it got so hot, and there seemed to be some peculiar vaporin the air. The last I remember was seeing some horrible shape rushfrom the storeroom, soon after the ship struck. Then I fainted away. When I woke up I managed to turn the lights on, and then I came backhere. "

"I wonder where we are, " the old man murmured. "I must find out. Wemust take every precaution. Washington, go and look at the gageindicating our depth. "

The colored man was gone but a few seconds. When he returned his eyeswere bulging in terror. 

"What is it?" asked Mr. Henderson, who, thanks to the battery, hadalmost completely recovered. 

"It ain't possible!" gasped Washington. "I'll never believe it!"

"What is it?" asked Mr. Henderson, while the others waited in anxietyfor the answer. 

"We're five hundred miles down!" declared Washington. 

"Five hundred miles!" muttered the inventor. "It does not seempossible, but it must be so. We fell very rapidly and the terribledraught sucked us down with incredible rapidity. But come, we must seewhat our situation is, and where we are. We are stationary, and areevidently on some solid substance. "

They all felt much recovered now, and, as the terrible fright of beingconsumed in a fiery furnace had passed, they all were in betterspirits. 

At the suggestion of the professor, the boys and Washington made atour of the ship. They found, for some unaccountable reason, thatnearly all the engines and apparatuses were out of gear. In some theparts had broken, and others were merely stopped, from the failure ofsome other machine, on which they were dependent. 

"I'm afraid this is the end of the Mermaid, " said Mark, in a sorrowfultone. 

"Nonsense!" replied Jack, who was of a more cheerful nature. "Thingsare not so bad as they look. The professor can fix everything. "

"I'm sure I hope so, " Mark went on, not much encouraged, however, byJack's philosophy. "It would be no joke to have to stay five hundredmiles underground the rest of our lives. "

"You don't know, " retorted Jack. "Don't judge of a country you'venever seen. This may be as fine a place as it is on the surface of theearth. I want a chance to see it, " and Jack began to whistle acheerful tune. 

They completed the tour of the ship, and found, that, aside from thedamage to the machinery, the Mermaid had not sustained any harm. Thehull was in good order, though of course they could not tell about thegas holder. It was not possible to see this except by going into theconning tower or out on the small deck, and this they did not ventureto do. The connections between the holder and the main ship seemed tobe all right, and there was still a small quantity of gas in the bigtank, as Mark found on opening a stop-cock. 

They went back to the professor and told him what they had observed. He seemed somewhat alarmed, the more so as the experience he had justpassed through had weakened him considerably. 

"I hope I shall be able to make the repairs, " he said. "It is our onlyhope. "

As he spoke he looked up at the electric lights that shone overheadfrom wall brackets. 

"Who is shutting down the power?" he asked. 

"There is no power on, Professor, " replied Mark. "I am running thelights from the storage battery. But something is the matter, for theyare growing dim. "

The filaments were now mere dull red wires, and the ship was beingshrouded in gloom again. 

"The battery is failing!" exclaimed Mr. Henderson. "We shall be leftin darkness, and there is no other way to produce light. I ought tohave brought some lamps or candles along in case of emergency, "

The next instant the Mermaid became as black as Egypt is popularlysupposed to be, and something like an exclamation of terror came fromthe professor. 

For several minutes they all sat there in the blackness and gloom, waiting for they knew not what. Then, suddenly, there soundedthroughout the ship, a creaking as of metal sliding along metal. Somebig lever creaked, and, a second later the whole place was floodedwith light. 

"What has happened?" cried the professor, starting to his feet inalarm. 

"We are going to be burned up!" exclaimed old Andy. 

"It's all right! It's all right!" yelled Washington from the engineroom where the boys had left him. "Don't git skeered! I done it! Iopened the port holes, by yanking on the lever. Golly, but we'sarrived at the new land! Look out, everybody!"

 CHAPTER XVII

 A STRANGE COUNTRY

THEY all ran to the port holes, which were openings in the side of theship. They were fitted with thick, double glass, and covered on theoutside with steel shutters. These shutters were worked by a singlelever from the engine room, so that one person could open or closethem in a second or two. Washington, by accident, it appeared later, had slid back the protecting pieces of steel, and the rest followed. 

As the adventurers looked from the glass ports they saw that the lightwhich had flooded the ship came from without. They were in the midstof a beautiful glow, which seemed to be diffused about them like raysfrom a sun. 

Only, in place of being a yellow or white light, such as the sun givesoff at varying times, the glow was of violet hue. And, as theywatched, they saw the light change color, becoming a beautiful red, then blue, and again green. 

"Well, this is certainly remarkable!" the professor said. "I wonderwhat causes that. "

"We've arrived! We're here, anyhow!" Washington cried, coming into theroom. "See the country!"

Then, for the first time, the travelers, taking their attention fromthe curious light that was all around them, saw that they had indeedarrived. They were on a vast plain, one, seemingly, boundless inextent, though off to the left there was a range of lofty mountains, while to the right there was the glimmer of what might be a big lakeor inland sea. 

"See, we are resting on the ground!" exclaimed Jack. He pointed out ofthe window, and the others, looking close at hand, noted that theMermaid had settled down in the midst of what seemed to be a field offlowers. Big red and yellow blossoms were all in front, and some grewso tall as to almost be up to the edge of the port. 

"I wonder if we can be seeing aright, " the professor muttered. "Isthis really the interior of the earth; such a beautiful place asthis?"

There could be little doubt of it. The ship had descended through thebig shaft, had been sucked down by the terrible air current, and hadreally landed in a strange country. 

Of its size, shape and general conditions the adventurers, as yet, could but guess. They could see it was a pleasant place, and one wherethere might be the means to sustain life. For, as the professor saidafterward, he felt that where there were flowers there would befruits, and where both of these provisions of nature were to be foundthere would likely be animal life, and even, perhaps, human beings. 

But, for the time, they were content to look from the port on thebeautiful scene that lay stretched out before them. The ship rested onan even keel and had landed so softly that none of the plates werestrained. 

"We have plenty of air, at all events, " said the professor as he tooka deep breath. "I was afraid of that, but it seems there was no need. The air appears to be as good and fresh as that on the surface of theearth, only there is a curious property to it. It makes one feellarger. I imagine it must be thinner than the air of the earth, whichis a rather strange thing, since the higher one goes the more rarefiedthe air becomes, and the lower, the more dense. Still we can not applynatural philosophy to conditions under the earth. All the usualtheories may be upset. However, we should be content to take things aswe find them, and be glad we were not dashed to pieces when the shipwas caught in the terrible current. "

"What do you suppose caused the awful heat, and then made it go awayagain?" asked Jack. 

"I can only make a guess at it, " Mr. Henderson answered. "There aremany strange things we will come across if we stay here long, Ibelieve. As for the fire I think we must have passed a sort ofinterior volcano. "

"But what sort of a place do you think we have come to, Professor?"asked Mark. 

"It is hard to say, " the scientist replied. "We are certainlysomewhere within the earth. Our gage tells us it is five hundredmiles. That may or may not be correct, but I believe we are severalhundred miles under the crust, at all events. As to what sort of aplace it is, you can see for yourselves. "

"But how is it we can breathe here, and things can grow?" asked Bill, who was beginning to lose his fright at the thought of beingpractically buried alive. 

"I do not know what makes such things possible, " Mr. Hendersonreplied, "but that there is air here is a certainty. I can hardlybelieve it is drawn from the surface of the earth, down the big hole, and I am inclined to think this place of the under-world has anatmosphere of its own, and one which produces different effects thandoes our own. "

"They certainly have larger flowers than we have, " said Mark. "See howbig they grow, and what strong colors they have. "

He pointed to the port, against which some of the blooms were noddingin the wind that had sprung up, for, in spite of the many differences, the under-world was in some respects like the upper one. 

"Probably the difference in the atmosphere accounts for that, " theprofessor said. "It enables things to grow larger. And, by the way, Mark, that reminds me of something you said about seeing some horriblemonster fleeing from the ship. Did you dream that?"

"I did see something horrible, Professor, " he answered. "I'm notpositive what it was, but I'll tell you as nearly as I can what it waslike. "

Thereupon Mark detailed what he had seen. 

"But how could anything, least of all some big monster, be concealedin the storeroom, and we not know anything about it?" asked Mr. Henderson. 

"I thought you did know something of it, " replied Mark. 

"Who, me? My dear boy, you must be dreaming again. Why should I wantto conceal any being in the storeroom? Come, there is something backof this. Tell me all you know of it. I can't imagine why you think Iwas hiding something in the apartment. "

"I thought so because you were always so anxious not to have me gonear it, " answered the boy. "Don't you remember when you saw me goingtoward it, several times, you warned me away?"

"So I did!" exclaimed Mr. Henderson, a light breaking over his face. "But, Mark, it was not because I had hidden some human being or animalthere. I can't tell you what it is yet, save that I can say it ismerely a machine of mine that I have invented. For reasons of my own Idon't want any one to see it yet. Perhaps it may never be seen. Ithought, not long ago, that we might have to undertake a terrible riskin escaping from this place. I directed you to go to the storeroom--but there, I can't say any more, my friends. Sufficient that I hadnothing in the animal line concealed there. "

"But I am certain there was some beast or human being in there, "insisted Mark. "I heard curious noises in there. Besides, how do youaccount for the food disappearing and the door being open at times?"

"It might have been rats, " said Jack. 

"I don't believe there are rats in the ship, " put in the professor. "More likely it was one of us who got up hungry and took thevictuals. "

"I'm sorry I can't agree with you, " Mark added respectfully. "I amsure some strange being was on board this ship, and I believe it hasnow escaped. Who or what it was I can't say, but you'll find I'mright, some day. "

"All right, " spoke Mr. Henderson with a laugh. "I like to see any onebrave enough to stick up for his opinion, but, at the same time, Ican't very well imagine any person or thing being concealed in thatstoreroom ever since we started. How could it get in?"

Mark did not; answer, but there came to him the recollection of thatnight, previous to the sailing of the Flying Mermaid, when he hadobserved some strange shadow that seemed to glide aboard the craft. 

"Now let's forget all about such things, " the professor went on. "Weare in a strange country, and there are many things to see and do. Let's explore a little. Then we must see what we can do with the ship. We are dependent on it, and it will not do to allow it to remain in adamaged state. We expect to travel many miles in the interior of theearth if it is possible, and we have only our craft to go in. "

"I reckon we'd all better assimilate into our interior progressionsome molecules and atoms of partly disentegrated matter in order tosupply combustion for the carbonaceous elements and assist in themanufacture of red corpuscles, " said Washington, appearing in thedoor, with a broad grin on his good-natured face. 

"Which, being interpreted, " the professor said, "means, I suppose, that we had better eat something to keep our digestive apparatus ingood working order?"

"Yo' done guessed it!" exclaimed the colored man, relapsing into hisordinary speech. "I'se got a meal all ready. "

They agreed that they might not have another opportunity soon topartake of food, so they all gathered about the table, on whichWashington had spread a good meal. 

"Come on, let's go outside and view this new and strange land atcloser quarters, " the professor said, when they had satisfied theirappetites. "We can't see much from inside the ship. "

Accordingly the heavy door in the side of the Mermaid was slid back, and, for the first time the travelers stepped out on the surface ofthe land in the interior of the earth. 

At first it seemed no different than the ordinary land to which theywere accustomed. But they soon found it had many strange attributes. The queer shifting and changing light, with the myriad of hues was oneof them, but to this the adventurers had, by this time, becomeaccustomed, though it was, none the less, a marvel to them. It was oddenough to see the landscape blood red one instant, and a pale greenthe next, as it does when you look through differently coloredglasses. 

Then, too, they noticed that the grass and flowers grew much moreabundantly than in the outer part of the world. They saw clover sixfeet high, and blades of grass even taller. In some places the growthof grass was so big that they were in danger of getting lost in it. 

"If the grass is like this, what will the trees be?" asked Mark. 

"There are some away over there, " Jack replied. "We'll have to take asail over. They must be several hundred feet high. "

"Well, at any rate, here's a little brook, and the water looks good todrink, " went on Mark. "I'm thirsty, so here goes. "

He hurried to where a stream was flowing sluggishly between grassybanks. The water was as clear as crystal, and Mark got down on hisface and prepared to sip some of the liquid up. 

But, no sooner had his lips touched it, than he sprang up with a cryand stood gazing at the water. 

"What's the matter?" asked Jack. "Hot?"

"No, it isn't hot, " Mark replied, "but it isn't water. It's whitemolasses!"

"White molasses?" repeated the professor, coming up at that moment. "What are you talking about?"

He stooped down and dipped his finger into the stream. He drew it upquickly, and there ran from it big drops that flowed as slowly as theextract of the sugarcane does in cold weather. 

"You're about right, Mark, " he said. "It's water but it's almost asthick as molasses. " He touched his finger to his tongue. "It's good todrink, all right, " he went on, "only it will be a little slow goingdown. "

Then he dipped up a palm full, and let it trickle down his throat. 

"It is the strangest water I ever saw, " he added. "It must be that thelack of some peculiar property of air, which we have on the surface, has caused this. I must make some notes on it, " and he drew out penciland paper. He was about to jot down some facts when he was interruptedby a cry from Washington. 

"Come and see what's the matter with this stone!" he cried. 

 CHAPTER XVIII

 CAUGHT BY A STRANGE PLANT

"WASHINGTON is in trouble!" exclaimed Mr. Henderson. Followed by thetwo boys he ran to where the colored man stood in a stooping positionover a small pile of stones. 

"What is it? Has something bit you?" asked the scientist, as he cameup on the run. 

"No, but I can't git this stone up!" Washington said. "Look at what alittle stone it is, but I can't lift it. Something must have happenedto me. Maybe some one put th' evil eye on me! Maybe I'm bewitched!"

"Nonsense!" exclaimed the professor, "what did you want the stonefor?"

"Nothin' in particular, " replied Washington, still tugging away at thestone, which was the size of his head. "I was just goin' t' throw itat a big bird, but when I went to lift it this little stone 'peared t'be glued fast. "

Washington moved aside to give Mr. Henderson a chance to try to pickup the piece of rock. As the scientist grasped it a look of surprisecame over his features:

"This is most remarkable!" he exclaimed. "I can't budge it. I wonderif a giant magnet is holding it down. "

He tugged and tugged until he was red in the face. Then he beckoned tothe two boys, and they came to his aid. There was barely room for themall to each get one hand on the rock, and then, only after a powerfultug did it come up. Almost instantly it dropped back to the earth. 

"This is remarkable!" the professor said. "I wonder if the otherstones are the same. "

He tried several others, and one and all resisted his efforts. It wasonly the small stones he was able to lift alone, and these, he said, were so weighty that it would have been a task to throw them anydistance. 

"The water and the stones are strangely heavy in this land, " he said. "I wonder what other queer things we shall see. "

"I saw a bird a little while ago, when I went to pick up that stone, "observed Washington. 

"What kind was it?" asked the inventor. 

"I don't know, only it was about as big as an eagle. "

The travelers wandered about a quarter of a mile from the ship. Theyavoided the tall grass and the lofty nodding flowers that seemed togrow in regular groves, and kept to places where they could walk withcomparative freedom. 

"Have you formed any idea, Professor, as to the nature of thiscountry?" asked Mark, who liked to get at the bottom of things. 

"I have, but it is only a theory, " Mr. Henderson answered. "I believewe are on a sort of small earth that is inside the larger one we liveon. This sphere floats in space, just as our earth does, and we havepassed through the void that lies between our globe and this interiorone. I think this new earth is about a quarter the size of ours and insome respects the same. In others it is vastly different. 

"But we will not think of those things now. We must see what oursituation is, whether we are in any danger, and must look to repairingour ship. There will be time enough for other matters later. "

The travelers were walking slowly along, noting the strange things onevery side. As they advanced the vegetation seemed to become moreluxuriant, as if nature had tried to out-do herself in providingbeautiful flowers and plants. The changing lights added to the beautyand weirdness of the scene. 

The plain was a rolling one, and here and there were small hills andhollows. As the travelers topped a rise Jack, who was in advance, called out:

"Oh what queer plants! They are giant Jacks-in-the-pulpit!"

The others hastened forward to see what the boy had discovered. Jackwas too eager to wait, and pressed on. The hill which sloped away fromthe top of the little plateau on which he stood, was steeper than hehad counted on. As he leaned forward he lost his balance and toppled, head foremost, down the declivity, rolling over. 

"Look out!" cried Mark, who had almost reached his comrade's side. 

The scene that confronted the travelers was a strange one. Before themin a sort of hollow, were scores of big plants, shaped somewhat like aJack-in-the-pulpit, or a big lily, with a curved top or flap to it. 

The plants were about eight feet tall, three feet across the top, andthe flap or covering was raised about two feet. They were nodding andswaying in the wind on their short stems. 

"He's headed right for one of them!" Mr. Henderson exclaimed. "I hopehe'll not fall into one of the openings. "

"Is there any danger?" asked Mark. 

"I'm afraid there is, " the inventor added. "Those plants are a varietyof the well-known pitcher plant, or fly-trap, as they are sometimescalled. In tropical countries they grow to a large size, but nothinglike these. They are filled, in the cup, with a sort of sticky, sweetmixture, and this attracts insects. When one enters the cup the topflap folds over, and the hapless insect is caught there. The plantactually devours it, nature providing a sort of vegetable digestiveapparatus. These giant plants are the same, and they seem large enoughto take in a man, to say nothing of Jack!"

With anxious faces the adventurers turned to watch the fate of theircomrade. Jack was slipping, sliding and rolling down the hill. Hecould not seem to stop, though he was making desperate efforts to doso. He was headed straight for one of the largest of the terribleplants. 

In vain, as he saw what was in front of him, did he try to change thecourse of his involuntary voyage. Over and over he rolled, until, atlength, he struck a little grassy hummock, bounced into the air, andright into the opening of a monster pitcher plant. 

"It has him!" cried Mark. "We must save him! Come on everyone!"

He raced down the hill, while the others came closely after him. Theyreached the plant into which Jack had bounced. The flap, or top piece, had closed down, tightly over the unfortunate boy. 

"Quick! We must save him or he will be smothered to death or drownedin the liquid the cup contains!" Mr. Henderson exclaimed. "Attack theplant with anything you can find!"

"Let's cut through the side of the flower-cup!" suggested Mark. "Thatseems softer than the stem. "

His idea was quickly put into operation. Andy's long hunting knifecame in very handy. While the sides of the long natural cup weretough, the knife made an impression on them, and, soon, a small dooror opening had been cut in the side of the pitcher plant, large enoughto enable a human body to pass through. 

When the last fibre had been severed by Andy, who was chosen to wieldthe knife because of his long practice as a hunter, there was a suddencommotion within the plant. Then a dark object, dripping water, made aspring and landed almost at the feet of the professor. 

It was Jack, and a sorry sight he presented. He was covered from headto foot with some sticky substance, which dripped from all over him. 

With hasty movements he cleared the stuff from his eyes and mouth, andspluttered:

"It's a good thing you cut me out when you did. I couldn't have heldon much longer!"

 CHAPTER XIX

 THE BIG PEACH

JACK soon recovered from his remarkable experience. The terrible plantthat had nearly eaten him alive was a mass of cut-up vegetable matterwhich attracted a swarm of insects. Most of them were ants, but suchlarge ones the boys had never seen before, and the professor said theyexceeded in size anything he had read about. Some of them were aslarge as big rats. They bit off large pieces of the fallen plant andcarried them to holes in the ground which were big enough forWashington to slip his foot into, and he wore a No. 11 shoe. 

But the adventurers felt there were more important things for them tolook at than ants, so they started away again, the professor tellingthem all to be careful and avoid accidents. 

It was while they were strolling through a little glade, which theycame upon unexpectedly, that Washington, who was in the lead calledout:

"Gracious goodness! It must be Thanksgivin'!"

"Why so?" asked Jack. 

"'Cause here's th' remarkablest extraordinary and expansionist of apumpkin that ever I laid eyes on!" the colored man cried. 

They all hurried to where Washington had come to a halt. There, on theground in front of him, was a big round object, about the size of ahogshead. It was yellow in color, and was not unlike the goldenvegetable from which mothers make such delicious pies. 

"I allers was fond of pumpkins, " said Washington, placing his hand onthe thing, which was almost as tall as he was, "but I never thoughtI'd come across such a one as this. "

The professor and the two boys went closer to the monstrosity. Mr. Henderson passed his hand over it and then, bending closer, smelled ofit. 

"That's not a pumpkin!" he exclaimed. 

"What is it then?" asked Washington. 

"It's a giant peach, " the inventor remarked. "Can't you see the fuzz, and smell it? Of course it's a peach. "

"Well I'll be horn-swoggled!" cried Washington, leaning against thebig fruit, which easily, supported him. 

"Hurrah!" cried Jack, drawing his knife from his pocket and openingthe largest blade. "I always did like peaches. Now I can have all Iwant, " and he drove the steel into the object, cutting off a big slicewhich he began to eat. 

"It may be poisonous!" exclaimed Mark. 

"Too late now, " responded Jack, the juice running down from his mouth. "Taste's good, anyhow. "

They all watched Jack while he devoured his slice of fruit. Washingtonacted as if he expected his friend to topple over unconscious, butJack showed no bad symptoms. 

"You'd better all have some, " the boy said. "It's the best I evertasted. "

Encouraged by Jack's example, Mark thought he, too, would have some ofthe fruit. He opened his knife and was about to take off some of thepeach when suddenly the thing began to roll forward, almost upon him. 

"Hi! Stop your shoving!" he exclaimed. "Do you want to have the thingroll over me, Jack?"

"I'm not shoving!" replied Jack. 

"Some one is!" Mark went on. He dodged around the far side of theimmense fruit and what he saw made him cry out in astonishment. 

Two grasshoppers, each one standing about three feet high, werestanding on their hind legs, and with their fore feet were pushing thepeach along the ground. They had been attracted to the fruit by somejuice which escaped from a bruise on that side, which was the ripest, and, being fond of sweets had, evidently decided to take their find tosome safe place where they could eat it at their leisure. Or perhapsthey wanted to provide for their families if grasshoppers have them. 

"Did you ever see such monsters?" asked Jack. "They're as big asdogs!"

At the sound of his voice the two grasshoppers, becoming alarmed, ceased their endeavors to roll the peach along, and, assuming acrouching attitude seemed to be waiting. 

"They certainly are remarkable specimens, " Mr. Henderson said. "If theother animals are in proportion, and if there are persons in this newworld, we are likely to have a hard time of it. "

This time the immense insects concluded the strangers were not totheir liking. With a snapping of their big muscular legs and a whirrof their wings that was like the starting of an automobile, thegrasshoppers rose into the air and sailed away over the heads of theadventurers. Their flight was more than an eighth of a mile in extent, and they came down in a patch of the very tall grass. 

"Let's go after them!" exclaimed old Andy. "I was so excited I forgotto take a shot at them. Come on!"

"I think we'd better not, " counseled the professor. "In the firstplace we don't need them. They would be no good for food. Then wedon't know but what they might attack us, and it would be no joke tobe bitten by a grasshopper of that size. Let them alone. We may findother game which will need your attention, Andy. Better save yourammunition. "

Somewhat against his will, Andy had to submit to the professor'sruling. The old hunter consoled himself with the reflection that ifinsects grew to that size he would have some excellent sport huntingeven the birds of the inner world. 

"I wonder what sort of a tree that peach grew on, " Jack remarked, ashe cut off another slice, when the excitement caused by the discoveryof the grasshoppers had subsided. "It must be taller than a churchsteeple. I wonder how the fruit got here, for there are no treesaround. "

"I fancy those insects rolled it along for a good distance, " Mr. Henderson put in. "You can see the marks on the ground, where theypushed it. They are wonderful creatures. "

"Are we going any farther?" asked Mark. "Perhaps we can find the peachtree, and, likely there are other fruit trees near it. "

At the professor's suggestion they strolled along for some distance. They were now about three miles from the airship, and found that whatthey had supposed was a rather level plain, was becoming a successionof hills and hollows. It was while descending into a rather deepvalley that Jack pointed ahead and exclaimed:

"I guess there's our peach orchard, but I never saw one like itbefore. "

Nor had any of the others. Instead of trees the peaches were attachedto vines growing along the ground. They covered a large part of thevalley, and the peaches, some bigger than the one they firstdiscovered, some small and green, rose up amid the vines, just aspumpkins do in a corn field. 

"Stranger and stranger, " the professor murmured. "Peaches grow onvines. I suppose potatoes will grow on trees. Everything seems to bereversed here. "

They made their way down toward the peach "orchard" as Jack called it, though "patch" would have been a better name. Besides peaches theyfound plums, apples, and pears growing in the same way, and all of asize proportionate to the first-named fruit. 

"Well, one thing is evident, " Mr. Henderson remarked, "we shall notstarve here. There is plenty to eat, even if we have to turnvegetarians. "

"I wonder what time it is getting to be, " Jack remarked. "My watchsays twelve o'clock but whether it's noon or midnight I can't tell, with this colored light coming and going. I wonder if it ever sets asthe sun does. "

"That is something we'll have to get used to, " the professor said. "But I think we had better go back to the ship now. We have manythings to do to get it in order again. Besides, I am a little afraidto leave it unguarded so long. No telling but what some strangebeast-- or persons, for that matter-- might injure it. "

"I'm going to take back some slices of peaches with me, anyhow, " Marksaid, and he and Jack cut off enough to make several meals, whileBill, Tom and Washington took along all they could carry. 

As they walked back toward the ship the strange lights seemed to bedying out. At first they hardly noticed this, but as they continued onit became quite gloomy, and an odd sort of gloom it was too, firstgreen, then yellow, then red and then blue. 

"I believe whatever serves as a sun down here is setting, " theprofessor observed. "We must hurry. I don't want to be caught out hereafter dark. "

They hurried on, the lights dying out more and more, until, as theycame in sight of their ship, it was so black they could hardly see. 

Mark who was in the rear turned around, glancing behind him. As he didso he caught sight of a gigantic shadow moving along on top of thenearest hill. The shadow was not unlike that of a man in shape, but ofsuch gigantic stature that Mark knew it could be like no human beinghe had ever seen. At the same time it bore a curious resemblance tothe weird shadow he had seen slip into the Mermaid that night beforethey sailed. 

"I wonder if it can be the same-- the same thing-- grown larger, justas the peach grows larger than those in our world, " Mark thought, while a shiver of fear seemed to go over him. "I wonder if that-- thatthing could have been on the ship----"

Then the last rays of light died away and there was total darkness. 

 CHAPTER XX

 OVERHAULING THE SHIP

"KEEP together!" shouted the professor. "It will not do to become lostnow. We are close to the ship, and will soon be there. Come after me. "

It was more by following the sound of the scientist's voice, than byany sight which the others could get of him, that they managed totrail along behind. They reached the ship in safety, however, andentered. There was no sound as of beasts or insects within, and, though Mark felt a little apprehensive on account of what he had seen, he and the others as well, were glad to be again in something thatseemed like home. 

"I wish we had some candles, or some sort of a light to see by, " theprofessor remarked. "We can do nothing in the dark, and there is notelling how long this night is going to last once it has set in. If Icould have a little illumination, I might be able to fix the dynamo, and then we could turn on the incandescents. That portable light wehad is broken. 

"By cracky!" exclaimed Andy. "I believe I have the very thing!"

"You don't mean to say you have a torch or a candle with you, do you?"asked Mr. Henderson. 

"No, but I have my patent pipe lighting apparatus, " the hunter said. "I always carry it. It gives a little light, but not much, though itmay be enough to work by. "

Not until after several hours work, handicapped as they were by lackof light, were the repairs to the ship completed. 

"Now we'll start the engine and see how we will come out, " theinventor exclaimed, as he wiped his hands on some waste. 

It did not take long to generate enough power to turn the dynamo. Soonthe familiar hum and whirr was heard, and, a few seconds later thefilaments in the lamps began to glow a dull red, which graduallybrightened until they were shining in all their usual brilliancy. 

"Hurrah!" cried the boys. "Now we can see!"

They all felt in better spirits with the restoration of the lights, and, washing off the grease and dirt of their labors in the engineroom, they prepared to sit down to the meal which Washington prepared. 

As soon as the dynamo was working well, care had to be taken not tospeed it too much on account of a mended belt. The professor turnedoff part of the lights and switched some of the current into thestorage batteries, to provide for emergencies. For there was notelling how long the night might last. 

Jack was the first one to finish the meal-- they did not know whetherto call it dinner, supper or breakfast. He went into the conningtower, and, as soon as he reached it he called out:

"Come on up here, professor! There's something strange going on!"

Mr. Henderson, followed by Mark, hurried to the tower. As he reachedit and looked out of the forward window, a beautiful white glowilluminated the whole scene, and then, from below the horizon, therearose seven luminous disks. One was in the centre, while about itcircled the other six, like some immense pin-wheel. 

"It's the moon!" cried Mark. 

"It's seven moons!" Jack exclaimed. "Why it's almost as light as day!"

And so it was, for the seven moons, if that is what they were, gave anillumination not unlike the sun in brilliancy though it was like thebeams from the pale moon of the earth. 

"I guess we need not have worried about the darkness, " the professorremarked. "Still it is a good thing I fixed the dynamo. "

For some time he and the other adventurers watched the odd sight ofthe moons, as they rose higher and higher overhead. The scene was abeautiful, if weird one, for the whole plain was bathed in the softlight. 

"I guess we can turn off the incandescents, and use all the power forthe storage batteries, " Mr. Henderson went on, as he descended intothe ship, and opened the port shutters which had been closed when theystarted off on their exploring tour. The interior of the Mermaid wasalmost as light as when the odd colored beams had been playing overthe new earth to which they had come. 

"I think we had better continue with our work of making repairs, " Mr. Henderson said. "We can't count on these moons remaining here anylength of time, and I want to take advantage of them. So though someof us perhaps need sleep, we will forego it and fix up the Mermaid. Iwant to take a trip and see what other wonders await us. "

They all agreed that they would rather work than sleep, and soon theentire force was busy in the engine room. There was much to be done, and the most important things were attended to first. The motive powerwas overhauled and found to be in need of several new parts. Thesewere put in and then the gas generator, and the negative gravitymachine, were put in shape. 

It would have taken something very substantial to have awakened anyone on board the Mermaid that night. They all slept soundly and awoketo find the strange colored lights shining in through the glasscovered port holes. 

"Well, the sun, or what corresponds to it, is up, " observed Jack, "andI guess we had better do as the little boy in the school reader did, and get up, too, Mark. "

Soon all the travelers were aroused, and the sound of Washingtonbustling about in the kitchen, whence came the smell of coffee, baconand eggs, told the hungry ones that breakfast was under way. 

After the meal work was again started on repairing the ship, and bynoon the professor remarked:

"I think we shall try a little flight after dinner. That is, if onething doesn't prevent us. "

"What is that?" asked Jack. 

"We may be held down, as were those stones, " was the grave answer. 

 CHAPTER XXI

 THE FISH THAT WALKED

IT was with no little apprehension that the professor prepared to takehis first flight aboard the ship in the realms of the new world. Heknew little or nothing of the conditions he might meet with, thedensity of the atmosphere, or how the Mermaid would behave underanother environment than that to which she was accustomed. 

Yet he felt it was necessary to make a start. They would have toattempt a flight sooner or later, and Mr. Henderson was not the one todelay matters. So, the last adjustment having been made to therepaired machinery, they all took their places in the ship. 

The boys and the professor went to the conning tower to directmatters, while Washington and the others were in the engine room tosee that the machinery worked properly. Mark gave a last look outsideas he closed the big steel cover over the hole through which admissionwas had to the craft. He thought he might catch a glimpse of the queershadow, but nothing was in sight. It was like a beautiful summer'sday, save for the strange lights, shifting and changing. But thetravelers had become somewhat used to them by this time. 

The professor turned the valve that allowed the gas to enter theholder. There was a hissing sound and a sort of trembling throughoutthe entire ship. The dynamos were whizzing away and the negativegravity machine was all ready to start. 

For several minutes the travelers waited until the big lifting tankwas filled with the strong vapor. They watched the gages whichindicated the pressure to be several hundred pounds. 

"I think we can chance it now, " remarked Mr. Henderson, as he threwover several levers. "We'll try, at any rate. "

With a tremor the Mermaid left the surface of the inner earth and wentsailing upward toward the-- well it wasn't exactly the sky, but it waswhat corresponded to it in the new world, though there were no cloudsand no blue depths such as the boys were used to. At all events theMermaid was flying again, and, as the adventurers felt themselvesbeing lifted up they gave a spontaneous cheer at the success which hadcrowned their efforts. 

The ship went up several hundred feet, and then, the professor, havingbrought her to a stop, sent her ahead at a slow pace. He wanted to besure all the apparatus was in good working order before he tried anyspeed. 

The Mermaid responded readily. Straight as an arrow through the airshe flew. 

"Well, this is almost as good as being on the regular earth!"exclaimed Jack. 

"It's better, " put in Mark. "We haven't seen half the wonders yet. Let's open the floor shutter, and see how it looks down below. "

He and Jack went to the room where there was an opening in the floorof the ship, covered by heavy glass. They slid back the steel shutterand there, down below them, was the strange new, world they had cometo, stretched out like some big map. 

They could see mountains, forests, plains, and rivers, the watersparkling in the colored light. Over green fields they flew, thenacross some stretches where only sand and rocks were to be seen. Faster and faster the ship went, as the professor found the machinerywas once more in perfect order. Jack was idly watching the play oftinted lights over the surface of the ground. 

"I wonder what makes it, " he said. 

"I have tried to account for it in several ways, " said the professor, who had called Washington to the conning tower and come to join theboys. "I have had first one theory and then another, but the one I amalmost sure is correct is that hidden volcanic fires cause theillumination. 

"I think they flare up and die away, and have become so regular thatthey produce the same effect as night and day with us. Probably thefires go out for lack of fuel, and when it is supplied they start upagain. Perhaps it is a sort of gas that they burn. "

"Well, it's queer enough, whatever it is, " Jack remarked. "Whatstrikes me as funny, though, is that we haven't seen a single personsince we came here. Surely this place must be inhabited. "

Mark thought of the strange shadow he had seen, but said nothing. 

"I believe it is, " the professor answered. "We will probably come uponthe inhabitants soon. I only hope they are a people who will do us noharm. "

"If they tried any of their tricks we could mount up in our ship andescape them, " said Andy. 

"Provided they gave us the chance, " Mr. Henderson put in. "Well, we'llnot worry about that now. "

For several hours the ship traveled on, until it had come to adifferent sort of country. It was wilder and not so level, and therewere a number of streams and small lakes to be seen. 

"Are you going to sail all night?" asked Jack. 

"No, " replied the professor. "I think we'll descend very soon now, andcamp out for a while. That lake just ahead seems to offer a goodplace, " and he pointed to a large sheet of water that sparkled in thedistance, for by this time they had all gone back to the conningtower. 

The lake was in the midst of a wood that extended for some distance onall sides, and was down in a sort of valley. The ship headed towardit, and in a short time a landing was made close to shore. 

"Maybe we can have some fresh fish for supper, " exclaimed Jack as heran from the ship as soon as the sliding door in the side was opened. "Looks as if that lake had some in it. It is not thick water like inthat stream we stopped at, " he added. 

"I believe you're right, " old Andy put in, as he turned back to lookfor some lines and hooks among his traps. He soon found what hewanted, and gave them to the boys, taking his trusty gun along forhimself. 

While the professor, Washington, Tom and Bill remained behind to makesome adjustments to the machinery, and to get things in shape for thenight, which, they calculated would soon be upon them, Jack, Mark andAndy went down to the shore of the lake. The boys cut some poles fromthe trees, and baiting the hooks with some fat worms found under thebark, threw in. 

"Let's see who'll get the first bite, " spoke Jack. "I'm prettygenerally lucky at fishing. "

"Well, while you're waiting to decide that there contest, I think I'lltake a stroll along shore and see if I can see anything to shoot, "Andy remarked. 

For several minutes the boys sat in silence on the bank of the lake, watching the play of the vari-colored lights on the water. SuddenlyJack felt a quiver on his line, and his pole began to shake. 

"I've got something!" he cried. Then his pole bent almost double andhe began to pull for all he was worth. "It's a whopper!" he cried. "Come and help me, Mark!"

Mark ran to his friend's aid. Whatever was on the other end of theline was strong enough to tax the muscles of both boys. They couldhear the pole beginning to break. But for the excellent quality ofAndy's line that would have parted some time before. 

All at once there came a sudden slacking of the pull from whatever wasin the water. And so quickly did it cease that both boys went overbackward in a heap. 

"He's got away!" cried Jack, getting up and brushing some of the dirtfrom his clothes. 

"There's something that didn't get away!" cried Mark, who had risen tohis knees, and was pointing at the lake. Jack looked and what he sawmade him almost believe he was dreaming. 

For, emerging from the water, dragging the pole and line the boys haddropped along with it, was a most curious creature. It was a big fish, but a fish with four short legs on which it was walking, or ratherwaddling along as much as a duck, with a double supply of feet, mightdo. 

"Say, do I see that or is there something the matter with my eyes?"sung out Jack, making ready to run away. 

"It's there all right!" exclaimed Mark. "Hi! Andy! Here's something toshoot!" he yelled, for indeed the creature was big enough to warrantattack with a gun. It was about five feet long and two feet through. 

On and on it came, straight at the boys, as if to have revenge for thepain the fish hook must have caused it, for the barb could be seendangling from its lip. On and on it came, waddling forward, the waterdripping from it at every step. It had the body and general shape of afish, save that the tail was rather large in proportion. As it camenearer the boys noted that the feet were webbed, like those of a waterfowl. 

"Come on!" cried Jack. "It may attack us!"

At that moment the creature opened its mouth, showing a triple row offormidable teeth, and gave utterance to a sort of groan and gruntcombined. 

This was enough to send Jack and Mark off on a run up the bank, anddid they stop until they heard Andy's voice hailing them. 

"What's the matter, boys?"

"Come here! Quick!" answered Jack. 

The fish-animal had halted and seemed to be taking an observation. Todo this, as it could not turn its neck, it had to shift its wholebody. Old Andy came up on the run, his gun held in readiness. 

"Where is it?" he asked, and the boys pointed silently. 

The hunter could not repress a start of astonishment as he saw thestrange creature. But he did not hesitate a second. There was a crackof the rifle, and the thing, whatever it was, toppled over, dead. 

Andy hurried up to it, to get a closer view. 

"Well, this is the limit!" he exclaimed. "First we have grasshoppersthat can roll peaches as big as hogsheads, and now we come across fishthat walk. I wonder what we will see next. "

"I don't want to go fishing in this lake any more, " spoke Jack, as helooked at the repulsive creature. "I never want to eat fish any more. "

"Same here, " agreed Mark, and old Andy was of the opinion that thething killed would not make a wholesome dish for the table. 

"There don't seem to be any game in this section, " he remarked. "Not asign could I see, nor have I since we have been here, unless you countthose grasshoppers. But the fruit is good, I'll say that. "

"Come on, we'd better be getting back, " Mark said, as he noticed itwas getting dark. "I'm hungry. "

 CHAPTER XXII

 THE SNAKE-TREE

THEY managed to make a good meal of the food supplies they had broughtalong, and as a dessert Washington made some peach short-cake from theslices of the giant fruit they had found, the day before. Just as theyfinished supper it got very dark, but, in about an hour, themoon-beams, as the travelers called them, came up, and illuminated thelake with a weird light. 

As the machinery of the Mermaid was now in working order there was nofurther alarm because of the darkness. The ship rested on a level keelabout a hundred yards back from the lake, and, seeing that all wassnug, and the fastenings secure, the travelers went to bed. 

Though they had to forego fish for breakfast the travelers made a goodmeal. After seeing that the ship was in readiness for a quick start, the professor suggested they take a walk around and see what sort ofcountry they might be in now. 

They tramped on for several miles, meeting with no adventures, andseeing nothing out of the ordinary. It was a pleasant day, just warmenough to be comfortable, and a little wind was blowing through thetrees. 

"It would be almost like home if it wasn't for the strange lights, andthe memory of the queer things here, " said Jack. "I feel fine. Let'ssee if you can hit that dead tree over there, Mark. "

Jack stooped to grab up a stone, but no sooner had his fingers touchedit than he called out:

"There! I forgot all about the stones here being heavier than lead. Guess we can't throw any of 'em. But come on. I'll race you to thedead tree!"

Mark was willing, so the two boys set off at a fast pace. 

"Look out where you're going!" the professor called after them. "Notelling what may be in those woods, " for the boys were approaching alittle glade, on the edge of which the dead tree stood. 

Jack reached the goal first, and stood leaning against the trunk, waiting for Mark. 

"You'd better practice sprinting!" exclaimed the victor. 

Mark was about to excuse himself for his poor showing, on the plea ofhaving eaten too much breakfast, when to his horror he saw what seemedto be a long thin snake spring out from the branches of a nearby treeand twine itself about Jack. 

"Help me! Save me!" cried the unfortunate boy, as he was lifted highinto the air and pulled within the shadow of the wood. 

For an instant Mark was too horror-stricken to move. Then with a shoutthat alarmed the others, who were coming along more slowly, he made adash for the place he had last seen Jack. 

Had old Andy not been on the watch, with those keen eyes of his, theremight have been a double tragedy. He had seen from afar the suddensnatching up of Jack, and noted Mark's rush to save his chum. 

"Stand still! Don't go in there for your life!" yelled the hunter, atthe same time running forward with gun ready. 

His example was followed by the professor, Washington and the othertwo men. 

"A snake has Jack!" called Mark, when Andy was at his side. 

"No! It's not a snake!" replied the hunter. "It's worse. It's thesnake-tree!"

"What's that?" asked Mr. Henderson, hurrying up. 

"The snake-tree has Jack, " the hunter went on. "It is a plant, halfanimal, half-vegetable. It has long branches, not unlike a snake inshape. They can move about and grab things. "

"One of them got a grip on Jack as he leaned against the dead treetrunk. I just caught a glimpse of it, and called to prevent Mark fromrunning into danger. "

"Can't we save him?" asked Mr. Henderson. 

"I'm going to try!" replied Andy. "Quick! Gather up some pieces of drywood. I have some paper, and my pipe lighter. We must fight thesnake-tree with fire!"

 CHAPTER XXIII

 THE DESERTED VILLAGE

JACK'S Cries were growing fainter and fainter. Peering in through thebranches of the dead tree the professor could see the whip-like limbswinding closer and closer about the boy. 

"I am afraid we will be too late!" he said. 

Andy had twisted some paper into a rude torch. He set fire to it withhis pocket lighter, and, when Bill and Mark brought him some littlepieces of dead wood the old hunter added them to his bundle, which wasnow blazing brightly. 

"How are you going to do it?" asked the professor. 

"I'll show you, " replied Andy. He bound the sticks and paper togetherwith wisps of grass and then, when it was so hot he could hardly holdit longer, he ran as close as he dared to the snake-tree and tossedthe torch at the foot of it. 

The blazing bundle fell among some damp leaves and grass, as Andy hadintended it should, and soon a dense smoke arose, pouring straight upthrough the branches of the animal-tree, the limbs of which weregathered in a knot about the half-unconscious form of the boy. 

For a few minutes they all waited anxiously. Would Andy's tricksucceed? Had the terrible tree not already squeezed the life fromJack?

But, while they watched, there seemed to come a change over the tree. The snake-like arms waved less and less. They seemed to straightenout, as though deprived of power by the smoke which was now so denseas to hide Jack from sight. Then the arms suddenly relaxed andsomething rolled from them and fell to the ground. With a quickmovement Andy darted in, crawling on his hands and knees beneath thelimbs, and brought Jack out. The boy was white and his eyes wereclosed. 

"Get some water!" cried the old hunter. 

Mark ran toward a stream a little distance away. He brought some ofthe curiously thick liquid in his hat, and while Andy held the boy theprofessor sprinkled some of the drops on his face, and forced somebetween his lips. In a little while Jack's eyes slowly opened. 

"Don't let it eat me!" he begged. 

"You're all right now, " said Andy heartily. "Not a bit harmed, Jack. But, " he added in a low tone, "it was a close call. "

A few whiffs from a bottle of ammonia the professor carried soonbrought Jack's color back. 

"Do you feel better now?" asked Mark. 

"I guess so. Yes, I'm all right, " replied Jack, struggling to hisfeet. "What happened? Feels as if I had been tied up with a lot ofrope. "

"That's about what you were, " Andy replied, "only it was the worstkind of rope I ever saw. Those snake-trees are terrible things. I'veread of 'em, but I never saw one before. The book that told of themsays they squeeze their victims to death just as a snake does. Theonly way to do is to make some smoke and fire at the bottom. This sortof kills the branches or makes them stupid and they let go. The treesare half animal, and awful things. I hope we don't meet with anymore. "

"Same here, " added Jack fervently, as he grasped Andy's hand, andthanked him for saving his life. 

"Do you think you can go on, or shall we return to the ship'?" theprofessor asked. 

"Oh I can trail along, if you move a little slowly, " Jack replied. "I'm a bit stiff, that's all. "

So they resumed their journey. They had gone, perhaps, three mileswhen Washington, who was in the lead, suddenly stopped and called:

"Sounds like thunder. "

The others listened. Sure enough there was a dull rumble and roaraudible. It seemed off to the left, but they could see no clouds inthe sky, nor any signs of a storm. 

"Let's take a walk over that way and see what it is, " Mr. Hendersonsuggested. 

As they walked on the noise became louder, until in about half an hourit was like the sound from a blast furnace. 

"What do you suppose it can be?" asked Mark. 

"Perhaps some new freak of nature, " the professor replied. "We seem tohave a good many of them here. "

They were all on their guard now, for there was no telling into whatdanger they might run. As they went up a little hill the noise becamemuch louder. The professor and Andy, who had taken the lead, kept asharp lookout ahead, that they might not unexpectedly fall into somehidden stream or lake. As they topped the hill they saw before them adeep valley, and in the midst of it was that which was causing theroaring sound. 

From the centre of an immense mound of rock and earth there spouted upa great column of water, three hundred feet or more, as straight as aflag staff. It was about ten feet in diameter, and at the top it brokeinto a rosette of sparkling liquid, which as the vari-colored lightsplayed on it, resembled some wonderful flower. 

"It's a great geyser!" the professor exclaimed. "We have come to aplace like Yellowstone Park. We must be very careful. The crust may bevery thin here, and let us down into some boiling spring. "

The others gathered around the professor, and, from a safe distancewatched the ever rising and falling shaft of water. 

It was not regular in motion. Sometimes it would shoot up to a greatdistance, nearly a thousand feet, the professor estimated. Again itwould sink down, as the power sending it out lessened, until it wasonly a few hundred feet above the rounded top of the mound from whichit spurted. But it never fell below this. All the while there was theconstant roaring sound, as though the forces of nature below thesurface were calling to be let out. 

"I hope there are not many of those about, " Mr. Henderson remarkedafter a pause. "If the ship should hit one during the night it wouldbe all up with us. We must keep a careful look-out. "

The spouting column had a fascination which held them to the spot forsome time. From the hill they had a good view of the surroundingcountry, but did not see any more geysers. 

"Do you think it is hot water?" asked Mark. 

"There is no vapor, " the professor answered, "but most of the geysersare produced by the action of steam in the interior of the earth. However we'll not take any chances by investigating. I fear it wouldnot be safe to go into that valley. "

"Look there!" cried Andy. "I guess we're better off here!" He pointeda little to the right of where the water spouted. The others looked, and saw, coming from a hole in the ground, some shaggy black object. 

"What is it?" asked Jack. 

"It looks like a bear, " replied the hunter, "but I never saw one likeit before. "

Nor had any of the others, for the creature was a terrible one. It hadthe body of a bear, but the feet and legs were those of an alligator, while the tail trailed out behind like a snake, and the head had along snout, not unlike the trunk of an elephant. The creature wasabout ten feet long and five feet in height. 

"Let me try a shot at it!" exclaimed Andy. "That is something worthshooting, " and he cocked his rifle. 

"Don't!" exclaimed the professor shortly. "You might only wound it, and it would pursue us. We are not ready to fight such creatures asthat, and you are the only one armed. "

"I never missed anything I aimed at yet, " said Andy, a little hurtthat any one should doubt his ability to kill at the first shot. 

"Perhaps not, but how do you know but what this creature has a bulletproof armor under its hide. This is a strange world, Andy. It isbetter to take no chances. "

"I hate to see him get away, " the hunter said. 

But, as it happened, the beast was not to get away. As they watchedthey saw the horrible animal approach the mound from which the waterspurted. Up the sides it climbed. 

"I guess he's going to get a drink, " said Mark. 

That was evidently the beast's intention. It went close to thespouting column of water, and thrust its head out so that its tonguecould lap from the side. It seemed to have been in the habit of doingthis. 

For once, and for the last time, however, it made a mistake. The waterseemed to veer to one side. In its eagerness to get a drink the animaltook another step forward. At that moment the direction of the columnchanged again, and it tilted over toward the beast. 

Suddenly, as the travelers watched, the full force of the big columncaught the beast just under the fore shoulders. Up into the air thecreature shot, propelled by thousands of pounds pressure. Right up tothe top of the column it went, and this time the water rose a thousandfeet into the air. 

Up and up went the animal, struggling to get away from the remorselessgrip. Then, when the water had reached its height, it shot the beastoff to one side. Then the brute began to fall, twisting, turning, wiggling and struggling. Down it came with a thud that could be heardabove the noise of the geyser. 

"I reckon that finishes him, " observed Andy. And it had, for there wasnot a sign of life from the creature. 

"I guess we have seen enough for one morning, " the professor said, "Let's go back to the airship. It must be nearly dinner time. "

They started away. Mark gave a last look at the queer column of waterand the dead body of the strange animal. As he passed down the hill hethought he saw the creature move, and stayed to see if this was so. But a second glance convinced him he was mistaken. 

The others had gone on and were some distance ahead. Mark hurried onto join them. As he got a last glance at the top of the column, overthe brow of the hill, he happened to look off to the left. There wasanother hill, about the size of the one they had been on. 

And, as Mark looked he saw something move. At first he thought it wasanother beast. But, to his terror he saw that the creature had onlytwo legs, and that it stood upright like a man, but such a man as Markhad never seen before, for he was nearly twelve feet tall. 

He was about to cry out and warn the others, when the thing, whateverit was, sunk down, apparently behind some tall bushes, and disappearedas if the earth had opened and swallowed it. 

"I wonder if I had better tell them, " thought Mark. "I can't show themanything. I wonder if I really saw it, or if it was only a shadow. Iguess I'll say nothing. But it is very strange. "

Then he hurried on to join the others. 

"What makes you so pale?" asked Jack of his chum. 

"Nothing, " said Mark, somewhat confused. "I guess I'm a little tired, that's all. "

They reached the ship in safety, and, having dinner started themachinery and took the Mermaid up into the air. 

"We'll travel on and see if we can't find some human beings, " theprofessor said. 

All that afternoon they sailed, the country below them unfolding likea panorama. They passed over big lakes, sailing on the surface ofsome, and over rivers, and vast stretches of forest and dreary plains. But they never saw a sign of human inhabitants. 

It was getting on to five o'clock, the hour when the brilliant lightsusually disappeared, when Mark, who was steering in the conning tower, gave a cry. 

"What is it?" asked the professor, looking up from a rude map he wasmaking of the land they had just traversed. 

"It looks like a town before us, " said the boy. 

Mr. Henderson and Jack looked to where Mark pointed. A few miles aheadand below them were great mounds, not unlike that from which thegeyser had spouted. But they were arranged in regular form, likehouses on a street, row after row of them. And, as they approachednearer, they could see that the mounds had doors and windows to them. Some of the mounds wer rger than others, and some were of double andtriple formation. 

"It's a city! The first city of the new world!" cried Jack. 

"It is a deserted village!" said the professor. "We have found wherethe people live, but we have not found them. " And he was right, forthere was not a sign of life about the place, over which the airshipwas now suspended. 

 CHAPTER XXIV

 THE GIANTS

"LET'S go down and investigate, " suggested Jack. 

"Better wait, " counseled the professor. "It will soon be dark, and, though we will have moonlight, we can not see to advantage. I think itwill be best to keep the ship in the air to-night, and descend in themorning. Then we can look about and decide on what to do. "

They all agreed this was the best plan, and, after making a circleabove the deserted village, and noting no signs of life, the Mermaidwas brought to a halt over the centre of the town, and about threehundred feet above it. There the travelers would be comparativelysafe. 

It was deemed best to keep watch that night, and so, Mark, Jack, Billand Tom took turns, though there was nothing for them to do, as not athing happened. With the first appearance of dawn Mr. Henderson gaveorders to have the ship lowered, and it came to rest in the middle ofwhat corresponded to a street in the queer mound village. 

"Now to see what kind of people have lived here!" cried Jack. "Theymust have been a queer lot. Something like the Esquimaux, only theyprobably had more trouble keeping cool than the chaps up at the northpole do. "

Now that they were down among the mound houses, they saw that thedwellings were much larger than they had supposed. They towered highabove the boys' heads, and some of them were large enough in area tohave accomodated a company of soldiers. 

"Say, the chaps who lived in these must have been some pumpkins, " saidJack. "Why the ceilings are about fifteen feet high, and the doorsalmost the same! Talk about giants! I guess we've struck where theyused to hang out, at any rate. "

The houses were a curious mixture of clay and soft stone. There weredoors, with big skins from animals as curtains, and the windows weredevoid of glass. Instead of stairs there were rude ladders, and thefurniture in the mound houses was of the roughest kind. 

There were fire-places in some of the houses, and the blackened andsmoked walls showed that they must have been used. In one or two ofthe houses clay dishes, most of them broken, were scattered about, andthe size of them, in keeping with everything else, indicated thatthose who used them were of no small stature. 

"Some of the bowls would do for bath tubs, " said Jack, as he cameacross one or two large ones. 

By this time the professor, Bill and Tom had joined the boys, and thefive went on with the exploring tour, while Washington and Andyremained in the ship to get breakfast. 

"The inhabitants are evidently of a half-civilized race, " theprofessor said. "Their houses, and the manner in which they live, showthem to be allied to the Aztecs, though of course they are much largerthan that race. "

"What's bothering me, " Bill said, "is not so much what race theybelong to, as what chance we'd stand in a race with them if they tookit into their heads to chase after us. I've read that them thereAzhandled races----"

"You mean the Aztecs, " interrupted the professor. 

"Well the Aztecs, then. But I've read they used to place their enemieson a stone altar and cut their hearts out. Now I'm not hankerin' afteranything like that. "

"Don't be foolish, " spoke Mr. Henderson. "Wait until you meet some ofthe giants, if that is what they are, and then you can decide what todo. "

"It may be too late then, " remarked Bill in a low tone, and the boyswere somewhat inclined to agree with him. 

However, there seemed to be no immediate danger, as there was no signof any of the big people about the village. The adventurers walkedabout for some time, but made no discoveries that would throw anylight on the reason for the place being left uninhabited. It seemed asif there had been a sudden departure from the place, for in a numberof the houses the remains of half-cooked meals were seen. 

"Well, I think we have noted enough for the time being, " the professorremarked, after they had traversed almost half the length of whatseemed to be the principal street. "Let's go back to the ship and havesomething to eat. Washington may have become alarmed at our absence. "

They made a circle in order to take in another part of the town ontheir way back. While passing through a sort of alley, though it wasonly narrow by comparison with the other thoroughfares that were verywide, Mark came to a place where there was a circular slab of stone, resting on the ground. In the centre was a big iron ring. 

"Hello! Here's something new!" he exclaimed. "Maybe it leads to asecret passage, or covers some hidden treasure. "

"I guess it will have to continue to cover it then, " Jack spoke. "Thatprobably weighs several tons. None of us could move it. "

They made their way back to the ship, where they found Washington andAndy discussing the advisability of going off in search of them. 

"Breakfast is mighty near spoiled, " said the colored man with aninjured air. 

But the travelers did full justice to the meal, notwithstanding this. Deciding there was nothing to be gained by staying in that vicinity, the professor started the ship off again. 

They traveled several hundred miles in the air, and, as the afternoonwas coming to a close, Jack, who was in charge of the conning tower, spied, just ahead of them, another village. 

"We will descend there for the night, " the professor said. "Does thereseem to be any sign of life about?"

"None, " replied Mark, who was observing through a telescope the townthey were approaching. "It's as dead as the other one. "

The airship settled down in a field back of some of the mound houses. 

"Now for supper!" cried Jack. "I'm as hungry as----"

He stopped short, for, seeming to rise from the very ground, all aboutthe ship, there appeared a throng of men. And such men as they were!For not one was less than ten feet tall, and some were nearly fifteen!

"The giants have us!" cried Bill, as he saw the horde of creaturessurrounding the ship. 

 CHAPTER XXV

 HELD BY THE ENEMY

"KEEP the doors closed!" cried the professor. "It is our only hope! Iwill send the ship up again!"

But it was too late. Washington, who had obeyed the signal from theconning tower to shut off the engines, had disconnected most of themso they could not be started again save from the main room. At thesame time there came a yell of dismay from the colored man, who hadslid back the steel covering of the main side entrance to the Mermaid. 

"I'm caught!" cried Washington. 

As the professor and the boys hurried from the tower, they could heara struggle from where Washington was, and his voice calling:

"Let me go! Let me go!"

Reaching the engine room, which opened directly on the side entrance, the professor saw a pair of enormous hands and arms dragging poorWashington, feet first, out of the ship. Bill and Tom were crouched inone corner, pale with fright. 

"Wait until I get my gun!" cried Andy, as he ran for his rifle. 

"Hold on!" called the professor in a loud voice. "It will be folly toshoot them! We must try strategy!"

Washington's cries ceased as he was drawn entirely from the ship, thegiant hands disappearing at the same time. 

"Follow me!" yelled Mr. Henderson, running out of the door. 

Hardly knowing what they did, the boys went after him, and theirhearts almost stopped beating in fright as they saw the terriblethings, which, in the glare of the changing lights, were on every sideof them. 

For the men were very repulsive looking. They there attired inclothes, very similar in cut to those worn by the travelers, and whichseemed to be made of some sort of cloth. But they were loose and baggyand only added to the queer appearance of the giants. Veritable giantsthey were too. Their faces seemed as large as kegs, and they were soclumsy in shape that Mark, even, frightened as he was, exclaimed:

"They look like men made of putty!" At the same time he saw they borea resemblance to the creature he had observed on the hill top. 

"What shall we do?" asked Andy of the professor. "They are reallycarrying Washington away!"

Three of the giants were dragging the colored man along the ground, while the other terrible beings stood about as if waiting to see theoutcome of the first sally. 

"I will try to speak to them, " Mr. Henderson said. "I know severallanguages. They may understand one. "

But before he could start on his parley a surprising thing happened. There was a struggle in the little group about Washington. The coloredman seemed to be fighting, though the odds, it would appear, were toogreat to enable him to accomplish anything. But, making a desperateeffort to escape, Washington quickly wrenched himself free from thegiants' hands and then, striking out with his fists, knocked the threedown, one after another. 

"I never knew Washington was so strong!" exclaimed Jack. 

"Nor I, " put in Mark. "Why I should think the men could carry him inone arm as if he was a baby. "

The three giants rose slowly to their feet. They uttered strangecries, and motioned with their hands toward the professor, the boys, and the others in the crowd. 

"Look out! They're goin' t' grab yo'!" cried Washington. 

Three of the giants approached Mark, and a like number closed in onJack. 

"Back to the ship!" cried the professor. "We must defend ourselves!"

But by this time the big men had grabbed the two boys. Then a strangething took place. Mark and Jack, though they felt that the giants mustovercome them in a test of strength, struggled with all their mightagainst being captured. They fought, as a cornered rat will fight, though it knows the odds to be overwhelming. But in this case theunexpected happened. 

Both boys found they could easily break the holds of the giants, andMark, by a vigorous effort, pushed the three men away from him, one ata time violently so that they fell in a heap, one on top of the other. 

"Hurrah! We can fight 'em!" cried Mark. "Don't be afraid. They're likemush! They're putty men!"

And, so it seemed, the giants were. Though big in size they wereflabby and had nothing like the muscle they should have had inproportion to their build. They went down like meal sacks and wereslow to rise. 

Jack, seeing how successful his comrade was, attacked the three giantswho were striving to make him a captive. He succeeded in disposing ofthem, knocking one down so hard that the man was unable to rise untilhis companions helped him. 

"That's the way!" cried Washington. "They're soft as snow men!"

The vanquished giants set up a sort of roar, which was answered bytheir fellows, and soon there was a terrible din. 

"All get together!" called the professor. "They are evidently going tomake a rush for us. If we stand by one another we may fight them off, though they outnumber us a hundred to one. Besides it will soon bedark, and we may be able to escape!"

Washington, Jack and Mark retreated toward the ship, in the directionof which the others had also made their way. The big men had gatheredin a compact mass and were advancing on the adventurers. 

"What do you suppose makes them so soft?" asked Mark. "I believe Icould manage half a dozen. "

"It must be the effect of the climate and conditions here, " theprofessor replied. "Probably they have to be big to stand the pressureof the thick water, and the increased attraction of gravitation. Thentoo, being without the weight of the atmosphere to which we areaccustomed, they have probably expanded. If they were to go up toearth, they might shrink to our size. "

"Do you think that possible?"

"Of course. Why do you ask?"

"Nothing in particular, " replied Mark. But to himself, he added: "Thatwould explain it all. "

It was getting dusk now. The travelers had reached their ship, andrushed inside and tried to close the doors in the face of theadvancing horde. But, by this time the giants were so close that oneor two of them thrust their big feet in, and prevented this movement. At the same time they set up a great howling. 

"Quick!" cried the professor. "We must start the ship and get away!"

"I can't close the door!" yelled Washington, who had been the last toenter. 

"Never mind that! Go up with it open! Drag them along if they won'tlet go!" answered Mr. Henderson, as he ran toward the engine room. 

There was a sudden rush among the giants, and a sound as if somethingwas being thrown over the top and ends of the ship. Mark turned thegas machine on, while Jack worked the negative gravity apparatus. Theywaited for the ship to rise. 

"Why don't we go up?" asked the professor. 

"'Cause they've caught us!" called out Washington. 

"Caught us? How?"

"They've thrown ropes over the top and ends of the ship, and fastenedthem to their big houses!"

Running to a side window the professor saw that the Mermaid wasfastened down by a score of cables, each one six inches thick. Theywere held captives by the enemy. 

 CHAPTER XXVI

 A FRIEND INDEED

THOUGH the giants, man for man, were no match for the travelers, collectively the horde proved too much. They had swarmed about theship, and, by passing the big cables over her, effectively held herdown. 

"Let me get out and I'll cut 'em!" cried Andy. "We must get away fromthese savages!"

"No, no, don't go out!" exclaimed the professor. "They wouldeventually kill you, though you might fight them off for a time. Wemust wait and see what develops. They can have no object in harmingus, as we have not injured them. "

"I'd rather fight 'em, " insisted the old hunter. 

But the professor had his way and Andy was forced to obey. The giantshad withdrawn their big feet from the side door and Washington hadclosed it. But nothing else had been accomplished, and the ship couldnot rise. The gas and negative gravity machines were stopped, as theywere only under a useless strain. 

Suddenly, the colored lights which had been growing dimmer and dimmer, with the approach of night, went out altogether. Almost as suddenly, Mark, who was watching the giants from the conning tower, as they madefast the loose ends of the cables, saw them make a dash for the moundhouses. 

"They're afraid of the dark!" he cried. "Come on! We can go out nowand loosen the ropes!"

He hurried to tell the professor what he had noticed. 

"Good!" exclaimed Mr. Henderson. "Perhaps we can escape now!"

They waited a few minutes, listening to the sound of many big feetrunning away from the ship, and then, Bill cautiously opened the sidedoor. The others were behind him, waiting, with knives and hatchets intheir hands, to rush out and cut the restraining cables. 

"All ready!" called Bill. "There doesn't seem to be a one in sight!"

He stepped out but no sooner had he set foot on the ground than therecame a thud, and Bill went down as if some one had knocked his feetfrom under him. 

"Go back! Go back!" he cried. "They hit me with something. I'm beingsmothered!"

"Bring a light!" cried the professor, for the sally had been startedin the dark. 

Jack brought the portable electric it having been repaired and flashedit out of the door. In the gleam of it, Bill was seen lying prostrate, half covered by an orange, about half as big as himself. The fruit wasas soft and mushy as some of the giants themselves, or Bill would nothave fared so easily. 

Then, as the others stood watching, and while Bill arose and wipedsome of the juice from his face, there came a regular shower of themonstrous oranges. 

"Get inside quick! We'll be smothered under them!" Mr. Hendersoncried. 

Pausing only to rescue Bill, the adventurers retreated inside theship, and made fast the door. Outside they could hear the thud as theoranges were thrown, some hitting the Flying Mermaid and many droppingall about her. 

"I guess they are going to have things their own way, " observed Bill, as he gazed down on his clothes, which were covered with juice fromthe fruit. 

The night was one of anxiety. The travelers took turns standing guard, but nothing more occurred. The giants remained in their houses, andthe heavy ropes still held the ship fast. 

"We must hold a council of war, " the professor decided as theygathered at breakfast, which was far from a cheerful meal. 

With the return of the colored lights the giants again made theirappearance. They came swarming from the mound houses, and a greatcrowd they proved to be. Several thousand at least, Jack estimated, and when he went up into the conning tower and took a survey he couldsee the strange and terrible creatures pouring in from the surroundingcountry. 

"I'm afraid there will be trouble, " he said, as he came down andreported what he had seen. 

"We must hold a council of war, " repeated the professor. "Has any oneanything to suggest?"

"Get a lot of powder and blow 'em up!" cried Andy. 

"Arrange electric wires and shock 'em to death!" was Bill's plan. 

"Can't we slip the ropes in some way and escape?" asked Jack. "I don'tbelieve we can successfully fight the giants. They are too many, evenif they are weak, individually. "

"I think you're right there, " Mr. Henderson said. "We must try somesort of strategy, but what? That is the question. "

For a few minutes no one spoke. They were all thinking deeply, fortheir lives might hang in the balance. 

"I think I have a plan, " said Mark, at length. "Did we bring anydiving suits with us?"

"There may be one or two, " the professor replied. "But what good willthey do?"

"Two of us could put them on, " continued Mark, "and, as they affordgood protection from any missiles like fruit, we could crawl out onthe deck of the ship. From there, armed with hatchets or knives wecould cut the ropes. Then the ship could rise. "

"That's a good plan!" cried the scientist. "We'll try it at once. "

Search revealed that two diving suits were among the stores of theMermaid. Jack and Mark wanted to be the ones to don them, but as thesuits were rather large, and as the professor thought it would takemore strength than the boys had to do the work, it was decided thatAndy and Washington should make the attempt to cut the ropes. 

The hunter and colored man lost little time in getting into the modernarmor. In the meanwhile Jack, who had been posted as a lookout, reported that there seemed to be some activity among the giants. Theywere running here and there, and some seemed to be going off towardthe woods, that were not far away. 

"Now work quickly, " urged the professor. "We will be on the watch, andas soon as the last rope is cut we will start the machinery and sendthe ship up. We will not wait for you to come back inside, so holdfast as best you can when the Mermaid rises. "

"We will, " answered Andy, just before the big copper helmet wasfastened on his head, and Washington nodded to show he understood. 

The two who were to attempt the rescue of their comrades were soon ondeck. In the conning tower Jack and the professor kept anxious watch, while Mark, Bill and Tom were at the various machines, ready, at thesignal, to start the engines. 

The giants had now become so interested in whatever plan they hadafoot, that they paid little attention to the ship. ConsequentlyWashington and Andy, crawling along the deck in their diving suits, did not, at first attract any attention. 

In fact they had cut several of the big ropes, and it began to look asif the plan would succeed, particularly as they were partly hiddenfrom view by the upper gas holder. They were working with feverishhaste, sawing away at the big cables with keen knives. 

"I guess we'll beat 'em yet!" cried Jack. 

"I hope so, " replied the professor. "It looks----"

He stopped short, for at that moment a cry arose from the midst of thegiants, and one of them pointed toward the ship. An instant later theair was darkened with a flight of big oranges, which the queercreatures seemed to favor as missiles. Probably they found stones tooheavy. 

"Well, those things can't hurt 'em much with those heavy suits on, "observed Mr. Henderson. "There, Washington got one right on the headthat time, and it didn't bother him a bit. "

Jack had seen the fruit strike the big copper helmet and observed thatthe colored man only moved his head slightly in order to get rid ofthe orange. 

In fact the giants, seeing for themselves that this mode of warfarewas not going to answer, since the two men on the ship continued tocut the restraining cables, gave it up. There was a good deal ofshouting among them, and a number ran here and there, seeminglygathering up long poles. 

"I wonder if they are going to try the flailing method, and beat poorAndy and Washington, " said Mr. Henderson. "It looks so. "

The two rescuers were now about a quarter through their hard task. Thethrowing of the oranges had ceased. But the giants were up to a newtrick. They divided into two sections, one taking up a position on oneside of the ship, and the other on the opposite. There were about twohundred in each crowd, while the others in the horde drew somedistance back. 

"They're up to some queer dodge, " observed Jack. "What are theyplacing those sticks to their mouths for?"

The professor observed the throng curiously for a few seconds. Then heexclaimed:

"They are using blow-guns! They are going to shoot arrows atWashington and Andy! We must get them in at once!"

He darted toward a door that opened from the conning tower out on thedeck. 

"Don't go!" cried Jack. "It's too late! They are beginning to blow!"

He pointed to the throng of giants. The professor could see theircheeks puffed out as the big creatures filled their lungs with air andprepared to expel it through the hollow tubes. 

Then there came a sound as if a great wind was blowing. It howled androared over the ship, not unlike a hurricane in its fury. But therewas no flight of arrows through the air, such as would have come fromregular blow guns. 

"That is strange, " said the professor. He thought for a moment. "Ihave it!" he cried. "They are trying to blow Washington and Andy, offthe ship by the power of their breaths! They are not blowing arrows atthem! My, but they must have strong lungs!"

And, in truth, that was the plan of the giants. The hollow tubes, madefrom some sort of big weed, sent a blast of air at the two men on theship's deck, that made them lie flat and cling with both hands toavoid being sent flying into the midst of the giants, on one side orthe other. But the giants had reckoned without the weight of thediving suits, and it was those, with the big lead soles of the shoes, that helped to hold Washington and Andy in place. 

"Come back! Came back!" cried the professor, opening the conning towerdoor and calling to the two brave men. "Come back, both of you! Do youhear?"

As the portal slid back the rush of air was almost like that of acyclone. Then it suddenly ceased, as the giants saw their plan was notlikely to succeed. 

But now there arose from the outer circle of the horde a shout oftriumph. It was caused by the return of those who had, a little whilebefore, hurried off to the woods. They came back bearing big trees, tall and slender, stripped of their branches, so that they resembledflag staffs. It took a dozen giants to carry each one. 

The whole throng was soon busy laying the poles in a row in front ofthe ship. 

"What can they be up to now?" asked Jack. 

"It looks as if they were going to slide the ship along on rollers, "the professor replied. 

Sure enough this was the giant's plan. A few minutes later those inthe Mermaid felt her moving forward, as the giants, massed behind, shoved. On to the poles she slid. The ropes were loosened to permitthis, but not enough to enable the boat to rise. 

Then the travelers felt the ship being lifted up. 

"They are going to carry us away, with the poles for a big stretcher!"cried the professor. 

Looking from the side windows the boys saw that a great crowd of thebig men were on either side of the Mermaid, each giant grasping apole, and lifting. Farther out were others, holding the ends of thecables which Washington and Andy had not succeeded in cutting. 

The ship was being carried along by a thousand or more giants, as theancient warriors, slain in battle, were carried home on the spears oftheir comrades. 

"This is the end of the Mermaid!" murmured Mr. Henderson in sorrowfultones. 

As they looked from the conning tower the professor and the two boysobserved a commotion among the leaders of the giants. They seemed tobe wavering. Suddenly the forward part of the ship sank, as thoseahead laid their poles down on the ground. Then those behind did thesame, and the Mermaid, came to a stop, and once more rested on theearth. 

"What does this mean?" asked the scientist in wonder. 

All at once the entire crowd of giants threw themselves down on theirfaces, and there, standing at the bow of the ship, was a giant, halfagain as large as any of the others. He was clad in a complete suit ofgolden armor on which the changing lights played with beautifuleffect, and in his hand he held an immense golden sword. He pointedthe weapon at the ship as if he had raised it in protection, and hishand was stretched in commanding gesture over the prostrate giants. 

"Perhaps he has come to save us!" cried Mark. 

 CHAPTER XXVII

 A GREAT JOURNEY

SUCH indeed, seemed to be the case. The golden-armored giant, afterstanding for a few moments in an attitude of command, waved his swordthree times about his head, and uttered a command, in a voice thatsounded like thunder. Then the prostrate ones arose, and, making lowbows hurried away in all directions. 

Watching them disappear, the golden one sheathed his weapon andapproached the ship. He caught sight of the professor and the two boysin the conning tower, for Mark had gone there when he found the shipbeing transported, and held up his two hands, the palms outward. 

"It is the sign of peace in the language all natives employ, " said theprofessor. "I think I shall trust him. "

Followed by the boys he descended from the little platform in thetower, and to the door that opened on the deck. 

"Shall we go out?" he asked. 

"We can't be much worse off, " replied Mark. "Let's chance it. "

So, not without many misgivings, they slid back the portal and steppedout to face the strange and terrible being who had so suddenly come totheir rescue. 

The giant in the golden armor did not seem surprised to see them. Infact he acted as though he rather expected them. He continued to holdup one hand, with the palm, outward, while, with the other, he removedhis helmet and bowed low. Then he cast his sword on the ground andadvanced toward the ship. When within ten feet he sat down on theground, and this brought his head nearer the earth, so that hisauditors could both see and hear him to better advantage. 

As soon as the giant saw the travelers were outside their ship hebegan to speak to them in a voice, which, though he might have meantit to be low and gentle, was like the bellowing of a bull. At the sametime he made many gestures, pointing to the ship, to himself and toMark. 

"What is he saying, professor?" asked Jack. 

"I can't understand all he says, " Mr. Henderson replied. "He uses somewords derived from the Latin and some from the Greek. But by piecingit out here and there, and by interpreting his motions I am able toget at something. "

"And what is it all about?"

"It is a strange story, " the scientist replied. "He has only goneabout half way through it. Wait until he finishes and I will tellyou. "

The golden-armored giant, who had stopped in his narrative while Jackwas speaking, resumed. His gestures became more rapid, and his wordscame faster. Several times Mr. Henderson held up his hand for him tocease, while he puzzled out what was meant. 

At one point, the professor seemed much startled, and motioned for thestrange being to repeat the last part of his discourse. When this hadbeen done Mr. Henderson shook his head as though in doubt. 

At length the story was finished, and the lone giant, for there wereno others in sight now, folded his arms and seemed to await what theprofessor's answer might be. Mr. Henderson turned to the boys, and tothe others of the Mermaid's company, who, by this time, had joinedhim, and said:

"Friends, I have just listened to a strange story. It is so strangethat, but for the fact that our own adventures are verging on themarvelous, I could hardly believe it. In the first place, this manhere is the king of this country. That is why all the other nativesobeyed him. 

"In the second place it seems he has been a passenger in our boat, andcame here from the earth's surface with us!"

"What's that?" cried Jack. 

"That explains the strange happenings!" ejaculated Mark. "No wonder Icould never solve the secret of the storeroom. "

"You are right, it does, " replied Mr. Henderson. "I will not go intoall the details of how it happened, but it seems the big hole throughwhich we came is only one of two entrances to this inner world. Ratherit is the entrance, and there is another, close to it, which is theexit. Through the latter a big stream of water spouts up, just as onepours down through the opening we used. 

"Hankos, which is the name of the king, was for many years a studentof science. He longed to see where the big stream of upward spurtingwater went, and wanted to know whence came the down-pouring one. So heundertook a daring experiment. 

"He constructed a great cylinder, and, keeping his plans a secret, conveyed it to the spouting water, entered it, and, by means ofpulleys and levers, after he had shut himself inside, cast himselfinto the up-shooting column. He took along compressed air cylinders tosupply an atmosphere he could breathe, and some food to eat, for itappears our giant friends are something of inventors in their way. Thecurrent of water bore him to the surface of the earth, and he was castup on the ocean, in what was probably taken for a waterspout if anyone saw it. 

"Then a strange thing happened. No sooner did Hankos open hiscylinder, which served him as a boat, than he lost his gigantic size, owing to the difference of the two atmospheres. He became almost ofthe same size as ourselves, except that his skin hung in great foldson him, and he seemed like a wrinkled old man. His clothes too, were aworld too large. 

"He had a terrible time before he reached shore, and a hard one afterit, for his strange appearance turned almost every one against him. Hewas sorry he had ventured to solve the mystery of the up-shootingstream of water, for he was worse than an outcast. 

"Then he began to plan to get back to his own inner world. But hecould not find the downward stream, and, not knowing the language ofthe countries where he landed, he had no means of ascertaining. Hetraveled from place to place, always seeking for something that wouldlead him back to his own country. 

"Finally he heard of us, and of our ship, though how I do not know, asI thought I had kept it a great secret. By almost superhuman struggleshe made his way to our island. He says he concealed himself aboard theMermaid the night before we sailed, but I hardly believe it possible. It seems----"

"He did it, for I saw him!" interrupted Mark. 

"You saw him!" cried Mr. Henderson. 

Then Mark told of the many things that had puzzled him so, how he hadseen the queer figure slinking aboard the boat, of the disappearanceof food from time to time, and of the strange noises in the storeroom. 

"That bears out what he told me, " the professor said. "Hankos says heused to steal out nights and take what food he could get, and he alsomentions some one, answering to Mark's description, who nearlydiscovered him once as he hurried back into the apartment. 

"However, it seems to be true, since Mark confirms it. At any rateHankos stayed in hiding, and made the entire trip with us, and, justas we all became overcome with the strange gas he escaped, havingbegun to expand to his original giant size, and being unable to remainany longer in his cramped quarters. "

"That's so, he did!" cried Mark. "I saw him come out of the place justbefore I lost my senses. It was a terrible sight, and none of youwould believe me when I told you some of the occurrences afterward. "

"You must forgive us for that, " the professor said. "We have learnedmuch since then. "

"What did Hankos do after he left the ship when it landed in thiscountry?" asked Jack. 

"He traveled until he came to this village, which is the chief one ofthis country, " replied the professor. "Part of the time he followed usat a distance, being able to travel very fast. "

Mark remembered the strange figure of a giant he had seen on the hilltops several times, and knew that he had been observing the being whohad played such a queer part in their lives. 

"When he came back among his own people, " went on Mr. Henderson, "theywould not receive him at first, believing him to be an impostor. ButHankos convinced them of his identity and was allowed to don thegolden armor, which is the badge of kingship. He had only been inoffice for a little while when he heard of the arrival of the strangething, which turned out to be our ship. He recognized it from thedescription, and, learning that we were likely to be sacrificed to thefury and ignorance of the giants, he hurried here and saved our lives. 

"He says he can never thank us enough for being the means whereby hewas able to get back to his own country, and says the freedom of thiswhole inner world is ours. He has given orders that we are to gowherever we like, and none will molest us. He tells me the land is awonderful one, compared to our own, and urges us to make a longjourney. He would like to go with us, only, now that he has resumedhis natural size, he can not get inside the ship. "

"Hurrah for King Hankos!" cried Jack and the others joined him in ahearty cheer. 

The giant in the golden armor evidently understood the complimentwhich was paid him, for he waved his helmet in the air and respondedwith a shout of welcome that made the ground tremble. 

Hankos waited until the professor had translated all of the story tothe other travelers. Then the genial giant began to talk some more, and the professor listened intently. 

"He says, " spoke Mr. Henderson to his friends, "that we will besupplied with all the fruit we want, and with the best of the housesto sleep in on our journey. He also tells me he has great stores ofshining stones and piles of the metal of which his armor is made, andthat we are welcome to as much as we want. If this means unlimitedgold and diamonds, we may make our fortunes. "

"Jest let me git ma' hand on a few sparklers an' I'll quit work!"exclaimed Washington. 

"I have told him, " the scientist went on, "that we will take advantageof his kind offer. We will start on our trip in a day or so, after wehave looked over the ship to see if it is not damaged. He tells me thegold and sparkling stones are several thousand miles away, on top of ahigh mountain. We will make that our objective point. "

The interview between the king and Mr. Henderson having ended, theformer waved his sword in the air and the swarm of big men came back. They had been hiding back in the woods. Now their manner was verydifferent. They carefully removed the rollers and ropes, and soonthere was brought to the adventurers an immense pile of fine fruits. If our friends had stayed there a year they could not have eaten itall. The giants were judging the appetites of the travelers by theirown. 

That night the adventurers slept more soundly than they had sinceentering the strange world. They felt they had nothing to fear fromthe giants. In the morning they were not molested, though big crowdsgathered to look at the ship. But they kept back a good distance. Themachinery was found to be in good shape, save for a few repairs, andwhen these were made, the professor announced he would start on a longjourney. 

For several weeks after that the travelers swung about in their ship, sometimes sailing in the air and again on big seas and lakes viewingthe wonders of the inner world. They were many and varied, and theprofessor collected enough material for a score of books which he saidhe would write when he got back to the outer world once more. 

One afternoon, as they were sailing over a vast stretch of woodland, which did not seem to be inhabited, Mr. Henderson, looking at one ofthe gages on the wall, asked:

"Boys do you know how far you have traveled underground?"

"How far?" asked Jack, who hated to guess riddles. 

"More than four thousand miles, " was the answer. 

"But we haven't come to that mountain of gold and diamonds, " saidMark. "I am anxious to see that. "

"Have patience, " replied the professor. "I have not steered toward ityet. There are other things to see. "

Just then Washington's voice could be heard calling from the conningtower:

"We're coming to a big mountain!"

 CHAPTER XXVIII

 THE TEMPLE OF TREASURE

"WHAT'S that?" fairly yelled the professor. 

"We am propelling ourselves in a contiguous direction an' in closeproximity to an elevated portion of th' earth's surface which rises inantiguous proximity t' th' forward part of our present means oflocomotion!" said the colored man in a loud voice. 

"Which means there may be a collision, " the professor said, as he andthe boys hurried toward the tower, "Jest what I said, " retorted Washington. "What'll I do?"

"Send the ship a little higher, " answered Mr. Henderson. "We mustn'thit any mountains. "

Washington forced more gas into the holder, and speeded the negativegravity machine up some, so that the Mermaid, which was flying ratherlow, ascended until it was in no danger of colliding with the peakwhich reared its lofty height just ahead of them. 

As the ship sailed slowly over the mountain, Mark gazed down andexclaimed:

"Doesn't that look like the ruins of some building?"

The professor took a pair of field glasses from a rack in the wall andtook a long view. 

"It must be the place, " he said in a low voice. 

"What place?" asked Jack. 

"The temple of treasure, " was the answer. "Hankos told me it was ontop of the highest mountain in the land, and this must be it, for itis the loftiest place we have seen. But we must be careful, for thereis danger down there. "

"What kind?" asked Mark. 

"The place was long ago deserted by the giants, " Mr. Henderson wenton. "Ages ago it was one of their storehouses for treasure, but therewere wars among themselves, Hankos said, and this part of the countrywas laid waste. Savage beasts took up their abode in the temple, andsince then, in spite of the great size of the giants, they have notdared to venture here. If we brave the animals we may have all thegold and diamonds we can take away. "

"Then for one, I'm willin' t' go down an' begin th' extermination atonce, " put in Andy. "I've always wanted t' be rich. "

"We must proceed cautiously, " the professor said. "We are ill preparedto fight any such beasts as we saw at the big geyser. At the same timethey may have deserted this place. I think we will lower the ship downover the temple, and spend several hours in observation. Then, ifnothing develops, we can enter and see if the treasure is there. "

This plan was voted a good one, and the Mermaid after having beensteered directly over the ruined temple, was brought to a halt, andenough gas let out so that it fell to about fifty feet in the airabove it. 

The adventurers began their watch. The afternoon waned and there wereno signs of any beasts in or about the temple. 

"I reckon we can take a chance, " said Andy, who was anxious to get hishands on some diamonds. 

"Better wait until morning, " counseled Mr. Henderson. "It will soon bedark, and it doesn't look like a nice place to go stumbling about inby moonlight. "

So, though all but the scientist were anxious, they had to wait untilthe night had passed. Several times Washington got up to see if thetemple had, by any chance, taken wings during the long hours ofdarkness, but each time he found it was still in place. 

"Seems laik it'll never come mornin'. " he said. 

But dawn came at length, and, after a hasty breakfast, preparations toenter the temple were made. Andy loaded his gun for "bear" as heexpressed it, and the boys each took a revolver. 

The ship was lowered to as level a place as could be found, and then, seeing that everything was in readiness for a quick departure, theprofessor led the way out of the Mermaid. 

The entrance to the temple was through a big arched gateway. Some ofthe stones had fallen down, and the whole structure looked as if itmight topple over at any moment. 

"Go carefully, " cautioned Mr. Henderson, "Watch on all sides and upabove. Better let Andy and me go ahead. "

The scientist and the old hunter led the way. Through the arch theywent, and emerged into what must at one time have been a magnificentcourtyard. Before them was the temple proper, a vast structure, withan opening through which fifty men might have marched abreast. But thedoors were gone, and the portal was but a black hole. 

"I hope there ain't any ghosts in there, " said Washington, with ashiver. 

"Nonsense!" exclaimed the professor. "There may be things as bad, butthere are no such things as ghosts. Have your gun ready, Andy. "

With every sense on the alert, the old hunter advanced. Every one wasa bit nervous, and, as Mark and Jack afterward admitted, they halfexpected some terrible beast to rush out at them. But nothing of thekind happened, and they went into the interior of the temple. 

At first it was so dark they could see nothing. There were vast dimshapes on every side, and from the hollow echo of their footsteps theyjudged the roof must be very high and the structure big in every way. 

Then, as their eyes became used to the darkness, they could make out, up front, something like an altar or pulpit. 

"Perhaps that's where they offered up the gold and diamonds as asacrifice to their gods, " spoke Mark in a whisper. 

"Sacrifice to their gods!" came back a hundred echoes and the soundmade every one shudder. 

"Oh!" said Washington, in a low voice. 

"Oh! Oh! Oh!" repeated the echoes in voices of thunder. 

"Well, this is pleasant, " spoke Andy, in his natural tones, and, tothe surprise of all there was no echo. It was only when a personwhispered or spoke low that the sound was heard. After that theytalked naturally. 

"You stay here, and Andy and I will go up front and see what thereis, " said Mr. Henderson. "Be on your guard, and if you hear us comingback in a hurry, run!"

It was with no little feeling of nervousness that the boys, Bill, Tomand Washington watched the two men move off in the darkness. Theycould hear their footsteps on the stone flags and could dimly seethem. 

"They must be almost to the altar by this time, " said Mark, after along pause. 

Hardly had he spoken than there came a loud, sound from where Mr. Henderson and Andy had gone. It was as if some giant wings werebeating the air. Then came shrill cries and the voice of the oldhunter could be heard calling:

"Kneel down, Professor! Let me get a shot at the brute!"

Those waiting in the rear of the temple huddled closer together. Whatterrible beast could have been aroused?

The next instant the place seemed illuminated as if by a lightningflash, and a sound as of a thousand thunder claps resounded. 

"I think I winged him!" cried Andy's voice, and the boys knew he hadfired at something. 

Then there came a crash, and from the roof of the old temple a dozenstones toppled off to one side, letting in a flood of colored light. 

By this illumination could be seen, flapping through the big spaceoverhead, an enormous bat, as large as three eagles. And, as it flewabout in a circle it gave utterance to shrill cries. 

"Bang!" Andy's gun spoke again, and the bat with a louder cry thanbefore, darted through the hole in the roof made by the fallingstones, which had been loosened by the concussion from the rifle. 

"Come on!" cried the old hunter. "That was the guardian of thetreasure! We are safe now!"

Then, in the light which streamed through the broken roof, theadventurers could see, heaped up on a great altar, behind which sat ahorrible graven image, piles of yellow metal, and sparkling stones. Inlittle heaps they were, arranged as if offerings to the terrible godof the giants. There were bars and rings of gold, dishes of odd shape, and even weapons. As for the sparkling stones, they were of manycolors, but the white ones were more plentiful than all the others. 

"Gold and diamonds! Diamonds and gold!" murmured the professor. "Thereis the ransom of many kings in this ancient temple. "

"Wish I had a big bag!" exclaimed Washington, as he began filling allhis pockets with the precious metal and gems. "If I had a-thought I'dhave brought a dress-suit case!"

"A dress-suit case full of diamonds!" exclaimed Mark. 

Then he too, as did all the others, fell to filling his pockets withthe wealth spread so lavishly before them. There was the riches of awhole world in one place and no one but themselves to take it. 

For several minutes no one spoke. The only sound was the rattle of thestones and the clink of gold, and when some of the diamonds dropped onthe floor they did not bother to gather them up. There were too manyon the altar. 

"We will be rich for life!" gasped old Andy, who had been poor all hisyears. 

"I can't carry any more!" gasped Washington. "I'm goin' back for----"

What he was going back for he never said, for, at that instant, happening to look up at the hole in the roof, he gave a startled try:

"Here come the terrible bats!"

They all gazed upward. Through the opening they could see a greatflock of the awful birds, headed for the temple, and they were led byone which seemed to fly with difficulty. It was the guardian of thetreasure that Andy had wounded. 

"Quick! We must get out of here!" shouted the old hunter. "They arebig enough and strong enough to tear us all to pieces. Hurry!"

Down the centre of the temple they rushed, and not a moment too soon, for, ere they had passed half way to the entrance, the opening in theroof was darkened by the coming of the bats, and soon the flapping oftheir wings awoke the thundering echoes in the ruined structure, whiletheir shrill cries struck terror to the hearts of the travelers. 

Up to the altar circled the bats, and then wheeling they flapped downthe dim aisles toward the adventurers. 

"Hurry! Hurry!" shouted Andy, who was in the rear. 

He raised his rifle and fired several shots into the midst of theterrible creatures. 

A number of the bats were wounded, and the others were so frightenedby the sound of the shots and the flashes of fire that they turnedback. This enabled the fleeing ones to gain the entrance to thetemple, and soon they were outside. 

"To the ship!" yelled Bill. 

"There's little danger now!" called Andy, panting, for the run hadwinded him. "They will hardly attack us in the light!"

And he was right, for, though they could hear the bats flying aboutinside the temple, and uttering their cries, none came outside. 

But no one felt like staying near the uncanny structure, and littletime was lost in reaching the Mermaid. Then the doors were fastened, and the ship was sent high up into the air. 

"Which way?" asked Jack, when Mr. Henderson told him to go to theconning tower and steer. 

"Back to where we first met the giants, " replied the professor. "Wemust prepare to start for our own earth again soon. "

"I've almost forgotten how real sunlight looks, " thought Jack, as heheaded the ship around the other way. As he turned the levers a bigdiamond dropped from his pocket and rolled on the floor. 

"This will be a good reminder of our trip though, " he added. 

The travelers, even including Mr. Henderson, were so taken up withtheir suddenly acquired riches that they hardly thought of meals. Atthe professor's suggestion they tied their gold and stones up in smallpackages convenient to carry. 

"Better place them where you can grab them in a hurry in case ofaccident, " the old scientist went on. "Of course if there should betoo bad an accident they would never be of any use to us down here, but we'll look on the bright side of things. "

"Do you anticipate any accident?" asked Jack anxiously. 

"No, Oh no, " replied Mr. Henderson, but Jack thought the aged man hadsomething weighing on his mind. 

 CHAPTER XXIX

 BACK HOME-- CONCLUSION

ON and on sped the Mermaid. Now that the travelers felt their journeyaccomplished they were anxious to begin the homeward trip. They made astraight course for the village where they had so nearly met withdisaster, and where the king of the giants had saved them. They wentin a direct line, and did not travel here and there, as they had afterthey left the town. Consequently they shortened the route by a greatdistance. Yet it was long enough, and when they finally came in sightof the place the dial registered a trip of five thousand milesunderground. 

It was one evening when they landed almost at the spot whence they hadtaken flight eventually to reach the temple of the treasure. Most ofthe giants had betaken themselves to their mound houses, but Hankoswas walking in the fields, and, when he caught sight of the airshiphovering above him he waved his great sword in welcome. 

He rushed up to shake hands with the travelers when they came out ofthe ship, though to greet him it was only possible for the adventurersto grasp one of his immense fingers. 

As soon as the greetings were over Hankos began to speak rapidly tothe professor, at the same time going through many strange motions. 

"It is as I feared!" suddenly exclaimed the scientist. 

"What is the matter?" asked Mark. 

"The worst has happened!" went on Mr. Henderson. "The great hole bywhich we came into this place has been closed by an earthquake shock!"

"The hole closed?" repeated Jack. 

"An earthquake shock!" murmured Mark. 

"Then how are we going to get back to earth?" asked old Andy. 

A terrible fear entered the hearts of the travelers. The closing ofthe opening by which they had come to the strange world meant, in allprobability that they would have to spend the rest of their lives inthis underground place. 

"What good did it do us to get all those diamonds and that gold?"asked Mark in a sorrowful tone. 

Hankos began to speak again, using his gestures which were almost aseloquent as words. The professor watched and listened intently. Thenthere seemed to come a more hopeful look to his face. He noddedvigorously as Hankos went on with what seemed to be an explanation. 

"It's worth trying, at all events!" the scientist exclaimed. "It isour only hope!"

"What is?" asked Jack. 

"Friends, " began the professor in solemn tones. "I must admit ourplight is desperate. At the same time there is a bare chance of ourgetting back to our own earth. As you remember, Hankos went from thisplace to the upper regions through the upward spouting column ofwater. "

"If we had our submarine we might also, " interrupted Jack. "But theMermaid isn't built to sail in that fashion. "

"Nor would the Porpoise have served us in this emergency, " said theprofessor. "It would prove too heavy. But, nevertheless, I think Ihave a plan. Now, Mark, you are about to learn the secret of thestoreroom. The real one, not the hiding of Hankos in there, which youimagined to be the cause of my desire to keep something hidden. Whenwe planned a trip to this underground world I had a dim idea that wemight meet with trouble. So I planned and made a cylinder lifeboat. "

"A cylinder lifeboat?" repeated Mark. 

"Yes, " replied Mr. Henderson. "I have it in the storeroom. I did notwant any of you to see it for fear you would have faint hearts. Ithought there might be no necessity of using it. But, since there is, we must do our best. I will admit it may be a fearful ordeal, but wewill have to risk something in order to escape. 

"I have in the storeroom a large cylinder, capable of holding us all. It will also contain food and drink for a month, but we will all haveto go, packed almost like sardines in a box. My plan is to take theMermaid to the place where the column of water shoots up. There wewill get into the cylinder, close it, and trust ourselves to theterrible force that may bring us back to the upper world. What do yousay? Shall we attempt it?"

For a few seconds no one spoke. Then Jack said slowly:

"I don't see that we can do anything else. I don't want to stay hereall my life. "

"I wants a chance t' wear some of them sparklers, " put in Washington. 

"Then we will make the attempt, " the professor added. "Now all aboardfor the place where the water shoots up!"

Questioning Hankos, the professor learned how to reach the strangeplace. It was in the midst of a desolate country where none of thegiants ever went, so afraid were they of the strange phenomenon. 

It was a week's journey. Sometimes the Mermaid flew through the air, and again it sailed on vast lakes or inland seas. On the trip they metwith big waterfalls and terrible geysers that spouted a mile or moreinto the air. They traveled by night as well as day, though it wasnecessary to keep a sharp watch. 

Sometimes the ship passed through great flocks of birds thatsurrounded her and sought to pierce the aluminum hull with their sharpbeaks and talons. Over the mountains and valleys the ship saileduntil, one evening, there sounded through the air a strange rumblingsound. 

"It is thunder, " said Old Andy. 

"It is the water column, " replied the scientist. "We are at the end ofour trip. May the remainder be as successful!"

The ship was lowered to the surface, as it was deemed best to approachthe column when the lights were shining. No one slept much that night, for the roaring and rumbling never ceased. 

In the morning the ship was sent forward slowly. Ever and ever theterrific sound increased, until it was almost deafening. They had tocall to each other to be heard. 

Then, as the Mermaid passed over a mountain, the adventurers saw, in avalley below them, the up-shooting water. 

It was a vast column, nearly three hundred feet in thickness, and assolid and white as a shaft of marble. Up, up, up, it went, until itwas lost to sight, but there were no falling drops, and not even aspray came from the watery shafts. 

"There is a terrible power to it, " the professor said. "May it proveour salvation!"

The ship was lowered about a hundred feet away from the waterspout. All around them the ground was vibrating with the force of the fluid. 

"To think that connects with the world above!" exclaimed Jack. 

"It's a good thing for us that it does, " Mark answered. 

"We must lose no time, " the professor put in. "If the earthquakedestroyed the downward shaft, it may effect this one in time. We mustescape while we can. "

Then, for the first time, he opened the storeroom and the big cylinderwas disclosed to view. It was made of aluminum, and shaped like animmense cigar. The hull was double, and it was strongly braced. Insidewere padded berths for the occupants, and there was just room enoughfor the seven adventurers. Once they had entered they could not moveabout, but must stay in their little compartment. 

Compressed air in strong cylinders furnished a means of breathing, andthere were tiny electric lights operated by a storage battery. Therewas also a chamber to be filled with the lifting gas. The cylinder wasso arranged that it would float on it's long axis if thrown into thewater. A trap door hermetically sealed gave access to the interior. Asmall propeller, worked by compressed air, furnished motive power. 

The food supply consisted of compressed capsules on which a man couldsubsist for several days. There was also some water, but not much, since that can not be compressed and would, therefore, takeconsiderable room. 

"The only thing for us to do, " said the professor, "is to get into thecylinder, seal it up, and trust to Providence. This is what I intendedto use when we were caught in the draught. "

"How can we get into the column of water after we shut ourselves intothe cylinder?" asked Mark. 

"The cylinder fits into a sort of improvised cannon, " said Mr. Henderson. "It is fired by electricity and compressed air. "We willaim it at the column, press the button and be projected into the midstof the water. Then----" He did not finish the sentence, but the othersknew what he meant. 

"When are we to start?" asked Mark. 

"As soon as possible, " replied the professor. "I must arrange thecylinder, compress the air and lay out the food supply. "

It took the rest of the day to do this, as the inventor found it wouldbe advisable to attach a weight to the end of the cylinder, to hold itupright in the column of water. The weight could be detachedautomatically when they were shot up into the midst of the ocean, where, as Hankos had told them, the column spurted forth. 

Then some food was stored in the tiny ship that was destined to betheir last hope, and some tanks of water were placed in it. 

"I think we are almost ready, " Mr. Henderson said about noon the nextday. 

"What about our gold and diamonds?" asked Jack suddenly. "Can we takethem with us in the cylinder?"

"That's so!" exclaimed Mr. Henderson. "I forgot about them. I'm afraidwe'll have to leave the riches behind. We will not be able to carrythem and the food we need, for it may be a week or more before we canleave the cylinder. Gold and diamonds will be a poor substitute forsomething to eat. "

"I'm goin' t' take mine!" said Washington with much conviction. "Imight as well starve rich as starve poor!"

"We may be able to take a few diamonds, " the professor answered. "Thegold will be too heavy. Let each one select the largest of thediamonds he has and put them in his pockets. "

Then began a sorting of the wealth. It was strange, as they recalledafterward, throwing away riches that would have made millionairesenvious, but it had to be done. All the wealth in the world would notequal a beef capsule when they were starving, and they realized it. Sothey only saved a few pieces of gold as souvenirs, and took the bestof the diamonds. But even then they had a vast fortune with them. 

At last all was in readiness. The cylinder had been placed in the tubefrom which it was to be shot gently forth by compressed air, so thatit would fall into the upward spouting column of water. The charge ofcompressed air was put in and the electric wires arranged. 

"Are we all ready?" asked Mr. Henderson. 

"I think so, " said Jack, in what sounded like a whisper, but which wasloud, only the noise of the water muffled it. 

"Then we had better enter the cylinder, " spoke the inventor. "Take alast look at the Flying Mermaid, boys, for you will never see againthe ship that has borne us many thousand miles. She served us well, and might again, but for the freak of nature that has placed us inthis position. "

For the first time the adventurers realized that they must abandon thecraft in which they had reached the new world. So it was with nolittle feeling of sadness that they climbed up the ladder that hadbeen arranged and slid down into the cylinder. One by one they tooktheir places in the padded berths arranged for them. It was a snugfit, for the professor knew if there was too much room he and theothers might be so tossed about as to be killed. 

Mr. Henderson was the last to enter. Standing at the manhole he took afinal look at his pet creation, the Mermaid. Through the openedwindows the colored lights came, shifting here and there. Outside theterrible column of water was roaring as if anxious to devour them. 

"Good-bye, Mermaid!" said the professor softly. 

Then he closed down the manhole cover and tightened the screws thatheld it in place. He touched a button that turned on the electriclights and the interior of the cylinder was illuminated with a softglow. 

"Are you all ready?" he asked. 

"Jest as much as I ever will be, " replied Washington, who, as thecrisis approached, seemed more light-hearted than any of the others. 

"Then here we go!" exclaimed Mr. Henderson. 

His fingers touched the button that connected with the electricmachine, which operated the compressed air. 

There sounded a muffled report. Then it seemed to those in thecylinder that the end of the world had come. They shot upward andoutward, through the top of the conning tower which had been removed. The cylinder, launched straight at the column of water struck itsquarely and, an instant later was caught in the grasp of the giantforce and hurled toward the upper world. 

Up and up and up the mass of metal with its human freight went. Now itwas spinning like a top, again it shot toward the earth's crust likean arrow from the archer's bow. 

It was moving with the velocity of a meteor, yet because of beingsurrounded with water, and traveling with the same velocity as thecolumn, there was no friction. Had there been, the heat generatedwould have melted the case in an instant. 

For the first few seconds those in the cylinder were dazed by thesudden rush. Then as it became greater and greater there came acurious dull feeling, and, one after another lost consciousness. Theterror of the water column, and the frightful speed, had made themsenseless. _______

It seemed like a month later, though, of course, it could have beenonly a few hours or a day at most when Jack opened his eyes. He sawhis companions, white and senseless all around him, and at firstthought they were dead. Then he saw Mark looking at him, andWashington asked:

"Is any one livin' 'sides me?"

"I am, " replied Jack decidedly. 

Then, one after another they regained their senses. But they were in astrange daze, for they were being carried along like a shooting star, only, as they went at the same rate as did the element carrying them, they did not realize this. 

"I think I'm hungry, " said Bill, who had the best appetite of any ofthe travelers. 

"You'll find a beef capsule in the little compartment over your head, "spoke the professor. 

Bill was about to reach for it, when they were all startled by asudden side motion of the cylinder. Then came a violent shock, and asound as of splashing water. Next the cylinder seemed to be falling, and, a few minutes later to be shooting upward. Following this therewas another splash and the cylinder began to bob about like a cork ona mill pond. 

"We have reached the sea! We are afloat on the ocean!" cried theprofessor. 

Hurriedly he disengaged himself from the straps that held him to hisbunk. He pushed back the lever that opened the manhole. Into theopening glowed the glorious sunlight, while to the occupants came thebreath of salt air. 

"Hurrah!" cried Jack. "We are safe at last!"

"Safe at last!" the professor answered, and then they all gave acheer. 

For their cylinder, which might now be termed a boat, was floating onthe great Atlantic. The blue sky was overhead and the air of the seafanned their cheeks. 

They had shot up from the underground earth, in the column of water, had been tossed high into the air, had fallen back when the liquidshaft broke into spray, had descended into the ocean, gone down ahundred feet or more, and then had shot up like a cork to bob aboutthe surface. 

For a week they were afloat, and then they were picked up by a passingvessel, rather weak and very much cramped, but otherwise in goodshape. They said nothing of their adventures, save to explain thatthey were experimenting in a new kind of boat. About a month later, for the ship that had rescued them was a slow sailer, they were backon the island whence that wonderful voyage was begun. _______

"Well, we solved the mystery of the center of the earth, " remarkedJack, one evening, when they were gathered in the old shack where somany wonderful adventures had been planned. 

"Yes, we did, " said Mr. Henderson. "And no one else is ever likely togo there. "

"Why?"

"Because the only way of getting there was destroyed by theearthquake, and no one could ever force his way down through thatupward-shooting column of water. "

"That's so. Well, we have the diamonds, anyway, " spoke Mark. "Theyought to make us rich. "

And the jewels did, for the stones proved to be of great value, eventhough the adventurers had saved only a few of the many they found inthe ruined temple. 

But there was money enough so that they all could live in comfort; therest of their lives. As the professor was getting quite old, andincapable of making any more wonderful inventions, he closed up hisworkshop and settled down to a quiet life. As for Washington, Andy, and Bill and Tom, they invested their money received from the sale ofthe diamonds in different business ventures, and each one did well. 

"I am going in for a good education, " said Jack to Mark. 

"Just what I am going to do, " answered his chum. "And after we've gotthat----" He paused suggestively. 

"We'll go in for inventing airships, or something like that, eh?"

"Yes. We've learned a great deal from Mr. Henderson, and in the courseof time we ought to be able to turn out something even more wonderfulthan the Electric Monarch, the Porpoise, or the Flying Mermaid. "

"Yes, and when we've invented something better----"

"We'll take another trip. "

"Right you are!"

And then the two chums shook hands warmly; and here we will saygood-bye. 

 THE END.