THE FLYING MERMAID SANK LOWER AND LOWER TOWARD THE MYSTERIOUS HOLE.

Five Thousand Miles Underground
Or
The Mystery of the Centre of the Earth
BY
ROY ROCKWOOD
Author of “Through the Air to the North Pole,” “Under
the Ocean to the South Pole,” “The Rival
Ocean Divers,” Etc.
ILLUSTRATED
NEW YORK
CUPPLES & LEON COMPANY

GOOD BOOKS FOR BOYS
By Roy Rockwood
THE GREAT MARVEL SERIES

THROUGH THE AIR TO THE NORTH POLE
Or The Wonderful Cruise of the Electric Monarch
UNDER THE OCEAN TO THE SOUTH POLE
Or The Strange Cruise of the Submarine Wonder
FIVE THOUSAND MILES UNDERGROUND
Or The Mystery of the Centre of the Earth

Cloth. Illustrated
Price per volume, 60 cents

Copyright, 1908, by
Cupples & Leon Company
Five Thousand Miles Underground

CONTENTS

FIVE THOUSAND MILES UNDERGROUND

CHAPTER I
WASHINGTON BACKS OUT

“Washington! I say Washington!”

Throughout a big shed, filled for the most part with huge pieces of machinery, echoed the voice of Professor Amos Henderson. He did not look 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 aluminum came the voice of a colored man.

“Yas sir, Perfesser, I’se goin’ t’ saggasiate my bodily presence in yo’ contiguous proximity an’ attend t’ yo’ immediate conglomerated prescriptions at th’ predistined period. Yas, sir!”

“Well, Washington, if you had started when you began that long speech you 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 to help 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 a combined airship and watercraft. “Jack says as how yo’ gived him permission t’ occupy his indisputatious period of levity in endeavorin’ t’ extract from th’ liquid element some specimens of swimmin’ creatures.”

“If you mean I said he and Mark could go fishing in the brook, you’re right, Washington,” replied the professor with a smile. “But you waste a lot of time and breath trying to say it. Why don’t you give up using big words?”

“I reckon I was brought up t’ it,” replied the colored man grinning from ear to ear. He did not always use big words but when he did they were 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,” answered the messenger, and he went out.

Washington White, who in color was just the opposite to his name, a general helper and companion to Professor Henderson, found Mark Sampson 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. The lads 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. I reckon th’ new fangled contraption that th’ perfesser is goin’ t’ navigate th’ air an’ sail th’ angry seas in, am about done. He want’s t’ 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 eighteen years old, started toward the big shed.

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

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

Mark and Jack were orphans. After having rather a hard time knocking about the world trying to make a living, they chanced to meet, and resolved to cast their lots together. They boarded a freight train, and, as told in the first volume of this series, entitled, “Through the Air to the North Pole; or the Wonderful Cruise of the Electric Monarch,” the cars were wrecked near where Professor Henderson was building his strange craft.

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

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

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

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

What occurred on this great trip is described in the second book of this series, called “Under the Ocean to the South Pole, or the Strange Cruise of the Submarine Wonder.” In that is told how once more Tom and Bill, with Andy, the boys and Washington, accompanying Professor Henderson, had many thrilling experiences.

They were caught in the grip of the grass of the terrible Sargasso Sea. Monstrous suckers grasped the boat in their powerful arms, and had to be fought off. They were caught in a sea of boiling water and imprisoned between big fields of ice.

By means of strong diving suits they were able to leave the ship and walk about on the bottom of the sea. They visited a graveyard of sunken ships, saw many strange monsters as well as many beautiful fish in the great depths to which they sunk. Many times they were in dire peril but the resources of the professor, the bravery and daring of the 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 strange island which they came upon in the Atlantic Ocean, far from the coast of South America.

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

But, on going to another side of the island they were able to approach safely, 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 also round, but not in the center of the land. It was an immense cavity, so wide they could not see across, and as for the depth they could only guess at it. Looking down they could only see rolling masses of vapor and clouds caused by the water which poured down from the ocean with the force of a Niagara.

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

They had no means of investigating further the mystery of the opening and returned to their submarine, completing the voyage to the south pole.

It was now about two years since they had come back from that eventful trip. One of the first things the professor did, after docking the Porpoise, 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 on top 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 the new craft, so there was no need to get other help than that which the boys, Washington and Bill and Tom could give, since the two latter accepted an offer of the professor to remain and work for him. The boys, of course, would not leave their friend.

The professor realized that he had a more difficult task in his new venture than he had set himself on other occasions. For a ship to be light enough to rise in the air, and, at another time, and with no change, to be strong enough to navigate the ocean, was indeed something to tax Mr. Henderson’s ingenuity.

However, in the course of a little over a year the larger part of the work was done. Inside the big shed was the huge affair which, it was hoped, 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 altitude projected in an inverse direction by th’ square root of th’ new engine when operated at a million times inside of a few seconds, but he didn’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 had th’ thing goin’ soon.”

“Do you think he’ll be generating the new gas to-day?” asked Jack eagerly. “That’s the most troublesome part; to get that gas right.”

“He didn’t say nothin’ t’ me 'bout it,” Washington stated, as he walked along beside the two boys. “He jest seemed anxious like.”

“We’d better hurry,” advised Mark. “He may be at an important part in his experiments and probably needs us. I hope it will work. He has spent many days on it, and we all have worked hard. It ought to be a success.”

“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 a turn of the path through the wood. They noticed an elderly man approaching with a gun on his shoulder. On one arm he carried a game bag.

“Guess Andy got something for dinner,” remarked Jack.

“I hopes so, honey,” put in Washington. “I’se got a sort of gone feelin’ 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 good dinner to-morrow.”

While Andy entered the living part of the big shed to put away his gun and game, the boys and Washington kept on to the engine room. They found the professor, with Bill and Tom, busy fitting pipes to the small 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 the dynamo is in working order for Washington to attend to.”

In a little while the shop was a veritable hive of industry, and it resounded to the sound of hammers, wrenches and machinery. In the background was the big ship, which seemed like two immense cigars, one above 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 to the south pole?”

“I suah does,” answered the colored man.

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

“Go down into th’ earth!” exclaimed Washington, his eyes big with fright.

“Certainly; why not?”

“Not for mine!” cried the colored man, dropping the wrench he was holding. “No sir! I’m not goin’ t’ project myself int’ a grave while I’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, but Washington White stays on terra cotta! That’s where he stays; He ain’t ready t’ be buried, not jest yet!” and the frightened colored man started 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 be frightened. We’re not going to start at once.”

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

“Come on back!” said Mark. “There’s no danger, and if there was we’re not going to start to-day.”

“Ain’t yo’ foolin’ me?” asked Washington, pausing and looking doubtfully at the boys.

“Of course not,” answered Mark. “You know Professor Henderson would not make you do anything you didn’t want to do, Wash. He wishes you to stay and help him get ready, that’s all.”

“Well, Washington,” observed the aged scientist. “I didn’t think you’d go back on me.”

“I’d do mos’ anything fer yo’, Perfesser,” said the colored man, “but I got t’ beg off this time,” and he looked at the Flying Mermaid as if he thought the metal sides would open and devour him.

“Then help me get things in shape to generate the gas,” the scientist said. “I want to give the new vapor the first real test in lifting power 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 of the earth, Washington resumed his labors. The professor, the boys, Bill and Tom were also hurrying matters to enable a test to be made before night.

As will readily be seen, even by those not familiar with the construction of airships and submarines, the chief problem was to find some agent strong enough to lift from the earth a weight heavier than had ever before been put into an apparatus that was destined to traverse the clouds. For the Flying Mermaid was not only an airship but an ocean voyager as well. It had to be made light enough to be lifted far above the earth, yet the very nature of it, necessitating it being made heavy enough to stand the buffeting of the waves and the pressure of water, was against its flying abilities.

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

After long study he had been partially successful, but he knew from experiments made that the gas he had so far been able to manufacture would not answer. What he wanted was some element that could be mixed with the gas, to neutralize the attraction of gravitation, or downward pull of the earth.

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

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

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

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

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

As in the Porpoise and Monarch, electricity formed the motive power and was also used for many other purposes on board. Engines operated by 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 lower hull 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 a current of compressed air could be sent out from either pipe. Thus when floating above the earth the ship was forced forward by the blast of air rushing from the pipe at the stern. It was the same principle as that on which a sky rocket is shot heavenward, save that gases produced by the burning of powder in the pasteboard rocket form its moving impulse.

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

The engine room was a marvel of machine construction. It contained pumps for air and water, motors, dynamos, gas engines, and a maze of wheels and levers. Yet everything was very compact and no room was wasted.

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

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

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

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

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

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

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

“This cylinder is just one one-hundredth the size of the cylinder of the ship,” said the professor. “I am going to fasten to it a hundred pound weight. If it lifts that our latest contrivance will be a success.”

“You mean if the little cylinder pulls a hundred pounds up the big ship will take us and the machinery up?” asked Mark.

“Certainly,” answered the professor. “If this cylinder lifts a hundred pounds, one a hundred times as big (as that of the Mermaid is), will lift a hundred times as much, or ten thousand pounds. That is five tons, or more than a ton over what I figure to be the weight of our ship 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 be disappointed.”

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

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

The scientist gave a last look at everything. The boys got behind some boards whence they could see without being in danger. Washington, who had 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, stationed themselves in safe places.

“All ready!” called the professor.

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

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

“There!” he exclaimed at length. “It has all the gas it can hold. Now to see if it works!”

He disconnected the pipe leading from the generator. This left the cylinder free. It seemed to tremble slightly. There appeared to be a movement to the hundred pound weight which rested on the ground. It was 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, coming from the dynamo.

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

“It will work! It will work!” exclaimed the professor, strangely excited.

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

“Quick! We must get it back!” cried Mr. Henderson. “If it gets away my secret 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 blown to the east, the weight dangling below it, making it look like a miniature airship.

“We can never catch that!” cried Mark.

CHAPTER III
WASHINGTON DECIDES

“We must catch that cylinder!” the professor exclaimed. “Some one may find it when it comes down and analyze the gas. Then he would discover how to make it. The cylinder must come down!”

“Don’t see how we can proximate ourselves inter th’ vicinity of it lessen we delegate th’ imperial functions of ornithological specimens t’ some member of this here party,” observed Washington.

“If you mean we can’t catch that there contraption unless we turn into birds I’ll show you that you’re mistaken!” cried Andy Sudds. “I guess I have a trick or two up my sleeve,” and the old hunter quickly threw open the breech of his gun and inserted a couple of cartridges.

He raised the piece to his shoulder and took quick aim. There was a sliver of flame, a puff of smoke and a sharp report. The professor and the boys who were watching the cylinder saw it vibrate up in the air. Then there came a whistling sound. An instant later the metal body began 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 Andy with a queer smile, “but it was the only way I saw of bringing it down. Hope it isn’t damaged much.”

“It doesn’t matter if it is,” the scientist answered. “I can make more cylinders, 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 vapor out just in time.”

“Then we may consider the experiment a success,” said Mark, as Washington went to where the cylinder had fallen, to detach it from the weight and bring both to the shed.

“It seems so,” Mr. Henderson answered. “True, it was only an experiment. 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 inventor said. “It does not require much work to make a ship which will do that. But the air proposition is another matter. However, since the cylinder rose, I am pretty sure the Flying Mermaid will.

“But we have done enough work to-day. Let’s rest and have something to eat. Then, with Sunday to sit around and talk matters over, we will be ready for Monday’s test.”

Some of the game Andy had killed was soon on the table, for Washington, in addition to his other accomplishments, was an expert cook. During the evening the boys and their friends sat in the living room of the big shed and talked over the events of the day.

Sunday was spent in discussing what adventures might lie before them should they be able to descend into the big hole. Washington did not say much, but it was easy to see he had no notion of going. He even began to pack his few belongings in readiness to leave the service of Mr. Henderson, for whom he had worked a good many years.

No one remained long abed Monday morning. Even Washington was up early in 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 live folks,” he said.

In order to properly test the Flying Mermaid it was necessary to move the craft from the shed from which place it had never been taken since it’s construction was started. It had been built on big rollers in anticipation of this need, so that all which was now necessary was to open the doors at the end, and roll the craft out.

This was accomplished with no small amount of labor, and it was nearly noon before the big ship was moved into the open. It was shoved along to a little clearing in front of the shed, where no trees would interfere with its possible upward movement.

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

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

Up and down these the professor, the boys and Andy went, taking in tools and materials, and removing considerable refuse which had accumulated during the building of the craft.

Finally all was in readiness for starting the making of the gas. The ship was not wholly complete and no supplies or provisions for the long voyage had been taken aboard. The Flying Mermaid was about a ton lighter than it would be when fully fitted out, but to make up for this the professor had left in the ship a lot of tools and surplus machinery so that the craft held as much weight as it would under normal conditions. If the gas lifted it now it would at any other time.

“Start the generator,” said Mr. Henderson, to Mark. “We’ll soon see whether we are going to succeed or fail.”

The boy turned a number of levers and wheels. The machine which made the powerful vapor was soon in operation. The professor had already added enough of the secret compound to the tank containing the other ingredients, and the big pump was sucking in air to be transformed into the lifting gas.

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

The gas was being generated rapidly. Throughout the ship there resounded a hissing noise that told it was being forced through the pipe 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 we have 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 the addition of a small quantity to enable the ship to rise.”

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

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

“What is it?” asked Jack.

“I hope it is the lifting power of the gas making itself felt,” the professor answered. “Perhaps the Flying Mermaid is getting ready to try her wings.”

The trembling became more pronounced. The gas was being generated faster than ever. The whole ship was trembling. Tom and Bill came from the room, where they were stationed, to inquire the meaning, but were reassured 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 the flights she took. We may not go as high as we did in her, but it will answer the same purpose.”

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

“I think we shall rise presently,” said Mr. Henderson. His voice showed the pride he felt at the seeming success with which his invention was about to meet.

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

“Here we go!” cried Mr. Henderson. “The ship is a success. Now we’re off for the hole in the earth!”

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

“It’s a success! It’s a success!” shouted Mark, capering about in his excitement.

“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 the voyage.”

At that instant, when the ship was but a few feet from the ground, but slowly 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 ocean steamer, and looked out.

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

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

“Save me! Save me!” cried the colored man. “I’m goin’ to fall! Catch me, some one!”

“What is it?” asked the professor, making ready to shut off the power and let the ship settle back to earth, from which it had moved about fifty feet.

“It’s Washington,” explained Mark. “He evidently tried to walk up the steps just as the boat mounted skyward. He rolled down and managed to grab the end of the rope which was left over after the steps were tied. 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 until his 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. “You bet I’m goin’ to hold on, and I’m comin’ up too,” which he proceeded to 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 enough gas had been let out. Closer and closer came Washington, until he was able to grasp the edge of the opening, to which the steps were fastened.

“I thought you weren’t coming with us,” observed the professor, when he saw that his helper was safe.

“I changed my mind,” said the colored man. “It’s jest luck. Seems like th’ ship done wanted me t’ go 'long, an’ I’m goin’. I’ll take my chances 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. “Now come inside and we’ll see how the ship works.”

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

“She certainly am workin’” he observed with pride. “Are we still goin’ up, Perfessor?”

“Still mounting,” replied Mr. Henderson. “We are now three hundred feet 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 big stream of the compressed vapor rushed. It acted on the ship instantly and sent the craft ahead at a rapid rate. By elevating or depressing the tube the craft could be sent obliquely up or down. Then, by forcing the air from the forward tube, the Mermaid was reversed and scudded backward.

But it was more with the ship’s ability to rise and descend that Professor Henderson was concerned, since on that depended their safety. So various tests were made, in generating the gas and using the negative gravity apparatus.

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

Of course the machinery was new and did not operate as smoothly as it would later, but the professor and his friends were very well satisfied.

“Now we’ll try something new,” said the scientist to the two boys as they 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 rushed from 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’s all.”

“But good land! Perfesser!” exclaimed the colored man. “The ocean’s right under us! You forgot you sailed away from the island! We’ll be drowned suah!”

“Leave it to me,” said Mr. Henderson. “The Flying Mermaid is going to take a bath!”

“As long as it swims it will be all right,” observed Mark in a low tone 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 dive through the air. The next instant she struck the water with a splash that sent the waves rolling all about. The craft rocked violently to and fro on the surface of the sea. For a while there were anxious hearts aboard, for there was no certainty but that the ship might not sink to the bottom.

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

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

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

“She fits her name!” the professor cried. “She is indeed the Flying Mermaid, for she sails the ocean as easily as she navigates in the clouds!”

For a mile or two the craft was sent ahead over the waves. Then it was reversed and run backwards. Satisfied that his long months of work had not 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, Tom and Bill busied themselves in the engine room, Mr. Henderson began to generate the gas and start the negative gravity apparatus. All the while the craft was forging ahead.

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

Then like a bird rising from the waves, or like a flying fish leaping from the sea to escape some pursuing monster of the deep, the new ship shot up diagonally from the surface and winged its way into the upper regions of the air.

“Success! Success!” cried the professor. “This proves all I wanted to know. Now we are ready for our great trip!”

Great were the rejoicings in the camp that night. It was like living over again the days when they were aboard the diving Porpoise or the flying Monarch. To the recollections were added the anticipations of what 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 Flying Mermaid. The machinery, which was only partly completed, had to be finished. Besides this the professor was working on some apparatus, the use of which he did not disclose to any one. It was stored aboard the ship at the last minute.

Plenty of provisions had to be taken aboard, and many supplies needed to work the Mermaid and insure that it would go to the end of the voyage. The materials for generating the gas and negative gravity, spare parts, records for the automatic piano and other things were stored 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 the shape of enemies or wild beasts that might be met with in the interior regions.

It was decided to make the start by sailing along the surface of the sea for several days, as in the event of any weakness in the machinery being discovered there would be less danger. If, at the end of four days, no trouble developed, the professor said he would send the Mermaid 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 the boys, Washington and the other helpers, went about through the various shops and buildings, locking them up securely. For they could not tell how long they would be away, and they had to leave behind much valuable material.

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

“I wonder who that can be,” he thought. “All the others are near the machine shop, for I just left them there. Perhaps it’s some one trying to spy out how the Mermaid is built.”

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

Though the object had some of the characteristics of a man it did not walk like a human being, but shuffled along more like a huge ape or monkey. 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 than before, with a curious, shuffling walk. It was approaching the ship.

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

“If it’s some tramp trying to find a place to sleep he’d better not go aboard the ship, he might do some damage,” the boy thought.

He could hardly see the figure now as it had passed into the shadow cast by the boat. He was about to summon the professor to make an investigation, when Washington started going the search light which was placed just over the door of the living cabin. It was kept there as a sort of beacon light, as, near the island was a dangerous ledge of rocks.

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

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

For an instant Mark was so startled he cried out, and the professor and 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 of the 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. “Are you sure you saw something, Mark?”

“Positively,” replied the lad with a shudder. He described the vision of the darkness.

“I guess it was a big otter, or maybe an enormous turtle,” the professor said.

CHAPTER V
ATTACKED BY A WHALE

But Mark was certain it was nothing like that, though a careful search failed to reveal anything or any person near the ship. It was too dark to examine for footprints, and even Mark, after taking a look all about, felt he might have been deceived by shadows. Still he was a little nervous, and could hardly sleep for imagining what the thing he saw 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 after noon, final preparations having been made, they all got aboard the Mermaid and started off.

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

However, there was no other vessel in sight, and the island, as far as the 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 engine bearings. There will be time enough for speed later.”

“Yes, and we may need it more when we get into the centre of the earth than we do now,” observed Mark.

“Why so?” asked Jack.

“No telling what we may run up against underneath the ground,” went on Mark. “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 thinking deeply.

“I will tell you what I believe,” he said at length. “I have never spoken of it before, but now that we are fairly started and may eventually have a chance to prove my theory, I will say that I think the 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, similar to ours in some respects which revolves inside this larger sphere.”

They were well out to sea now, as they could observe when they emerged on 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 to make her steady, yet not deep enough to encounter much resistance from the water. In fact it could not have been arranged better for speed or comfort.

“I think we will sail well to the eastward before making our course south,” Mr. Henderson said. “I do not care to meet too many ships, as those aboard will be very curious and I do not want too much news of this venture to get out. We will take an unfrequented route and avoid delays by being hailed by every passing vessel whose captain will wonder 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 the prospect 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 shoot or that ought to be shot,” he used to say, “and it’s always the man without a gun who needs it most. So I’m taking no chances.”

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

Morning found the Mermaid about a hundred miles from the island where she had been launched. The night had been uneventful, except that Mark told Jack he heard some strange noise near his bunk several times. He was nearest the storeroom where spare parts, and the curious cylinder the 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 a rat 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 considerable thinking. However, the next night there was no further disturbance.

The fourth day out, when everything had passed off well, the engines doing their best, the professor decided to speed them up a bit, since he 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 well beyond the ordinary lines of travel now.”

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

“I might see a big fish, and we could vary our bill of fare,” he said with a laugh.

“Here we go!” exclaimed the professor as he shifted the levers and turned some wheels and valves. “Now we’ll see how fast we can travel.”

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

“I guess that will do,” said the scientist. “I think we have speed enough for almost any emergency. I’ll let her run at this rate for a while, and then we’ll slack up.”

Looking ahead, the boys could see the green waters parting in front of the bow of the Mermaid, as if to make room for her. Two huge waves were 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 was steering.

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

At that instant from the rock two small fountains of water rose in the air, 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 to hit him!”

The professor had miscalculated the speed of the craft, or else had not thrown her far enough to larboard, for, a second later, the Mermaid was almost upon the big leviathan.

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

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

“Hurrah!” the boys 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 a goner!”

“I’m afraid not,” muttered the professor. “That was a bad blow we struck him, but I think it will only ruffle his temper. We’ll have to look sharp now, boys.”

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

“He’s bleeding!” exclaimed the professor. “I guess Andy hit him in a vital 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 the pain of the bullet and the blow, was coursing after the ship, coming on with the speed of an express train. Straight at the Mermaid he lunged his huge bulk.

“We must escape him!” cried Mr. Henderson. “If he hits us he’ll send us to the bottom!”

He had made ready to slow up the Mermaid to see if it had sustained any damage from the impact with the whale, but when he saw the monster coming 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 sudden inspiration.

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

Faster through the water went the Mermaid, and faster after her came the whale. Above the hum of the engines was heard the hiss of the powerful 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 to her as if they hated to lose her. The boys knew the gas was beginning to 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 foam with his terrible flukes, and sending aloft a bloody spray. His speed was 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 a battle ship, forced forward by the tons of blubber, flesh, bone and fat 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 herself worthy of the name. Now, if ever, was the time for her to leave the watery element and take to the lighter one.

And she did. With a last tremble, as if to free herself from the hold of the waves, the gallant craft soared up into the air, leaving the water, which dripped from her keel like a fountain’s spray, and shooting aloft like a bird, escaped her terrible enemy which passed under her, so close that the lower part of the Flying Mermaid scraped the whale’s back.

“Saved!” exclaimed the professor.

THE LOWER PART OF THE FLYING MERMAID SCRAPED THE WHALE’S BACK.

CHAPTER VI
THE CYCLONE

It was only in the nick of time, for a second later and the big mammal of the ocean would have struck the ship and split it from stem to stern.

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

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

“I guess he would have taken after us whether you had fired at him or not,” said Mr. Henderson. “He was probably looking for trouble, and took 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, exiled from the school to which they once belonged, they get like mad creatures and know neither friend nor foe. Something like rogue elephants, I imagine.”

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

Once recovered from their fright caused by the whale, and having lost sight 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 with a relish. The electric cooking stove worked to perfection, for the colored man had learned how to use that aboard the Porpoise and Monarch, 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.