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