“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 sway 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.