“Well, I’m glad you’ve decided¹ 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 gage².
 
The great air pump was set going and soon from the after tube, a big stream of the compressed vapor³ 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 obliquely⁴ up or down. Then, by forcing the air from the forward tube, the Mermaid⁵ was reversed and scudded⁶ backward.
 
But it was more with the ship’s ability to rise and descend⁷ 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 apparatus⁸.
 
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 machinery⁹ was new and did not operate as smoothly¹⁰ 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 hissing¹¹ 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 Jack¹². “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 vessel¹³ 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 conning¹⁴ 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 steer¹⁵, 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 foamed¹⁶. 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 navigates¹⁷ in the clouds!”
 
For a mile or two the craft was sent ahead over the waves. Then it was reversed and run backwards¹⁸. Satisfied that his long months of work had not gone for naught¹⁹, 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 aluminum²⁰ holder²¹ being filled. For a few minutes there seemed to be no change, the Mermaid plowing²² forward.
&nbs............