“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.