“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!”