Mark nodded his head, and the mate cried: 

“I knew I could fetch ’em.  I have hypnotic power.  This boy will raise the ship for us.  Loosen his bonds, some of you.”

Satisfied that they were now on the way to experiencing a new sensation, the sailors took the ropes off Mark’s arms and legs, and he was allowed to rise.  With a reassuring nod toward the professor he led the way to the engine room, followed by half the men.  He resolved to start the gas machine slowly, so as to make the upward trip last longer, thinking before it had gone far, some way of escape from the mutineers might be found.

While a crowd of the sailors stood near him, Mark operated the machinery in the engine room that started the gas generating, and set the negative gravity apparatus working.

“You’d better not try any tricks on us,” said one of the men in an ugly tone of voice.

“I’m not going to,” replied Mark.  “If you go out on deck you will soon see the ship leaving the water and mounting into the air.”

“Some of you go,” ordered a man with a big bushy red beard.  “See if the ship rises.  When she begins to go up sing out.  I’m going to stay here and see how the young cub does it so I can work it myself.”

Obeying the red-bearded man, who seemed to be a leader, several of the sailors went out on the deck.  It was quite dark, but there was a phosphorous glow to the water which made the rolling waves visible.

The gas was being generated, as could be told by the hissing sound.  Mark watched the machinery anxiously, for he knew much depended on him, and the professor was not at hand to guide and instruct him.  He watched the dial of the gage which registered the gas pressure and saw it slowly moving.  In a little while it would be at the point at which the ship ought to rise.

Presently a quiver seemed to run through the Mermaid.  Now a shout came from the watchers on deck.

“She’s going up!”

The ship was indeed rising.  The red-bearded man, who was addressed as Tony, ran from the engine room to the deck.  He saw that the ship was now ten feet above the water.  Back he came to where Mark stood by the gas machine.

“Lucky for you that you didn’t fool us, lad,” he said with a leer.  “See that you mind me hereafter.  Now show me how the shebang works.”

When the ship had risen as far as Tony desired he made Mark send it straight ahead.  The boy adjusted the air tube to carry the craft toward the south, but Tony, seeing by a compass in which direction they were headed, ordered Mark to steer due east.

“Fix things so they will stay so, too,” added Tony.  “I don’t want to stop until I get a thousand miles away.  Then we’ll come down, sail to some sunny island, and enjoy life.”

Mark locked the steering apparatus so as to keep the Mermaid headed due east.

“Now you can go back to your friends,” Tony said.  “When I want you I’ll send for you.”