“Don’t let her get too low,” the mate whispered.

“I’ll watch out,” Mark replied.  “I want to give them a good scare while I’m at it.”

The ship was now within fifty feet of the water.  There was a cry of terror from the sailors.  Some of them leaped over the rail and started to swim ashore, as the ship was by this time close to a group of islands.

Suddenly, from the engine room the mate rushed.

“Jump!  Jump for your lives!” he exclaimed.  “The ship is about to blow up!”

CHAPTER XI

 Mysterious happenings

The voice of the mate echoed through the Mermaid.  Those on deck heard it, as did Tony in the engine room, where he was vainly trying to understand the complicated machinery.

An instant later there sounded from beneath the ship a series of splashes.  More sailors were leaping from the deck of the craft to the ocean.  The distance was not great, particularly as they all landed in water.

“Quick!” cried the mate to a group of sailors that hesitated before taking the jump.  “The ship may blow up any minute now.”

The men needed no second urging.  As soon as they struck the water they began to swim ashore, as it was not far away.  One after another they jumped over the rail.  Tony was the last to go.  He urged the captives to follow him, but they all refused.

A minute later the only one of the pirate crew left on the ship was the mate.  The others were all struggling in the sea.  Eventually they all reached shore in safety.

The airship was now within about twenty feet of the water.  It was still falling but not so rapidly.

“Better send her up, now,” said the mate to Mark, and the boy turned the necessary levers to accomplish this.

Dipping into the water as a sea gull does when searching for food on the wing, for she had come quite low, the Mermaid mounted once more into the air, and was soon sailing along over the heads of Tony and his gang.

“What’s it all about?” asked Mr. Henderson, who seemed in a sort of stupor.  “I thought the ship was broken.  How, then, can it rise?”

“It was only a trick of mine,” Rodgers said.  “The gas machine is not broken.  I had Mark fix it so that only a little vapor would be generated.  When the supply in the holder was not enough, and no more was being made, the ship had to sink.  Mark and I pretended it was worse than it really was just to scare the scoundrels.”

“And you evidently succeeded,” observed Mr. Henderson.  “They have all left us.  I am glad you stayed.”

“So am I,” said Rodgers.  “I was just waiting for a chance to escape from that crowd.  This was the plan I thought of that night.  I wanted to see the men put on some island where they could manage to live, and which was not too far away.”

The Mermaid was now mounting upward rapidly, as Mark had adjusted the machinery properly.  The craft was well rid of the pirate crew, and was able to proceed on its way, and enable Mr. Henderson to carry out his plans.