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."