Having oiled the bearings well, and seen that everything was in place
and properly adjusted, the professor and the boys took their places in
the conning tower, while Washington, Tom and Bill remained in the
engine room. Andy stayed on deck with his gun.

"I might see a big fish, and we could vary our bill of fare," he said
with a laugh.

"Here we go!" exclaimed the professor as he shifted the levers and
turned some wheels and valves. "Now we'll see how fast we can travel."

As he spoke the Mermaid responded to the added impulse of the
compressed air and shot through the water at a terrific speed. The
sudden increase in momentum almost threw the boys from their feet, and
they would have fallen had they not grasped some projecting levers.

"I guess that will do," Said the scientist. "I think we have speed
enough for almost any emergency. I'll let her run at this rate for a
while, and then we'll slack up."

Looking ahead, the boys could see the green waters parting in front of
the bow of the Mermaid, as if to make room for her. Two huge waves
were thrown upon either side.

Suddenly, dead ahead, there loomed up a big black object.

"Look out you'll hit the rock!" cried Mark to the professor, who was
steering.