ch that, because to run was
impossible. However, they hurried all they could, and, by dint of quick
firing kept the ugly creatures at bay until the side of the ship, where
the diving tank was placed, was reached.

The professor stepped to one side, and motioned for the others to
proceed him in entering. Little time was lost. As Bill, the last one in,
stepped past the steel door the inventor attempted to enter. To do so he
had to let go of his gun.

Instantly one of the sharks made a rush for the old man. But Andy was
on the watch. He leaned forward, and, from his weapon sent a bullet
straight down the throat of the monster. The electric missile did its
work well, and the lifeless body of the shark was devoured by the others
of its tribe.

The professor pulled the door shut behind him. Then he set the pump to
work to empty the tank. As he did so there was a tremor to the ship.
What could it mean?

In a few minutes the tank was empty and the divers stepped out into the
ship, freed from the oppressive weight of water. The ship continued to
vibrate and seemed to be in motion.

"What is it?" asked Mark as soon as he had his helmet off.

"De ship am free! We've got off de mud bank!" exclaimed Washington,
running in from the engine room.

It was true. Enough had been dug so that, with the power of the screw
working backward, there was sufficient force to pull the _Porpoise_ from
her perilous position.

"Empty the tanks and rise to the surface," said the professor.

In a few minutes the ship was on top of the waves, the adventurers freed
from the double danger of the mud and sharks. They congratulated each
other on the good outcome of the fight with the monster fishes.

Wearied with their labors and the battle under the waves, the travelers
sat up on the deck breathing in the fresh breeze. Then, after a while,
supper was made ready and eaten with good appetites.

It was decided hereafter to sail along near the surface at night, and
not to submerge the ship deeply save during daylight, when it was easier
to distinguish objects under the water.

Following this plan the _Porpoise_ steamed along just awash that night,
and the next day was sent down about fifty feet below the surface.

One afternoon, when the travelers were resting, having partaken of a
fine meal, the professor went on deck to make some observations, the
ship having been raised for that purpose. He came down, somewhat
excited.

"Well, we're half wa