.

"Electric guns," replied the professor. "But come on now, we have no
time to lose."

Further conversation was impossible, for the boys had their heavy copper
helmets on, and they were as tightly enclosed as if inside a box. They
grasped their weapons and waited for the next move.

The professor led the way to the stern of the ship. The boys found it
hard to walk, as they were weighted down by the heavy suits, and also
the boots, the soles of which were of lead.

They followed the inventor into what seemed a small room. Inside they
found themselves in darkness. There was a clanking sound as Washington
fastened and clamped the door shut. Then came a hissing.

The boys felt water rising about them. They could experience its
coldness, even through the diving suits. They were much afraid, but the
professor put a reassuring hand on their shoulders.

They seemed to feel a great weight. It gradually lessened, however, and,
in a few minutes, they saw something move in front of them. The
professor pushed them gently forward.

In another instant they were walking on the bed of the ocean, having
stepped from the _Porpoise_. They had gone into a locked compartment,
the inner door of which had been tightly closed, after which water from
outside had been gradually admitted until the pressure was equal, and
then the boys and the professor had merely to emerge out into the bottom
of the sea when the outer portal was swung aside by Washington, who
worked the lever from inside.

The boys were in intense darkness, but, suddenly a light glowed about
them, and they saw that the professor had switched on his miniature
search lamp. They remembered how he had told them to work the apparatus,
and soon tiny gleams shot out from their helmets.

The professor pointed ahead, for not a sound could be heard, and the
boys followed him.

It was a new sensation, this walking along the bed of the ocean. At
first the great pressure of water, even though the steel lined diving
suits kept most of it off, was unpleasant. Gradually, however, the boys
became used to it. They had to move slowly, for the water was denser
than the air and impeded their progress.

In a few minutes they reached the forward end of the _Porpoise_. Now
they were to solve the mystery of what had stopped the submarine. For a
few moments they could distinguish nothing.

Suddenly the boys felt the professor grasping their arms. They looked in
the direction he pointed. The