days after this the _Porpoise_ continued on her way south.
Now and then appearing on the surface to renew the supply of fresh air,
and again skimming along under the surface, or deep down, the strange
craft kept on. It grew much warmer, and even when some distance below
the surface the heat could be felt in an uncomfortable manner.

"We're getting near the equator," explained the professor.

One afternoon, when dinner had just been finished, and the ship, under
the direction of Washington, was gliding along well under the sea, there
came a sudden shock.

"We've hit something!" exclaimed Mr. Henderson as he jumped for the
conning tower. The shock was repeated.

"What was it?" asked someone.

"Shut down the engine!" yelled the inventor to the colored man. "What do
you want to go on ramming an object after you've once hit it? Slow down
the engine!"

"Power's shut off!" cried Washington. "We didn't hit nothin'! Something
hit us!"

"What do you mean?" asked Mr. Henderson.

"Somethin's rammin' us," went on Washington.

"It must be a big monster. I was sterrin' along an' there was nothin' in
de road, when all of a suddint, ker-plunk! We's hit. Look ahead, an' you
can't see nothin'!"

The professor, and the boys, who had followed him, gazed out of the
conning tower window. There was nothing forward but a vast expanse of
water.

The next instant the ship careened as something struck her a violent
blow on the port side. Everyone almost toppled over from the force of
the impact.

"Dar he goes agin!" cried Washington.

"We're attacked by a whale!" said the professor. "We must rise to the
surface or it may damage the ship."

"If it's a whale I'd like to get a shot at it," put in Andy Sudds, from
the foot of the companion ladder leading into the tower.

"I don't know that it is a whale," went on the inventor. "But it must be
something very big and strong."

"It's a monster of some sort," put in Andy, "and I want a chance at
him."

"It's too risky," murmured the professor. "We couldn't get down to
bottom here, as the water is several miles deep, and the pressure would
crush the _Porpoise_, strong as she is."

Once more came a terrible blow and the ship rocked in a swirl of foam
beneath the waves. In quick succession two more fierce onslaughts were
made by the unseen monster.

"We'll have to do something," muttered Andy.

"You're right," agreed the professor. "Our only chance is to rise to the
surface, for I