In this time Mark had several times recalled the curious happenings in regard to the disappearing food, and the mystery of the storeroom.  But there were no further manifestations, and no other signs that there might be a strange visitor aboard.

“I couldn’t have imagined it all,” said Mark, “but I guess what did happen may have been caused by natural means, only I can’t discover them.”

It was about two days after this, the ship having sailed scores of miles on the surface of the water, that Mark, who was in the conning tower exclaimed: 

“That looks like a waterspout ahead of us.”

“That’s what it is!” Jack agreed.  “What shall we do?”

“Call the professor!” said Mark.  “He’ll know.”

When Mr. Henderson came, he looked for a long time at a cloud of black vapor which hung low in the east.

“It may be a waterspout,” he said.  “We’ll rise in the air and see if we can avoid it.”

The ship was sent up into the air.  As it rose higher and higher, the professor, making frequent observations from his conning tower, cried out: 

“That is no waterspout!”

“What is it?” asked Mark.

“It is the steam and vapor rising from the big hole in the earth!  Boys, we are almost there!”

“Are you sure that’s it?” asked Mark.

“Almost positive,” Mr. Henderson replied.  “You can see how much warmer it has become of late, as we approached the equator.  We are almost due at the island, and I have no doubt we have reached it.”

As the ship flew forward the mass of dark vapor became more pronounced.  Through the glasses it could be noticed to consist of rolling masses of clouds.  What lay beneath them no one knew.  The adventurers were going to try to find out.

Now that they had arrived at the beginning of the main part of their journey, the travelers felt their spirits sink a little.  It was one thing to plan to go down into the depths of the earth, but it was quite another to make the actual attempt.  Still, they were not going to give up the project.  The professor had confidence in his ship and believed it could safely make the trip.  Still it was with no little apprehension that Mr. Henderson watched the nearer approach of the craft to that strange island.

“Perfesser, are yo’ really an’ truly goin’ t’ depress this elongated spheroid an’ its human consignment int’ that conglomerous convoluted mass of gaseous vapor regardless of th’ consequences?” asked Washington, as he gazed with wide opened eyes at the sight before him.

“If you mean am I going to let the Mermaid go down into that hole you are perfectly correct,” the scientist answered, “though you could have said it in fewer words, Washington.”

“I—­ I guess I’ll get out an’ walk,” the colored man made reply.

“This isn’t any trolley car,” observed Mark.  “Don’t lose your nerve, Wash.  Stay with us, and we’ll discover a gold or diamond mine, maybe.”