"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 ma.s.s of dark vapor became more p.r.o.nounced. Through the gla.s.ses it could be noticed to consist of rolling ma.s.ses 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 ma.s.s 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."

"Is there diamonds down there?" asked the colored man, his fright seeming to leave him.

"There are all sorts of things inside the earth," the professor answered.

"Then I'm goin' along!" Washington declared. "I always did want a diamond ring, an' I knows a little colored gal that wants one, too.

I'm goin' all right! This suttenly am th' most kloslosterous conjunctivity of combativeness that I ever sagaciated!" and he began to do a sort of impromptu cake-walk.

CHAPTER XIII

DOWN INTO THE EARTH

IT was now noon, but the adventurers did not think of dinner in the excitement of approaching the mysterious island. The speed of the ship was increased that they might the more quickly come to it. As they approached they could see the ma.s.ses of vapor more plainly, and it appeared that some great commotion must be going on inside the big hole, since clouds of steam arose.

"I only hope it doesn't prove too hot for us," observed the professor.

"However, I provided a water jacket for the ship, and we may need it, as well as the vacuum chambers to keep the heat from us."

It was about three o'clock when the flying ship reached the edge of the island. From there it was about a mile to the rim of the big hole, over one side of which the waters of the ocean poured with a roar that could be heard over half a mile off.

"I think we had better halt and see that everything is in good shape before proceeding," said Mr. Henderson. "Jack, you and Mark make a thorough inspection of the engine room, and see that all the apparatus is in working order."

The two boys prepared to do as they were told. Mark, who was walking a little ahead of Jack, entered the apartment from which the storeroom opened. As he did so he saw, or thought he saw, the door of the place where the extra supplies were kept, close. Without saying anything to Jack he hurried forward, and tried the k.n.o.b. It would not turn.

"That's funny," said Mark to himself. "I could almost swear I saw some one go into that room. Yet I know the professor did not enter, for I just left him. And none of the others would dare to. I wonder if I will ever solve the mystery."

But he had too much to do to allow him to dwell on that matter.

Several of the dynamos needed adjusting and for two hours he and Jack had all they could do.

In the meanwhile the professor had gone over the other parts of the ship, and gotten everything in readiness for the descent. The Mermaid was lowered to within a few hundred feet of the sea, and, through a hose that was let down, the compartments, provided for this emergency were filled with water. These compartments were between the outer and inner hulls of the lower part of the craft, and were designed to prevent the interior becoming heated in case the travelers found they had to pa.s.s close to fire. There were also vacuum chambers, and from these the air was exhausted, as of course every schoolboy knows a vacuum is a non-conductor of either heat or cold.

"Now I think we are ready," the professor announced at length.

"Everything's all right in the engine room," announced Jack.

"Yes, an' everything's all right in th' kitchen," put in Washington.

"I've got a good meal ready as soon as any one wants to eat."

"It will have to wait a while," Mr. Henderson remarked. "We are going to start to make the descent before we dine."

The hose was reeled up, and the ship was sent a few hundred feet higher into the air, as Mr. Henderson wanted to take a last good observation before he went down into the hole.

But having risen some distance above the ma.s.ses of rolling vapors he found he was at no advantage, since the strongest telescope he could bring to bear could not pierce the cloud ma.s.ses.

"We'll just have to trust to luck," the scientist said. "I judge we're about over the centre of the opening. Lower away Mark!"

The boy, who, under the watchful eye of the professor, was manipulating the levers and wheels in the conning tower, shifted some handles. The gas was expelled from the holder, the negative gravity apparatus ceased to work, and the Flying Mermaid sank lower and lower, toward the mysterious hole that yawned beneath her.

The hearts of all beat strangely, if not with fear, at least with apprehension, for they did not know what they might encounter. Perhaps death in some terrible form awaited them. But the desire to discover something new and strange had gripped all of them, and not one would have voted to turn back.

Even old Andy, who seldom got excited, was in unusual spirits. He took down his gun and remarked:

"Maybe I can kill some new kind of animal, and write a book about its habits, for surely we will see strange beasts in the under-world."

Lower and lower sank the ship. Now it was amid the first thin ma.s.ses of vapors, those that floated highest and were more like a light fog, than anything else. By means of a window in the bottom of the craft, which window was closed by a thick piece of plate gla.s.s, Professor Henderson could look down and see what was beneath them.

"The clouds seem to be getting thicker," he said, as he peered through the small cas.e.m.e.nt. "If they would only clear away we could see something."

But instead of doing this the vapors acc.u.mulated more thickly about the ship. It was so dark inside the Mermaid now that the electric lights had to be switched on. In the room with the floor-window the lights were not used, as had they shone one could not have seen down below.