At first he believed the professor had some strange animal concealed in the storeroom, but he dismissed this idea almost as soon as he thought of it.  For what could the scientist want with an animal when they were going to the interior of the earth?  That some beast had slipped aboard was out of the question.  Mark was much puzzled, but finally, deciding the matter did not concern him a great deal, gave up trying to solve the mystery, at least for a time.

The ship was now in the neighborhood of the equator and the climate had become much warmer.  So hot indeed were some nights that they slept out on deck, with the Mermaid flying through the air at a moderate pace, for it was deemed best not to go at any great speed after dark.

One night the professor, after consulting various charts and maps, and making calculations which covered several sheets of paper announced: 

“We should sight the mysterious island to-morrow.”

“That’s good news!” exclaimed Jack.  “I’m anxious to see what’s below inside of that big hole.”

“Everybody git ready for their funerals!” exclaimed Washington in a deep voice.  “I ain’t got many——­”

“Cheer up,” interrupted Jack, poking Washington in the ribs.  The colored man was very ticklish, and he began to laugh heartily, though, perhaps, he did not feel like it.

Suddenly, above the sound of his shouts, there came a crashing, grinding noise from the engine room.

CHAPTER XII

 The big hole

“Something has gone wrong!” exclaimed the professor as he jumped up.  He reached the engine room ahead of any one else, and when the two boys got there they found him busy twisting wheels and shifting levers.

“Anything serious?” asked Jack.

“It’s the gas machine again,” Mr. Henderson replied.  “It broke where we fixed it.  However it doesn’t matter.  I was going to lower the ship anyhow, as I want to approach the island from the water.  We will go down a little sooner than I counted on.”

The disabling of the gas machine caused the vapor to escape slowly from the tank, and this made the ship sink gradually.  By means of the emergency stop-cock the descent could be controlled almost as well as though the machinery was in working order.  Half an hour later the Mermaid rested on the water.

It was a little rough, as there was quite a swell on, and not so pleasant as floating in the air on an even keel, but they made the best of it.

On account of the little accident, and not being certain of its extent, it was deemed best not to send the ship ahead.  So they laid to until morning.

For the better part of two days all those on board the Mermaid had their hands full mending the break and making other repairs found necessary.  In that time they lay to, floating idly with the currents, or blown by the wind, for the professor would not start any of the engines or apparatus until the ship was in good condition.