“What has happened?” he asked in a faint voice.

“I don’t know; none of us knows,” Mark answered.  “We all lost our senses when it got so hot, and there seemed to be some peculiar vapor in the air.  The last I remember was seeing some horrible shape rush from the storeroom, soon after the ship struck.  Then I fainted away.  When I woke up I managed to turn the lights on, and then I came back here.”

“I wonder where we are,” the old man murmured.  “I must find out.  We must take every precaution.  Washington, go and look at the gage indicating our depth.”

The colored man was gone but a few seconds.  When he returned his eyes were bulging in terror.

“What is it?” asked Mr. Henderson, who, thanks to the battery, had almost completely recovered.

“It ain’t possible!” gasped Washington.  “I’ll never believe it!”

“What is it?” asked Mr. Henderson, while the others waited in anxiety for the answer.

“We’re five hundred miles down!” declared Washington.

“Five hundred miles!” muttered the inventor.  “It does not seem possible, but it must be so.  We fell very rapidly and the terrible draught sucked us down with incredible rapidity.  But come, we must see what our situation is, and where we are.  We are stationary, and are evidently on some solid substance.”

They all felt much recovered now, and, as the terrible fright of being consumed in a fiery furnace had passed, they all were in better spirits.

At the suggestion of the professor, the boys and Washington made a tour of the ship.  They found, for some unaccountable reason, that nearly all the engines and apparatuses were out of gear.  In some the parts had broken, and others were merely stopped, from the failure of some other machine, on which they were dependent.

“I’m afraid this is the end of the Mermaid,” said Mark, in a sorrowful tone.

“Nonsense!” replied Jack, who was of a more cheerful nature.  “Things are not so bad as they look.  The professor can fix everything.”

“I’m sure I hope so,” Mark went on, not much encouraged, however, by Jack’s philosophy.  “It would be no joke to have to stay five hundred miles underground the rest of our lives.”

“You don’t know,” retorted Jack.  “Don’t judge of a country you’ve never seen.  This may be as fine a place as it is on the surface of the earth.  I want a chance to see it,” and Jack began to whistle a cheerful tune.

They completed the tour of the ship, and found, that, aside from the damage to the machinery, the Mermaid had not sustained any harm.  The hull was in good order, though of course they could not tell about the gas holder.  It was not possible to see this except by going into the conning tower or out on the small deck, and this they did not venture to do.  The connections between the holder and the main ship seemed to be all right, and there was still a small quantity of gas in the big tank, as Mark found on opening a stop-cock.