“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 masses 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 knob.  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 pass 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.