“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 masses of rolling vapors he found he was at no advantage, since the strongest telescope he could bring to bear could not pierce the cloud masses.

“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 masses 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 glass, 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 casement.  “If they would only clear away we could see something.”

But instead of doing this the vapors accumulated 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.

The professor maintained his position.  The descent was a perilous one, and he wanted to be on the watch to check it at once if the Mermaid was liable to dash upon some pointed rock or fall into some fiery pit.  His hand was on the signal levers.

Suddenly he looked up and glanced at a gage on the wall.  The hand of it was slowly revolving.