He and Jack went to the room where there was an opening in the floor of the ship, covered by heavy glass.  They slid back the steel shutter and there, down below them, was the strange new, world they had come to, stretched out like some big map.

They could see mountains, forests, plains, and rivers, the water sparkling in the colored light.  Over green fields they flew, then across some stretches where only sand and rocks were to be seen.  Faster and faster the ship went, as the professor found the machinery was once more in perfect order.  Jack was idly watching the play of tinted lights over the surface of the ground.

“I wonder what makes it,” he said.

“I have tried to account for it in several ways,” said the professor, who had called Washington to the conning tower and come to join the boys.  “I have had first one theory and then another, but the one I am almost sure is correct is that hidden volcanic fires cause the illumination.

“I think they flare up and die away, and have become so regular that they produce the same effect as night and day with us.  Probably the fires go out for lack of fuel, and when it is supplied they start up again.  Perhaps it is a sort of gas that they burn.”

“Well, it’s queer enough, whatever it is,” Jack remarked.  “What strikes me as funny, though, is that we haven’t seen a single person since we came here.  Surely this place must be inhabited.”

Mark thought of the strange shadow he had seen, but said nothing.

“I believe it is,” the professor answered.  “We will probably come upon the inhabitants soon.  I only hope they are a people who will do us no harm.”

“If they tried any of their tricks we could mount up in our ship and escape them,” said Andy.

“Provided they gave us the chance,” Mr. Henderson put in.  “Well, we’ll not worry about that now.”

For several hours the ship traveled on, until it had come to a different sort of country.  It was wilder and not so level, and there were a number of streams and small lakes to be seen.

“Are you going to sail all night?” asked Jack.

“No,” replied the professor.  “I think we’ll descend very soon now, and camp out for a while.  That lake just ahead seems to offer a good place,” and he pointed to a large sheet of water that sparkled in the distance, for by this time they had all gone back to the conning tower.

The lake was in the midst of a wood that extended for some distance on all sides, and was down in a sort of valley.  The ship headed toward it, and in a short time a landing was made close to shore.

“Maybe we can have some fresh fish for supper,” exclaimed Jack as he ran from the ship as soon as the sliding door in the side was opened.  “Looks as if that lake had some in it.  It is not thick water like in that stream we stopped at,” he added.

“I believe you’re right,” old Andy put in, as he turned back to look for some lines and hooks among his traps.  He soon found what he wanted, and gave them to the boys, taking his trusty gun along for himself.