Jack let out a yell that could be heard all over the ship. He made a spring for the object, determined to discover what it was or die.

At that instant the whole ship seemed to rise in the air. It left the water and began moving skyward. Right out of the waves the _Porpoise_ was lifted until the big screw was clear of the water and it was churning around in the tunnel without any resistance, racing at top speed now that it had no water to thrust against.

Then the ghost seemed to vanish into thin air, and Jack felt himself falling down the hatchway.

CHAPTER XX

ON A VOLCANIC ISLAND

In an instant the ship was in confusion. The professor, followed by old Andy, Washington, Mark, Bill and Tom, came rushing from their berths, all in their night clothing, to see what the trouble was. They met in a tangled ma.s.s, stumbling over Jack at the foot of the steps.

"Is the ship on fire?" called Mrs. Johnson from her cabin.

"I hope not!" called the professor. "But something has happened. Don't be frightened!"

By this time Jack, who had been somewhat stunned, recovered his senses and worked his way out of the ma.s.s of bodies.

"The ghost! The ghost!" he cried. "I saw him again!"

"Land a' ma.s.sy!" yelled Washington.

"What has happened to the ship?" cried the professor. "Is it a tidal wave?"

"I was on deck," panted Jack. "I saw the white thing! I crept up on it!

All at once the ship rose in the air!"

"And it's still rising!" shouted the inventor. "I must see what this means!"

He made his way to the deck, and his loud shout soon brought the others up to him.

"Shut off the engine!" Mr. Henderson called down to Washington, who hurried to obey.

"What has happened?" asked Andy, rushing towards him.

"We have run upon an island," answered the professor. "This is the worst thing that has yet happened to us."

"What sort of an island is it that shoots you up in the air?" asked the old hunter.

"It's hard to say," replied Mr. Henderson. "We will have to wait until morning to find out."

The boys and men went up on deck and there beheld a curious sight. The _Porpoise_ had been lifted bodily from the surface of the ocean where she had been sailing and was now raised about ten feet above the crest of the billows. It was too dark to see the extent of the island she rested on, but, from the circle of foam around the outer edge it did not appear to be very big.

The excitement occasioned by the appearance of the ghost, Jack's yells and fall, and the rising of the ship, had subsided somewhat. Mrs.

Johnson and her daughter, who were much frightened, were a.s.sured there was no immediate danger, and the men and boys put on more substantial clothing than that of their night robes.

It seemed as if morning would never come, but at length there was a pale light in the east and soon it changed to a rosy glow, showing that the sun was coming.

The professor was early on deck, and Mark and Jack were not far behind.

As soon as it was light enough they could see that the ship was held fast on top of a small rocky isle, about one hundred feet in diameter, which rose abruptly from the water.

"It's a volcanic island," decided the professor. "We are in the midst of subterranean disturbances and this is probably one of the effects of some under-sea eruption. The pinnacle of rock rose from the ocean, forced up by some power underneath, just as our ship came over it. That accounts for the sudden rising into the air of the _Porpoise_. No wonder we were all scared."

"The next question," began old Andy, "is how are we to get off?"

"That's the point," agreed Mr. Henderson. "Here we are, high and dry, and we might as well be a broken flying machine as a submarine for all the power we have."

"Will we have to stay here forever?" asked Nellie, who had come up on deck.

"I hope not," answered the professor, smiling for the first time since the accident. "We will find a way to get down, never fear, little girl."

"I suppose we might dig some sort of a ca.n.a.l down to the water,"

remarked Jack. "If we could we might float the ship."

"I'm afraid you'd find it slow digging through this volcanic rock,"

answered Andy. "It's like flint."

"Well, there's no use worrying over it," went on the professor in as calm a tone as he could muster. "It's time for breakfast, and we have to eat whether we're on the top of an island that shoots out of the water when you least expect it, or sailing along as we ought to."

Accordingly Washington prepared the morning meal, and they all found they had appet.i.tes for it, in spite of their fright. Afterward they all came on deck again and looked about them.

They were in the midst of a wild waste of water. Not a sign of land could be seen in any direction, and there was no evidence of a sail or steamship as far as the horizon showed.

The little island which held the _Porpoise_ so close a prisoner was a mere speck in the vast ocean, but it was large enough to put an end, temporarily at least, to the progress of the powerful submarine.

The professor and the boys went over the side and climbed down to the rock. Then the inventor verified his surmise that the rocky point was of volcanic origin. It was also seen that there was little chance to get the craft back into the ocean.

"I guess we're doomed to stick here for some time," remarked Mr.

Henderson, with a grim smile. "The rock has caught us squarely and nothing short of dynamite will free us. To use the explosive might mean the destruction of the ship, and I dare not risk it."

Gloom settled over the party in spite of the efforts the professor made to be cheerful. Washington, after the first few minutes of fright, regained his usual good spirits, but, no matter how he laughed and joked, there was a feeling of terror in every heart.

They realized their helplessness, and knew that unless another upheaval of nature occurred there was small likelihood of their release.

On the third day of their strange adventure Professor Henderson resolved on a bold step.

"We must use dynamite," he declared. "If we stay here on this desolate rock we are bound to perish sooner or later, for our food cannot last many months, though we have a large supply. We are out of the path of steamers and only by chance would one pa.s.s here. With care we may be able to blast the rock so that the ship will not be permanently damaged. What do you all say? I would like your advice, for this concerns all of us."

One after the other all said they were willing to abide by whatever the inventor did. Accordingly he made his preparations. Washington, with a hammer and chisel, was set to cutting a fair sized hole in the big rock, as far away from the ship as possible.

He was two days at the job, and, during this time those on the stranded _Porpoise_ watched in vain for the sight of a vessel.

"I am going to put the dynamite in," announced Mr. Henderson one morning. "We must all get into the small boat and row some distance away, as there is no telling what the result of the explosion may be."

"Suppose the submarine is destroyed?" asked Mrs. Johnson.