"But why don't we rise again when the ice floe slips off us?" asked Mark.

"Because, in all probability the ice will not slip off us," answered the professor grimly. "It may be so large that it has caught us like a bug under a barn door."

"Then we are fast in the ice under water," spoke Andy after a pause.

"It looks like it," came from the inventor. "However we will not give up yet. We may be able to make our way out. Start the engine at full speed, Washington."

The machinery which the professor had shut down at the first cry of alarm was set going. Soon the throb and hum told that the big screw was revolving.

Meanwhile the _Porpoise_ had regained an even keel, and had stopped sinking, remaining at the depth of seventy feet below the surface.

"We will first try to go straight ahead," said the captain.

He turned on more power and they all waited in anxiety. The test would tell whether they could escape in that direction or not.

But, though the powerful screw churned the water to foam in the tunnel, the _Porpoise_ never budged. It was as if she was held in a vice.

"It's of no use," remarked Mr. Henderson with a shake of his head as he watched the speed gage and noted that it remained stationary. "We must now try the other way."

Once more the big screw was set going, this time in the opposite direction, so as to pull the ship out of the ice if it was possible. But this, too, was of no avail.

"It looks as if the ice had us," said Andy, trying to speak in a cheerful tone. "But there's one way more to try."

"What is that?" asked Mr. Henderson.

"If we were in the air ship we could go up," replied the old hunter.

"But, as it is, we had better go down. Why don't you fill all the water tanks, and try to sink beneath the iceberg? It can't go down so very far into the water, and I reckon we could slip under it."

"The very thing!" exclaimed the professor, whose mind was too sorely troubled over the happening to enable him to think of plans of escape.

"That's the best thing to do."

Under the inventor's direction Washington filled the tanks and then, ere the pumps had ceased working, the screw was started and the deflecting rudder inclined to cause the ship to dive.

One, two, three minutes pa.s.sed, and still the _Porpoise_ did not move toward the bottom of the sea. She remained submerged and stationary.

Anxious eyes gazed at the dials. The indicating hands trembled under the throbbing of the engines, but did not move.

"It will not work!" exclaimed Mr. Henderson in sorrowful tones.

"What does it mean?" asked Bill, who had come up to where the others stood.

"It means that we are prisoners in the ice; caught between the upper and lower parts of a gigantic berg, and held here under the water."

"Can't we ever get out?" asked Jack, a tremor coming into his voice.

"Can't we escape when the ice melts?"

"The ice of the southern polar sea seldom melts in this lat.i.tude,"

replied the professor.

An ominous silence followed his words.

CHAPTER XXIV

THE SHIP GRAVEYARD

Truly the adventurers were in a position that might well cause the stoutest heart to quail. With hundreds of tons of ice above, below, and on every side of them, their chances of escaping alive from this frozen tomb were very small.

"Can't we make an attempt to get out of this prison?" asked Jack.

"Indeed we will," said the professor. "We will try all the means at our command. If they all fail--"

He dared not finish the sentence, but they all knew what he meant. It was now about one o'clock in the morning. The ship had become stationary after the uneasy motion caused by the oscillation of the big berg.

"We may as well turn in and get a little sleep," remarked Mr. Henderson.

"We can all work better if we get some rest."

It is doubtful whether any of them slept, for the horror of their position was too fresh in their minds. Still, lying down in the bunks rested them.

It was six o'clock when Washington awoke. In spite of the dangers of the icy grave, he had managed to get a little sleep. He prepared breakfast and called the others.

"Make a good meal," advised Mr. Henderson. "We have plenty of work ahead of us."

"Are you going to free the ship?" asked Mark.

"I am going to try," was the answer.

A little later the inventor was busy in one of the small store rooms aft when Jack came up. The professor was carefully taking out a box labelled:

DYNAMITE! DANGEROUS!

"What are you going to do?" asked the boy.

"I am going to try the same experiment we attempted on the volcanic island," was the reply. "Only, this time, I am afraid we shall have to complete it to the end. There is little likelihood of the ice falling apart."

"Then you are going to blow it up?" went on Jack.

"That's what I hope to do," the inventor went on. "I see no other way, and, though there is a risk, it is not so great a one as to wait to be crushed in the ice as it freezes more solidly."

Under the directions of Mr. Henderson they got out the diving suits. The professor, the two boys and Andy put them on. The dynamite, in specially prepared water-proof packages, with long fuses was laid in readiness close to the door of the diving chamber.

Into the cell, the four who were to make the perilous journey under the ice, took their places. The water was slowly admitted, and then, with the electric lights in their helmets throwing out powerful gleams, they started forward as the outer door swung open.

It was well they had all taken the precautions to don thick undergarments and clothing, for, even through the heavy rubber diving suits, the terrible cold of the southern polar sea struck a chill to their very bones.

As the professor had said, the ship was caught between the upper and lower parts of the iceberg. On either side, ahead and to the rear there was open water. Beneath their feet there was a floor of ice. It was as if they and the ship had been placed between two great sheets of the frozen matter.