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 passed, 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!" excla