"What has happened?" asked Andy, as he tried to climb up the companionway ladder, that was tilted backward. "I guess we've hit your iceberg!" cried Mr. Henderson. "I knew I smelled the frozen stuff," replied the old hunter. They got the covers on the manhole only just in time and they all crowded into the cabin, while Jack switched on the electric lights. "Is the ship damaged?" asked Mark. "I think not," replied Mr. Henderson. "But we are sinking. Look at the depth gage." The hand on the clock-face was moving slowly around. From ten it went to twenty feet, then to thirty and kept going until it stood at seventy. "Look to the air tanks," ordered Mr. Henderson to Washington, who, by this time had recovered from his fright. "See if they are all right." The colored man came back in a few minutes and reported that the supply of compressed atmosphere was safe and that there was plenty of it. "That's good," remarked Mr. Henderson. "Whatever else happens we can breathe for a while." "But what has happened?" asked Andy. "I think the top part of an iceberg toppled down on us," was the reply. "You know about nine-tenths of a berg is under water. Sometimes there is a warm current of the ocean underneath the ice, and it melts. Then it becomes top-heavy and tilts over. One of that sort must have caught us, and has shoved us down into the sea." "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.