"But it may be thinner now," persisted Jack. "At any rate it will do no harm to try," the inventor admitted. "We can not last much longer down here." Again the tanks were filled, and by the aid of the deflecting rudder the _Porpoise_ went down into the depths. Then the ballast tanks were quickly emptied, and the rudder turned so as to force the craft upward on a slant. The engine was set going at top speed. "Hold fast everybody!" called the professor. "It is kill or cure this trip!" Like an arrow from a bow the _Porpoise_ shot upward. On and on it sped, gathering momentum with every foot she traveled. Suddenly there came a terrible crash, a grinding sound and a rending and tearing. The ship trembled from end to end. Every one was knocked from his feet. There were bumpings and scrapings all along the sides of the submarine. Then, with one final spurt of speed, the little ship tore her way through the ice and emerged, with a splash and shower of foam into the open sea! Quickly the man hole was opened and, half dead from lack of fresh air, the adventurers crawled out on deck. It was night and the stars glittered in the sky above. They were just beyond the edge of the ice field, and all about them was a wide open sea. "I was right after all," said the professor, "but I miscalculated the distance. Had we gone on a few feet farther it would not have been necessary to break through the ice." "I guess it's a lucky thing we didn't try it before either," remarked Andy. "We never could have bored through fifteen feet of the frozen stuff. Where we plowed up it is less than two feet," and he pointed to where the immense floe came to an end. It was decided to go no farther that night, however, as the professor wanted to take some observations by daylight and ascertain his position. So filling their lungs with the air, cold and piercing though it was, the adventurers descended to their cabin, and lots were drawn to see who would stand the two night watches. It fell to Mr. Henderson to take the first, and Washington the second. The captain accordingly took up his position in the conning tower and prepared to pass several hours. He was busy thinking over the exciting times he and his companions had passed through, and planning new trips to see more wonders of the world, when his attention was attracted by slight noise near the man hole leading to the amidship companionway. The professor looked up, and was startled to see a tall white object, with outstretched arms advancing toward him with slow and stealthy tread. "The ghost again!" exclaimed the inventor softly. "I must catch it now, and see what foolishness it is," for the professor did not believe in spirits. He got down on his hands and knees the better to escape observation, should the white thing prove to be a bodily substance, and started to crawl toward it. He came within ten feet of the thing, and could make out that it was a man, or at least the semblance of one, all clothed in white.