As soon as they were well out to sea, and all sight of the canoes of the savages had been lost, supper was served, and all brought good appetites to the table. For, though the improvised meals on shore had tasted good, there had not been much to them. For several days the _Porpoise_ was kept on her course, sailing along under the water by day, and upon the surface at night. It was one pleasant afternoon, while Nellie, Jack and Mark were sitting out on the deck, during one of the times when the boat had risen to the surface to renew the air supply, that a strange commotion was observed off their lee. The ocean seemed to be boiling. "What is that?" asked the little girl. The two boys looked to where she pointed. Indeed the ocean seemed to be bubbling up and down in a strange manner. "It's a school of porpoises," said Jack. Just then the water became alive with big fish. They leaped over each other, springing high into the air and falling back into the sea with resounding splashes. "They're not porpoises! They're whales! Baby whales!" yelled Mark. "Look out or some of the big ones may ram the boat!" As he spoke the water all about the submarine was seen to be fairly swarming with the small whales. There were scores of them, and, at times, they were so thick that it appeared possible to walk out upon them without getting very deep into the water. Suddenly the ship careened to one side and the sea rushed over the deck. It was evident that one of the big whales, which were deeper down in the water, had struck the vessel. Nellie screamed and tried to grab the hand rail that was about the platform. She missed her grip. The next instant she was floundering in the ocean, in the midst of the school of whales. "Man overboard!" yelled Jack, remembering vaguely that he had read this was the proper call to make in case of accident. His cry brought Washington and the professor up the companionway on the jump. "Launch the boat!" cried the inventor as he saw what had happened. Mark was already in action. At the first sight of Nellie slipping over the side he had thrown off his coat, broken the laces of his shoes in order the more quickly to remove the foot coverings, and had dived into the swirling water which surrounded the submarine. He struck out in the direction where the little girl had disappeared, and as her golden head appeared above the mass of foam he yelled in encouragement. By this time the small boat was launched and the colored man and Jack were pulling toward him. Mark succeeded in reaching Nellie as she was going down the second time. He grabbed her long locks and managed to keep her up until the little craft was alongside of him. "Git in quick, 'fore dem whales eat yo' up!" cried Washington.