"Some scientists believe it," commented the professor. "This looks like a big enough hole to lead clear through to China. Hark, you can hear the roar of the water now." They listened, and the wind brought to them the sound of the sea pouring down into the unfathomable depths. "Let's throw a big rock down," suggested Jack. "Maybe we can hear it strike bottom." With the aid of Mark he cast a big boulder down into the depths. They listened intently, but not the slightest sound echoed back. "I guess the bottom is too far away for you to hear the stone land," said the professor. CHAPTER XVI THE GHOST AGAIN They spent some time looking down into the hole. The masses of vapor, or clouds, rolled and swirled hundreds of feet below them, but never broke sufficiently to allow of a clear sight. "Well, we had better go back to the ship," remarked the professor. "We must continue our voyage." They were soon on the _Porpoise_ and steaming away from the strange island, the inventor deciding to get far off out of the influence of the terrible waterfall. The night was, as usual, spent with the ship slowly steaming ahead on the surface of the water. It was getting on toward twelve o'clock and Washington had the watch. He was to be relieved by Jack. The latter had been awakened by the alarm clock at the head of his bed, which time-piece he had set to arouse him so that he might take Washington's place. Jack was just getting the sleep from his eyes by a vigorous rubbing when he heard a loud yell. "Land a' Massy!" cried Washington from the deck above. "I's goin' t' die suah! De ghostess am after me ag'in!" Without waiting to dress, Jack sprang up the ladder and was soon out on the deck. He saw Washington kneeling down in front of the conning tower door while, at the after end of the deck, was a mysterious white object; the same strange shape that had been observed before. "I'm going to solve this puzzle!" exclaimed Jack to himself as he made a dive toward the object in white. "This ghost business will have to stop!" But, unfortunately for his plans, his foot slipped on the smooth steel deck, and he went down in a heap. When he got up the ghost was nowhere to be seen. Washington, however, was still kneeling down and praying to be spared from the attack of the midnight visitor. Jack limped over to the colored man. "Keep still," said the boy. "It's gone now. What was it, anyhow?" "Some ghost from de grabeyard," replied Washington. "When did you see it first?" went on Jack. "'Bout ten minutes ago," replied Washington. "Well it's gone now," said Jack, though he had to admit to himself that the affair was somewhat puzzling. Professor Henderson had been awakened by the yells of the colored man and came on deck to see what the trouble was. He appeared somewhat annoyed when Washington told him what had happened. "There are no ghosts!" declared the inventor in positive tones.