He could hardly see the figure now as it had passed into the shadow cast by the boat. He was about to summon the professor to make an investigation, when Washington started going the search light which was placed just over the door of the living cabin. It was kept there as a sort of beacon light, as, near the island was a dangerous ledge of rocks. Then, in the blinding white glare from the big lantern as Washington accidentally swung it toward the _Mermaid_, Mark beheld a strange sight. The figure he had been watching stood out in bold relief. Though it was shaped like a human being it was not like any person the boy had ever seen. It seemed covered with a skin twice too large for it; a skin, which, in spite of the clothes that concealed it, hung in folds about the arms and legs, dropping pendent like from the neck like a big garment, and flapping in the wind. For an instant Mark was so startled he cried out, and the professor and the others ran to see what was the matter. “There—by the ship! A horrible creature!” exclaimed Mark. Shouting to Washington to keep the light steady in the direction of the dock, Mr. Henderson ran toward the moored _Mermaid_. Jack, Andy, Bill and Tom, with Mark in the rear followed him. “Nothing here,” said the scientist, after a careful search about. “Are you sure you saw something, Mark?” “Positively,” replied the lad with a shudder. He described the vision of the darkness. “I guess it was a big otter, or maybe an enormous turtle,” the professor said. CHAPTER V ATTACKED BY A WHALE But Mark was certain it was nothing like that, though a careful search failed to reveal anything or any person near the ship. It was too dark to examine for footprints, and even Mark, after taking a look all about, felt he might have been deceived by shadows. Still he was a little nervous, and could hardly sleep for imagining what the thing he saw could have been. The next day every one was so busy that no one, not even Mark, recalled the little excitement of the night before. Shortly after noon, final preparations having been made, they all got aboard the _Mermaid_ and started off. It was a bright sunshiny day, and the craft, speeding away from the island where it had been constructed, over the dancing blue waves, must have presented a strange sight had there been any spectators. For surely no such ship had ever before sailed those waters. However, there was no other vessel in sight, and the island, as far as the professor and his friends knew, had never been inhabited. “We will not try for any great speed,” Mr. Henderson remarked as he, with Mark and Jack, stood in the conning tower managing the _Mermaid_. “We don’t want to strain any joints at the start or heat any engine bearings. There will be time enough for speed later.” “Yes, and we may need it more when we get into the centre of the earth than we do now,” observed Mark. “Why so?” asked Jack.