I guessed the reason of his cries, for I saw a black fin in the distance. Had I been alone when I saw that ill-omened fin I believe that I should have quickly sunk; but the feeling that I had my messmate to support, and that the honest boatswain was coming to my help, kept me up. I did as Mr Johnson directed me, and kept kicking with all my might, and shouting too, whenever I could get my mouth clear of the water. Still I got more down it than was pleasant. I saw something gleaming in Mr Johnson's hand. It was a long Spanish knife. Gogles had been quiet for some time, but just then he began to struggle, and again clasped me round the neck. I felt as if I was sinking, and was earnestly wishing that Mr Johnson was a few yards nearer, when I saw him suddenly turn aside and strike off to the left. My eye followed him with an intensity of interest such as I cannot describe. It caught the gleam of his knife, and then what was my horror to find that he had disappeared. It was but for a moment. Directly afterwards he rose again, surrounded by a circle of crimson, and a huge black body floated up near him, lashing the water. He darted forward, and, seizing Gogles, released me from his grasp. "Swim on, Mr Merry, swim on," he shouted, shoving me before him. "Here comes the boat." The men bent to their oars, and the brave boatswain swam on with all his might. With a jerk he threw Gogles into the boat, and gave me a shove up as I was climbing in, which very nearly sent me over on the other side; he then sprang after us with surprising agility, turning as soon as he had got his feet out of the water, and striking with all his might at a huge creature which followed close at our heels. I saw the flash of the monster's white throat. "Habet," shouted our third lieutenant, who was--a rare thing in those days in the navy--somewhat of a scholar. Mr Johnson had inflicted a mortal wound on another shark, who was immediately surrounded by his amiable brethren, eager to devour him as they had missed us. It is not difficult to conceive what would have been our fate had we remained another minute in the water, after the boatswain had killed the first shark. "You indeed did that bravely, Mr Johnson," said Mr Haisleden, as we returned to the frigate. "I never saw anything like it. Where did you learn that trick?"