"Hand me that wrench, Mark," called Professor Amos Henderson to a boy who stood near some complicated machinery over which the old man was working. The lad passed the tool over. "Do you think the ship will work, Professor?" he asked. "I hope so, Mark, I hope so," muttered the scientist as he tightened some bolts on what was perhaps the strangest combination of apparatus that had ever been put together. "There is no reason why she should not, and yet-" The old man paused. Perhaps he feared that, after all, the submarine boat on which he had labored continuously for more than a year would be a failure. "Is there anything more I can do now?" asked Mark. "Not right away," replied the professor, without looking up from the work he was doing. "But I wish you and Jack would be around in about an hour. I am going to start the engine then, and I'll need you.