It was now about two years since they had come back from that eventful trip. One of the first things the professor did, after docking the _Porpoise_, was to shut himself up in his study and begin to draw plans. To the questions of the boys he returned no answer for several days. Then he announced he was working on a craft which could both sail on top of the water and navigate the air. In time the plans were done, and, in order to keep the work secret, the shop was moved to an island which the professor owned. Parts of the _Monarch_ and the _Porpoise_ were used in constructing the new craft, so there was no need to get other help than that which the boys, Washington and Bill and Tom could give, since the two latter accepted an offer of the professor to remain and work for him. The boys, of course, would not leave their friend. The professor realized that he had a more difficult task in his new venture than he had set himself on other occasions. For a ship to be light enough to rise in the air, and, at another time, and with no change, to be strong enough to navigate the ocean, was indeed something to tax Mr. Henderson’s ingenuity. However, in the course of a little over a year the larger part of the work was done. Inside the big shed was the huge affair which, it was hoped, would enable its owner to be master of both air and water. “Did the professor say anything special?” asked Mark of Washington. “Nope. I reckon he were too busy problamatin’ the exact altitude projected in an inverse direction by th’ square root of th’ new engine when operated at a million times inside of a few seconds, but he didn’t say nothin’ t’ me. I were busy underneath th’ ship, fixin’ bolts when he tole me t’ find yo’. I wouldn’t be s’prised if he had th’ thing goin’ soon.” “Do you think he’ll be generating the new gas to-day?” asked Jack eagerly. “That’s the most troublesome part; to get that gas right.” “He didn’t say nothin’ t’ me 'bout it,” Washington stated, as he walked along beside the two boys. “He jest seemed anxious like.” “We’d better hurry,” advised Mark. “He may be at an important part in his experiments and probably needs us. I hope it will work. He has spent many days on it, and we all have worked hard. It ought to be a success.” “Perfesser allers makes things work,” declared Washington stoutly. “That’s a good way to feel about it, anyway,” observed Mark. “Well, we’ll soon know.” The three hurried to the shed which they could see as they rounded a turn of the path through the wood. They noticed an elderly man approaching with a gun on his shoulder. On one arm he carried a game bag. “Guess Andy got something for dinner,” remarked Jack. “I hopes so, honey,” put in Washington. “I’se got a sort of gone feelin’ in my stomach!” “Any luck, Andy?” called Mark, when he came within hailing distance. “Fine,” replied Andy Sudds. “Rabbits and quail. We’ll have a good dinner to-morrow.”