CHARACTERS THAT APPEAR IN THIS STORY. Motor Matt, a lad who is at home with every variety of motor, and whose never-failing nerve serves to carry him through difficulties that would daunt any ordinary young fellow. Because of his daring as a racer with bicycle, motor-cycle and automobile he is known as "Mile-a-minute Matt." Motor-boats, air ships and submarines come naturally in his line, and consequently he lives in an atmosphere of adventure in following up his "hobby." Dick Ferral, a young sea dog from Canada, with all a sailor's superstitions, but in spite of all that a royal chum, ready...