An Act to render more effectual an Act, passed in the Fifth Year of the Reign of His present Majesty, relating to the Discovery of the Longitude at Sea, and for continuing the Encouragement of Persons making certain Discoveries for finding the Longitude at Sea, or other useful Discoveries and Improvements in Navigation, and for making Experiments relating thereto; and for discharging certain Debts incurred by the Commissioners of the Longitude in carrying the Acts relating thereto into Execution.