Corrections to compasses on iron ships, with related correspondence. The papers include preparations for ascertaining the disturbance of the compasses by magnets on iron vessels; B. Darondeau's French corrections to compasses; disturbances of the compasses on board the vessel 'Fame' from Glasgow to Calcutta, and also the 'Pacha'; E.J. Johnson's deviations of compass needles in fifteen iron ships; and the correction of the compass on the 'Great Britain'. The correspondents include E. Sabine, F. Beaufort and W.H. Sykes.