Corrections to compasses on iron ships, with related correspondence. The papers include a report on the correction of compasses on iron ships; experiments in compass corrections for the vessel 'Ironside'; a paper by Airy titled 'Account of experiments on iron-built ships instituted for the purpose of discovering a correction for the deviation of the compass produced by the iron of the ships'; W. Hendry's table of magnetic observations; and directions for correcting the compasses on iron built ships. The correspondents are requested for assistance and for observations. They include C. Wood, F. Beaufort, J. Barrow, H. Roper, E. Sabine, R. Sheepshanks and J. Weale.