V. On the magnetic character of the armour-plated ships of the royal navy, and on the effect on the compass of particular arrangements of iron in a ship
The present paper may be considered as a sequel to a paper published in the Philosophical Transactions for 1860, page 337, under the title “Reduction and Discussion of the Deviations of the Compass observed on board of all the Iron-built Ships, and a selection of the Wood-built Steam-ships in Her Majesty’s Navy, and the Iron Steam-ship ‘Great Eastern’; being a Report to the Hydrographer of the Admiralty. By F. J. Evans, Master R. N.” Like the former, the present paper is presented to the Royal Society, with the sanction of the Lords Commissioners of the Admiralty. In the brief interval which has elapsed since the publication of that paper, changes of the greatest importance have taken place in the construction of vessels of war, which have been accompanied by corresponding changes in the magnetic disturbance of their compasses. Not only has there been a great increase in the surface and mass of iron used in the construction of those parts of the ship in which iron was formerly used, but iron has been adopted for many purposes for which it was not then used, and much of the iron thus added far exceeds in thickness any that was formerly in use. Among the masses thus added we may specially mention iron masts and yards, armour-plating, and gun-turrets.