For many years the problem of obtaining a satisfactory compass for naval vessels, especially for use as battle compass, has been one beset with all manner of difficulties. In order to avoid errors caused by masses of iron and steel about the compass, chart houses, bridge rails, fittings and instruments on the bridge or in the vicinity of the compass have been made of brass or other nonmagnetic material. If the compass is to be below in some protected position, it is naturally surrounded by various masses of metal. With all precautions that seem to appear feasible, it has been impossible to secure a satisfactory magnetic compass that can be used in the conning tower or central station of a battleship, or below in a submarine. Even those compasses which are above decks, on the bridges and steering stations, are very erratic under battle conditions. Electric alarms, distant control, search-light appliances, telephones, etc., when near the compass, affect it in various ways; while the shock of firing guns and the training of the turrets throw the compasses off to a very material extent.