V. On the present amount of westerly magnetic declination [variation of the compass] on the Coasts of Great Britain, and its annual changes

Abstract

The rapidly accelerating value within the last few years of the annual decrease of the westerly magnetic declination over the whole area of the United Kingdom and the adjacent seas, as observed at the fixed magnetic observatories of Greenwich, Kew, Brussels, Paris, and also at Christiania in Norway, is a subject of importance in practical navigation as affecting the compass-bearings derived from charts and those laid down for the guidance of pilots. The attention of the Hydrographic Department of the Admiralty has been constantly directed to this interesting physical fact; and as the duties of Her Majesty’s surveying-vessels employed on our shores between the years 1866 and 1870 embraced nearly the whole extent of coast-line, advantage was thus taken, undert he orders of Rear-Admiral Richards, C. B., F. R. S., the Hydrographer, to determine, with great attention to accuracy, the magnetic declination at widely spread and favourable localities.