Philosophical Transactions of the Royal Society of London
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XIV. On the present amount of westerly magnetic declination [variation of the compass] on the coast of Great Britain, and its annual changes

    From the rapid decrease in late years of the amount of Westerly Magnetic Declination over the whole area of the United Kingdom and the adjacent seas, the attention of the Hydrographic Department of the Admiralty has been constantly directed to this interesting physical fact as one specially affecting coast navigation and the accuracy of compass-bearings derived from the current charts. The duties of Her Majesty’s Surveying-vessels engaged on our own shores having within the last few years included districts embracing nearly the whole extent of coastline, the opportunities thus afforded for a careful determination of the magnetic declination at widely spread and favourable localities were, under the direction of Admiral Richards, C. B., F. R. S., the Hydrographer of the Admiralty, taken advantage of, and suitable instruments furnished to the Commanding Officers from the Admiralty Compass Department.

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