C 319 ] 
XIV. On the present amount of Westerly Magnetic Declination [Variation of the Com- 
pass ] on the Coast of Great Britain, and its Annual changes. By Staff Captain 
Frederick J. Evans, B.N., F.B.S., Hydrographical Department , Admiralty , in charge 
of Magnetic Department * . 
Received June 15, — Read June 20, IS 72. 
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 coast- 
line, the opportunities thus afforded for a careful determination of the magnetic decli- 
nation 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. 
Experience has shown that the accurate determination of the magnetic declination 
requires very careful manipulation and attention to instrumental details, and especially 
so if observed by the suspended collimator magnet, or by the reflecting apparatus devised 
by Dr. Lloyd and employed by the late Mr. Welsh in his Magnetic Survey of Scot- 
land, in the years 1857-58, the account of which will be found in the Report of the British 
Association for the Advancement of Science for 1859. 
Partly from these considerations and from the time required in the use of such deli- 
cate instruments, instead of them the well-known Admiralty Standard Compass was in 
general employed, supplemented occasionally with a Kater’s Azimuth Compass of supe- 
rior construction. Every precaution was adopted to ensure the accuracy of the several 
adjustments of these instruments before they left the Admiralty Compass Observatory 
(now established in Her Majesty’s Victualling Yard at Deptford) prior to the annual 
resumption of the duties of the surveying-vessels, as well as in the re-examination of 
their errors on return from the season operations. 
The most extended of the series of observations recorded in this paper were made by 
Staff Captain E. K. Calver in Her Majesty’s Ship ‘ Porcupine,’ assisted by Staff Com- 
mander George II. Inskip ; they include Stornoway in the Hebrides, Lerwick in the 
* Communicated with the sanction of the Lords Commissioners of the Admiralty. 
2 x 
MDCCCLXXII. 
