SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY I, 1886. 
55 
Page. Page. 
Summaiy. . 320,321 
Tables for the Calculation of the Magnetic Elements.322 
Table VIII. Declination. 
,, IX. Horizontal Force. 
„ X. Dip. 
Rate of Secular Change. 323-326 
Table XII. Rates of Secular Change.325 
Two Magnetic Surveys of the British Isles have been made previous to that of which 
an account is given in this paper. The observations necessary for these were taken 
between the years 1834-38 and 1857-62, and the results were reduced to the epoch 
1842-5 by Sir E. Sabine, in a paper published in the ‘ Philosophical Transactions’ for 
1870 (‘Phil. Trans.,’ vol. 160, 1870, p. 265). As a full account of both surveys is given 
in that paper, it is unnecessary to describe them in detail here. The first was made by 
five observers, viz.. Sir E. Sabine, Captain J. C. Ross, Mr. R. W. Fox, and Professors 
Lloyd and John Phillips. In the second survey (1857-58), Mr. Welsh, Superin¬ 
tendent of the Kew Observatory, made an admirable series of observations in Scotland, 
though, unfortunately, the exposure to which he was subjected brought on an illness 
which terminated in his death. Sir Edward Sabine made observations on the Force 
and Dip at 24 stations in England, and some declinations determined by several naval 
officers between the years 1855 and 1861, were utilized. Altogether observations w’ere 
made at 243 stations. (‘Phil. Trans.,’ vol. 162, 1872, p. 319.) 
It has, we believe, for some time been thought by those interested in terrestrial 
magnetism, that another survey of the United Kingdom should be undertaken, and 
we ourselves drew attention to the matter in a paper “ On the Irregularities in 
Magnetic Inclination on the West Coast of Scotland ” (‘Roy. Soc. Proc.,’ vol. 36,1884, 
p. 10). Not only was this desirable in order that the secular changes in the direction 
of the lines of equal Inclination, Force, and Declination might be re-determined, 
but also because the earlier surveys left much to be desired w'ith regard to the 
distribution of the stations and the number of the Decimation observations. Thus 
the Declination was determined about the epochs 1836 and 1857 at 84 stations only, 
of which 11 were common to the two surveys. The maps given by Sir E. Sabine 
in the paper already referred to show that ditlerent districts have received very 
different degrees of attention. Stations where the Dip has been determined cluster 
thickly about the coast of Scotland to the south of Oban, about the English lakes, 
and the south coast of England, and are thinly distributed in the North of Scotland, 
in the eastern counties of England, and in the centre of Ireland. In like manner, 
while (owing chiefly to the labours of Mr. Welsh) the Declination had been 
measured at 40 places in Scotland, it had been observed with adequate instruments at 
only 28 stations in England, and 16 in Ireland. We have therefore undertaken, and, 
in the course of the five years 1884-88, both inclusive, have completed a new' 
magnetic survey of the British Isles. 
