SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 188G. 243 
Fig. 2. 
Isomagnetics in tlie border district of tbe English and French Surveys, 
- R. and T., — • — • — • — Moureaux, .hypothetical connections. 
We think the agreement between our calculated and observed curves is too close to 
leave any doubt that in this and neighbouring latitudes the law that the distance 
between the points of intersection with a line of latitude is constant is very approxi¬ 
mately true. At all events, there is no trace of a change in this distance amounting 
to a quarter of a degree as is shown by the 1872 lines. As the observations on which 
Sir F. Evans’s map were based were comparatively few in number and were made 
exclusively at coast stations the accurate delineation of the isogonals was not easy. 
He makes the observed Declinations too small in the eastern counties. If the 
distances between the isogonals had been kept constant the 19° line would have been 
pushed further to the west, and a closer agreement with our observations would have 
been attained. Considering the circumstances under which Sir F, Evans’s map was 
drawn, we think the concordance between the general directions of the lines is satis¬ 
factory.* We are also of opinion that our 17° isogonal is not too far to the west, and 
that the fact that in the eastern counties the calculated are less than the observed 
Declinations is due to a real physical cause. M. Moureaux’s results confirm our own 
as to the 18° isogonal, and if we suppose that the easterly tendency of the lines which 
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