306 
MR. A. VV. RUCKER AKD DR. T. E. THORPE OX A MAGNETIC 
Scotch isomagiietics are linear functions of the coordinates which determine the 
geographical 2 ;)osition, and that the errors involved in the assumption would chiefly 
alFect stations such as these, which are on the border of the district. 
If it is necessary to prove that these results are independent of the method of 
calcnlation, Fig. 28 is sufficient for the purpose. 
The lines of equal Horizontal Force converge in a most remarkable way towards 
North Wales, which is one of the most certain indications of a centre of attraction. 
Again the Declinations at Holyhead and Llandudno differ only by 0'*4, while the 
difference of longitude corresponds to 25'. This again is strong evidence of the 
existence of a centre of attraction between them. 
If, as appears probable, there are two regions of high Vertical Force in the district, 
it is possible that the northern one may be connected rather with the Cumberland 
Lakes than with North Wales. However this may be, and while fully admitting 
that it requires further study, we think that this district appears to obey the rules 
which hold good elsewhere. 
The North-Eastern District. 
This district is bounded on the north and west by valley lines which have been 
already described. On the south we have drawn a line which passes through the 
centres of twm regions of negative Vertical Force disturbance. 
The southern portion lies wdthin the limits of our special surveys and has been so 
fully discussed that nothing need be added here. The northern part presents a 
feature of peculiar interest. 
The results as directly observed do not furnish such clear indications as in a district 
where the presence of crystalline rocks is more obvious. The isogonals are, how^ever, 
bent in the peculiar manner which indicates centres of attraction. Thus the 19° 6' 
line (Fig. 29) points to such a centre to the south of Thirsk, the 18° 48' isogonal 
points to another between Hull and Gainsborough. As botli these lines depend in 
part upon the same stations, it is satisfactory to find that they are completely con¬ 
firmed by the quite independent 18° 16' line wdiich runs nearly due east and w^est 
between Lincoln and Mablethorpe. 
The Vertical Force isomagnetic which corresponds to 4'516 metric units bends 
southward to Thirsk in a way that is again an indication of a centre of attraction. 
There are thus signs of an attractive region lying between the following pairs of 
stations, viz., Mablethorpe and Lincoln, Hull and Gainsborough, Thirsk and Leeds. 
On turning to the disturbances (Plates IX. and X.), we find that both the 
Declination and the Horizontal Force give nearly coincident ridge lines running 
along the line just indicated. The declination line passes northw^ard to the Cumber¬ 
land Lakes and southward to tlie Wash. The Horizonal Force line turns south amid 
the Yorkshire Hills and runs toward North Wales. 
