626 
MR. A. W. RUCKER AND DR. T. E THORPE ON A MAGNETIC 
Disturbing Forces would be explained in several cases if we suppose that a very 
nai'iow ridge line runs from the south of Mary port to the north of Armathwaite. A 
prolongation of this line would also account for the Horizontal Disturbances at Alston 
and Haltwhistle, and for the local maximum of Vertical Force at Morpeth. 
The direction of the Horizontal Disturbing Force at Ravenglass is anomalous, but it 
is so small that this need excite no surprise. 
District 10. —Lincolnshire and Yorkshire. 
The next magnetic district is one of the most important. It was clearly indicated 
in the Maps of our previous survey as extending from the Wash to the neighbourhood 
of the English Lakes. It was also described as possibly throwing out a branch 
towards Wales. A centre of attraction was shown to be probable in the neighbour¬ 
hood of the Derbyshire Peak. A second centre was discovered near Melton Mowbray, 
and finally it was suggested that the main ridge line was connected with the 
magnetic disturbances in the South of England by a less important continuation 
which passed near Cambridge. 
It is satisfactory to be able to state that all the more doubtful points in this 
description have now been verified, and further that the various parts of tin’s complex 
system of magnetic disturbances are so closely related that it is difficult to find 
clearly-defined minor valley lines to separate them. For convenience of description 
the district may be confined to the neighbourhood of the great ridge line which runs 
from Morecambe Bay to the Wash, but it will be seen that if thus defined the 
southern boundary is at one point quite arbitrary. 
The places between which the ridge line was previously detected were Appleby 
and Giggleswick, Thirsk and Leeds, Hull and Gainsborough, Mablethorpe and 
Lincoln, Clenchwarton and Spalding, and perhaps Thetford and March. 
The average distance between the two stations in each of these pairs is about 
30 miles. 
The line is now more accurately fixed as running between 
Kendal and Milnthorpe, which are ... 7 
Sedbergh and Kirk by Lonsdale, which are 10 
Aysgarth and Kettlewell, which are. . . 11 
Boroughbridge and Harrogate,'''■ which are 6 
Sutton-on-Derwent and Selby, which are . 11 
Howden and Selby, which are .... 9 
Brig g and Gainsborough, which are . . . 16 
Market Easen and Lincoln, which are . . 15 
Horncastle and Lincoln, which are ... 19 
Boston and Sleaford, which are .... 17 
miles apart. 
?5 55 
5 5 5 5 
5 5 5 5 
5 5 5 5 
5 5 5 5 
5 5 5 5 
5 5 5 5 
5 5 5 5 
5 5 5 5 
* The Horizontal Disturbing Force at Harrogate is so small that some doubt may exist as to this. 
Probably the ridge line runs thrbugh or close to Hari’Ogate itself. 
