628 MR. A. W. RtTCKER AND DR. T. E. THORPE ON A MAGNETIC 
this lln6 is very doubtful, we have drawn on Map 12 an almost arbitrary line to serve 
as an artificial boundary, and have marked it by crosses. 
A valley line, which is very clearly marked, runs south from Leeds to Stamford, 
though at many of the places through which it is represented as passing the 
Vertical Disturbing Forces are positive. We have adhered to our plan of joining 
stations of minimum Vertical Force Disturbance by straight lines, which in this 
case makes the line appear more tortuous than, in all probability, it leally is. 
There is an important maximum of Vertical Disturbing Force at Market V eighton, 
but the focus of the Disturbance appears to the west of that town. From this point 
the ridge runs S.F. bv S. in an almost straight line to between Boston and Sleafoid. 
There are indications of centres of attraction to the north of Butterwick-on-Trent, 
and between Lincoln and Horncastle. 
In the south of Lincolnshire this great ridge line, which we have now followed for 
about 170 miles, becomes more diflicult to trace. 
It is, no doubt, connected with a well-marked centre of attraction to the south of 
the Wash, but it is also connected by a minor ridge with the next district on its 
western flank. 
At Melton Mowbray the Vertical Disturbing Force is a maximum, and at Corby is 
a magnetic col, whence the line of maximum Vertical Distuiba.nce luns to Sleafoid 
and Boston. The existence of this line accounts for the direction of the Forces at 
Corby and Manton. The direction of the Horizontal Disturbing Force at Grantham 
is not in good accord with the other indications, but, as its magnitude is only just 
greater than the limit of the accurate determination of direction, it cannot serve as 
the basis of a valid objection. 
From Stamford a valley line runs to Thetford in Norfolk, and thence south to 
Colchester and Harwich. The main ridge line runs through the western end of this 
district, passing through the magnetic peak near King s Lynn. 
The remainder of the district is for the most part characterized by large Vertical 
and small Horizontal Forces, the directions of which are somewhat irregular. The 
Vertical Forces indicate a ridge line from the W^ash to Holt, and there aie traces of 
another between Ipswich and Diss. The directions of the Horizontal Forces are in 
fair accord with these, but, taken as a whole, our work in East Norfolk and Sufiblk 
has led to less definite results than in any other part of the Kingdom. 
District 11. — Derbyshire. 
This district, named after the county in which one of its most salient mag-netic 
features appears, lies to the south of the northern portion of that which has just 
been discussed. 
Indeed, in the north—as has been stated—it is divided from the Lincolnshire and 
