SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1886. 245 
Table VII. 
District. 
Central Station. 
1 
> 
II 
Q 
de' 
^ ~ dl' 
1 
I'TS 
II 
Lat. N. 
Long. W. 
I. 
56 48-0 
4 19-0 
71 80 
3U1 
5-8 
II. 
55 27-3 
3 41-6 
70 19-6 
31-9 
8-2 
III. 
53 26-7 
2 26-0 
69 3-0 
36 T 
7T 
IV. 
51 47-7 
0 17-4 
67 45-6 
40-8 
7-6 
V. 
54 1-4 
7 39-3 
69 59-8 
38-3 
9-8 
VI. 
53 267 
5 42-0 
69 24-8 
3G-2 
6-3 
VII. 
51 8T 
3 9-6 
67 41-2 
38-8 
6-6 
VIII. 
52 57T 
8 I3T 
69 24-3 
387 
8-5 
IX. 
51 49'5 
4 47-4 
68 18-2 
39T 
6-8 
A general formula was next found to embrace the whole country. For this purpose 
a Table similar to Table VI., pp. 238-9, was prepared, and the district isoclinal lines 
were drawn from it on curve paper, on a purely artificial system, in which all degrees 
of latitude and longitude were regarded as of equal length. When thus drawn the 
mean directions of the isoclinals were nearly straight lines and practically parallel. 
The equation to the 67° isoclinal wms 
I - 49°-92 + 0-2 (X - 4) = 0, 
where I and X are the latitude and longitude expressed in degrees and fractions of 
a degree. If then s be the length of the perpendicular on this line from any point, 
the Dip at the station indicated by that point would (if the lines were equidistant) be 
given by the equation 
^ = 67 + Ks, 
where A is a constant. This condition was not fulhlled. The distance between the 
lines increased approximately in the proportion of their distance from the 67° line, 
but a small periodic term was necessary in addition to this correction to produce the 
desired accuracy. 
The following plan was finally adopted ;— 
If we write 
j) = l - 49-92 + 0-2 (X - 4) 
f^i^d 9 _ — V — b’l sin (20 _p) 
we get the Dip in degrees from the equation 
0 _ 0^0 I 1‘0083 q ^ 
1-456 + 0-03 q 
