510 
MR. A. W. RUCKER AND DR. T. E. THORPE ON A ilAGNETIC 
Longitudes of* the points of intersection with given Lines of Latitude of the 
Isogonals deduced from the District Lines and the Formula respectively. 
Latitude . 
23°. 
22°. 
21°. 
20°. 
19°. 
18°. 
17°. 
58-5 
0 / 
1 58 
5 30 
O 1 
3 28 
3 39 
o . 
1 58 
1 48 
0 , 
0 t 
O / 
57-5 
7 5 
7 45 
5 31 
5 54 
3 57 
4 4 
2 23 
2 13 
j 56-5 
7 41 
8 10 
6 4 
6 14 
4 26 
4 25 
2 48 
2 39 
5^-5 
8 18 
8 20 
6 36 
6 31 
4 54 
4 50 
3 12 
3 7 
1 30 
1 25 
54-5 
8 59 
9 2 
7 12 
7 14 
5 26 
5 21 
3 39 
3 40 
1 52 
1 51 
0 6 W. 
0 9 E. 
53-5 
9 45 
9 46 
7 53 
7 53 
6 2 
6 1 
4 11 
4 13 
2 19 
2 20 
0 27 
0 20 
52-5 
8 41 
8 40 
6 45 
6 42 
4 50 
4 47 
2 53 
2 56 
0 55 
0 49 
1 4 E. 
1 34 E. 
51-5 
9 35 
9 27 
7 35 
7 29 
5 34 
5 32 
3 31 
3 37 
1 27 
1 38 
0 38 E. 
0 49 E. 
50-5 
•• 
4 15 
4 7 
2 3 
2 11 
0 10 E. 
0 4 E. 
The relation between these two sets of figures is perhaps better illustrated by the 
isogonal curves shown in Map 1. The district curves are dotted. The calculated 
are drawn in continuous red lines. 
The agreement in the. centre of the kingdom is all that could be desired. The 
divergences in the North of Scotland are very large. Thus taking lat. 58° 30' N., 
long. 7° W. as an example, the Declination as given by the district curves is 22° 48'’7 
(Table II.) and as calculated 23° 20'’7 (Table III.), a difierence of no less than 32'. 
A glance at Map 1 shows that the district curves bend suddenly to the West in 
the North West of Scotland. A similar peculiarity was exhibited (though to a less 
extent) by the results of the 188G survey (“ 1890 Memoir,” Plate 2), and a comparison 
of the values of dS/dX in Table I of this Paper proves that the district curves are 
affected with some irregularity in Scotland. The four districts IV, III, II, and I, 
are on the Eastern side of the United Kingdom. The values of dS/dX are 25 '"4, 30'’3, 
