268 
MR. A. W. RUCKER AND DR. T. B. THORPE ON A MAGNETIC 
which is about a mile distant, in 1884 and 1885. In the Sound of Islay we had two 
stations about four miles aj)art, viz., Port Askaig in 1884 and Bunnahabhain in 1888. 
All these places, though ty 2 :)ical Scotch stations, w^ere on ground which elsewhere 
would be considered but indifferently good for our purpose. At three other places 
more favourably situated we also observed twice, viz., at Stranraer in 1884 and 1888, 
at Beadinof in 1886 and 1888, and at Bude Haven in 1886. At the two former the 
stations were as nearly as possible the same on the two occasions, at Bude Haven 
they were less than half a mile a]Dart. 
The results are summed up in the following Table. The resultant Horizontal 
disturbing Force is indicated by F, and the angle which its direction makes with the 
geographical meridian by (/>. The latter is taken as positive on the western side, due 
north being represented by 0”. 
Station. 
Rock. 
Date. 
F. 
(p. 
Z. 
Stornoway— 
O 
(1) Castle Grounds 
Gneiss 
1884 
•0175 
129-6 
-•0113 
(2) Ard Point . 
1885 
■0179 
109-2 
Dip not observed 
1888 (T) 
•0198 
119-7 
-p-ooie 
1888 (R) 
■0278 
113-5 
+ •0120 
LocLi Ay lor t . 
Gneiss 
1884 
•0267 
1411 
-•0326 
1888 
•0139 
112-3 
+ •0178 
Oban— 
(1) Mainland . 
Trap 
1888 
•0143 
10-9 
-•0129 
(2) Kerr era . 
1884 
•0196 
169 
-•0132 
1885 
•0219 
16-2 
-•0124 
Sound of Islay— 
(1) Port Askaig . 
Primary 
1884 
•0309 
53-1 
+ •0141 
(2) Bunnahabhain. 
Limestone 
1888 
•0265 
69-9 
+ •0122 
Stranraer .... 
Clay, Slate 
1884 
•0038 
178-5 
-•0072 
1888 (R) 
n (T) 
•0065 
•0062 
181-8 1 
175-4/ 
-•0034 
Reading .... 
Clay 
1886 
•0049 
- 8-3 
+ •0235 
1888 
•0084 
-10-2 
Dip not observed 
Bude Haven . 
Shale 
1886 
•0065 
143-1 
+ •0091 
•0048 
180-0 
+ •0030 
The annexed small map (tig. 11) illustrates these numbers by showing the direction 
and magnitudes of the disturbing foi’ces as determined on two occasions at stations in 
Scotland. 
An inspection of this map and of tlie table justifies the statement that the magni¬ 
tude and direction of the disturbing forces can be determined with an accuracy 
sufiicient to enable us to draw conclusions from groups of stations even if it would 
not abvays be safe to argue from one, 
