296 
MR. A. W. RUCKER AKI) DR. T. E. THORPE ON A MAGNETIC 
Declination Disturbances. 
1 
1857. 
1872. 
1886. 1 
i 
Aberdeen. 
+ 5-1 
- 4-0 
- 6-7 
Edinbui £;-h . 
+ 19-8 
+ 10-0 
+ 4-2 
Kyle Akin. 
+ 38-2 
+ 27-0 
+ 24-9 
Oban. 
- IIT 
-f- 55'0 
- 8-3 j 
Ken-era. 
-- 5-0 
- 6-8 
Thnrso. 
+ 13-8 
+ 7-0 
- 5-2 ^ 
Wick. 
+ no 
+ 7-0 
- 8-5 1 
It is difficult to offer any satisfactory suggestion as to the causes of the apparently 
regular change. It may be due only to the fact that the three methods of deducing 
the disturbances by calculations are different, or it may be due to real changes in the 
local forces. Such alterations are not impossible since if the rocks were magnetised by 
induction on the earth’s field tbe direction and intensity of the induced magetisation 
would be subject to secidar change, but the differences are too great to be explained thus. 
But whether local changes have taken place or not, there can be no doubt that the 
neneral distribution of the Declination disturbances in Scotland is the same now as it 
was in 1857. 
In Ma]! 22 the dotted lines are the curves of no disturbance which would have 
been dravm from our own observations alone. The differences introduced by the 
addition of Welsh’s and Evans’s surveys are quite unimportant in the North. In the 
South they simplify the lines instead of introducing com])lications. As the disturb¬ 
ances at Edinburgh and Berwick are of opposite signs, we had to carry a line of no 
disturbance between them. Mr. Welsh, however, had two stations a little to the 
West of Berwick, viz., Makerstoun and Melrose, and at these the disturbance is of the 
same sign as at Edinburgh. 
The introduction of these justifies us in treating Berwick as an isolated station, and 
the simple system represented by the continuous lines results. We have adopted 
these as the true lines of no Declination disturbance in this part of the Kingdom. 
As Sir Frederick Evans did not add any Dips or Horizontal Forces to the list of 
those already known, we proceed at once to the direct comparison of the disturbing- 
forces deduced from our owm and Air. Welsh’s surveys. The magnitudes and 
directions of these calculated by us as above described are as follows :— 
