SURVEY OP THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1886. 269 
Fig. 11. 
If the station is on good ground we may place more confidence in the results. 
Stranraer is interesting as being the only place where we both took complete sets of 
observations simultaneously on good ground. The results are in very close accord. 
But those obtained elsewhere leave no doubt as to the order of the magnitude of the 
disturbing force nor as to its direction to within (in unfavourable cases) 15° or 20°. 
The difference in the signs of the Vertical Forces obtained at Loch Aylort and 
Stornoway in different years may in part be due to the uncertainty of the secular 
correction for the Dip, which appears to be very abnormal, especially at Loch Aylort 
(see p. 86). In this case we should be driven to the conclusion that a real change 
in the local Force had taken place. It is noticeable that the Vertical Force disturb¬ 
ance was apparently (algebraically) greater at Stornoway, Loch Aylort, Kerrera, and 
Stranraer on our second visits to these places. 
The following Table contains the particulars as to the disturbing force at every 
station in accordance with the notation described above. On Plate XIIL, the 
directions and magnitudes of the Horizontal disturbing Forces are sliown, and regions 
of positive and negative Vertical Force disturbance are indicated, the former being 
shaded. 
