622 
MR. A. W. RUCKER AND DR. T. E. THORPE ON A MAGNETIC 
The existence of a magnetic col near Glasgo^v is proved by the low \ertical Force 
at Hamilton, while, as the Horizontal Disturbing Forces at these two places point 
in almost exactly opposite directions, there is no doubt the ridge line passes between 
them. They are 11 miles apart. Further to the west the line is traced between 
Cumbrae and Ardrossan (11 miles), both of which are again stations of high Vertical 
Force, and on Arran between Loch Ranza and Brodick (9 miles). 
The average distance of these pairs of stations being 11 miles, the position of this 
ridge line is known at six points to within 6 miles. 
Again : the extension north of the Forth of the regions of high vertical force 
previously proved to exist near Edinburgh and Berwick w^as, at the conclusion of our 
earlier survey, very hypothetical. It was based largely upon the existence of a 
considerable Vertical Force disturbance at Crieff, at which, however, on this hypothesis, 
the direction of the Horizontal Disturbing Force was anomalous, as it pointed towards 
a valley line 1890 Memoir,” pp. 301, 810, and 312), The difficulty has now been 
cleared up. The existence of a ridge line near Crieff has been proved at Callander, 
Killin, and Dunkeld. 
The fact that there are also large Vertical Forces in the Fifeshire District is proved 
at Kinross and Cupar. This high level region is completely separated from the Cried 
District by a very clearly-marked valley line, which runs from Stirling to Perth and 
Dundee, but is connected with the main Scotch Coal Field ridge line by a high level 
magnetic col at Kirkcaldy, so that it must be considered as an outlier of the district 
to the south of it. 
The secondary valley line which intersects the main ridge line at the Glasgow 
magnetic col runs from the top of Loch Goil to the mouth of the Clyde, and follows 
the course of that river as far as Abington, i.e., for more than 50 miles. 
We next come to two points on which our recent observations have done more than 
confirm and make more definite the conclusions drawn from our earlier survey. 
In the first place, we have now proved the existence of a centre of attraction near 
the Cheviot Hills. (See also p. 654 below.) 
At Jedburgh, Wooler, and Kelso the Vertical Disturbing Force is large, at Kelso 
larger than at any other place within 130 miles. 
At Selkirk, although the Vertical Force is not large, the disturbance is greater than 
at neighbouring places; but the ridge line apparently dies out to the north of that 
town. 
This centre is partly separated from the main ridge line to the nortn of it by a 
secondary valley line, which starts from Hawick, passes via Peebles to Greenlaw, and 
then, crossing the main ridge by a high-level magnetic col at Grant’s House, joins the 
v^alley line which comes from the north to Dunbar. 
The fact that the two ridge lines are v^ery near together at Berwick, and that, as 
the valley line crosses the main ridge, it is only of secondary importance, is evidence 
that the Cheviot mao-netic district is connected with that which lies to the north of 
O 
