320 
MR. A. W. RUCKER AND DR. T. E. THORPE ON A MAGNETIC 
Mr. Whipple writes, “ I have now looked over all the MSS. papers I can find, 
referring to this Observatory in 1842, and I am quite unable to find any reference to 
the observation C[Uoted in the ‘Phil. Trans.’for 1870, p. 274. There was no Staff 
here at the date, nor any official publication, hence I do not see how “ Observatory,” 
or, as printed, “ Offi,” could be any authority. Again, in Sabine's contribution, ‘ Phil. 
Trans.,’ 1849, p. 208, Greenwich and Bushey are both given with the names of the 
observers, and 1 think there can be no doubt that if Sabine had observed here in 
1842, he would have certainly quoted the observations in that table. ... I fear we 
must consider it somewhat too hypothetical to trust to.” 
On the whole then, it appears to us most likely that the number given by Sabine 
was not deduced from an observation made in 1842, hut was reduced to that epoch 
from the Kew Observatory records, which did not begin till some years afterwards, 
and that in the deduction some numerical blunder was made. 
Summary. 
We may now attempt to sum up the result of our studies of local aiad regional 
magnetic forces in the United Kingdom. 
We have proved beyond possibility of doubt that two centres of attraction exist 
near Beading and the Wash respectively, and in the former case it is evident that the 
Horizontal disturbing Forces tend towards regions of maximum Vertical disturbing 
Force. 
We have then gone through the United Kingdom district by district, and have 
shown that the same rule holds good everywdiere. Putting aside stations of 
maximum or minimum Vertical Force and stations on valley lines (wdiich do nob 
furnish real exceptions) there are not half a dozen which are clearly anomalous in 
the whole 200 ; nor has this result been obtained by splitting the whole area of the 
survey up into a large number of small districts which have been carved cut so as to 
secure an appearance of uniformity of behaviour. Omitting the border stations on the 
south of Scotland, in Devonshire and Cornwall, the Channel Isles and Dover, the 
magnetic constitution of the rest of Great Britain is accounted for by five principal 
ridge lines only. 
The first is coincident for a great part of its length with the direction of the great 
fault of the Caledonian Canal. The second and third are connected with the masses 
of basalt in the Western Isles and the Scotch Coal-field respectively. 
The foiu’th runs for 100 miles parallel to, if not coincident with, a line in Yorkshire 
and Cumberland along which geologists believe that crystalline rocks may occur near 
the surface, and sends out a branch toward the igneous rocks ’which occur in North 
Wales. 
The fifth runs for nearly 200 miles from London to Milford Haven along another 
similar geological line, and sends out a branch to the south coast from near Beading. 
