292 
MR. A. W. RUCKER AUD DR. T. E. THORPE OH A MAGNETIC 
On the whole, then, if we take the region bounded by the sea, by lat. 53° and 
long. 2° W., which includes about 50 stations, we think the Horizontal Forces 
unmistakeably tend to act toward the region of great Vertical Force. There is one 
striking exception at Birmingham, and one or two more doubtful ones on the lower 
reaches of the Thames, and the rule must be construed subject to the obvious condi¬ 
tion that a true maximum of Vertical Force, though probably near to, is not 
necessarily at the station at which we happen to have found the largest among the 
Vertical Forces we have measured. 
Subject to these exceptions and to this proviso the rule holds good. 
General PtESULTs or the Investigation oe the Local and Begional 
Disturbances. 
Having described the results obtained in districts to which we have devoted special 
attention we now proceed to apply the same methods to the whole area of the survey. 
In adopting this course we are fully aware that the number of our stations is not 
sufficient to enable us to speak with any certainty as to the details of the magnetic 
peculiarities of the districts wm are about to discuss, and it is quite possible that we 
may have arrived at some conclusions which must hereafter be modified. It appears 
to us that even under these conditions our work is much more likely to be useful if we 
give wdiat only professes to be a first rough sketch map of the magnetic forces in play 
in the country than if wm leave our successors to get what hints they can from 
observations which we ourselves have made no attempt to collate. Even, therefore, 
if our conclusions were much less certain than we believe them to be we think it 
would be better to state them. 
Fortunately, however, we are able to take up a much stronger position than this. 
Our conclusions may be tested, (1) by the agreement of the results of the various 
methods of attacking the problem, (2) by the agreement of our results in Scotland 
with those which can be deduced from Mr. Welsh’s survey, (3) by the establishment 
of relations between the magnetic phenomena at stations scattered over wide areas, 
and (4) by the establishment of a connexion between the magnetic and geological 
characteristics of various districts. In all these particulars we venture to assert that 
they will bear investigation, and we cannot but believe that we have detected the 
main directions of the lines of disturbing magnetic force. 
The method we adopt is as follows ; — 
We draw the ridge and valley lines (see p. 265) which mark the centres and the 
Iioundaries of districts which are under the influence of a dominant locus of attraction. 
We take each district bounded by two valley lines, and study it by means of the true 
isomagnetics of the disturbances and disturbing forces, and lastly, wm discuss the 
relations between its magnetic and geological characteristics. 
