310 
MR. A. W. RUCKER AKD DR. T. E. THORPE OH A MAGNETIC 
Vertical Force, and therefore tire direction of the Horizontal Force cannot be deter¬ 
mined from the rnle. 
The Wicklow and Arklow mountains, which are composed of granite, do not 
appear to exert any important effect on neighbouring stations, hut there is a region of 
high Vertical Force in Wexford. 
o 
Magnetic Map of the United Kingdom. 
In Plate XIII. we have attempted to represent the magnetic state of the whole 
country by bringing together the results of our studies of the magnetic districts into 
which it may be divided. 
The valley and ridge lines are shown. The unshaded parts are regions of 
negative Vertical Force disturbance, and the three shades employed indicate that the 
disturbance is greater than 0 but less than '01, greater than ‘01 but less than 
'02, and greater than '02 metric unit respectively. 
The lines representing the Horizontal Forces are drawn to a scale on which 
1 mm. = O'OOl metric unit, except at Ganna and Soa, where the disturbances are so 
large that the arrows would be inordinately long. 
Considerations which have been adduced in the foregoing discussion have led us to 
depart, in a few minor points, from the strict rules by which the valley and ridge 
lines have been drawn. Thus, the line which separates the Highland and Scotch 
Coal-field Districts has been drawn so as to include Crieff in the latter. 
The rather uncertain valley line in Mid-Wales, which was taken from the 
Horizontal Force disturbances (Plate X.), is replaced by the closely neighbouring- 
ridge line, taken from the Declination disturbances (Plate X.). This would necessitate 
valley lines on each side of it, the ]:)Osition of which is uncertain. 
In Ireland too, the ridge line which runs from Anti’im to the neighbourhood 
of Kells, is not very definite, and it is best to consider the clearly marked portion of it 
in Antrim as only doubtfully connected with the centre of attraction near Kells. 
These points must be left for future investigation, but the unquestionable existence of 
widespread regional disturbance in the districts we have specially studied in England, 
together with the general agreement between the two maps of Scotland, deduced from 
the surveys of 1857 and 1886, leads us to hope that Plate XHI. gives the first approxi¬ 
mation to a map of the disturbing magnetic forces in play over the whole kingdom. 
On the Relation behveen the Magnetic and Geological Constitution of the Magnetic 
Districts. 
Up to the present, we have discussed the various districts into which we 
have divided the country from the point of view of their magnetic peculiarities only. 
