290 
MR. A. W. RUCKER AND DR. T. E. THORPE ON A MAGNETIC 
Fig. 21 is an attempt to realise the magnetic constitution of this part of England 
from this point of view. In studying it we must remember that the direction of the 
Horizontal Force at a station where the Vertical Force is a maximum or minimum must 
be indeterminate in the sense that it cannot be deduced from the Vertical Forces 
Pig. 21. 
Contour lines of Vertical Disturbing Eorce and Horizontal Disturbing Eorces in South-Eastern 
England. Each darker tint corresponds to an increment of O'OlOO metric unit in the Vertical 
Disturbing Force. 
at neighbourino' stations. All that we know when the Vertical Force is a maximum 
is, that a peak is probably in the neighbourhood, but on which side of the station we 
do not know, unless, as in the case of the Reading disturbance, other stations indi¬ 
cate it. 
