SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1891. 517 
a neighbouring district. It is, therefore, a very doubtful question whether we 
should trust the general formula or the district lines. 
The calculations were first made with the general formula as above given, but the 
differences between the calculated and observed values of the Dip at the different 
stations in the extreme north were so great that we were led to believe that the 
district lines were a better representation of the state of the district. 
There was other evidence of their trustwoiThiness, as at lat. 56° 30' (see Table VIII.) 
where Districts I and II overlap the Dips deduced from the lines for District I never 
differ by more than 1' from the mean of the two. 
On the whole, therefore, we decided to bring the formula, into closer agreement 
with the district lines. 
For values of 6 in the above formulae >71° we took the true dip (6') to be given 
by the formula 
61'= (11 - 7l)/10. 
In Table IX. (p. 520) the Dips calculated by these formulae for the intersections 
of whole degrees of latitude and longitude are exhibited, as in the case of the other 
elements. 
The discontinuity due to the above correction introduces into the part of the 
Table which refers to the North of Scotland some irregularities which we have not 
smoothed out. 
