116 



SIXTH REPORT — 1836. 



By the statical metliod we have found the intensity at the 

 central station 1*0326 ; the angle with the meridian made by the 

 isodynamic line 46" 15'*5 ; and the intervals between isodyna- 

 mic lines representing differences of intensity of '005, to be 

 32*29 geographical miles. 



The agreement of the two methods cannot be considered 

 otherwise than as very remarkable. They have no element in 

 common except the dip, which, whilst it is very influential in the 

 horizontal method, might be many minutes in error without 

 sensibly affecting the results by the statical method. The close 

 agreement of two methods, which are thus independent of each 

 otlicr, forms a strong mutual corroboration. 



By substituting in the original equations the values thus 

 found of/', X, andtj, we may compute the intensity assigned by 

 the combination of the observations at all the stations to the 

 geographical position of each station in particular, and we shall 

 tiius see what degree of accordance the observations at each 

 station exhibit, with the indications of the combined results. The 

 following table shows the differences between the observed and 

 the combined result at each station by both the horizontal and 

 statical methods ; the sign + signifies that the observed inten- 

 sity is in excess ; — that it is in defect. 



Table VII. 

 Differences of Observed and Comjnited Results. 



We have seen that each of tlie two methods gives, when 

 taken separately, general results agreeing in a very remarkable 

 manner w ith those of the other method. When however we 

 examine the contents of the preceding table, we remark that in 

 the horizontal method much greater differences appear between 

 the observed and the combined results at single stations, than i.s 



