186 



TAGtiTH REPORT — 1838. 



the intensity in London being unity. The value of this ratio 

 obtained by Captain Ross in 1838 is 1-0186 ; and the former 

 result being equivalent to the mean of six distinct comparisons, 

 the final mean is 1-0195. 



Of these results, deduced by the two methods, the difference 

 is only -0006 ; and we should therefore err very little from the 

 truth in taking their arithmetical mean. But the probable error 

 of a single comparison in the latter method is so much less than 

 in the former, that we shall certainly be nearer to the truth in 

 adopting the latter result. We shall accordingly consider the 

 number 1*0195 as expressing the ratio of the intensities of the 

 magnetic force in Dublin and London. 



Report resumed by Major Sabine. 



Collecting in one view the values of u and r resulting from 

 the several series of intensity observations, we have as follows : 



Table LXXX. 



The values of u in England and Scotland, or the angle whicli 

 the isodynamic lines in those countries make with the meridian, 

 appear to be very nearly the same ; the difference in the mean 

 values is much within the order of the differences of the partial 



