444 



THE THEORY OF TERRESTRIAL MAGNETISM. 



Taking the values of X and Y from the Tables and taking their differ- 

 ences with respect to longitude and latitude, we have for X 



Similarly for Y 



Hence at the origin, where x 0, y = 0, taking the mean differences, 

 we have 



*.= 1030-3, (^-) = -9-55, ( d ?) = -26-35, K\ = -167, 

 \dx/o \ dy Jo \ dx 2 / 



- -17-3 

 ~ ' 



dxdy 



.- -154-4, (*) =-1-25, (f ) =2-65, (*) =127, 

 \dxjo \dyjo \dx>) 



, , , -j j 

 \ df / \dxdylo 



_ 



o /o. 



