SOLUTION OF THE EQUATIONS. 609 



was then compared with the value of the corresponding absolute term 

 derived from the observations which had been used in the solution of the 

 equations. 



The following table gives some of these comparisons between the 

 calculated and observed values of the absolute terms of the equations of 

 condition for the period 1880 for m = 0, m = l and m = 2, for odd and 

 even values of n, and for m 3, for odd values of n, i.e. for all the more 

 important magnetic constants. 



The observed values are taken from the Admiralty Charts and are 

 the values used in the solution of the equations, and it will be seen by 

 the comparison of the calculated and observed values that a chart drawn 

 to give the results of the calculations would not differ much from the 

 Admiralty Charts from which the observations have been taken. 



In the equations of condition and the final equations which have been 

 used above no account is taken of observations within the area of a 

 portion of the surface of the Earth immediately around the poles, i. e. 

 within an area bounded by a small circle of radius 2 30' round the pole 

 when we take all the above equations, or of radius 12 30' when we stop 

 at the belt (c) given by latitude Tl\. This area will be bounded by a 

 circle of radius 22 30' when we stop at equations (e) or latitude 67-|, 

 as in the determinations of the magnetic constants given in the above 

 tables (pp. 605607). 



77 



A. 11. " 



