626 SOLUTION OF THE EQUATIONS. 



For the period 1845 

 c ~ c> ' - 13-29 , C + C = - -991 , hence c = 12'30 and c'=-14'28 , 



a ~ a ' 



a = - -855 , - = T563 , hence a= 708 and of = 2'418 , 



2 2 



-~- -= -8184, ~-= '0647, hence 6= "883 and V= - 7537, 



2i 



whence we derive for the horizontal force, at the north pole 1'13 and 

 at the south pole 2 -5 3 units, and for the total force, at the north pole 

 12'35 and at the south pole 14 P 50 British units. 



For the period 1880 



-= 13-16 , -"j"-=- -5717, hence c = 12-59 and c' = -1373 , 



2i 2* 



C ^^=- 1-0324, ^ = 1-7417, hence a = '7093 and a' = 27741, 



^~= '9624, li-- -1347, hence 6= '8277 and V =- 1-0971, 



Zt _ 



whence we derive for the horizontal force, at the north pole 1'09 and 

 at the south pole 2'98 units, and for the total force, at the north pole 

 12'64 and at the south pole 14'05 British units. 



19. On referring to the Charts for Sabine's Arctic and Antarctic 

 Magnetic Surveys (1840 1845) and to the Admiralty Charts constructed 

 by Captain Creak for 1880 we find a very close agreement between the 

 above calculated values of the horizontal and vertical magnetic forces for 

 the polar areas and the values of those forces derived from the observations 

 and recorded in the Charts. 



Thus the values given by Captain Creak for 1880 are: 



for the horizontal force at the north pole 1 British unit and at the south 

 pole 2'75 British units; 



for c, the vertical force at the north pole, 12' 6 units and for c', the 

 vertical force at the south pole, 13' 7 British units. 



