DISCUSSION ON THE MAGNETIC VERTICAL FORCE. 



(B.) Lunar-Diurnal Variation of the Inclination. 



2". 8 



2.4 



2.0 



1.6 



12 



.8 



A 



.0 



.4 



.8 



1.2 



1.6 



2.0 



2.4 





'■■'i 



^ 



\/ 



In \/ \- 



S?v 





// 



4 



-.Ai- 







\l 



Hi 



u. c. 



0" 12345 67 



9 10 11 1 2 3 4 5 6 V 8 9 10 11 12" 



Maxima at S** and 20'' (principal), minima at 3'' (principal) and ISg*". 

 Total range 3". 6. Probable error of any single hourly representation + 0".7. 

 The lunar diurnal variation in the total force is represented by the equation : — 

 M M M 



^^= — 1-3 + 8.9 sin {d + 63°) + 6.3 shi (20 + 84°) 



an expression not differing much from T\ owing to the large dip. The observed 

 and computed values of — ? are shown in the diagram, which nearly resembles that 

 of the vertical force. 



<P 





\\ 



(C.) Lunar-Diurnal Variation of the Total Force. 

 + 0.000027 

 24 

 21 



18 



15 



12 



09 

 i 06 



1 03 



; 0.000000 



'" 03 



I 



' 06 



09 

 12 



15 



— 0.000018 



\i\ 



-/r 



-Ai- 





N 



./(/ 



-T~- 



X 



-/^ \ 



t 



7-> 



f 



M— 



n. c. 

 012345 G7 



9 10 11 1 2 3 4 5 6 7 8 9 10 11 12 



Maxima at I*" (principal) and IP ; minima at 1^^ and 17"" (principal). 

 Total range 0.000026. Probable error of any single hourly representation 

 ,0.000006. 



