OF THE MAGNETIC DECLINATION. 



11 



(A). — Mean Solar-Diurnal Variation op the Declination for Summer, Winter, and the whole Yeah. 

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East ° h - l 2 3 4 5 6 7 8 9 10 11 N'n 13 14 15 16 17 18 19 20 21 22 23 42&- 



Philadelphia mean time. 



The second diagram (B) exhibits the same phenomenon in a different way; the 

 yearly curve of the first diagram being straightened out and forming the axis of 

 the second diagram, which thus shows the deviations from the annual mean value 

 for the two seasons when the sun has north and south declination. The ordinates 

 are obtained by subtracting the annual mean from either the summer or winter 

 mean in the preceding table. This diagram exhibits, in quite a characteristic 

 manner, the course of the annual variation at the different hours of the day at 



(B). — Semi-Annual Irregularities op the Solar-Diurnal Variation of the Declination. 

 2' 

 West 



1 *- 123456789 10 11 N'n 13 14 15 16 17 18 19 20 21 22 23 24h- 

 Philadelphia mean time. 



