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Solar-diurnal Variation of the Magnetic Declination. Semiannual Inequality. 



The Black line indicates the Mean Solar-diurnal Variation in the year. 

 The Broken line indicates Semiannual Means, October to March. 

 The fine dotted line indicates Semiannual Means, April to September. 



Astronomical Hours. 



12 13 14 15 16 17 18 19 20 21 22 23 1 234 56 7 8 9 10 11 12 



.- i ' ' ' ' 1 . F L. ! ! U_ I ! 1 1 1 1 



12 13 14 16 16 17 18 10 20 21 22 23 



4 5 6 7 8 9 10 11 12 



