HORIZONTAL FORCE, AND DECLINATION. 



107 



Table I. — Magnetic Dip. 



The six numbers marked with an asterisk result from 

 observations of one needle only ; but as the mean annual 

 difference of the readings for the two needles for these 

 years differed by less than the tenth of a minute, no cor- 

 rection has been applied to them. 



The annual and semiannual inequalities of the dip can- 

 not be accurately deduced from four years' observations ; 

 but an approximation to the former is exhibited in the 

 following Table. 



Annual 

 decrease. 



Mean dip in 1873.... 

 „ „ 1874.... 



.. .. 1875 



„ „ 1876 



Mean 



69 17-71 



69 14-94 



69 13-62 



69 12-28 



2-77 

 1-32 

 »-34 



69 14-64 



i-8i 



