Magnetic Dip. 



393 



TABLE LVI. — Variations of Magnetic Dip, with reference to the Moon's Hour- Angle, as deduced 



fi-om Tables XXXI. and XLVII. 



The following are the means at nearly two-hourly intervals :- 



Groups, Qi' 0" 



Winter, 0'-15 



Summer,... 0'-24 

 Year 1844, 0'-13 



In the ivinter group — 



The principal maximum of dip occurs about 4 hours after the moon's inferior transit. 

 The principal minimum occurs 4 hours before and at the inferior transit. 

 A secondary maximum occurs about 2 hours after the supei'ior transit. 

 A secondary minuuum occurs about 6 hours before the superior transit. 



There is a secondary maximum 2 hours before the inferior transit, which is perhaps accidental. 



In the summer group the law of variation is most distinct — 



The principal maximum occurs 4 hours before the moon's superior transit. 

 The principal minimum occurs about 2 hours after the inferior transit. 

 The secondary maximum occurs about 4 hours before the inferior transit. 

 The secondary minimum occurs about 3 hours after the superior transit. 



In the mean for the year the secondary maximum and minimum are not well marked — 



The principal maximum occurs about 6 hours after the inferior transit. 

 The principal minimum occurs about 1 hour after the inferior transit. 

 The secondary maximum occurs about 2 hours before the inferior transit. 

 The secondary minimum occurs about 6 hours before the inferior transit. 



The whole range of these variations is very small, the greatest range is that for the summer group, which 

 is 0'"4, this however is equivalent to a range of l'-2 for the declination : if we examine the similar discussion 

 for the magnetic declination, p. 342, it will be seen that the greatest range is that for the winter group, which 

 is r-5 ; so that the diumal range of the variation due to the moon is nearly the same for the magnetic declina- 

 tion in winter as it is for the magnetic dip in summer. 



If we determine the variations from those for the horizontal and vertical components after Tables XXXI. 

 and XLVII., from which the large disturbances have been removed, we have for the variations of dip for the 

 year — 



These quantities give nearly the same law as that obtained above. 



MAG. AND MET. OBS. 1844. 



5g 



