436 



Table I. — Diurnal Variation of the Declination, related to the Moon's 

 Hour- Angle. Yearly Means. 



Hours. 



1841. 



1842. 



1843. 



Mean. 







-0 / -36 



-0'-20 



-0'-23 



-0'26 



2 



-0-26 



-0-15 



-0-14 



-0-18 



4 



-0-05 



+ 0-04 



+ 0-14 



+ 0-04 



6 



+ 0-57 



+ 0-43 



+ 0-27 



+ 0-42 



8 



+ 0-36 



+ 032 



+ 0-02 



+ 0-23 



10 



+ 0-43 



-0-25 



-0-43 



-0-08 



12 



-0-45 



-0-50 



-0-48 



-0-48 



14 



-0-72 



-0-38 



-0-43 



-051 



16 



-0-01 



-027 



+ 0-06 



-007 



18 



+ 0-06 



+ 032 



+ 0-56 



+ 031 



20 



+ 0-52 



+ 0-42 



+ 0-37 



+ 0-44 



22 



-0-09 



+ 0-19 



+ 0-23 



+ 0-11 



It will be seen from the foregoing Table that the posi- 

 tion of the freely-suspended horizontal magnet varies with 

 the moon's hour-angle, the north pole deviating twice to the 

 east, and twice to the west, in the course of the lunar day. 

 The extreme westerly deviations occur about and 13 (lunar) 

 hours, or soon after the moon's meridian passage, above and 

 below; and the extreme easterly about 6 \ and 20 hours, or 

 soon after the moon's rising and setting. The mean range, 

 measured from the mean of the two greatest westerly elon- 

 gations to the intervening easterly, is 0'*82, when the moon 

 is to the east of the meridian, and 0''80 when the moon is west. 

 The mean range due to the sun's action being 9'* 6, the lunar 

 range is to the solar as 1 to 1 2, — a result which accords very 

 neai'ly with that before derived from a different analysis of 

 the phenomenon. 



A marked difference having been elsewhere obtained be- 

 tween the laws of this phenomenon in summer and in winter, 

 it has been thought necessary to separate the results of the 

 summer and winter lunations : they are given in the two fol- 

 lowing Tables, of which Table II. contains the mean results 

 for summer, and Table III. those for winter. 



