U LUNAR EFFECT OF THE MAGNETIC DECLINATION. 



an eastern one, as compared with the normal position. The following table con- 

 tains the result : — 



The effect is very small, scarcely much beyond the probable error, but the table 

 indicates that the north end of the magnet is deflected to the westward O'.l at the 

 full, and as much to the eastward at the change day, the range between full and 

 new moon being 0'.2. A more definite result could hardly be expected from a 

 series of observations extending over but five years. 



Treating the subject of the effect of the moon's variation in declination in pre- 

 cisely the same manner, we obtain the following result : — 



Mean deflection 



One day before . 



At moon's max. declination 



One day after 



Mean . 



One day before . 



At moon's min. declination 



One day after 



Mean . 



— 0'.20 from 54 days of observation. 



—0.10 " 53 



—0.09 " 55 



_0'.13 " 1G2 



_0'.04 " 54 



—0.07 " 52 



+ 0.14 " 52 



+ 0'.01 " 158 



These results do not positively fix a deflection of the magnet as depending on 

 the moon's greatest north and south declination, the amount resulting from the 

 comparisons being of nearly the same magnitude as its probable error. 



A similar investigation, with respect to the moon's distance from the earth, gives 



the following results :— 



Mean deflection. 



One day before . 

 At moon's perigee 

 One day after 



Mean 



One day before . 

 At moon's apogee 

 One day after 



Mean 



— O'.l 8 from 50 days of observation. 



— 0.1S " 41 



0.00 " 59 



_(!>'. 12 " 150 



_0'.02 " 55 



—0.20 " 55 



—0.13 " 47 



_0'.12 " 155 



The differences being of the same order of magnitude as the probable errors, no 

 conclusion as to the effect of distance can be drawn from thorn. 



I propose hereafter to extend the discussion of the moon's effect on the declina- 



tion to the effect on the earth's magnetic force 



