C “8 ] 
IV. Abstract of the daily variation of the magnetic needle No. 2, 
by Lieut . Foster. 
In the following tables are given the times of maximum and 
minimum diurnal variation, together with the instrumental 
range and value in arc of such daily change. In an adjoining 
column are placed indications of the relative position of the 
moon with respect to the sun ; as there seems some reason 
to think that these bodies have each its influence on the 
needle : at all events it will be seen, that in every case the 
daily variation was always greater when the southern decli- 
nation of the moon was greatest, and commonly a minimum 
when her declination was increasing to the northward.* 
The action of the sun, however, was much less equivocal, 
and its increasing effect on the daily variation was rendered 
very manifest as he advanced to the northward. 
* The following are the means of the maximum ranges of the needle, for every 
three days nearest to each quadrature, opposition and conjunction. 
Months. 
1st. Quadrature. 
Conjunction. 
2d. Quadrature. 
Opposition. 
January 
0 / 
1 2 S 
O / 
2 OO 
O / 
* 33 
0 t 
2 64 
February 
I 50 
1 45 
0 572 
O 41 
March 
2 23 
4 15 
1 20J 
2 53 
April 
3 20 
3 20J 
3 5 
2 24 
May 
3 57 
4 6 
4 z 
1 41 
Means 
2 35 
3 5 i 
2 11 
2 9 
From these means it appears, that the maximum deviation about the time of 
conjunction, exceeds those at the quadratures, and opposition, in the ratio of 3 to z 
nearly. 
