245 
M. Kreil’s Magnetic Ohsermtions. 
be nearly the same in the summer and in the winter months. 
We must therefore give up the idea of the effect being pro- 
duced by the sun, and must seek its cause rather in the posi- 
tion of the moon’s path, by which in winter the moon when 
new is but little raised above the horizon, whereas in summer 
when she is in this phase she approaches the zenith. If she 
has a sensible influence on the horizontal needle, it must be 
greatest when she is near the horizon, and thus the alterna- 
tion of the phenomena at different parts of the year would 
be explained. If this be the true reason, it must show itself 
also when the observations are combined by another method, 
that is to say, when they are arranged according to the 
moon’s declination. The daily means were therefore formed 
into series, one of which always comprehended all the obser- 
vations of the same or of two successive months during which 
the moon’s declination was south, and the other, all those 
during which the moon w'as north of the equator. These 
series, when freed from the gradual increase of the time of 
vibration caused by the diminishing magnetism of the needle, 
and collected into two general means, showed that the time 
of vibration (which is nearly 22' 5" mean time) is less by 
0"'00168 when the moon has south declination than when 
she is north of the equator, which confirms the above-men- 
tioned hypothesis. 
14. As the influence of the moon differs so sensibly ac- 
cording to the difference of her position in the heavens, it 
seemed worth while to examine whether her greater or less 
distance from the earth might be indicated by our magnetic 
needles. The daily means were collected for this purpose 
into series, in such manner that the middle of one series should 
coincide with the moon’s apogee, and the middle of the next 
with her perigee, then proceeding as before. The general 
means showed that the times of vibration at the time of the 
perigee were 0"*00198 less than at the time of the apogee, 
agreeing also with what has been said above. 
15. If the intensity of the magnetic force is so sensibly 
subject to the influence of the moon, it is highly probable 
that the direction of our needles may also be altered by it, 
and it must be possible, by a suitable mode of combination of 
the observations, to recognise such an alteration. It is plain 
that the daily means are inapplicable for this purpose. The 
observations of each hour must be considered apart, and di- 
vided into series according to whether at the time of obser- 
vation the moon was east or west of the magnetic meridian. 
It is true that in single months, the effect of this influence is 
obliterated by the annual alteration in the declination, which 
