M. Kreil's Magnetic Obser'vatioiis. 245 



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 Httle 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 the}? 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 was north of the equatore 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 gi*eater 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 tlie 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 



