416 Lunar-diurnal Variation of the Magnetic Declination. [March 28, 



if we pay due attention to the facts which may be gleaned from the Table. 

 Indeed it is afterwards shown, in discussing the individual years of observa- 

 tion, that in some cases the lunar-diurnal variation manifests itself in a very 

 striking manner during the winter months. 



On examining the results of the inquiry for the several years of observa- 

 tion, obvious differences are recognized on comparison. This was espe- 

 cially remarkable as regards the year 1861, which was the more striking as 

 the 'year 1860 did not exhibit any such extraordinary deviations from the 

 mean values. At first some error was suspected in the deduction of the 

 results ; but a perfectly independent and fresh discussion gave results 

 agreeing in the main points with those previously arrived at. 



In the course of the year 1861 the instruments previously in use were 

 replaced by fresh ones obtained from Munich, which came into use for re- 

 gular registration at the beginning of June. Though every care was taken 

 to ensure uniformity of registration, it was deemed satisfactory to repeat the 

 discussion, including that part only of 1861 in which the old instruments 

 were employed ; and accordingly the lunar-diurnal variation was discussed, 

 with special regard to the moon's declination, for the year May 1860 to 

 April 1861, and likewise for the year May 1858 to April 1859 ; but it was 

 still found that towards the latter part of the former period the anomalies 

 above pointed out made themselves clearly felt. 



The results for the years 1860 and 1861 were given numerically in a 

 special Table, and delineated in curves. 



In conclusion, the author expressed a hope that the few facts he had 

 brought forward might operate as an inducement to those who are engaged 

 in similar pursuits, to enter upon such a laborious task as that of classifying 

 magnetic observations for the purpose of examining into the law and nature 

 of the lunar-diurnal variation, according to the moon's position north or 

 south of the equator. 



