226 



REPORT 1895. 



measurement of the curves proceeds only to the nearest 0''1 in the case of 

 the declination, and to the nearest 1 x 10"'' in the case of the horizontal 

 force, I do not think too much confidence should be placed upon details. 



The results for the annual inequality of declination show unques- 

 tionably a good general agreement with those deduced by General Sabine ' 

 from the undisturbed readings of the Kew magnetograph during the five 

 years 1858-62. General Sabine's own paper treated each week of the 

 mean year separately ; but a summary giving mean results for the several 

 months appears on p. 76 of Walker's ' Terrestrial and Cosmical Magnetism,' 

 where there is an interesting discussion of the question. According to 

 the summary, General Sabine's results made the annual inequality 

 negative from May to August inclusive, and positive throughout the rest 

 of the year, the range amounting to almost exactly 2'. From General 

 Sabine's own table one would deduce a principal maximum of westerly 

 declination in the latter half of October, with a second and only slightly 

 smaller maximum early in December, whilst the easterly movement was 

 conspicuously largest about the middle of July. The times at which 

 General Sabine observed the inequality to change sign are substantially 

 in accord with Table X. ; and if the range he observed was decidedly 

 larger, this might be associated with the fact that the secidar variation 

 during the epoch he dealt with was greater than during 1890-94. In case 

 this agreement should be referred to identity of apparatus, it may be as 

 well to mention that the declination magnet employed for the absolute 

 observations at Kew of late years came into use only in the beginning 

 of 1890. 



A comparison of the declination results with those at other British 

 stations is unfortunately by no means so reassuring. For Dublin the 

 annual inequality got out from the mean of the years 1842-50 by 

 Dr. Lloyd "^ makes the westerly declination below the mean from December 

 to June, and gives a range exceeding 4'. There are also conspicuous 

 diflFerences between Table X. and the Greenwich results obtained by Sir 



• Phil. Trans, for 1863, p. 292. 

 " Treatise on Magnetism, p. 162. 



