106 Major-General Sabine on the Cosmical Features 



and 2) the diurnal variation of the disturbances of the declina- 

 tion at stations widely remote from each other, separating the 

 disturbances into their easterly and westerly constituents. I 

 have selected for this purpose Kew in England, and Hobarton 

 in Tasmania, as being stations divided from each other by nearly 

 half the circumference of the globe. The eye can judge of the 

 correspondence made known to us by the analysis which has 

 been described. For the more ready comprehension of the Plate, 

 the eye of the observer must be supposed to be at the centre of 

 the magnet looking towards its north pole at Kew in the north- 

 ern hemisphere, and towards its south pole at Hobarton in the 

 southern hemisphere. The hours marked at the top and bottom 

 of figs. 1 & 2 are those of local astronomical time at both stations. 

 The curves represent the ratios of disturbance at the several 

 hours, to the mean in the twenty- four hours taken as the unit. 

 The ratios are read on the left side of the diagram. The un- 

 broken curves are those at Kew, the broken those at Hobarton. 

 The upper half of the diagram (fig. 1) represents westerly de- 

 flections, j. e. westerly as seen by the eye looking towards the 

 north pole of the magnet at Kew, and towards its south pole at 

 Hobarton. The lower half of the diagram (fig. 2) represents in 

 like manner easterly deflections. It is scarcely possible when 

 viewing the diagrams to doubt, on the one hand, that the east- 

 erly and the westerly deflections have distinct and independent 

 laws, or, on the other hand, to resist the impression that the ac- 

 cordance of the allied phenomena in parts of the globe so remote 

 from each other indicates community of origin and of laws*. 



The ratios of the easterly and westerly deflections at the 

 stations hitherto examined (amounting to several, and in both 

 hemispheres), present generally diurnal variations conforming 

 to one or other of the two types exhibited in the diagrams. 

 So far there is a general agreement. But there are points of 

 systematic difference at different stations which are no less 

 noteworthy. These may perhaps be best explained, within the 

 space which we can allot to them, by limiting our attention 



* The deflections at Kew are derived from the hourly positions of the 

 declination magnet tabulated from the Kew photograms in the four years 

 1858 to 1861 inclusive. Those at Hobarton from hourly observations 

 continued during seven years and nine months, viz. from January 1, 

 1841, to September 30, 1848. The value taken as the indication of a 

 disturbed position or observation has been a difference equalling or exceed- 

 ing 3''3 at Kew, and 2'*13at Hobarton, from the respective normals of the 

 same month and hour. 



It happens that at Kew and Hobarton the hours of maximum easterly 

 disturbance are nearly the same as the hours of minimum westerly dis- 

 turbance; it may be proper, therefore, to remark that this is not a general 

 rule ; there are even stations where the easterly and westerly disturbance 

 have their respective maxima nearly at the same hour. 



