( 31? ) 



— 1.1—3.4 



iiiid iiegalive focus : ,/\, = = — z..i, and //„ llie lueaii 



Cl 



— 10.7 — 10.2 

 tbr llio ifs for the foei: //„ = = — 10.5, (lic values of 



(«'■o/^— ■"«)' — (•''i.'<— •'■o). 0/«/'-.Vo) ^'1^^ (— .Vis/— //n) i^»*^! SO on, 

 uiusl represent the same (|uantit_y, from wliicli we may compute a 

 set of '12 means. The harmonic formulae representiiig this set is : 

 xj^ = —2.3 + 14.5 sin {.r -f- 22') + 1.3 sin 2 {.>; + 28°). 

 The term of the second order, already small in comparison with that 

 of the first order, having been still more diminished by this operation, 

 it may be safely neglected. So we may adopt (for Greenwich time): 



.i'_^ -= — 2.3 + 14.5 sin {.V + 12°) 



7/_^ =: -10.5 + 14.5 sin {,v -f- 12°— 00°). 



The centre of the circular path, which is best called "pole of dis- 

 turbance" lies accordingly in 



79^ N. and 78° W. 

 For the pole of aurora borealis I acce[)led 

 80°.5 N. and 80° W. 

 and according to Schmidt the niagnctic axis for 1885 cuts the surface in 



78^5 N. and 68^5 W. 



So we have arrived at the remarkable result, that fj/c (hiili/ niore- 

 mciit of the arctic foci of diAiiri>in(j force take*; pJocc in ri circuhir 

 [Hith of 14°. 5 vddiiis around a pole jiracticalli/ coi,ncidin(j with the 

 jjoh' of aurora horealis and hjiinj ccnj }n'ar to the nortJi end of the 

 magnetic axi.'^. 



When now supposing this fluctuation of dislurbing force lo be 

 caused l\y a field, which slides around the earlli from East to West 

 (as has already been remarked by Lüdeling in his jiaper (pioted 

 above) and this in analogy with our actual views regarding the field 

 of the ordinary daily varialion, we are obliged to assume fhe field 

 of dislurbauce to revolve ai'ound (he axis just found, viz. 

 78' N. 79^ W. (o 78'' S. 101° E. 



In order to represent the daily field, we have to study fhe vector- 

 diagrams themselves. Of course the vector-diagrams of one grouj) 

 show mutual differences caused partly by insufficient material (for 

 the arctic stations 2 or 3 months only) and partly by local iulliuMiccs, 

 as has already been indicated by Schmidt (Met. Z. 1899). 



In order to avoid irregularities bringing confusion in the result, 

 wliicli may prevent interpretation of this phenomenon (this being of 



