PART a. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. i. 



Current- Arrows for the 1st February, 1883. 

 Chart VII at 23 '' 15 m . 



397 



Fig. 1 66. 



THE PERTURBATIONS OF THE 15th December, 1882. 



(PI. XXIV.) 



89. The interest that attaches to the perturbations occurring on the above date, consists in the 

 fact that we at first have a clearly developed positive equatorial storm. In the storms previously de- 

 scribed, it was principally, at any rate, polar precipitation that showed itself, and the effects of which we 

 studied. On this occassion, therefore, a special opportunity is afforded of studying perturbation-conditions 

 in the polar regions about the auroral zone during an equatorial perturbation. 



It may seem difficult to prove that it is really an equatorial perturbation with which wo are con- 

 cerned, seeing that our observations are chiefly from polar stations. It appears, however, that the more 

 southern European stations are quite sufficient to determine this; for the perturbation-conditions that we 

 have learnt to consider as characteristic of positive equatorial storms always come out very distinctly 

 there. 



If we compare Christiania, Pawlowsk and Gottingen, we find the conditions during the period 

 previous to io h 15 fairly normal; but then, at all three stations, there suddenly appears a perturbing 



Birkeland. The Norwegian Aurora Polaris Expedition, 1902 1903. 51 



