286 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903. 



THE PERTURBATIONS OF THE 26th & 27th JANUARY, 1903. 



(PL XV). 



72. After the conclusion of the characteristic equatorial perturbation at 14'' 20 on the 26th 

 January (Art. 27), the conditions are comparatively quiet until about i8 h . At that hour they begin to be 

 disturbed, especially in the north; and at about I9 h they assume the character of a powerful storm. 

 From now on, powerful storms alternate with calmer periods, the most powerful being at about 23 h ; 

 and it is not until late in the morning of the 2yth that comparative calm once more ensues. 



While this is going on, there are powerful storms in low latitudes, both in the eastern and in the 

 western hemisphere. We may at once mention, as a characteristic circumstance, that the deflections in 

 the curves both in the western hemisphere and in Europe remain fairly uniform in direction throughout, 

 notwithstanding the length of the storm. The strength of the perturbation diminishes greatly on the 

 whole towards the equator. When we come as far south as Christchurch, it is very slight during the 

 period up to 22** on the 26th January. It subsequently becomes somewhat more powerful, though not 

 more so than, for instance, at Dehra Dun. 



(a) Concerning the Occurrence of the Storm at the Norwegian Stations. 



The curves for Dyrafjord are indistinct, to some extent, indeed, altogether invisible. There is, 

 however, sufficient to show that the storms have been violent. The declinometer especially has oscillated 

 violently. From the vertical intensity curve, which is reproduced the best, we obtain an impression of 

 two storms. The first of these commences at i8 h 35 m , and lasts until about 21 h o m . P, is powerful 

 here, and directed upwards. The second storm, which is of much longer duration and greater strength, 

 reaches its maximum at about midnight. During this storm P v is directed downwards. 



From Kaafjord we have registerings only for the first part, up to 23^ o m . Here too, a relatively 

 independent perturbation is observable, which is particularly powerful in V, where a maximum is reached 

 at I9 h 45 m . Subsequently the storm increases, and is very powerful at about 22 h 30, after which time 

 it once more diminishes. 



At Axeleen, very disturbed conditions commence at about i6 h 35, and from that time storms 

 continue until far on in the morning of the day following. The two storms already mentioned are very 

 distinct here, and very powerful. The first is particularly powerful in H, where it begins and ends very 

 suddenly at ig* 1 io m and 2o h 32 respectively. This is followed by an interval of comparatively quiet 

 conditions. The second powerful storm, which is so powerful in H that the curve runs off the paper 

 a thing which at this station very rarely happens commences very suddenly at 22 h 24 m . In D it 

 begins earlier and more gradually. It is very violent between 22 h 30 and 23'' 30. The storm 

 decreases until midnight, when another powerful storm commences, reaching a maximum at about o h 35 

 on the 27th. 



The first storm, as we see from the curves, occurs almost simultaneously at the above three stations. 

 As regards the second storm there is a remarkable circumstance, in that it appears earlier at Kaafjord 

 than at Axeleen. At 22 h its strength at Kaafjord is considerable, while at Axeleen, at the same hour, 

 it is comparatively slight. There is a movement of the storm from Kaafjord to Axeleen; and from this 

 too we may conclude that the cause of the storm must come comparatively near to the earth in that 

 region. 



The first part of the perturbation at Matotchkin Schar up to i9 h 45 is wanting. Even by that 

 time it is exceedingly violent. It then diminishes for some time, and reaches a distinct minimum at 

 2i h 6 m , whereupon it once more suddenly increases, and maintains a considerable strength until 2 h . It is 

 particularly violent in the horizontal intensity. The light from the principal reflector passes, as is usual in 



