PART I. ON MAGNETIC STORMS. CHAP. III. 233 



that the arrows are small; and as we have only taken out total forces, we cannot know how much is 

 due to local storms. The circumstances are explained quite naturally, however, by assuming that the 

 storm-centre now lies farther east. As the perturbing forces at Toronto and Baldwin are very small, 

 we must then make the assumption that the point of convergence of the system is now situated in the 

 vicinity of these stations, a little to the east of them; but as the conditions here, if minutely entered 

 into, are rather complicated, we must not investigate the matter more closely. 



In this connection we may refer to the previously-described perturbation of the 28th December, 

 where we also met with an area of convergence in North America. On that day, however, the storm- 

 centre seems to lie at a greater distance from Sitka, the curves having a far less disturbed character 

 than now. There we also found that the field of precipitation was at first situated farther to the east, 

 and then moved westwards. 



(2) Charts IX, X and XI represent the conditions as they appear during the first powerful inter- 

 mediate storm. The perturbing force at Sitka has about the same direction as before, but is much 

 greater. This perturbation, moreover, is particularly powerful at Axeleen, with a perturbing force that 

 is directed SSE all the time. 



We have endeavoured to separate the effect of the intermediate storm from the rest, the total 

 force being decomposed. Owing to the manner in which the decomposition has been carried out, one 

 of the systems of arrows gives a field with almost the same form as the one already described. 



With regard to the field in the intermediate storm, we first notice how rapidly the force dimi- 

 nishes, both in the neighbourhood of Sitka and in that of Axel0en, at any rate in the districts from 

 which we have observations. 



In the district of Zi-ka-wei, Dehra Dun, and Batavia, the direction of the intermediate perturbing 

 force on the whole is almost the reverse of what it had been earlier, and the magnitude is very consi- 

 derable. This circumstance also occurred during the intermediate storms of the 27th October, 1902, and 

 the 8th and i5th February, 1903. 



In Europe there is a peculiarity in the conditions, namely, that the effect of the intermediate storm 

 is very small. The perturbing forces throughout are smaller than in the Asiatic district, and exhibit 

 considerable variableness, although the current-arrows all through are directed south-west. 



At Baldwin and Toronto the effect is great, but the conditions are somewhat different, as the per- 

 turbing force has rather a different direction. 



(3) The remaining charts, XII to XIX, embrace the period from 17'' 45 to i 1 ' on the ist 

 November. 



We have no observations of this period from America and Honolulu. In the eastern hemisphere 

 the perturbation-conditions change very slowly. During the day-period the current-arrows at the Norwe- 

 gian stations Kaafjord and Matotchkin Schar are directed eastwards; at the beginning of the night-period 

 they begin to turn. In the case of Matotchkin Schar, this has already taken place at i7 u 45 (Chart XII). 

 At i8 h 3o m , the current-arrow for Kaafjord has its usual direction westwards along the auroral zone. 

 Throughout this last period, Axeleen has a comparatively small horizontal component, which sometimes 

 varies greatly in direction. The vertical component, on the other hand, is very considerable, and is 

 directed downwards, thus indicating that it is perhaps an effect of the current that causes the powerful 

 perturbations in H at Kaafjord and Matotchkin Schar. The vertical components at these stations indi- 

 cate that the main bulk of the current is passing right over, or a little to the south of, Matotchkin Schar, 

 and south of Kaafjord. Simultaneously with this reversal of the force, we notice a great change with 

 regard to the force in the rest of Europe, this, on the chart for i8 h 30, being about as powerful 

 as at Dehra Dun; but on the other hand the force has now diminished considerably at Zi-ka-wei. The 

 current-arrows in Central Europe on the whole at this point of time are south-west in direction. 



Birkeland. The Norwegian Aurora Polaris Expedition, 19031903. 30 



