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



THE PERTURBATIONS OF THE 15th OCTOBER, 1882. 



(PI. XXII). 



90. This observation-period differs from those already described, in the occurrence of fairly powerful 

 perturbations almost throughout the day, only the last part of the period being a little quieter. The posi- 

 tion of the normal line is therefore to some extent difficult to determine, especially at Christiania and Got- 

 tingen, where there is less to go by. In the case of the last-named station, therefore, no such line has been 

 drawn for the vertical intensity. It will nevertheless be possible, from the course of the curve, to deter- 

 mine the direction of the deflections when these are greatest. We have employed this quieter district 

 as the starting-point for the placing of the normal line, assuming the conditions there to be more or 

 less normal. 



At the beginning of the period, a well-developed negative polar storm of considerable strength is 

 found in the district from Jan Mayen to Bossekop. The most powerful forces appear in Jan Mayen. At 

 the same time, we find at the stations to the south of this district, deflections which evidently appear to 

 be governed by the same forces that produce the storm in the north. At Christiania and Guttingen we 

 find serrations similar to those that are especially distinct in Jan Mayen. On the other hand we also 

 find positive polar precipitation developed in America, especially at Fort Rae. 



At Kingua Fjord too, there seems to be the effect of a similar system, but, as we have said, the 

 conditions there will be better studied by the aid of the charts; for a mere consideration of the curves 

 may possibly be misleading. 



The first part of the observation -period is at a time when it is night in Europe and afternoon in 

 North America. These storms are thus of exactly the same kind as those which we are accustomed to 

 find at this time of day. 



Chart I represents the perturbation-conditions at the above-mentioned time. The district of pre- 

 cipitation of the negative storm is distinctly visible in Jan Mayen and Bossekop, and the effects of the 

 positive system at Fort Rae. 



It will further be seen that round the district of negative precipitation, the current-arrows are 

 grouped in the manner generally, if not always, found in the polar storms. The current-arrows to the 

 south fit very well into the system of convergence, which corresponds to a negative system of precipitation. 

 At i h 2o m Christiania appears to be in the immediate vicinity of the point of convergence of the system, 

 which, at the last hour given, 2 h 20, seems to have moved towards Pawlowsk. At the same time the 

 powerful forces in Jan Mayen are considerably reduced, and thus the storm-centre seems to have moved 

 a little eastwards. 



Another circumstance that may possess some interest is the direction of the current-arrows at 

 Godthaab, Kingua Fjord and Cape Thordsen, where the forces at certain times are rather small, and 

 there thus appears to be no particular local precipitation. It would therefore seem probable that we 

 should here find effects of the powerful negative system acting in the neighbourhood of Jan Mayen. As 

 effects of this there should be an area of divergence in these regions, and the arrows do indeed admit 

 of being arranged in such a system; for if we follow a current-line in this district from Bossekop west- 

 wards across Jan Mayen, to Godthaab and Kingua Fjord, we see that it turns off" here to the right and 

 runs northwards. Fort Conger, unfortunately, cannot give satisfactory information concerning the further 

 course of the current-line, the conditions indicating only that the direction is somewhat easterly. This too 

 is in accordance with what we should expect. 



The direction at Cape Thordsen indicates that the current-line turns southwards, back to the 

 regions about Bossekop. Thus the course of the current-lines seems to be similar to that which we 

 should expect to find in the system's area of divergence. 



