PART II. TOLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 34! 



that we had before us the effect of a negative system of precipitation, which is, indeed, in accordance 

 with what we have already noticed when considering the condition of the curves. 



After this first section, there supervenes, at most of the stations, a brief period of fairly quiet 

 conditions. The only exceptions to this are the stations Kingua Fjord, Godthaab and Jan Mayen, where 

 there are now quite distinct oscillations. At Cape Thordsen too, there are distinct oscillations in the 

 declination, but the perturbing forces are very small. 



This intermediate period of time, commences at about 16'', that is to say at about the time when 

 the sun crosses the meridian of the magnetic axis. 



Fairly powerful storms, however, soon develope at all the stations from which we have observa- 

 tions, some of them appearing as negative polar storms, and some as positive. 



The perturbations in this last section also exhibit in the main exactly the same conditions as the 

 preceding perturbation of the I5th January. 



Exclusively negative storms appear, as we see, at the stations Kingua Fjord, Fort Rae, Uglaamie 

 and Cape Thordsen. At Godthaab, Bossekop and Sodankyla there are almost exclusively positive storms; 

 but these have not so distinctly the character of a positive storm, as the course of the curve is fairly 

 quiet, and the perturbing forces are comparatively small. In the declination, moreover, there are perturbing 

 forces that exceed in magnitude the values of Ph. 



Little Karmakul is now, as also in the preceding storm, situated just on the boundary between the 

 two areas of precipitation. On the east and north of the station are the negative storms, on the west 

 the positive. In consequence of this, the conditions here become rather peculiar, as sometimes the 

 negative system, sometimes the positive, exerts the strongest influence, and the horizontal-intensity 

 curve accordingly oscillates now to the one side, and now to the other. 



This condition comes out very characteristically here in this period. 



In Jan Mayen also, we find similar conditions. There we evidently have a negative storm, which, 

 during the period from 17'' to 19'', breaks in upon a positive storm. The latter is of much longer 

 duration than the former, but of comparatively smaller strength; and therefore, when the negative storm 

 breaks in, it will gain the ascendancy and cause the deflections in the horizontal-intensity curve to go to 

 the negative side. In the declination also, at about the same time, there is a corresponding change in 

 the direction of the deflections. 



From about i8 h 30 to ao' 1 , there are once more positive deflections, but then the curve changes 

 again, and from the last-named hour until the close of the period, we find once more negative values of 

 /',. It is not easy to say, merely from a direct consideration of the curves, whether, at the close of the 

 period, positive storms are also exerting an influence here. 



At Bossekop and Sodankyla the positive deflections are only slight, and the character of the cur- 

 ves is fairly quiet. It might therefore possibly be assumed that the deflections were the effect of the 

 negative system, whose area of convergence was situated to the north of these stations. Such an assump- 

 tion, however, cannot at any rate be applied to the conditions in Jan Mayen, at Little Karmakul or at 

 Godthaab, as the positive deflections there are far too considerable in amplitude. 



If we endeavour to fix the position of the centres of these storms from the intensity of the deflec- 

 tions, we find as regards the negative storms that the greatest forces on the night-side are at Ssagastyr 

 and Cape Thordsen at about i8 h , when the storms are at their height. 



At Uglaamie, the deflections in this section are of exactly the same character as those in the pre- 

 ceding section, and of very nearly the same strength. 



At Fort Rae, on the other hand, there is a deflection which is very distinct, but far slighter than 

 that in the preceding section, and also considerably slighter than the deflections at Uglaamie. 



Birkeland. The Norwegian Aurora Polaris Expedition, 1902 1903. 



ii 



