PART II. POLAR MAGNETIC PHENOMENA AND tERRELLA EXPERIMENTS. CHAP. I. 



It is probable, however, that there will also be other forces in operation, and that the conditions 

 are not so simple as here described. One circumstance, for instance, that has not been touched upon 

 is the connection that seems to exist between the deflections at the southern stations and the system 

 in North America. 



At the hours here observed there do not, it is true, appear to be any conditions that point distinctly in 

 this direction; but at about 3 h the deflections, especially in H, at Fort Rae on the one hand and Christiania 

 and Gottingen on the other, exhibit so great a resemblance to one another that it would seem probable 

 that a more or less close connection existed. Simultaneously with these deflections at about 3'', we 

 also find similar changes at several other stations, e. g. at Kingua Fjord, where there is a characteristic 

 and well-defined deflection in declination towards the east, the forces here having previously had a west- 

 ward direction. This, as will appear from Chart II, seems to indicate the intrution of a positive storm. 

 At Fort Rae, on the other hand, it is evidently a negative storm; and at Jan Mayen we find at the 

 same time a corresponding change in the deflections, perhaps here, too, the effects of a positive storm 

 asserting itself, as the negative deflections diminish considerably, although none go over to the other side. 



In the field of perturbation at 2 h 5o m , represented on Chart II, the negative system of precipitation 

 comes out very distinctly in Jan Mayen, Bossekop and Fort Rae, while at Kingua Fjord there are signs 

 of a positive polar storm. 



The current-arrows at the southern stations, on the other hand, exhibit conditions that appear 

 more peculiar. If they are due entirely to the negative system of precipitation to the north, even 

 Gottingen must be situated to the north of the point of convergence of this system, or perhaps more 

 strictly speaking to the north of the neutral area of the system. 



There will, however, be some difficulties in the way of an assumption such as this, and moreover 

 the course of the curves appears to indicate that the cause should be sought in a system that is closely 

 connected with that which appears most distinctly at Fort Rae and Kingua Fjord, and which in all 

 probability also causes the great diminution in the negative deflections in the horizontal intensity in Jan 

 Mayen just at this time. We have frequently observed a similar resemblance between the conditions in 

 Central Europe and those in North America; and in discussing our experiments in a later chapter, we 

 shall find conditions that are apparently similar to these. 



The next phenomenon that strikes one on looking at the plate is a perturbation that is especially 

 characteristic and well defined at Cape Thordsen, more particularly in the horizontal intensity, where it 

 appears as a negative storm. Its effects are also distinctly apparent in Jan Mayen, where the perturbing 

 forces even exceed those at Cape Thordsen in strength. Of the arctic stations, it is only at these two 

 that this storm is distinct; even at Bossekop there is no distinct effect of the system. 



On looking at Little Karmakul, however, and comparing its horizontal-intensity curve with that of 

 Cape Thordsen, we find, on closer examination, quite a remarkable resemblance. The deflections in H 

 at Little Karmakul, from about 3'' until about I5 U , are positive nearly all the time. On the other hand 

 there are no perturbing forces of any magnitude at the same time as the negative storm at Cape Thord- 

 sen; but the commencement of the decrease in the positive deflections is exactly simultaneous with that 

 of the increase in the negative deflections at Cape Thordsen, and the maximum of the negative storm 

 at Cape Thordsen with the lowest position of the horizontal-intensity curve at Little Karmakul, and we 

 then have distinctly negative perturbing forces there. Lastly, the curves again increase at both stations 

 simultaneously, while the deflection at Cape Thordsen decreases, and the positive deflections at Little 

 Karmakul increase. It would thus seem reasonable to suppose that at the latter station we have before 

 us the effects of two simultaneous storms, the positive storm continuing all the time, and the negative 

 intruding upon it, and partly compensating the positive deflections, partly effecting their reversal. The 

 similarity between the curves is in fact so striking that this assumption seems very probable. 



Birkeland. The Norwegian Aurora Polaris Expedition, 1902 1903. 53 



