276 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



We see further from the figure, that near those places at which -~ = 0, even a very small 

 change of altitude will produce comparatively great displacement of the systems. It would perhaps be 

 interesting to examine a little more closely the velocities of the displacement corresponding to the two 

 components of the motion; but this would carry us too far. We are only considering these conditions for 

 the purpose of finding analogies, and not in the hope of finding perfect correspondence in the details. 

 In conclusion we must also remark that the system with the eastward-directed arrows on the 3ist 

 October, was of far greater strength than the corresponding system in the present perturbation. 



When all these circumstances are taken into consideration and there might be many others that 

 also exerted an influence there is no necessity whatever for supposing that they contradict the results 

 previously found. Nor is this in reality anything new or unknown; it is only a negative night-system, 

 which, at the Norwegian stations, appears to move eastwards along the auroral zone, a condition that 

 we have continually found in earlier perturbations. The storms that occur in this section prove also to 

 be of the form that is typical of these night-storms with centre at the Norwegian stations. 



As in the earlier perturbations, we might also here separate several intermediate storms from one 

 long main storm; but as in this case in southern latitudes they do not stand out so distinctly from one 

 another as in the previous perturbations, we have thought it better not to attempt any such decomposi- 

 tion, as its uncertainty would be too great. At our Norwegian stations we find, almost all the time, 

 deflections in the horizontal intensity curve, indicating a diminution in H. Two or three times there is 

 a slight, brief deflection to the opposite side, e. g. at Kaafjord at about 23 h 3o m , and at Axeleen from 

 2 h to about 2 h 2o m . Both the declination and the vertical intensity curve for Dyrafjord oscillate above 

 and below the normal line all the time, while at the other three stations the deflections are nearly uni- 

 form in direction, with only a few short interruptions where the curve goes over to the other side. 

 The direction of this long deflection is easterly at all three stations. In V the perturbing force is 

 directed upwards at Matotchkin Schar and at Kaafjord, and downwards at Axeleen, indicating that the 

 horizontal part of the current is situated to the north of the first two places, and to the south of 

 Axeleen, or in a manner exactly similar to that of the preceding storms. Between 23*" and 24'', we 

 find a brief deflection to the west in the declination-curve for Kaafjord, corresponding to the above- 

 mentioned brief reversal in the //-curve, but a little earlier. We also find a similar reversal of direc- 

 tion in the vertical intensity curve for Axeleen, the perturbing force at that time being directed upwards 

 for a short time. 



With regard to the other European stations, we find that the greatest deflections, at any rate 

 during the greater part of the perturbation, are in the declination-curve. These deflections are in the 

 same direction at all the stations, namely east, indicating that the current-arrows have a southerly direc- 

 tion. Between 2 h and 4'' however, P/, sometimes prevails over P&. At the same time we notice at 

 our northern stations a powerful intermediate storm, which, however, has the same direction as the 

 main storm. 



The horizontal intensity curve is very sinnous in form at all the stations, and the deflections are 

 now positive, now negative. At Pawlowsk, however, they are positive throughout, with the exception 

 of two or three short, slight deflections to the opposite side. In southern Asia also, comparatively 

 powerful disturbances are distinctly observable, occurring both in H and in D. The deflections here are 

 not in one direction all the time, but in different directions at different times. On comparing the curves 

 with the registerings at the Norwegian stations, we find that the stronger impulses at the latter are also 

 accompanied by similar impulses at the stations of southern Asia, a circumstance which clearly indicates 

 that the two are closely connected. 



