PART I. ON MAGNETIC STORMS. CHAP. III. 



289 



In the area of divergence, at the time when it is rather well developed in Europe, there are also 

 positive values of I\ at the western stations. This appears on Chart II both at Potsdam, Pola and 

 Tiflis. It may however be a little doubtful whether it is the positive polar storm that produces these 

 values at the last-named station; it is perhaps more probable that they are brought about by a storm 

 that was caused by perturbations of a more equatorial nature. That this was the case seems probable, 

 moreover, from the conditions at the other stations of Southern Asia, which also appear to run a slightly 

 abnormal course. There, however, the perturbing forces are so small that nothing certain can be said. 

 At Pola, the positive deflections in the vertical intensity curve continue until nearly 23**, when they go 

 over to the opposite side. 



On Chart IX, the conditions at Dehra Dun and Bombay seem once more to be a little abnormal ; 

 and a study of the curves for the succeeding period will show that the perturbing forces there continue 

 to act far on into the 27th. These forces, as we have said, occur principally in H, which they serve 

 to diminish. We have also already remarked that before the end of the period we find at Honolulu 

 an abnormally low horizontal intensity curve, which thus seems to agree with the conditions at the 

 stations in Southern Asia. The character of the curve is comparatively quiet, and it is therefore pos- 

 sible that this is the effect of a storm of a more equatorial nature, perhaps a negative equatorial storm. 



If we now in conclusion compare the perturbation-fields that have appeared during this perturbation 

 with those that we have found in the preceding storms, we at once notice the great resemblance. The 

 storms here described occurred, as we have seen, about Greenwich midnight; and we found the characteristic 

 large area of convergence on the night-side in Europe and Asia. There also appeared more or less certain 

 indications of an area of divergence upon the day-side. And these are the very conditions that we have 

 continually met with before. 



We therefore feel justified, after having gone through this long series of perturbations, in concluding 

 that the phenomena that we have previously described as elementary, viz. the positive and negative polar, 

 the positive and negative equatorial, and the cyclo-median perturbations, generally are sufficient to explain 

 the fields that will be formed during the most varied magnetic storms. All the fields that we have met 

 with thereby receive a very simple explanation, and no serious disagreement has presented itself, although, 

 of course, the material has very often been insufficient to allow of certain conclusions being drawn. 



TABLE XLII. 

 The Perturbing Forces on the 26th & 2?th January, 1903. 



Hirkclancl. The Norwegian Aurora Polaris Expedition, 1903 1903. 



