440 ISIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 



The deflections in horizontal intensity always increase at the beginning of the storm rather rapidly 

 and to a certain height, after which the perturbing forces remain more or less constant in strength for 

 a long period. 



In the horizontal-intensity curve, there are always a number of very characteristic serrations, which 

 are found again at all the stations situated in low and medium latitudes, and these serrations appear at 

 any rate very nearly simultaneously all over the globe. This is also the case with the time of the 

 occurrence of the perturbation. We have made some determinations for the purpose of finding out 

 whether any differences in time could be proved in these at various stations. We have also found 

 differences of some minutes; but as, in many cases, the accuracy with which the time can be determined 

 is not as great as could be desired, we will not venture to express any certain opinion upon this foundation. 



If, on the other hand, we approach the auroral zone, the perturbation-conditions alter to some extent. 

 We also find in declination deflections like those in horizontal intensity. A peculiar impulse at the 

 beginning of the perturbation, which was less noticeable in lower latitudes, now comes out distinctly, 

 this being that the deflections in horizontal intensity are not first in a positive direction, but in a negative; 

 and the current-arrow, or, if preferred, the perturbing force, oscillates here, at first quite distinctly, 

 through a more or less considerable angle. This condition is most distinct in the immediate vicinity ( 

 the auroral zone. Here too, we find again serrations to some extent similar to those at southern stations, 

 but often considerably larger. 



At one station in polar regions, Kingua Fjord, in the only instance of such a perturbation found in 

 the material from 1882 and 83, we came upon a storm in which the perturbing forces, which \vc i 

 considerably greater strength, seemed to be distinct from the perturbations at the other stations. 



Very frequently, perhaps as a rule, the positive equatorial storm is interrupted by the breaking in 

 upon it of a polar storm. 



The two best examples we have of perturbations of this type are the storms of the 26th January, 

 1903, and the 151)1 December, 1882. Plates XIV and XXIV show very clearly the above-descrilx-d 

 characteristics of this type of perturbation. 



Fig. 31, on p. 69 of Part I, gives an excellent idea of the perturbation-area of such a storm. 



Figs. 167 & 168, pp. 406 & 407, show the area of perturbation about the auroral zone during a 

 positive equatorial storm. The characteristic turning of the perturbing force at the beginning of the 

 perturbation is seen on Chart I. The same peculiar condition is also shown in fig. 57, Chart I, p. 133, 

 at the two stations, Dyrafjord and Axeleen, where the movement is especially distinct. 



Other instances of positive equatorial storms are found on the gth December and 23rd October, 

 1902, the 22nd and 3oth March, 1903, the 29th 3oth and the nth I2th October, 1902, and the 23rd 

 241)1 November, 1902. 



We have sought for the cause of these positive equatorial storms in corpuscular rays, which \vi 

 imagine issuing from the sun, their main mass being gathered in the magnetic equatorial plane of the 

 earth. In fig. 37 we see cathode rays, under certain circumstances, may concentrate themselves in such 

 a manner. In this case, the rays go from west to east round the earth, in such a manner that cor- 

 responding current-arrows would have to be directed as in the negative equatorial storms. It is probable, 

 however, that the rays in the innermost parts swing round once or oftener, so that those nearest the 

 earth pass it from east to west. In fig. 38 b, we have shown how the rays can bend round before the 

 earth in this manner, and the nearest part will therefore produce on the earth a magnetic force-effect 

 directed northwards, which thus answers to a positive perturbing force in the horizontal intensity. It is 

 in rays of this kind, which turn round and pass nearest to the earth in a direction from east to west 

 (if they are rays with negative particles), that in our opinion the cause of these positive equatorial storms 

 must be sought. Fig. 39 shows a number of rays of this kind, lying in the magnetic equatorial plane, 



