IO6 BIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903. 



In the more central parts it is evident that the downward and upward-going rays destroy each the 

 others' effect, so that only the effect of the outer parts is left. In the figure, we have made the direc- 

 tion of the arrow indicate the direction in which the . negatively-charged corpuscles should move; and the 

 galvanic currents must be imagined flowing in the opposite direction. 



The paths of the separate corpuscles do not, indeed, coincide with those here indicated ; but on 

 the whole a system of rays such as this might not be so far removed from those that actually produce the 

 magnetic storms. 



We have hereby only wished to prove that these two systems of rays fully explain the principal 

 features in the two typical fields found in the polar elementary storms. Fig. 50 a represents those in 

 which the current-directions at the storm-centre are directed westwards, and 50 b those in which the 

 currents move eastwards. 



Such cosmic current-systems in the polar regions as are here assumed, will of course induce a 

 very complicated system of currents all over the earth itself, this being a conducting sphere composed 

 of sea and land. 



In a later part of this work we shall deal with this question, and see how such earth-currents would 

 affect the magnetic instruments in different places. 



THE PERTURBATION OF THE 10th FEBRUARY, 1903. 



(PI. XVIII.) 



37. This magnetic disturbance is brief, and commences without any previous equatorial perturbation 

 on an otherwise very quiet day. First a small disturbance appears rather suddenly at about 21 h 6 m . 

 This precursor of the real storm partakes on the whole of the latter's character. It is most powerful 

 at the northern stations, especially at Matotchkin Schar, but is also perceptible in Europe and North 

 America. After about 30 minutes, the conditions are once more almost normal; but disquiet still prevails 

 at the northern stations, and at the other European stations a slight deflection is noticeable, especially in 

 the declination. 



The powerful perturbation, with which we are especially concerned,and which we shall now follow, 

 does not commence until 23 h . 



As the copies of the curves show, it is very powerful, and especially so at the four arctic stations ; 

 while southwards, in Europe and America, there are simultaneous relatively powerful, violent pertur- 

 bations. 



After about an hour and three quarters, the storm is over. At most of the stations, the con- 

 ditions have now become quite normal, the arctic ones only being still somewhat disturbed. At 2 h 30 

 on the nth February, another short, slight perturbation appears, which is especially remarkable for the 

 sharply-defined northern limits of its sphere of action (cf. perturbation of I5th Dec., 1902). Thus 

 while fairly powerful at Axeleen and Dyrafjord, it is almost imperceptible at Matotchkin Schar and 

 Kaafjord; while it is tolerably distinct in America, and less powerful on the continent of Europe. 



This storm belongs to the class of perturbations that we have called elementary storms, and has 

 a peculiar resemblance to the perturbations of the I5th December, 1902, and the 3131 March, 1903; but 

 the curves for the northern stations in this perturbation are of a more disturbed character than those 

 of the perturbation of the I5th December. 



It is difficult to say exactly when the powerful perturbation begins; but we shall see from the curves 

 that in the case of most of the stations, the time when the perturbation begins to be very powerful 



