344 



BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



dominant magnitude that it had in the two preceding charts, the positive area of precipitation once more 

 shows up distinctly, extending from Godthaab, across Jan Mayen, to Bossekop. 



The shape of the negative system of precipitation is the same as before, but the forces throughout 

 are considerably weaker, the strength being more or less uniform at all the stations of the group in 

 which the storm is acting. The strongest perturbing force is at Uglaamie, but this is comparatively little 

 greater than those at Ssagastyr, Cape Thordsen and Kingua Fjord. 



With regard to the conditions in the vertical intensity, we notice all the time in Jan Mayen the 

 strong negative forces. This may be explained as the effect of the negative system to the north of the 

 place, or of the positive system, which must be situated to the south of the place, or best of all, of 

 course, as a co-operation of these two factors. 



The probability of the correctness of the last assumption is manifest. Whether the one or the 

 other of the two systems has the greater influence in a horizontal direction, and causes the current- 

 arrow to point to one side or the other, as these systems here counteract one another, the conditions 

 in the vertical intensity do not change the direction of their deflections, as the two systems act in the 

 same direction, the strength alone varying so that when the storms are at their height, the vertical arrow 

 is also greatest. 



After I9 h 20 the magnetic elements are a little disturbed before the close of the period, but the 

 disturbances are of little strength, and therefore do not give rise to perturbation-areas of sufficient power 

 and coherence to make them worthy of being studied in detail. For one reason, our observations are 

 too few, and for another these storms will have a more local character, so that the connection will not 

 come out so clearly. 



In conclusion we will point to a circumstance, which one cannot help noticing in going through this 

 perturbation, namely that the positive storms always occurred on the afternoon-side. The negative storms 

 formed as a rule a more or less circular or spiral area of precipitation round the geographical pole, or 

 the pole of the magnetic axis; but when there were strongly-marked storm-centres, these were formed, 

 as a rule, upon the night-side of the globe. 



Thus far then, this perturbation also furnishes a support to the view of the behaviour and course 

 of the perturbations, which we have previously put forward. 



Unfortunately we have no observations of this day from Fort Conger, as the ist January had been 

 taken there as the term-day, instead of the 2nd January. 



TABLE LI1. 

 The Perturbation of the 2nd January 1883. 





