94 BIRKELAND. T1IK NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903. 



Chart III. Time /'' jo m , 



The arrow at Axeleen has increased and assumed a direction more in accordance with Dyratjord, 

 where the force has decreased in strength, but is unchanged in direction. P, for Dyrafjord is directed 

 upwards, for Axeleen downwards. 



The conditions in America are very much like those at i h 15. In Europe, the arrows have 

 turned farther in the same direction. 



Chart IV. Time / h .// m . 



The perturbing force at Axeleen is now of about the same magnitude as at Dyrafjord. The 

 condition of the vertical components is the same. The arrow for Kaafjord has turned a little in direction, 

 so that it is more in accordance with Dyrafjord and Axeleen; but the force is still small. 



The conditions in America are almost unchanged, except that the forces have diminished in strength. 

 In Europe, the turning is continued in a positive direction. At Dehra Dun, where the horizontal com- 

 ponent of the perturbing force has been directed towards SW, the force has now also taken part in 

 the turning. The direction is now WNW. 



Chart V. Time 2 h . 



The force at Axeleen is now greater than at Dyrafjord. The condition of the vertical components 

 is the same as before. At Kaafjord and Matotchkin Schar, the direction of P l is now in accordance 

 with the two first-named stations, and P c for both is directed upwards. 



In the rest of Europe, the turning of PI is continued in the same direction. In America also, 

 the horizontal forces are turned a little in the positive direction. 



Chart VI. Time 2 h // m . 



The distribution of force is the same, but the intensity is less. The turning in Europe is 

 continued a little. 



Chart VII. Time 2 h v/ m . 



The force on the whole weaker, except in America, where it seems to be somewhat greater 

 than it was at 2 h 15. Otherwise the distribution of force the same. 



We see, on the whole, that at each separate point of time, the field presents in its main features 

 the typical form mentioned in the introduction to this chapter. The position of this field is determined 

 in the following manner. 



The principal axis is tangent to the auroral zone, and the current-arrow is directed towards WSW. 

 As we have seen, the spot of the greatest effect moves in the direction from Dyrafjord and Axeleen, 

 or, in other words, the centre moves eastwards along the auroral zone, but in such a manner that the 

 principal axis always keeps its direction. While this strong impulse in the north is moving, the field 

 in lower latitudes moves with it. 



I he district of Central Europe here comes in the area of convergence, and outside the point oi 

 convergence. The regular turning of the force, both in this district and at Kaafjord, has its simple 

 explanation in the actual circumstance that the field in its entirety is moving forwards. 



