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BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



maximum. On the side on which the point of convergence lies, the direction of P v will be upwards, 

 and on the other side downwards. After reaching the maximum, P, again drops quite rapidly to a 

 trifling value (see lower diagram, fig. 40). 



With regard to the position of the point of convergence, we may note the following. 



If we imagine an observer swimming out from the centre in the direction of the current-arrows, 

 and with face turned towards the earth, the point of convergence will be to his left. 



Fig. 40. 



