PART I. ON MAGNETIC STORMS. CHAP. III. 



Current-Arrows for the 25th December, 1902; Chart II at 3 h 30 m and 3 h 40 m . 



16? 



Fig. ^g. 



Chart I; Time j h //"' and j 1 ' 2o m . 



At the first hour named, the conditions are similar to those prevailing at the time when the power- 

 ful perturbation in America commences. In the United States the current-arrows are directed southwards, 

 with some divergence; at Sitka, westwards. In Europe the direction of the arrows varies greatly from 

 place to place. This may certainly in a great measure be accounted for, partly by the fact that when 

 the arrows are small, their direction is rather liable to error, as the normal line cannot be so positively 

 determined, and partly that an inaccuracy in the time-determination, owing to the great variableness of 

 the conditions at this point of time, will result in a large error in the force. 



Turning to the Norwegian stations, we find the force to be especially strong at Dyrafjord and 

 Axeleen, and at both these places the current-arrow, as is usual in such circumstances, is directed WSW 

 along the auroral zone. 



At 3 h 20 the perturbation in America is at its height, and the field of force in southern latitudes 

 is now in the main determined by this brief perturbation. 



The field of force in Europe and North America now shows a strong resemblance to that during 

 the cyclo-median storm of the previous 6th October, the chief difference being that the latter was more 

 restricted in area, its remarkable field of action being principally confined to North America and Europe. 

 At Dyrafjord and Axel0en the conditions are almost as at 3 h 15. 



