or Aurora Borealis and Austmlis. 337 



The sky not being clear, no trace of the aurora borealis 

 could be seen in the evening, which was observed at Chris- 

 tiania and Hardanger*. It was just the time when M. Arago 

 noticed an unusual irregularity in the motion of the magnetic 

 needle. Thence we may conclude: 1. That the irregular va- 

 riations in the central direction of the magnetic powers of the 

 earth, which evince themselves by the wandering of the mag- 

 netic needle in a certain part on the surface of the earth, is 

 also connected with a contemporaneous change in the magni- 

 tude of the power's intensity. 2. That these irregular changes 

 show themselves at the same time in places at great distances 

 from each other (the distance between Paris and Tornea is 

 about 300 geographical miles), and probably extends from 

 pole to pole. 3. That therefoi'e they do not consist of any lo- 

 cal action on the needle of the material substance emanating 

 from the surface of the earth, which forms the aurora borealis ; 

 but are caused by a general disturbance of the whole globe : 

 i. e. by a removal of the equilibrium in the whole system of 

 magnetic powers, which is again a cause of the polar lights. 



As it is probable that M. Arago will proceed in his daily 

 observations of the deviation of the needle, I shall, in order to 

 contribute something towards our knowledge respecting the 

 connection of the aurora and magnetism, note for the future 

 with more care than hitherto, even the smallest traces of au- 

 rora that may appear in Christiania; and I have also re- 

 quested other naturalists in various places in Norway, to no- 

 tice all similar pheenomena that may come to their knowledge, 

 and to send me a list of them every six or twelve months, by 

 which the Edinburgh observations may be considerably im- 

 proved. 



• An irregularity exceeding 6" I only observed once at Christiania, viz. 



the 24th of June 1820, when the same cylinder had 300 oscillations in the 



following times: 8^ a.m. 811"-81 



lOi 812 -35 



4 J P.M. 810 -15 



7 810 -25 



11 818 -35 

 11 J 815 -96 



12 811 -68 



Here we have from 4 J to 7 p.m. an irregularity of 8" 1, and in the follow- 

 ing three quarters till midnight of 4" 3. So near the summer solstice one 

 may at Christiania, at midnight, read a book without a light, which renders 

 it impossible to perceive any aurora. 



Neva Series. Vol. 2. No. 1 1 . Nov. 1 827. 2 X 2. Ad- 



