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LVI. On the Polar Lights, or Ajirora Borcalis and Anstralis. 

 By Professor Hansteen*. 



]. Obserz'ations ofi M. Arago's Memoir on the hifluence of 



distant Polar Lights on the Magnetic Needle. 

 A LTHOUGH the observation of M. Arago— that distant 

 -^^ 2)olar lights, even if they are not seen iti a given place, 

 exercise an evident injiuence on the direction of the magnetic 

 needle there, — is not entirely new, it is nevertheless of great 

 interest with respect to the theory of the polar light, showing 

 that this meteor is not, like rain, thunder, lightning, &c. the 

 effect of a local agency in a small portion of the atmosphere, 

 but rather a disturbance of the equilibrium in the whole mag- 

 netic system of our globe. 



The experiment was made as early as the 5th of April, 

 1741, by Professor Celsius, in Upsal, and the instrument- 

 maker, Graham, in London. Celsius found on that day the 

 needle becoming restless at 2 o'clock P.M., so that at 5 o'clock 

 it was 1° 40' more west than it had been at 10 o'clock A.M. 

 At 5 o'clock 18 minutes it had receded to the E. by 20', and 

 6 minutes later it went again 18' westward. From that time 

 till half-past 8 o'clock next morning it went back to its usual 

 position. In the evening an aurora borealis was seen. A 

 few weeks previously Celsius had requested Mr. Graham in 

 London, also to observe his needle on the same day, in order 

 to ascertain whether the same irregular motions were observ- 

 able in two places so far apart at the same time : on the same 

 day, viz. Sunday, 5th of April, Mr. Graham observed in 

 London such extraordinary and frequent irregularities in the 

 needle as he had never seen before, sometimes even at inter- 

 vals of from 2 to 3 minutes. But Mr. G. makes no mention 

 of any aurora borealis. (See my Magnetism of the Earth, 

 p. 413.) 



The aurora borealis at Edinburgh not having been per- 

 ceived in all those days when the magnetic needle showed 

 such iri'egular motions in Paris, I searched my meteorologi- 

 cal diary, in order to discover whether any traces of aurora 

 borealis had been discovered in Christiania. On the 13th of 

 March 1825, 10 o'clock 21' P.M., the sky was overcast, so that 

 no aurora could be seen. On the 30th and 31st the sky was 

 perfectly clear, but there is no mention of aurora. It is never- 

 theless possible that weak traces may have been seen towards 

 the North, which I did not observe, the windows near which 



* From Schweigger's JahrbucJi dcr Chemic, Band xviii. p. 353. 



my 



