Causes of the Aurora BorcaUs. 247 



ence, but in no instance could they discern the least impulse of dif- 

 ference, although the meteor was so low as to be risible in strata, 



and so near, in one instance, as to stream down to the ground not 

 many furlongs from his ship. Humboldt, in conjunction with Mr. 

 Olimann, of Berlin, suspected " a change in the magnetic intensi- 

 ty," attributable to this cause ; and Capt. Franklin thought the vari- 

 ations at Fort Enterprize were much attected by the vividness of the 

 prismatic hues ; but as the observations of several naturalists in the 

 exploring expeditions, were made under circumstances to insure the 

 greatest possible accuracy, and in those latitudes where the phenom- 

 enon displays its most frequent and most wonderful phases, and 

 where its greatest influence should consequently be felt ; and their 

 testimony being unequivocal, it seems probable that its imagined ef- 

 fect upon the magnetic force is attributable to some other cause. 



Many have reported that the moving figures were accompanied by 

 crackling noises and explosions, but the evidence is not clear on this 

 point* No individual has at any time heard any report within the 

 polar regions. When the aurora was rolling, flashing, rushing, 

 and changing with a velocity that struck beholders with astonishment, 

 if the motions had not been noiseless, they must have been heard in 

 the deep stillness of the Arctic night. 



If it is objected that the examples adduced in support of principles, 

 have been taken from high latitudes, and are therefore not applica- 

 ble to the nature and origin of the meteor in other regions ; I reply 

 that 1 have done so, believing that in every place where it appears it 

 has the same cause ; is illuminated by the operation of the same 

 laws ; and that by their increased effect in the high northern regions, 

 the causes are more obvious, and their dev< lopement more attaina- 

 ble. Whenever the agency of caloric and electricity, in their do- 

 minion over the atmosphere, can be fathomed and estimated, the 

 value of many occult problems in meteorology will be understood ; 

 but until then, we can scarcely hope that the occurrence and dura- 

 tion of storms, the changes in temperature, and the formation of me- 

 teors, will be calculated with mathematical exactness. 



In conclusion, it appears probable, that the aurora borealis is a 

 meteorological phenomenon, caused by a vapor of extreme levity, 

 tenuity, and transparency ; susceptible of motion from the slightest 

 breath that stirs the air, and refracting to an extraordinary degree, 

 the rays of Solar Light. 



New York. October. 1830* 



