Aurora Borealis of the 1th of Jan., 1831. 531 



when the Aurora is carried through the air by its own direct 

 motion. The wind was E. by N., a strong gale, and the tem- 

 perature of the air 9*.' 



The circumstance here noticed by Lieutenant Hood, of the 

 columns having been borne away by the wind, clearly indicates 

 that they could not have been at a very great elevation. Mr. 

 Harris notices a similar appearance in the Aurora of the 7th of 

 January, and although I did not remark the circumstance, yet 

 the appearance of the detached masses of light, shortly after 

 the first luminous arch had disappeared, was precisely that of 

 low thin clouds illuminated by the moon ; indeed I found it 

 difficult to persuade myself that they were not clouds at no 

 great elevation, and only concluded they were not so, from 

 the circumstance, that the moon would not rise for many 

 hours. 



From the observations of the Aurora of the 29th of March, 

 1826, it appears that the luminous band was at right angles to 

 the magnetic meridian, and Mr. Dalton considers that this is 

 the general direction of the arches. I have before stated that, 

 if we suppose this to have been the case with the arch which 

 first appeared in the Aurora of the 7th of January, its height 

 will be reduced to about five miles ; so that the result would 

 differ more widely, than in any other case, from what he 

 assigns as the general height of such arches. 



Upon the whole, I think we must conclude, that, although 

 these luminous bands may sometimes be at the great height of 

 a hundred miles, yet at others they are at heights varying 

 from five to fourteen or fifteen miles above the surface of the 

 earth. 



Royal Military Academy, $th April, 1831. 



* Captain Franklin's Journey (First) to the American Shores of the Polar Sea, 

 Appendix, No. 2. 



