Aurora Borealis of the 1th of Jan., 1831 , 529 



or twenty-six miles above the surface of the earth, and that it 

 was probably not at a less distance than fourte.cn or fifteen 

 miles. These are wide limits, but we can scarcely expect, 

 unless under very favourable circumstances, to determine within 

 much narrower limits the region of such variable phenomena. 

 Had the two places of observation, in the present instance 

 been nearly on the same meridian, any error that might have 

 been made in determining the summit of the arch, would not 

 have produced so sensible a difference in the result, and it is 

 to be hoped that simultaneous observations may at future 

 opportunities be made on similar phenomena, by observers in 

 better relative positions than Mr. Harris and myself, and more 

 favourably circumstanced for observation than I was at the 

 time. The points principally to be determined are the alti- 

 tude and azimuth of the summit of the same arch, at the same 

 instant, by two observers at a considerable distance from each 

 other, in a direction nearly perpendicular to the arch. 



The limits which I have thus determined for the height of 

 this luminous arch are much below those which have, most 

 recently, been assigned to a similar phenomenon. From a 

 number of observations, made at very distant places, on a 

 remarkable Aurora on the 29th of March, 1826, Mr. Dalton 

 concludes that a luminous arch seen on that occasion could 

 not be less than one hundred miles above the surface of the 

 earth*. He likewise determines the height of an Aurora, 

 observed at Newton Stewart, Keswick, and Gosport, on the 

 17th of October, 1819, to have been one hundred miles ; and 

 infers, from the observations made at Kendal and Manchester 

 on one seen on the 27th of December, 1827, that its height 

 was nearly the same. In conclusion he says, ' I am induced 

 to believe that these luminous arches of the Aurora, which 

 occasionally appear stretching from east to west, are all of the 

 same height, about one hundred miles.' The following ex- 

 tracts from Lieutenant Hood's Journal at Cumberland House, 

 however, show that the observations made by himself and Sir 

 John Franklin, in North America, indicate a very inferior ele- 

 vation to the Aurora : 



Phil. Trans., 1828. 



