THE AURORA BOREALIS, 725 



** N.N.W., bounded by a bright line, the rest of the heavens being 

 *^ starry. Presently beams of an Aurora began to shoot towards 

 « the Great Bear." 



On the evening of Nov. 22, 1825, besides the small detached 

 clouds of the eastern and zenith part of the heavens coming slowly 

 from the north, another of quite different character extended 

 along the whole western part of the sky, to about 25° or 30° above 

 the horizon. It was one dense sheet of stratum, comparatively, 

 •with the other clouds, very dark below, waved or furrowed from 

 north to south, and cut off at its east side in an apparently straight 

 edge, trending nearly north and south. It was coming on very 

 slowly towards the east, and had before next morning prevailed 

 over the other clouds, covering the heavens, and accompanied with 

 a fresh westerly breeze, after a frosty night which the 22nd of 

 November was. This large sheet of cloud was much more 

 elevated than the small detached ones, as was fully proved by 

 some of the latter being projected in perspective on its dark under 

 surface, and there appearing as white masses fully enlightened 

 by the moon. 



Now the two arches of Aurora of that evening were abruptly 

 terminated at the points where they appeared over the eastern 

 edge of the large cloud ; and the abrupt terminations increased 

 their azimuth distances from the north as the arches came south- 

 wards, still ajopearing in their new positions over the east edge 

 of the cloud. The lower extremities of the streamers, which were 

 as long at these terminations as at any other parts of the arches, 

 appeared even in contact with the cloud, and 1 sometimes con- 

 ceived that they stretched before its eastern edge, but that part 

 being considerably illuminated by the moon prevented me from 

 being quite positive. Independently, however, of this uncertainty, 

 the appearances are surely decisive of the fact, that the Aurora 

 did not extend into the region occupied by the western cloud ; 

 and being seen over it at an angle not much higher than its own, 

 occupied therefore a region of nearly equal elevation above the 

 surface of the Earth. 



I should have estimated the height of the phosphorescent clouds 

 above described as so much as 2,000 feet above the surface, or 

 twice the height of some of the neighbouring hills ; but while 

 the lower ends of the vertical streamers were at this height their 

 upper might be 2,000 or 3,000 feet more. I have seen the 

 Aurora, however, when the clouds certainly occupied a much 

 more elevated region. 



[The additional observations made by Mr. Farquharson have 

 led him to think that the point to which the streamers are 

 directed is a little farther south of the zenith than he had sup- 

 posed, and that the luminous belt is sometimes a little broader 

 than he had estimated it at its maximum (5°). Also the extremity 

 of the zenith arch sometimes descends to the horizon. Another 

 observer describes a display as consisting of "a bow or arch 

 '' of silvery light passing a few degrees south of the zenith, while 

 " waves of light seemed to run along the arch."] 



