No. Ill ] 



Dr. RICHARDSON ON THE AURORA. 



597 



the following observations do not accord with the positions he lays down; that, 

 contrary to his statement, the beams would not always meet in a point if 

 prolonged upwards; that they do not always converge to the place in the 

 heavens to which the south pole of the dipping needle points ; and that the 

 rainbow-like arches do not invariably cross the magnetic meridian at right 

 angles. But, independent of all theory, I think the following notes will at 

 least serve to prove that the Aurora is occasionally seated in a region of the 

 air, below a species of cloud which is known to possess no great altitude. 

 I allude to that modification of cirro-stratus, which, descending low in the 

 atmosphere, produces a hazy continuity of cloud over-head, or a fog bank in 

 the horizon. Indeed, I am inclined to infer that the Aurora Borealis is con- 

 stantly accompanied by, or immediately precedes, the formation of one or 

 other of the various forms of cirro-stratus. On the 13th of November, and 

 18th of December, its connexion with a cloud intermediate between cirrus and 

 cirro-stratus is mentioned; but the most vivid coruscations of the Aurora were 

 observed when there were only a few thin attenuated shoots of cirro-stratus 

 floating in the air, or when that cloud was so rare that its existence was only 

 known by the production of a halo round the moon. The bright moonlight 

 of December was peculiarly favourable for observations of this kind. Had 

 the nights been dark, many of the attenuated streaks of cloud hereafter men- 

 tioned would have been totally invisible. The natives of this country pretend 

 to foretel wind by the rapidity of the motions of the Aurora; and say, that 

 when it spreads over the sky in an uniform sheet of light, it is followed by 

 fine weather, and that the changes thus indicated are more or less speedy, 

 according to the appearance of the meteor, early or late in the evening. Our 

 observations were not continued long enough to confirm or contradict these 

 notions ; but it may be perhaps worthy of notice that certain kinds of cirro- 

 stratus are also regarded by meteorologists as sure indications of wind and 

 rain. In reference to Mr. Dalton's opinion that the arches of the Aurora 

 always cross the magnetic meridian at right angles, it may be observed, that 

 there is very often an apparent convergence of the parts of the Aurora 

 towards the magnetic east or west, or to some point in their neighbourhood ; 

 but the light in its passage across the sky, even when it traversed the zenith, 

 very seldom appeared to the eye to describe the segment of a circle, but was 

 either elliptical, or formed various irregular curves and flexures. 



