48 An Account of an Aurora Borealis olservedai Glasgow. 



The circumstances vvliich struck me as most remarkable were 

 tlie play of the rays and their luminous undulations. These rays 

 were projected in large groups which alternately approached and 

 receded from each otlier : at one time they seemed to rise in a 

 body, in the sheaf-like form of an immense rocket {comme des 

 gerl'fs d'artifice), and at another time to descend like a shower 

 of light. Independently of these general movements, each cluster 

 of ravs presented a lateral movement, which could be distin- 

 guished by the greater or less intensity of parallel rays: the 

 parts more or less luminous moved in lines paralle Ito each other, 

 like regular waves ; and what was very remarkable, there often 

 appeared in the same cluster two opposite undulatory movements, 

 in such a manner that the masses of light and shade moved re- 

 gularly in opposite directions one above the other without being 

 in the least confounded. 



The light was generally of a silvery white, or rather of a light- 

 orange hue : — the lower extremity of the clusters, however,some- 

 times emitted the prismatic colours, as red, yellow, and blue; at 

 one instant a slight green tint ditfused itself over one of thie 

 clusters. — These are all the observations I was able to make as 

 to the colours of the aurora borealis. 



During the first twenty minutes the appearances of the aurora 

 were faint; during the ensuing twenty-five minutes they were 

 briUiant and continually varying; afterwards the light gradually 

 vanished. The longitudinal projection of the streamers and 

 their lateral movements first ceased, and then the rectilineal 

 figure of the rays became effaced. Nothing now remained in 

 the heavens but a pale glimmering light like to that of the 

 Milky Way, its point terminating in a grand circular arch, con- 

 cave towards the earth. This light continued visible for about 

 an hour after the aurora. 



The skv did not seem so transparent as to entitle us to sup- 

 pose that it was not charged with any vapour; but there were no 

 clouds visible, one small one only excepted, which appeared in 

 the hemisphere occupied by the aurora like a sort of rock, against 

 which the streamers played, indenting its edges but slightly. In 

 the intervals between the streamers the stars were distinctly per- 

 ceivable, even at the time when the aurora vvas most brilliant; 

 but under the streamers as far as the horizon the heavens were 

 blackish, and the stars were not seen without difficulty. 



XI, Nolkes 



