364 AURORA BOREALIS. 



expands like the electric spark in an exhausted 

 glass tube, into broad bands, or zones and co- 

 lumns; filling the sky with halos and crowns of 

 lambent light, or undulating corruscations. It 

 is highly probable, that the aurora is given off, 

 during the condensation of the upper equatorial 

 currents with the vapours which they contain, 

 in a mode similar to the evolution of silent 

 lightning on a summer's evening, which is ge- 

 nerally many miles off, and is seen through 

 numerous strata of atmospheric air, producing a 

 diffused or lambent phosphorescence, that re- 

 sembles the aurora much more than it does 

 lightning which is near at hand. 



Sometimes the whole northern hemisphere pre- 

 sents that kind of luminosity which announces 

 the dawn of morning in the east. At other 

 times the aurorse seem stationary during changes 

 of temperature from heat to cold. They often 

 present the appearance of a bank of light, (re- 

 sembling the effect of a distant conflagration,) 

 resting on, or flanked by a low dark cloud, which 

 is occasionally illuminated by broad flashes. 

 Captain Bonny castle, of Toronto, in Upper Ca- 

 nada, observes, that during the formation of all 

 remarkable aurorae, dark volumes of vapour sud- 

 denly appeared within the space comprehended 

 by the arch. (Silliman's Journal, vol. xxx. p. 

 132.) Sometimes, though rarely, the aurora 

 presents the appearance of a wide arch extending 



