PHOSPHORESCENCE. 47 



which often persists for a considerable time after 

 their passage (fig. 5). In his voyage round the 

 world, the Admiral de Krusenstern saw one of 

 these Aerolites leave behind it in the sky a 



Fig. 5. 



phosphorescent streak which persisted for a whole 

 hour, without sensibly changing its place. (See 

 Humboldt : ' Cosmos/ vol. i.) Phosphorescent 

 streaks left behind Aerolites not unfrequently re- 

 main visible for about a minute. 



We cannot do more than mention here the 

 lightning flash,* the Aurora Borealis, the Zodia- 

 cal light, the fire of St. Elmo, the light of fixed 



* On the various kinds of lightning, see Arago, " Notice sur 

 le Tonnerre," in his ' CEuvres,' or in the Ann. du Bureau des Longi- 

 tudes, for the year 1838 ; Phipson, in the ' Comptes-Rendus' of 

 the Academy of Sciences of Paris, April 13, 1857; and Du Moucel's 

 brochure, 'Sur le Tonnerre et les Eclairs.' Paris : Hachette, 1857. 



