THE AURORA. 197 



undulatory movements occurring, transverse to the 

 apparent vertical position of the rays, like the move- 

 ments of a banner floating in the breeze. 



This appearance is doubtless greatly modified by 

 perspective: the rays which are apparently vertical, 



Fig. 02 Auroral Curtain Formation, Observed at Bossekop, Lat. 70 N. 



being- horizontal; and probably emanating from the 

 edge of an arch; producing the single curtain shown in 

 Fig. 62 ; or from the edges of several concentric arches, 

 like those shown in Fig. 61 ; producing the series of 



Fig. 63 Auroral Curtain Formation, Observed at Bossekop, Lat. 70 N. 



curtains shown in Fig. 63. It is also evident from this, 

 that in the formation of coronse, the appearance is 

 probably often due to the edge of the arch, with the 

 streamers emanating from it, reaching the zenith of 

 the observer. 



