THE AURORA. 195 



towards the equator : and that its different aspects, at 

 different times and places, and its different phases, as 

 seen at the same time by observers at different points, 

 are greatly modified by its position with reference to 

 the position of the observer. 



Fig. GO Auroral Corona Observed at Bossekop, Lat. 70 N. 



AURORAL MOVEMENT, CURTAIN FORMATION. A 

 peculiar feature of the aurora is the continual move- 

 ment visible in every part. A streamer darts up 

 rapidly from the horizon, increasing in size and brill- 

 iancy; and as rapidly fades away. Along one part of 

 the arch a series of streamers form in rapid succession, 

 giving the impression of an undulatory, horizontal 

 movement, at right angles to the vertical movement of 

 the rising streamers : and, as the intensity of this phase 

 decreases, a similar movement, at some distant point, 

 rises and declines in a similar manner. At times there 

 occurs a curtain formation, composed of parallel rays ; 

 appearing either as a single curtain, as shown in Fig. 

 62, or as a series of curtains, hung one behind the 

 other, showing only their lower margins, as in Fig. 63; 



