8 LIGHT SCIENCE FOR LEISURE HOURS. 



even while the motion, of the curtain is stilled we see 

 its light mysteriously waxing and waning. Then as 

 we gaze, fresh waves of disturbance traverse the magic 

 canopy. Startling coruscations add splendor to the 

 scene, while the noble span of the auroral arch from 

 which the waving curtain seems to depend, gives a 

 grandeur to the spectacle which no words can ade- 

 quately describe. Gradually, however, the celestial 

 fires which have illuminated the gorgeous arch seem to 

 die out. The luminous zone breaks up. The scene 

 of the display becomes covered with scattered streaks 

 and patches of ashen gray light, which hang like 

 clouds over the northern heavens. Then these in turn 

 disappear, and nothing remains of the brilliant specta- 

 cle but a dark smoke-like segment on the horizon. 



Such is the aurora as seen in arctic or antarctic 

 regions, where the phenomenon appears in its fullest 

 beauty. Even in our own latitudes, however, strik- 

 ingly beautiful auroral displays may sometimes be 

 witnessed. Yet those who have seen the spectacle 

 presented near the true home of the aurora, recognize 

 in other auroras a want of the fulness and splendor of 

 color which form the most striking features of the 

 arctic and antarctic auroral curtains. 



Hitherto the nature of the aurora has been a 

 mystery to men of science ; nor, indeed, does the dis- 

 covery we are about to describe throw even now full 

 light on the character of the phenomenon. That dis- 



