2 LIGHT SCIENCE FOR LEISURE HOURS. 



its light mysteriously waxing and waning. Then as 

 we gaze, fresh waves of disturbance traverse the magic 

 canopy. Startling coruscations add splendour 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 grey light, which hang like 

 clouds over the northern heavens. Then these in 

 turn disappear, and nothing remains of the brilliant 

 spectacle 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, recognise 

 in other auroras a want of the fulness and splendour of 

 colour 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- 

 covery, however, affords promise of a speedy solution 

 of the perplexing problems presented by auroral dis- 



