THE AURORA. 7 



the sun, not indeed through a complete revolution, but 

 as far as the influence of other forces will permit. 

 This has been abundantly confirmed, and is a fact of 

 extreme importance in the theory of terrestrial magne- 

 tism. Wherever the sun may be, either on the visible 

 heavens or on that half of the celestial sphere which is 

 at the moment beneath the horizon, the end of the 

 ueedle nearest to the sun makes an effort (so to speak) 

 to point more directly towards the great ruling centre 

 of the planetary scheme. Seeing, then, that the daily 

 vibration of the needle is thus caused, we recognise the 

 fact that the disturbances of the daily vibration may 

 be referred to some peculiarity of the solar action. 



It was not, therefore, so surprising as many have 

 supposed, that the increase and diminution of these 

 disturbances, in a period of about eleven years, should 

 be found to correspond with the increase and diminu- 

 tion of the number of solar spots in a period of equal 

 length. 



We already begin to see, then, that auroras are 

 associated in some mysterious way with the action of 

 the solar rays. The phenomenon which had been looked 

 on for so many ages as a mere spectacle, caused perhaps 

 by some process in the upper regions of the air, of a 

 simply local character, has been brought into the range 

 of planetary phenomena. As surely as the brilliant 

 planets which deck the nocturnal skies are illuminated 

 by the same orb which gives us our days and seasons, 

 so are they subject to the same mysterious influence 

 which causes the northern banners to wave resplend- 



