POLAR LIGHT, OR AURORA. 183 



by Wrangel on the Siberian coast of the Polar Sea. 

 They all remark, that the Aurora shoots forth the most 

 vivid rays when masses of cirro-strati are hovering in the 

 upper region of the atmosphere, and when they are so thin 

 that their presence can only be discovered by the formation 

 of a halo round the Moon. These clouds sometimes ar- 

 range themselves in the day-time like the rays of the 

 Aurora; and in such cases the movements of the needle 

 are similarly affected by them. After a great nocturnal 

 display of Aurora, there have been recognised early in the 

 morning the same streaks of cloud which had before been 

 luminous. ( 173 ) The apparently converging "polar bands" 

 (streaks of cloud in the direction of the magnetic meridian), 

 which continually engaged my attention during my journeys 

 both on the high table lands of Mexico and in Northern 

 Asia, belong probably to the same group of diurnal phseno- 

 mena. ( 174 ) 



Southern lights have been repeatedly seen in England by 

 Daltori, and northern lights have been seen in the southern 

 hemisphere as far as 45 S. latitude (14th January, 1831) ; 

 it not unfrequently happens, also, that the magnetic 

 equilibrium is simultaneously disturbed in the direction of 

 both poles. I have distinctly ascertained that the polar 

 light has been seen within the tropics, in Mexico and Peru. 

 It is necessary to distinguish between the sphere of simul- 

 taneous visibility of the phenomena, and the zones of the 

 Earth in which it is seen almost nightly. Every observer 

 certainly sees his own Aurora as well as his own rainbow ; 

 but the phenomenon of the effusion of light is generated 

 by a large portion of the Earth at once. Many nights may 

 be cited when it was observed simultaneously in England 



