182 TEERESTHIAL PHENOMENA. 



zon, and unite in a quivering sea of flame, the splendour of 

 which no description can reach, for every instant its bright 

 waves assume new forms. The intensity of this light is 

 Sometimes so great, that Lowenorn (29th January, 1786) 

 discerned its corruscations during bright sunshine. Motion 

 increases the visibility of the phenomenon. The rays 

 finally cluster round the point in the sky corresponding to 

 the direction of the dipping needle, and there form what is 

 called the corona a canopy of light of milder radiance, 

 streaming, but no longer undulating. It is only in rare 

 cases that the phenomenon proceeds so far as the complete 

 formation of the corona ; but whenever this takes place, the 

 display is terminated. The streamers now become fewer, 

 shorter, and less intensely coloured ; the corona and the 

 luminous arches break up, and soon nothing is seen but 

 irregularly scattered, broad, pale, shining patches of an 

 ashy-grey colour ; and even these vanish before the trace 

 of the original dark segment has disappeared from the 

 horizon. The last that remains of the whole spectacle 

 is often merely a white delicate cloud, feathered at the edges, 

 or broken up into small round masses, like cirro cutnuli. 



This connection of the polar light with the most delicate 

 cirrous clouds deserves particular attention, because it 

 shews us the electro-magnetic evolution of light as part of a 

 meteorological process. The magnetism of the Earth is 

 here exhibited in its influence on the atmosphere, and on the 

 condensation of aqueous vapour. The observation of 

 Thienemann, in Iceland, who regarded the light detached 

 fleecy clouds as the substratum of the Aurora, has been 

 confirmed in modern times by Franklin and Richardson 

 in the neighbourhood of the American magnetic pole, aud 



