406 ADDITIONAL PHENOMENA OF NATUBAL MAGIC. 



life ; and yet a man with perfect integrity and justifiability 

 swears to his own handwriting, and others acquainted 

 with it do so also, in the perfect and conscientious 

 certainty of the fact. 



One of the subjects which it appears justifiable to 

 introduce here, along with the associated subject of the 

 mirage which has been so interestingly treated by Sir 

 David Brewster, is the aurora borealis, which is displayed 

 with remarkable brilliance within the Arctic circle during 

 the prolonged winter darkness of that region, which is 

 much indebted to this splendid phenomenon for the relief 

 of its prolonged and inhospitable gloom. Those who 

 observe this phenomenon attentively will find that its 

 point of convergence, or the centre towards which its 

 <: streamers " point, is generally identical with, or very 

 nearly approximate to, that point of the heavens which is 

 opposite to the sun during the manifestation of the 

 spectacle. It is a point, in fact, only seen in the northern 

 and southern regions beyond the range of the ecliptic 

 while the sun is within that plane, and on the opposite 

 side of the earth, and everything conspires to show that 

 while the atmosphere of the world acts like a sphere of 

 glass enclosing the earth, by which the rays of the sun 

 are refracted as if they were intercepted by a globular or 

 double convex lens, these rays so refracted are converged 

 on the opposite side of this atmospheric lens, from the 

 edges of the terrestrial disc exposed to the sun, according 

 to the greater or less purity of the atmosphere under that 

 region forming the edge of the disc, and that the coloured 

 rays seen to prevail sometimes are mere prolongations of 

 the gorgeous tints of sunset or of dawn then prevailing at 

 those points of the world's surface from which the re- 

 fraction takes place. The rapidity with which the aurora 

 darts its rays, and changes, is readily accounted for from 

 the presence of intercepting clouds, projecting ice, and 



