THE AUEORA BOREALIS. 89 



THE AURORA BOREALIS. 



THE AURORA BOREALIS is a luminous phenomenon, which appears in the 

 heavens, and is seen in high latitudes in both hemispheres. The term AURO- 

 RA BOREALIS, or NORTHERN LIGHTS, has been applied to it because the oppor- 

 tunities of witnessing it are, from the geographical character of the globe, much 

 more frequent in the northern than in the southern hemisphere. The term 

 AURORA POLARIS would be a more proper designation. 



This phenomenon consists of luminous rays of various colors, issuing from 

 every direction, but converging to the same point, which appear after sunset 

 generally toward the north, occasionally toward the west, and sometimes, but 

 rarely, toward the south. It frequently appears near the horizon, as a vague 

 and diffuse light, something like the faint streaks which harbinger the rising 

 sun and form the dawn. Hence the phenomenon has derived its name, the 

 NORTHERN MORNING. Sometimes, however, it is presented under the form of 

 a sombre cloud, from which luminous jets issue, which are often variously col- 

 ored, and illuminate the entire atmosphere. 



A meteor so striking as the aurora could not fail at an early period to attract 

 the attention of scientific inquirers, and to give rise to various theories. Some 

 supposed it to be the refraction of the solar rays ; others ascribed it to the 

 effects of the magnetic fluid. Euler identified it with the tails of comets. 

 Mairan supposed it to proceed from the intermixture of the far-extending atmo- 

 sphere of the sun with that of the earth. When, however, the luminous effects 

 of artificial electricity were shown when the electric light transmitted through 

 rarefied air was exhibited and when the identity of lightning with electricity 

 was established, these various hypotheses were by common consent abandoned ; 

 and the explanation proposed by Eberhart, of Halle, and Paul Frisi, of Pisa, 

 which ascribed the phenomenon to electricity transmitted through regions in 

 which the atmosphere is in a highly rarefied state, was adopted. Any doubt 

 which might have hung round this explanation was dispelled when the rela- 

 tions between magnetism and electricity were demonstrated ; and although the (. 

 complete explanation of the details of the aurora has not been accomplished, 



