THE LITERARY 



OF THE LINN^AN ASSOCIATIOX OP PENNSYLVANIA COLLEGE. 



Vol. in. OCTOBER, 1847. No. 12. 



THE AURORA BOREALIS. 



III. Its altitude. 

 Concerning this point there have been many conflicting opinions. — 

 Some have placed it at no greater elevation than that of the oirrus-cloud) 

 others in the npper strata of the atmosphere, and others without its lim- 

 its, at an elevation varying from 60 to 200 and even several thousand 

 miles ! But to whatever conclusion we may come in reference to its al- 

 titude in middle and low latitudes, it is generally conceded that in the 

 polar regions it is comparatively low, and that it gains elevation as it 

 progresses toward the equator. At least such is the universal opinion of 

 the natives of those regions, which are its birth-place, and with this 

 agree nearly all the navigators and men of science, who have spent sev- 

 eral winters there, and who have consequently had the most ample op- 

 portunities of becoming fully acquainted with its most important features. 

 "Mr. Trevelyan observed, that in the Faroe and the Shetland Islands, it 

 was often seen not more than forty or fifty feet above the sea, and learn- 

 ed that in both countries it is frequently heard. One person had per- 

 ceived in it, when red, an electrical smell." (Sill. Jour. vol. xxxv-151.) 

 "Lieut. Hood, at Fort Enterprise, found the aurora in one instance to be 

 only 2i miles high." (Ibid p. 155.) And Baron Von Wrangell estimates 

 it to be so low in the polar seas of Siberia, as to be influenced by the 

 wind. (See WrangelPs polar expedition, p. 302.) That it should have 

 a greater elevation in low latitudes than in high is, upon the supposition 

 that it is within our atmosphere at least near the pole, perfectly consist- 

 ent with the law of bodies moving through a resisting medium of varia- 

 ble density; the motion will be deflected towards the point of least re- 

 sistance. This takes for granted that it consists in the transfer of lumin- 

 ous matter, or the exertion of force from the polar towards the equato- 

 rial regions. The various estimates of its altitude, which have been 

 made, have all been based upon, what was at least, an imperfect paialax 

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