AI.'KOKA BORF.ALlr*. 19U 



ence of local influences can not, therefore, be denied in these 

 cases. Wraugel saw the brilliancy diminish as he left thd 

 shores of the Polar Sea, about Nischne-Kolymsk. The ob- 

 servations made in the North Polar expedition appear to prove 

 that in the immediate vicinity of the magnetic pole the de- 

 velopment of light is not in the least degree more intense or 

 frequent than at some distance from it. 



The knowledge which we at present possess of the altitude 

 of the polar light is based on measurements which, from their 

 nature, the constant oscillation of the phenomenon of light, 

 and the consequent uncertainty of the angle of parallax, are 

 not deserving of much confidence. The results obtained, set- 

 ting aside the older data, fluctuate between several miles and 

 an elevation of 3000 or 4000 feet ; and, in all probability, 

 the northern lights at different times occur at very different 

 elevations.* The most recent observers are disposed to place 

 the phenomenon in the region of clouds, and not on the con- 

 fines of the atmosphere ; and they even believe that the rays 

 of the Aurora may be affected by winds and currents of air, if 

 the phenomenon of light, by which alone the existence of an 

 electro-magnetic current is appreciable, be actually connected 

 with material groups of vesicles of vapor in motion, or, more 

 correctly speaking, if light penetrate them, passing from one 

 vesicle to another. Franklin saw near Great Bear Lake a 

 beaming northern light, the lower side of which he thought 

 illuminated a stratum of clouds, while, at a distance of only 

 eighteen geographical miles, Kendal, who was on watch 

 throughout the whole night, and never lost sight of the sky, 

 perceived no phenomenon of light. The assertion, so fre- 

 quently maintained of late, that the rays of the Aurora have 

 been seen to shoot down to the ground between the spectator 

 and some neighboring hill, is open to the charge of optical 

 delusion, as in the cases of strokes of lightning or of the fall 

 of fire-balls. 



Whether the magnetic storms, whose local character we 

 have illustrated by such remarkable examples, share noise aa 

 well as light in common with electric storms, is a question 



* Farquharsou in the EdtKburgh, Philos. Journal, vol. xvi., p. 304 ; 

 Philot. Transact, for 1829, p. 113. 



[The height of the bow of light of the Aurora seen at the Cambridge 

 Observatory, March 19, 1847, was determined by Professors Challis, of 

 Cambridge, and Chevallier, of Durham, to be 177 miles above the sur 

 face of the Earth. See the notice of this meteor in An Account of th>. 

 Aurora Borealis of Oct. 24, 1847, by John H. Morgan, Eso , 1848.] 

 7V. 



