232 ELECTRICITY OF THE ATMOSPHERE AND AURORA BOREALIS. 



as tlie height of the aurora. Polar light, however, has beeu often ob- 

 served at much less height. Farquharson, by means of observations 

 matle at two distinct places, a mile apart, found a height of 2,4Sl Eng- 

 lish feet ; and Captain Parry saw, on one occasion, polar light produced 

 between the place where he was stationed and a mountain only about 

 3,000 yards distant. The French observations made at Bossekop equally 

 proved the existence of polar light between the place of observation and 

 a neighboring mountain.* 



Although M. Loorais and M. Bravais himself believe that observa- 

 tions which give so low a height to polar light are erroneous, and the 

 result of an illusion, I cannot agree with them, and I can ofier in sup- 

 port of my opinion the phenomenou I observed on the 18th of October, 

 18G8, at the entrance of the Norwegian archipelago, when the whole 

 horizon was covered with rays, which were soon united around the 

 magnetic pole, forming a regular crown. All the phenomena I have 

 observed and described in regard to the illuminated edges of clouds, 

 show very plainly that in these cases the polar light was produced in 

 the region of clouds, and even lower. Moreover, we know by numerous 

 observations that the number of storms accompanied by lightning and 

 thunder diminishes considerably in proportion as we approach the polar 

 regions, so that at 70° they no longer occur. Must we then conclude ^ 

 that in these regions the clouds are completely deprived of electricity 1 

 Oertaiuly not, but only that the electrical discharges are made in some 

 other way. I have on several occasions observed discharges, accom- 

 panied with electric light, proceeding from scattered clouds or banks of 

 clouds such as produced true polar rays, and still more frequently I have 

 seen the edges of clouds illuminated with a yellow light. But, however, 

 in these high latitudes electricity is discharged not only by clouds, but 

 -also directly by damp air, as takes place in winter in the temi>erate 

 zones. A great many direct observations prove the existence of slow 

 discharges of this nature, and very remarkable confirmation is given of 

 it by M. Angstrom, who on one occasion i^roved the presence of the 

 yellow ray of polar light over almost the entire sky. 



If it is well established that the phenomenon of polar light has its 

 source in the electricity of the air, it follows that its appearance depends 

 less upon terrestrial magnetism than has been hitherto supposed. This 

 may exercise a direct actiou upon the discharge already produced, but 

 cannot contribute to its production, which must depend upon certain 

 conditions of the different strata of air. Although terrestrial magnetism 

 has an influence upon the position of the luminous bow of i)olar light, 



*M. A. W. Malin, inteiidaut of the Museum of Gotteuburg, relates, in a description of a 

 journey made iu 1842 in the Laplands of Sweden and Norway, that, during an excursion 

 from Maunu to Lyngen on the night of the JGth of March, lie observed, at a height of 2,000 

 feet, with the temperature at 40 degrees below zero, a polar light between himself aai the 

 neighboring mountains, and heard a crackling sound which accompanied it. 



