THE AURORA BOREALIS. 



483 



tremity of its own circuit.* Nearly every night after the installation of 

 the apparatus, a yellow-white light illuminated the points without any- 

 thing like it appearing on the heights in the neighborhood, while the 

 needle of the galvanometer by its motions betrayed the passage of an 

 electric current. The light was analyzed in the spectroscope, and gave 

 the greenish-yellow ray that characterizes the aurora borealis. The 



* 0' 



l 



intensity of the glow and the deviations of the needle, moreover, 

 varied continually. In the mean time the hoar-frost which was de- 

 posited on the wires quickly destroyed the insulation, and rendered an 

 experiment of any duration almost impossible. The numbness of the 

 fingers of the operators, induced by the cold, added to the difficulties 

 of the study. 



The apparatus afterward set up on Pietarintunturi, in more than 

 78 of latitude, was disposed in an almost identical manner, except that 

 the surface furnished with points was a half less ; but, M. Lenstrum 

 remarks, the proximity to the " maximum zone " of auroras compen- 

 sated for this inferiority. On the 29th of December an " auroral ray " 

 made its appearance above the net, which it dominated vertically from 

 a height of one hundred and twenty metres. 



The difficulties of the question of the exact origin and nature of 

 the auroral phenomena have not been solved yet ; but we have good 

 reason to believe that a long approach has been made in the recent ex- 

 periments toward a solution, and grounds to believe that science will 

 soon remove them all ; and we shall no longer be able to repeat what 

 Haiiy, less than a hundred years ago, said on the same subject, " It is 

 not always what has been known longest that is best." Translated for 

 the Popular Science Monthly from the Revue des Deux Mondes. 



* Professor Lenstrom's apparatus is represented in the figure. The wire begins at 0, 

 and connection with the galvanometer is made from the inner end. The letter i indicates 

 an insulator. 



