Io2 COSMOS. 



magnetic polar light. I have already fully treated, in the 

 Picture of Nature, of the peculiarities of this luminous pro- 

 cess, which is often so remarkable for the brilliant display of 

 colours with which it is accompanied ; and more recent ob- 

 servations have in general accorded with the views which 

 I formerly expressed. " The Aurora borealis has not been 

 described merely as an external cause of a disturbance in the 

 equilibrium of the distribution of terrestrial magnetism, but 

 rather as an increased manifestation of telluric activity, 

 amounting even to a luminous phenomenon, exhibited on the 

 one hand, by the restless oscillation of the needle, and on the 

 other, by the polar luminosity of the heavens." The polar 

 light appears in accordance with this view to be a kind of 

 silent discharge or shock as the termination of a magnetic 

 storm, very much in the same manner as in the electric shock, 

 the disturbed equilibrium of the electricity is renewed 

 by a development of light by lightning, accompanied by 

 pealing thunder. The reiteration of a definite hypothesis in 

 the case of a complicated and mysterious phenomenon has at 

 all events the advantage of giving rise with a view to its 

 refutation to more persistent and careful observations of the 

 individual processes. 4 



Dwelling only on the purely objective description of these 

 processes, which are mainly based upon the materials yielded 

 by the beautiful and unique series of observations, which were 

 continued without intermission for eight months (1838, 1839), 

 during the sojourn of the distinguished physicists, Lottin, 

 Bravais and Siljestrom in the most northern parts of Scandi- 

 navia, 8 we will first direct our attention to the sty- called black 

 segment of the Aurora, which rises gradually on the horizon 

 like a dark wall of clouds. 6 The blackness is not, as Argel- 



4 Cosmos, vol. i, pp. 187 199, and Dove,, in Poggend. Annalen, Bd. 

 xix, s. 388. 



5 The able narrative of Lottin, Bravais, Lilliehob'k, and Siljestrom, 

 who observed the phenomena of the northern light from the 19th of 

 September, 1838,till the 8th of April, 1839, at Bossekop (69 58' N. lat.) 

 in Finmark and at Jupvig (70 6' N. lat.) was published in the fourth 

 section of Voyages en Scandinavie, en Laponie, au Spitzberg et aux Feroes, 

 sur la Corvette, la Recherche (Aurores boreales). To these observations 

 are appended important results obtained by the English superinten- 

 dent of the copper mines at Kalfiord (69 56' N. lat.), pp. 401435. 



6 See the work above referred to (pp. 437444) for a description of 

 the Segment obscure de V Aware boreale. 



