AURORA BOREALIS. 



91 



arc, like a rainbow, which was not complete at first, but by degrees increased 

 its amplitude, and, after some moments, was completed, by the sudden forma- 

 tion of the remainder, which rose in a moment, accompanied by a multitude of 

 jets of light, which issued from all points of the northern horizon. The vertex 

 of the bow then reached very nearly to the zenith. This bow was at first ilet t- 

 ing and undecided in its character, as if the matter of which it was composed 

 had not yet taken a stable arrangement ; but all this agitation quickly subsided, 

 and then it remained hanging in the heavens in all its beauty for more than an 

 hour, having a progressive motion barely sensible toward the southeast, where 

 it seemed to be carried by a light wind which was then felt from the north- 

 east. M. Biot had thus full time to contemplate it ; and he observed its posi- 

 tion with the instruments he had provided for astronomical purposes. He 

 found that it embraced an extent upon the horizon of 128 42', and that its 

 centre was placed precisely in the direction of the magnetic meridian. The 

 whole extent of the firmament traversed by this grand arc, on the northwestern 

 side, was continually intersected, in every direction, by jets of light, the forms, 

 motions, colors, and continuance of which, strongly attracted his attention. 

 Each of these jets, when it first appeared, was a simple line of whitish light : 

 its magnitude and splendor were augmented rapidly, presenting sometimes sin- 

 gular variations of direction and curvature. When it attained its entire devel- 

 opment, it was contracted to a thin straight thread, the light of which was 

 extremely vivid and brilliant, and of a decided red tint. After this it grew 

 gradually fainter, and became extinct frequently at the same place precisely 

 where it commenced its appearance. This permanence of a great number of 

 jets, each in the same apparent place, while their brightness exhibited an infi- 

 nite variety of degrees, renders it probable, in the opinion of Biot, that their 

 light is not reflected, but direct, and that it is developed in the place where it 

 is seen. This inference is further confirmed by the circumstance that no trace 

 of polarization could be discovered in it. All these meteors, and the bow with- 

 in which their play was confined, must have occupied a region above the 

 clouds, since the latter occasionally intercepted their light. 



One of the most recent and detailed descriptions of the aurora borealis is 

 due to M. Lottin, an officer of the French navy, and a member of the scientific 

 commission sent some years ago to the north seas. 



During the winter of 1838-'9, M. Lottin observed the auroras at Bossekop, 

 in the bay of Alien, on the coast of West Fin mark, in the latitude of 70 N. 

 Between September, 1838, and April, 1839, being an interval of two hundred 

 and six days, he observed one hundred and forty-three auroras : they were 

 most frequent during the period which the sun remained below the horizon, 

 that is, from the 17th of November to the 25th of January. During this night 

 of seventy times twenty-four hours, there were sixty-four auroras visible, with- 

 out counting those which were rendered invisible by a clouded sky, but the 

 presence of which was indicated by the disturbance they produced on the mag- 

 netic needle. 



Without entering into the details of the individual appearances of these me- 

 teors, we shall here briefly describe the appearances and the succession of 

 changes which they usually presented. 



Between the hours of four and eight o'clock in the afternoon, a light sea- 

 fog, which almost constantly prevailed, extending to the altitude of from four 

 to six degrees, became colored on its upper border, or rather was fringed with 

 the light of the aurora, which was then behind it ; this border became gradu- 

 ally more regular, and took the form of an arc of a pale yellow color, the edges 

 of which were diffuse, an d the extremis s rested on the horizon. This bow 

 swelled upward more or less slowly, its vertex being constantly on the mag- 



