AURORA BOREALIS. 



25. One of the most recent and exact descriptions of this meteor 

 is the following, supplied by M. Lottin, an officer of the French 

 navy, and a member of the Scientific Commission sent some years 

 ago to the North Seas. Between September, 1838, and April, 

 1839, this savant observed nearly 150 meteors of this class. They 

 were most frequent from the 17th November to the 25th January, 

 being the interval during which the sun remained constantly 

 below the horizon. During this period there were sixty-four 

 auroras visible, besides many which a clouded sky concealed 

 from the eye, but the presence of which was indicated by the 

 disturbances they produced upon the magnetic needle. 



The succession of appearances and changes presented by these 

 meteors are thus described by M. Lottin : 



Between four and eight o'clock, P.M., a light fog, rising to the 

 altitude of six degrees, became coloured on its upper edge, being 

 fringed with the light of the meteor rising behind it. This border 

 becoming gradually more regular, took the form of an arc, of a 

 pale yellow colour, the edges of which were diffuse, the extremities 

 resting on the horizon. This bow swelled slowly upwards, its 

 vertex being constantly on the magnetic meridian. Blackish 

 streaks divided regularly the luminous arc, and resolved it into a 

 system of rays ; these rays were alternately extended and con- 

 tracted ; sometimes slowly, sometimes instantaneously ; some- 

 times they would dart out, increasing and diminishing suddenly 

 in splendour. The inferior parts, or the feet of the rays, pre- 

 sented always the most vivid light, and formed an arc more or 

 less regular. The length of these rays was very various, but they 

 all converged to that point of the heavens, indicated by the direc- 

 tion of the southern pole of the dipping needle. Sometimes they 

 were prolonged to the point where their directions intersected, and 

 formed the summit of an enormous dome of light. 



The bow then would continue to ascend toward the zenith : it 

 would suffer an undulatory motion in its light that is to say, 

 that from one extremity to the other the brightness of the rays 

 would increase successively in intensity. This luminous current 

 would appear several times in quick succession, and it would pass 

 much more frequently from west to east than in the opposite 

 direction. Sometimes, but rarely, a retrograde motion would 

 take place immediately afterward ; and as soon as this wave of 

 light had run successively over all the rays of the aurora from 

 west to east, it would return, in the contrary direction, to the 

 point' of its departure, producing such an effect that it was 

 impossible to say whether the rays themselves were actually 

 affected by a motion of translation in a direction nearly hori- 

 zontal, or if this more vivid light was transferred from ray to ray, 



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