144 Miscellaneous Intelligence. 



With reference to the relation between the column and the arches, 1 

 have shown, in discussing our observations on partial corona, that even 

 when the rays appear isolated and independent, they have a general 

 arrangement in files or ranges, parallel to the direction of the arches. 

 I have also shown a tendency in the arches to dissolve into columns; 

 whence it is obvious that the simple ray is the result of an arrange- 

 ment of the auroral light in lines parallel to the dipping needle. The 

 arched form results from this, that if two rays exist simultaneously, 

 they tend to place themselves so that their common place shall be per- 

 pendicular to the magnetic meridian, as if the equilibrium of two rays 

 were not stable except in this position. But how this condition of sta- 

 bility is consistent with the idea that the rays have an electric nature 

 and origin, is yet enveloped in mystery. 



The luminous currents, exhibited in the ranges of columns, passing 

 either from the east to the west or the reverse, are not equally frequent 

 in the different directions; the same remark applies to the modes of 

 progression in the arches from the north to the south and from the 

 south to the north. I state the facts on this subject without pretending 

 to offer any explanation. 



We have ebserved the extra-zenith corona so frequently, as to be 

 able to affirm that the coronas may appear in all possible directions in 

 relation to the observer, and that their connection with the magnetic 

 zenith is a simple result of linear perspective. 



In the fourth paragraph I have treated of the auroral sheets. They 

 are allied to the rays, but differ in their flickering or palpitating light 

 and also in appearing only at a later hour of the night. 



The fifth paragraph relates to the colors of the auroral light, which 

 are less varied than generally supposed ; for but three or four distinct 

 shades were observed by us. 



In the sixth paragraph I consider the facts which may lead the ob- 

 server to suppose that the aurora is situated but a small" distance from 

 him. Although believing that their appearances are mostly deceptive 

 I do not affirm that all observations of this kind hitherto made are ne- 

 cessarily incorrect. I next treat of a resemblance, between the mean 

 orientation of cirro-cumuli clouds in parallel bands optically convergent 

 and auroral arches. 



In order to determine the altitude of auroral arches, M. Lottin and 

 myself observed simultaneously, at opposite extremities of a base of 1^ 

 kilometers (10 miles) ; and we arrived at the result that the height at 

 least exceeded 50 kilometers (31 miles). A longer base is necessary f° r 

 a more precise determination. For such investigations, the base Iw e 

 should be about 100 kilometers long (60 miles), and in the direction 

 of a terrestrial magnetic meridian. 



The last paragraph contains general remarks on the frequency ° f 

 the phenomena, its duration, hour of appearance, its possible continu- 

 ance during a succession of days. I show that the progressive movt 

 ments of the arches are wholly independent of the motion of the earth 

 which sets aside any theory founded on the idea of the cosmica! ong in 

 of the Aurora, and sustains the view that it belongs to our atmosphere 

 and almost exclusively to its upper regions. 



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