De la Rive on the Aurora Borealis. 355 
serts his seeing an aurora depicted on the flank of a mountain: 
and it is said that a luminous arc has been seen on the surface 
even of the sea, around the magnetic pole. | 
Mairan and Dalton believed the aurora borealis to be cosmical, 
and not atmospheric. But Biot, who had an opportunity of ob- 
serving the anrora at the Shetland Isles in 1817, proved it to be 
an atmospheric phenomenon, from finding that it did not partake 
the movement of the stars from west to east, and consequent- 
ly moved with the earth’s rotation. Since then, nearly all ob- 
servers have come to the same conclusion ; and in particular MM. 
Lottin and Bravais, who have observed more than 143 auroras, 
and given detailed descriptions of them. 
It is therefore quite certain that the aurora is not extra-atmos- 
pheric. To the evidence from its appearances, we may also add 
the crackling noise sometimes affirmed to be heard by the inhab- 
itants in the far north, and the sulphurous odor which also has 
been observed. And, in fine, if the phenomenon is wholly beyond 
our planet, why should it be located about the polar regions? 
. de Tessan, in the voyage of the Venus around the world, saw 
@ fine aurora australis, which he describes with care. It was 14° 
in height, and the centre of the are was in the magnetic meridi- 
an. He heard no sounds connected with it, which he attributes 
to its distance: but he mentions that M. Verdier, a French naval 
Officer, on the night of Oct. 13th, 1819, while on the coast of 
New Holland, heard distinctly a kind of crepitation, during a 
brilliant aurora. All the details mentioned by M. de Tessan prove 
the exactness of the observations. 
As concomitant effects of the aurora, we have mentioned the 
crackling sound, and the sulphurous odor. M. Matteucci has also 
observed during the appearance of a late aurora, satisfactory evi- 
ence of positive electricity in the air. But of all the phenomena, 
those which are of most invariable occurrence are the magnetic. 
he magnetic needle undergoes perturbations, either to the west 
Or east, and usually the latter. These disturbances vary in 
this philosopher to tell, while in the basement of the Paris 
Observatory, when there was an aurora in our hemisphere. M. 
. 
