358 On the Meteors of 13th November. 
its centre of gravity, in such a manner as to admit of its taking its 
position freely, in obedience to the resultant of the magnetic forces 
exerted upon it by the terrestrial globe.” Again he says, “ But 
from whatever situation these jets (of light) are observed, they al- 
ways seem to describe arcs of great circles on the celestial dome, 
and to converge towards that part of the heavens to which the nee- 
dle points when perfectly free; whence we conclude that they are 
in reality cylindrical, and patéillel to the direction of the needle. But 
each jet, moreover, presents great varieties of size and lustre, from 
which we are led to believe that they are, in fact, composed of a 
great number of shorter cylinders independent of each other, and in 
part piled one above another. As these indications. are noticed 
throughout the whole region of space where the meteor is visible, 
we may conclude with geometrical rigor, that it consists of a forest 
of luminous columns, all parallel to the resultant of the magnetic for- 
ces, and of course for short distances, parallel to each other, and sus- 
pended at nearly equal heights on different sides of the horizon.” 
- Biot seems to consider it an established fact, that “the phenomenon 
of the aurora borealis takes place in our atmosphere ;” although for 
the most part it is more elevated than the clouds. He speaks also 
of a certain arc of light belonging to an aurora borealis which he ob- 
served in the Shetland Islands, and which had a progressive motion, 
and that almost insensible, towards the south-east, whither it seemed 
to be carried by a gentle north-western breeze that was then blowing.” 
‘At will still farther illustrate the resemblance between the aurora 
borealis and the phenomena under consideration, to make one or two 
more quotations from Biot, which exhibit the leading principles of 
the hypothesis proposed by him for accounting for the former on phi- 
losophical principles. For whether it be correct or not, its principal 
conditions correspond remarkably with observation... It was origin- 
ally proposed by the English philosopher Dalton. 
“ We may consider this meteor (aurora borealis,”) says Biot, ‘as 
consisting of real clouds, proceeding usually from the north, and 
composed of some very light substances, or at least of some substance 
so finely pulverized as to be capable of floating a long time in the atmos- 
phere, endued with the property of occasionally becoming luminous ; 
and especially (which is very important) sensible to terrestrial mag- 
netism, and spontaneously arranging themselves in columns which 
turn towards the earth, as real magnetic needles would do. But of 
all terrestrial substances, only the metals, so far as we know, are in 
