358 On the Meteors of I3th 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- 

 v^dijs 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 parallel 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, thai "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 Shedand 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." 



It 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 



