Miscellanies. 153 



3. On shooting stars. — Prof. Silliaian. — Dear Sir — The trans- 

 parent vapor, which was described in the last number of your Jour^ 

 nal as the basis of the aurora borealis, unquestionably exists in va^ 

 rious tracts of the atmosphere, independently of latitude. It possi- 

 bly gathers in larger quantities towards the pole, but the principal 

 reason why it appears more luminous and extensive as we recede 

 from the equator, is its relative position to the solar light. 



While examining the causes of the aurora borealis, I became con- 

 vinced, that shooting or falling stones are derived from the same ori- 

 gin. A flake of the vapor, which forms the basis of the aurora, by 

 reflecting the light of a star, vertical or nearly so to its apparent 

 place, becomes an image of the star, and while it remains quiet is 

 not distinguishable from others in the hemisphere. When an aerial 

 current crosses it, it is immediately removed from tlie direct rays of 

 the particular star whose image it reflected, and disappears, or in 

 common phrase, goes out, in the same way that the streams and 

 flashes of the aurora vanish by changing their relative positions to 

 the source of illumination. 



Falling stars descend diagonally, unlike the aurora of these lati- 

 tudes, which undulates, or shoots upwards when it moves at all; but 

 in the northern regions its motions are very often lateral, and in some 

 instances it falls perpendicularly. The levity of the vapor in the 

 aurora is one of its characteristics, and the increase of its specific 

 gravity so far as to cause its descent, is an exception to its prevailing 

 condition; in the star, however, as in the descending aurora, the va- 

 por becomes surcharged with moisture, or its elements form some 

 new combination sufficient to overcome in part, its buoyancy, and 

 the resistance of the atmosphere. And this is consistent with the 

 laws which regulate the clouds, which at one time float in the air, 

 and at another descend. We cannot follow the erratic movements 

 of this vapor after it leaves the position where the lines of light dis- 

 close its existence, because it is invisible except when locally lumin- 

 ous in the night; and whether it is dispersed in the expanse of the 

 heavens after it disappears from our sight, or whether it combines 

 with the clouds, or becomes itself a cloud, or whether by parting 

 with its superfluous moisture it retains its gaseous and invisible iden- 

 tity is unknown. 



Shooting stars increase in number and frequency towards the equa- 

 tor, as the aurora increases towards the pole. M. Humboldt describes 

 them as being innumerable over the seas between Maderia and Af- 



Vol. XX.—No. 1. 20 



