80 On the Origin of Meteoric Stones. 



quicksilver. That it evaporates at the ordinary temperature of 

 the atmosphere, every one may convince himself by daily obser- 

 vation of the Toricellian vacuum. But how inconceivably mi- 

 nute must this vapour be, since in an open vessel filled with 

 quicksilver, after ^years, scarcely the slightest diminution of 

 weight can be perceived ! 



If a vapour be, however, perhaps several thousand times light- 

 er than the atmosphere, it must ascend with the rapidity of light- 

 ning immediately on being disengaged. Should such a vapour 

 have only a slight affinity to any of the component parts of at- 

 mospheric air, it will either not commingle at all, or very sparing- 

 ly with it, but continue to ascend till it reach a stratum of air of 

 equal rarity with itself. These vapours would therefore collect in 

 the upper regions of the atmosphere, and rest upon the inferior 

 portions, which they would thus leave comparatively pure. 

 Something similar may be seen in fluids having little affinity to 

 each other, such as water and oils, or water and ether, where 

 the lighter separates of itself from the heavier fluid, and rests 

 above it. All known kinds of air unite, indeed, to form a ho- 

 mogeneous mixture ; at the same time these mixtures take place 

 more rapidly with some than with others, and with heavy car- 

 bonic acid gas so slowly, that it remains in a stratum under the 

 atmospheric air, and, if not disturbed, is very gradually dif- 

 fused through it. 



What becomes, however, of these vapours and gases which, 

 in the lapse of ages, must have been immensely augmented, un- 

 less Nature have the means of again disencumbering the atmo- 

 sphere ? Where the accidental mixtures, whose existence is as- 

 certained, are reserved, may be shewn with perfect certainty in 

 some, or conjectured with probability in others. Aqueous va- 

 pour returns either in the form of rain or snow. It is not so 

 evident where the carbonic, sulphuric acid, and hydrogen gases, 

 and organic exhalations, remain, which daily, in large quantity, 

 pass into the atmosphere. But it cannot be doubted that Na- 

 ture applies these to the support of organic life, since it is an es- 

 tablished fact that plants and animals receive part of their nou- 

 rishment from the air. It has also been remarked above, that 

 rains contain organic matter. But what now becomes of the ex- 

 halations from metals, earths, stones, and all solid bodies, which 



