On the Origin of Meteoric Stones. T7 



else than aqueous vapour. Even the odour, which most orga- 

 nic exhalations emit, sufficiently shews that they are not pure 

 aqueous vapour. When we reflect, however, that all changes 

 of organic substances are not sudden transformations, but proceed 

 imperceptibly by an infinite variety of steps, perhaps the most 

 just representation would be, that each organic exhalation is a 

 fluid vapour of a peculiar kind, the basis and chief ponderable 

 parts of which consist of aqueous vapour, with which, however, 

 other organic matter exists in intimate union, bearing the charac- 

 ter, not so much of a chemical as organic combination. Now, 

 although the existence of such be not indicated by any chemical 

 tests, they render themselves nevertheless perceptible in daily 

 experience. As a particular instance, all rain and snow water 

 is manifestly impregnated with organic matter. When careful- 

 ly filtrated, the paper must frequently be changed from the 

 pores becoming obstructed, — a proof that some slimy matter is 

 contained in it, and, when frozen in a strong cold, there general- 

 ly remains in the centre of the mass a small quantity of a yellow 

 viscous fluid uncongealed. The strongest proof of all, however, 

 appears to me to be the fertilizing power of rain. Such exhala- 

 tions frequently accumulate so as to become a palpable fog, and 

 the odour which this frequently has, shews plainly enough that 

 it is not simply aqueous vapour. It may be allowed us to con- 

 jecture, that it is the composition of such organic exhalations 

 which makes the inhalation of the air beneficial or hurtful to 

 health, and productive of prevailing distempers. 



But there must necessarily be in the atmosphere, not merely 

 exhalations of organic origin, but also many inorganic matters, 

 whose existence is not even conjectured, because either from their 

 subtilty or small quantity they escape all chemical tests. The 

 following considerations seem to place this in an interesting point 

 of view. 



We are acquainted witb two- diflP'erent methods of producing 

 a change on bodies, — heat, and chemical mixture. There are 

 many solids that oppose an obstinate resistance to the former ; 

 but certainly there are none which must not give way to the 

 second, nor can any be named which in some one chemical 

 mixture shall not assume either the fluid or the aerial form. 

 There is nothing which endures the action of fire so well as pure 



