108 Meteors. 



in this little elementary work. As eva- 

 poration, however, seems particularly to 

 be concerned in the production of the me- 

 teors, we shall take a view of that opera- 

 tion of nature, the extent of which we 

 have noticed in the preceding chapter. 

 This process may be reckoned in a par- 

 ticular manner the effect of heat. Upon 

 this principle vapour is shown to be a 

 compound of water and fire ; and such it 

 is supposed to be by philosophers of the 

 highest rank. In considering this opera- 

 tion, however, as carried on by nature, 

 we shall soon find, that it proceeds in a 

 manner very different from what takes 

 place in our chemical operations. In the 

 latter, evaporation is merely the effect of 

 heat; and the process cannot go on with- 

 out a considerable degree of it. In the 

 natural way, on the contrary, the process 

 goes on under almost every degree of cold 

 we know ; the vapours ascend to a height 

 which has never yet been determined ; 

 and, from the extreme cold which they 

 sustain, show evidently that they are con- 

 nected with our atmosphere by mrans of 

 some other agent besides heat. From the 

 continual ascent of vapour indeed, if the 



