196 PHYSICAL SCIENCE BK. v 



then a breeze springs up ; the particles have got 

 more room now, and the thickly packed crowd of 

 them is broken up. 



IV 



1 BUT how, you will say, are winds then formed, for 

 you won t deny that they are formed ? Not in any 

 single way, I reply. Sometimes the earth herself 

 emits a great quantity of air, which she breathes out 

 of her hidden recesses. At other times a great 

 and long -continued evaporation drives the emis 

 sions from the depths up on high, where the change 

 which the mixed breath undergoes issues in wind. 

 A suggestion has been made which I cannot make 

 up my mind to believe, and yet I cannot pass over 

 without mention. In our bodies food produces 

 flatulence,, the emission of which causes great 

 offence to one s nasal susceptibilities ; sometimes a 

 report accompanies the relief of the stomach, some- 



2 times there is a more polite smothering of it. In 

 like manner it is supposed the great frame of things 

 when assimilating its nourishment emits air. It is 

 a lucky thing for us that nature s digestion is good, 

 else we might apprehend some less agreeable con 

 sequences. Is it not, then, nearer the truth to say 

 that numerous particles are constantly borne up 

 from every part of the world ; and when they are 

 accumulated and subsequently begin to be rarefied 

 by the sun, wind starts up ? It is a general prin 

 ciple that anything contained in a narrow space 

 when it expands tries to get more room. 



