E VAPOR A TION AS CA USE 197 



WELL, then, do I ask you to believe that evapora- i 

 tion from land and water is the sole cause of wind ? 

 Do I affirm that it produces a weight in the atmo 

 sphere, the breaking up of which causes a rush of 

 air ? that at that moment what was previously dense 

 and stationary gets rarefied and strives, as its 

 nature requires, to obtain a wider space ? I do 

 approve of this as sometimes the explanation. But 

 there is a far truer and more potent one, to wit, 

 that the atmosphere by its constitution possesses a 

 native capacity of movement, this power not being 

 derived from an external source, but being like 

 others of its powers inherent. For can you suppose 2 

 that we men have been endued with strength to 

 move about, while the atmosphere has been left 

 sluggish and immovable ? Water, too, has its own 

 motion, even though the winds are at rest ; other 

 wise it could not produce animal life. We see also 

 forms of vegetable life like moss produced by 

 water, and certain kinds of herbage floating on its 

 surface. 



VI 



WELL, then, I take it, in water there resides some 

 vital principle. In water, did I say ? Why, fire, 

 the universal destroyer, has a creative function ; it 

 may not seem a likely thing, but all the same it is 

 but the truth that some animals are generated by 

 fire. The atmosphere, then, possesses some power 

 of- this kind ; and that is why it sometimes grows 

 thick, sometimes expands and throws off impurities, 



