THE FABRIC OF MATTER 9 



are always returning to it." This is surely acute, 

 subtle, and suggestive. 



Let us hear how Diogenes makes out his case 

 for air. 



" My view," he says, " is, to sum it up briefly, 

 that all things are differentiations of the same thing, 

 and are the same thing. And this is obvious, for 

 if the things which are now in the world — earth, 

 and water, and air, and fire, and the other things 

 which we see existing in this world — if any of these 

 things, I say, were different from any other, differ- 

 ent, that is, by having a substance peculiar to itself, 

 and if it were not the same thing that is often 

 changed and differentiated, then things could not 

 in any way mix with one another, nor could they 

 do one another good or harm. Neither could a 

 plant grow out of the earth, nor any plant or 

 animal come into being, unless things were com- 

 posed in such a way as to be the same. But all 

 these things arise from the same thing ; they are 

 differentiated, and take different forms at different 

 times, and return again to the same thing. But 

 this, too, appears to me to be obvious, that it is 

 both great, and mighty, and eternal, and undying, 

 and of great knowledge. For it would not be 

 possible for it to be divided as it is without in- 

 telligence, so as to keep the measures of all things, 

 of winter and summer, and day and night, of rains, 



