A HISTORY OF SCIENCE 



all the different substances with which experience 

 makes us familiar, is made up of unit particles which 

 maintain their integrity in whatever combination 

 they may be associated. This implies, obviously, a 

 multitude of primordial particles, each one having an 

 individuality of its own; each one, like the particle of 

 water already cited, uncreated, unchangeable, and 

 indestructible. 



Fortunately, we have the philosopher's own words 

 to guide us as to his speculations here. The frag- 

 ments of his writings that have come down to us 

 (chiefly through the quotations of Simplicius) deal 

 almost exclusively with these ultimate conceptions of 

 his imagination. In ascribing to him, then, this con- 

 ception of diverse, uncreated, primordial elements, 

 which can never be changed, but can only be mixed 

 together to form substances of the material world, 

 we are not reading back post-Daltonian knowledge 

 into the system of Anaxagoras. Here are his words : 

 "The Greeks do not rightly use the terms 'coming 

 into being' and 'perishing.' For nothing comes into 

 being, nor, yet, does anything perish; but there is 

 mixture and separation of things that are. So they 

 would do right in calling ' coming into being ' ' mixture ' 

 and 'perishing' 'separation.' For how could hair 

 come from what is not hair? Or flesh from what is 

 not flesh?" 



Elsewhere he tells us that (at one stage of the world's 

 development) " the dense, the moist, the cold, the dark, 

 collected there where now is earth ; the rare, the warm, 

 the dry, the bright, departed towards the further part 

 of the aether. The earth is condensed out of these 



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