GENERATION OF ANIMALS, V. i. 



Empedocles' statement is incorrect. And besides, 

 another method is open for explaining the cause of 

 the colours. But assuming the correctness of what 

 was said earlier in the treatise Of the Senses, and 

 before that in the treatise Of the Saul,'^ i.e., that the 

 sense-organ of sight is composed of water, and also 

 the correctness of the cause there assigned for its 

 being composed of water and not of air or of fire, 

 then we should take it that the following is the cause 

 responsible for the phenomena just described. Some 

 eyes contain too much fluid, some too little, to suit 

 the right movement,^ others contain just the right 

 amount ; and so those eyes which contain a large 

 amount of fluid are dark, because large volumes of 

 fluid are not transparent ; those which contain a 

 small amount are blue. (Sea-water is a parallel 

 instance. Transparent sea-water appears blue, the 

 less transparent appears paUid, and water so deep 

 that its depth is undetermined is dark or dark blue.) 

 Eyes intermediate between these two extremes differ 

 merely by " the more and less." " 



We ought to suppose that to the same cause is due Keenness 

 the fact that blue eyes are not keen-sighted during °' ^'*'"" 

 the daytime nor dark eyes at night. Blue eyes, on 

 account of the small amount of fluid in them, are 

 unduly set in movement by the light and by \-isible 

 objects, in respect both of fluidity and of trans- 

 parency. It is, however, the setting in movement of 

 this part in respect of its transparency that consti- 

 tutes sight, not in respect of its fluidity.'* Dark eyes 

 are set in movement less owing to the amount of 



■^ See Introd. § 70. 



■* For the details of Aristotle's theory of vision, see App. B 

 §§ 26 ff. 



497 



