STUDIES IN SPECIAL SENSE PHYSIOLOGY 385 



Thus the sun shining through a fog is red, the feebler lamp ray 

 sometimes appears purple. 



In this connection, Aristotle refers to positive and negative 

 after-images. After looking at the sun and closing the eyes we see 

 the object at first of the same colour as before ; this changes to 

 crimson, then to purple, then black, and finally vanishes. This 

 illustrates the genesis of colours from the blending of black and 

 white. Simultaneous contrast is explained along these lines the 

 brightest rainbow appears in the darkest cloud, white wool has its 

 colour intensified when placed next black wool, &c. 



Aristotle rejected altogether the theory of emanations and 

 pores (Empedocles, &c.), while his conception of a vibratile move- 

 ment imparted to the actualised " diaphanous " may, perhaps, be 

 regarded as a partial anticipation of the modern doctrine of a 

 luminiferous ether. We cannot, however, push this comparison 

 very far, since he maintained, in opposition to Empedocles, that 

 light does not travel. It is not, I think, necessary to summarise 

 the Aristotelian teaching in so far as it deals with structure, 

 since, for the reasons already mentioned, it is of purely anti- 

 quarian interest. The curious reader will find ample material, if 

 lie desires to pursue the matter further, in the works cited by 

 Professor Beare. 



We can now consider for a moment the relations subsisting 

 between Greek doctrines and the modern development of visual 

 physiology and psychology. 



The reader will have noticed already that the opinions I have 

 summarised are concerned both with the theory of visual sensations 

 proper, and the nature and functions of the eye itself. Or, roughly, 

 they are, in the modern terminology, partly psycho-physiological 

 and partly anatomical or histological. 



Subsequent progress in these two departments has not been 

 equal. Thus, while we are less ignorant than the Greeks regarding 

 the structure of the eye and have framed formula more accurately 

 descriptive of physical concepts, the development of physiological 

 psychology has not been so great and is largely the work of recent 

 times. The result has been that our present way of looking at and 

 thinking about the structure of the eye and the physical changes 

 associated with colour vision owes comparatively little to the 

 Greeks, and may be said to date from the epoch-making discoveries 

 of Newton. Theories of colour sensations, on the other hand, 



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