OCULAR SPECTRA. 531 



while the yellow and the blue rays still continue 

 to produce their usual effect ; and these, by com- 

 bining their influence, produce the impression of 

 green. For a similar reason, the spectrum of a 

 green object is red ; the rays of that colour 

 being those which alone retain their power of fully 

 impressing the retina, previously rendered less 

 sensible to the yellow and the blue rays com- 

 posing the green light it had received from the 

 object viewed. 



The judgments we form of the colours of 

 bodies are influenced, in a considerable degree, 

 by the vicinity of other coloured objects, which 

 modify the general sensibility of the retina. 

 When a white or grey object of small dimen- 

 sions, for instance, is viewed on a coloured 

 ground, it generally appears to assume a tint of 

 the colour which is complementary to that of 

 the ground itself.* It is the etiquette among the 

 Chinese, in all their epistles of ceremony, to 

 employ paper of a bright scarlet hue : and I am 

 informed by Sir George Staunton, that for a long 

 time after his arrival in China, the characters 

 written on this kind of paper appeared to him to 

 be green ; and that he was afterwards much sur- 

 prised at discovering that the ink employed was 

 a pure black, without any tinge of colour, and on 

 closer examination he found that the marks were 



* Any two colours which, when combined together, produce 

 white light, are said to be comi^lementary to one another. 



