CHAP. HI.] SIGHT. 1247 



The three several methods lead to three different results, the 

 one teaches that blue, the other that red or yellow, and the third 

 that green is the colour to which the eye is most sensitive. It 

 would be hazardous to found important conclusions on any of 

 them. 



There are several other facts of considerable importance 

 bearing on the theory of colour vision, but it will be best to 

 consider these in connection with certain modifications of visual 

 sensations with which we shall have presently to deal. Mean- 

 while having acquired some general notions of visual sensations, 

 we may turn from the study of the little we know concerning the 

 way in which these sensations originate through retinal changes, 

 to the study of the way in which light falling on the retina gives 

 rise to visual impulses. 



