1897.] on Some Curiosities of Vision. 365 



We have then to account, if possible, for the two facts that in the 

 formation of these transient borders the red sensation occurs in a 

 portion of the retina which has not been exposed to the direct action 

 of light, while the blue occurs in a portion which is exposed to un- 

 changed illumination. Accepting the Young-Helmholtz theory of 

 colour vision, the effects must, I think, be attributed to a sympathetic 

 affection of the red nerve fibres. When the various nerve fibres 

 occupying a limited portion of the retina are suddenly stimulated by 

 white or yellow light of moderate intensity, the immediately surround- 

 ing red nerve fibres are for a short period excited sympathetically, 

 while the violet and green fibres are not so excited, or in a much less 

 degree. And again, when light is suddenly cut off from a patch in a 

 bright field, there occurs an insensitive reaction in the red fibres just 

 outside the darkened patch, in virtue of which they cease for a 

 moment to respond to the luminous stimulus: the green and violet 

 fibres by continuing to respond uninterruptedly, give rise to the 

 sensation of a blue border. 



Whether or not the hypothesis which I have suggested is correct 

 in all its details, it is, I think, sufficiently obvious that the red and 

 blue colours of Benham's top are due to exactly the same causes as 

 the colours observed in my own experiments, for the essential condi- 

 tions are the same in both cases. 



I have mentioned only a few among many curious phenomena 

 which have presented themselves in the course of my investigation. 

 It is not improbable that a careful study of the subjective effects 

 produced by intermittent illumination would lead to results tending 

 to clear up many doubtful points in the theory of colour vision. 



[S. B.] 



