KNOWLEDGE AND OPINION IN REGARD TO COLOUR-BLINDNESS. 467 



facts, but rather stumbling-blocks in the way. Some of his remarks are quoted in 

 " Data," AB. 



Dr Berry. 



Krenchel's view has been adopted and amplified by Dr G. A. Berry of Edinburgh, 

 who published, in 1879 and 1891, some remarks showing intimate personal acquaintance 

 with both the literature and the facts of the subject. In regard to the facts, his testimony 

 entirely corresponds with those deduced in this paper. In regard to the application of 

 theories, the following extracts will give his chief opinions. 



It must be admitted, I think, that the idea of fundamental colours has rather impeded than 

 advanced our knowledge of the phenomena and nature of colour-blindness. The numerous and 

 laborious examinations that have been made, with the object of detecting and classifying cases of 

 colour-blindness, have been conducted mainly by those who have tried to reconcile the results 

 obtained with one or other of the current hypotheses. 



The author shows why the Hering theory, as a mode of explaining the facts, is much 

 preferable to that of the three fundamental colours ; but he says — 



The question rather which suggests itself is, — Is there any good reason for assuming that there 

 are any fundamental colour-sensations at all ? ... . One can readily understand that the fact 

 that it is possible to obtain all colours from three or more colours variously combined, taken along with 

 the doctrine of specific nerve energies of Johannes Muller, should create a strong leaning towards 

 the fundamental hypotheses. Apart, however, from this, there does not appear to be any reason for 

 making such an assumption ; there is, in fact, no evidence of the existence of primary colours, either 

 in the physical bases or final consciousness of colours; in other words, in all we know anything 

 about. 



I forbear to do more than just indicate Dr Berry's views, hoping he may himself 

 publish, further, his detailed opinions. 



Von Kries. 



This author may be mentioned here as having stated a new theory which endeavoured 

 to unite the chief points of the two rival hypotheses, and which raised a lively discussion. 

 It assumed, as a sine qua, non, yellow and blue for the dichromic colours. 



Bonders, 1879 to 1884. 



I have already had occasion to mention several special observations of this eminent 

 authority, but I have endeavoured to give an account of his more general views in the 

 Philosophical Magazine of November 1892.* From this we may gather the following 

 inferences. 



* In Donders's writings he laid some stress on my case ; and I hope I may be pardoned for quoting the following 

 passage from one of his letters to me, dated 15th March 1881 : — " I was very happy to mention your case as the model 

 case ; I mean, your description as the model description, even for the present time. It is indeed admirable, and I 

 understand now perfectly why it was appreciated so highly by Sir John Herschel." 



