insensibility to the imjn'essions of certain colours. 139 



As I do not understand how this negative support can be 

 affected by the great number of varieties of colour blindness, 

 I cannot re})ly to Prof. Wartmann's statement, but I shall en- 

 deavour to explain my own view of the matter. According 

 to the doctrine of the triple spectrum, the red space consists of 

 red, yellow and blue light, the red predominating and the blue 

 being extremely feeble. Now the late Mr. Troughton, whose 

 colour blindness was examined by Sir John Herschel and my- 

 self, on separate occasions, saw this red space, yellow. Hence, 

 according to my views, he saw a space containing mvich. yellow 

 and little blue, the 7-ed light being as it were absorbed, in conse- 

 quence of the nervous membrane being insensible to its action. 

 If this be the case, there must have been a diminution of light 

 in the red space seen by Mr. Troughton, and I am persuaded, 

 from the experiments* I made upon his eyes, that this was the 

 case ; but whether it was to the extent of the total defalcation 

 of the red rays I will not venture to assert. But it is not ne- 

 cessary that it should be so ; the defective perception of red 

 light may be accompanied with a more acute perxeption of the 

 other colours, in a manner analogous to what takes place in the 

 chemical spectrum, where the removal of the red rays produces 

 an increased action of the rays which are left; the luminous 

 rays may act upon the nervous membrane with negative and 

 positive influences ; and this view of the subject is greatly fa- 

 voured by the results which I published in 1832, relative to 

 the increase in the intensity of light by physiological actionf. 

 In many cases too of imperfect vision, I have long been of 

 opinion that the retina receives a more powerful luminous im- 

 pression from yellow light than from the pure white light, of 

 which this yellow forms but a part ; and I have therefore re- 

 commended the use of yellow glasses as best fitted to excite 

 a torpid retina. 



But whether these views be sound or not, I cannot conceive 

 how an infinite variety, even of cases of colour blindness, can 

 have any bearing whatever on the doctrine of the triple spec- 

 trum. In order to be a case of colour blindness, one or more 

 tints must be wanting or unseen, and there is no tint what- 

 ever which cannot be produced by the supposed absorption of 

 individual rays of the compound spectrum. 



We regret much that Prof. Wartmann has continued the 

 offensive name of Daltonism in his memoir on colour blind- 

 ness, especially as he agrees with Dr. Whewell in opinion, that 

 no person wishes to be immortalized by his imperfections. 

 We cannot but regard it as degrading to the venerable name 



* He confounded with green leaves red petals, which were far more lu- 

 minous than the leaves, 

 t Lond. and Edinb. Phil. Mag., vol. i. p. 173, 1832; vol. iv. p. 241, 1834. 



