NATURE 



53 



THURSDAY, MARCH 20, 191. 



COLOUR VISION. 



Rescarclics in Colour Vision and the Trichromatic 

 Theory. By Sir William de W. Abney, K.C.B., 

 F.R.S. Pp. xi + 418+5 plates. (London: 

 Longmans, Green and Co., igij-) Price 

 21s. net. 



THERE is certainly no living authority on 

 "colour-vision" more competent to throw 

 light on that intricate and perplexing subject than 

 the author of this work. Sir William Abney has 

 attacked the various problems which present them- 

 selves by his own methods and with the utmost 

 completeness of detail. In almost every con- 

 ceivable way he has tried to correlate the more 

 precise physical facts, elicited by carefully and 

 ingeniously modified experiments, with the vaguer 

 physiological conceptions arrived at from a study of 

 normal and abnormal sensations of colour. The 

 present work embodies and collects into a consecu- 

 tive whole a record of the author's previously pub- 

 lished researches. The book is consequently one 

 which will be regarded as a standard work. It 

 gives the most complete and clear exposition of the 

 trichromatic theory of Young-Helmholtz. It will, 

 we venture to think, be more readily understood 

 than Helmholtz's own latest treatment oi the sub- 

 ject as given in the last edition of his "Physio- 

 logical Optics." 



So far as Sir William Abney 's researches go, it 

 must be admitted that they afford strong evidence 

 of the fitness of the trichromatic theory to explain 

 how normal colour sensations may be evoked by 

 the known physical causes. The difficulty comes 

 in attempting to explain congenital and acquired 

 defects in colour sensation in accordance with that 

 theory. To do so by inferring that there is then 

 a complete absence of stimulability, or a weaken- 

 ing in the stimulability, of one of the three end- 

 organs supposed to correspond to a so-called 

 "fundamental sensation," leads to hypothetical 

 conclusions as to the way in which colours are 

 perceived by the colour-blind. The many interest- 

 ing experiments adduced by the author in support 

 of the idea of altered stimulability of the end- 

 organs in the colour-blind can scarcelv be said to 

 be convincing. It may indeed be asked : Why 

 should abnormal colour "sensation" depend at 

 all upon abnormal "stimulability"? There arc- 

 different stages in the production of colour sensa- 

 tions in response to objective stimuli. These are : 

 the effect of the physical cause on the percipient 

 elements of the retina, the conduction by the optic 

 nerve, and, lastly, the response in the brain-cells. 

 Might not an abnormality in the last stage, the 

 NO. 2264, VOL. 91] 



final "response," be consistent with colour con- 

 fusion complete and incomplete, altogether in- 

 dependent of any abnormality in the colour end- 

 organs of the retina? In cases of acquired colour- 

 blindness there is, in fact, good reason to refer 

 1 he defect both to altered conductivity in the optic 

 nerve-fibres and to changes in the central cells. 



From the way in which colours are matched by 

 the "colour-blind" it is difficult, apart from 

 theory, to believe that the colour-blind spectrum 

 is such as would appear to the normal eye any- 

 thing remotely comparable to that represented for 

 a "red-blind" and a "green-blind" individual 

 respectively in plate i. Even admitting that there 

 is an appreciable difference between the two 

 classes of cases, which are thus classified in ac- 

 cordance with theory, it is almost inconceivable 

 that the spectrum can appear so different in the 

 two cases. 



Some colour-blind people, it is true, are uncon- 

 scious or only vaguely suspicious of their condi- 

 tion. But there are others who are well aware of 

 it. Some are even keenly interested in analysing 

 their colour-impressions and in comparing them 

 with those of normal individuals. The writer of 

 this notice has met with several who have done 

 so. Without exception and without regard as to 

 whether they might be classified as " red colour- 

 blind " or as "green colour-blind," they have 

 arrived at the conclusion that their yellow and blue 

 sensations are not materially different from the 

 normal. Their absolutely dichromatic spectrum 

 consists of a "warm" and a "cold " colour sensa- 

 tion, which, when saturated, as compared with 

 other colours to them, are often described as 

 "vivid" and "pleasurable." 



In a letter received in 1879 from Dr. William 

 Pole, who was "colour-blind" and well known 

 for his own contributions to this subject, he 

 states : — " I am more than ever convinced of the 

 enormous difficulty normal-eyed persons find in 

 understanding what we, the colour-blind, really 

 see." Again, in 1890, referring to Clerk Maxwell, 

 he says : — " He examined me carefully with 

 spectral apparatus, but he spoilt all his results by 

 insisting that my warm colour must be the Young- 

 Helmholtz fundamental 'green,' and as I obstin- 

 ately refused to adhere to what seemed to me a 

 preposterous contradiction of all my experience, 

 he never published his trials. . . . Now the 

 general opinion seems to agree with my own im- 

 pression that it is yellow, i.e. no Young-Helm- 

 holtz fundamental at all." 



Again there is surely no proof that the colour- 

 blind see white otherwise than the normal-eyed. 

 No difference in a white object can be seen as it 

 is passed from the periphery of the field of vision 



