152 REVIEWS — RESEARCHES ON COLOUR-BLINDNESS. 



not recall ; and if they have known them, they can, as the seeing do in dreams, re- 

 call them, it may be dimly, but yet on the whole as they are. But for Mr. B., the 

 colours which he saw, are not only efi'aced, but are replaced by tints the most un- 

 like those which they once bore. 



It is only due to Dr. Wilson that we should distinctly state 

 some of the important facts and laws of which he may claim in this 

 work to he the discoverer. These are — 



1. That the colour bed produces to some eyes the sensation of pos. 

 itive blackness ; a most valuable fact which goes a long way to 

 explain some of the difficulties of this subject. 



2. That the colour-blind have a perception of intensity more acute 

 and also discordant with that of ordinary vision. 



3. That the sensitiveness to colour of a colour-blind eye, suffers 

 sooner from the withdrawal of light, (or by deepening of shades) 

 than that of a normal eye, and at the same time that the percep- 

 tion of form and outline is more persistent to the abnormal. 



4. That there is a ' chromic myopia,' or short-sightedness to colour, 

 not accompanied by a corresponding short-sightedness to form 

 or outline, so that, whereas to the ordinary short-sighted eye, 



form disappears before colour ; in this myopia the colour becomes 

 undistinguishable while the outline still remains distinct. 



"We cannot readily present in a separate form other valuable facts or 

 suggestions for which Science owes much to our author, but we would 

 particularly refer to the observations on the effect of artificial light in 

 influencing the perceptions of the colour-blind ; to those made with 

 the colours of the spectrum, and to the practical method of relieving 

 to some degree this natural defect by artificial means. What we 

 have specified above will undoubtedly throw fresh lustre on an 

 already brilliant reputation, and the more so when we consider the 

 difficulties which meet us on the threshold of such an investigation 

 as this. Our nomenclature of colour is altogether vague and indefinite ; 

 the term ' red' for instance includes an infinite variety of tints differ- 

 ing from each other both in hue and intensity, and there are (or at 

 least there were) no ready means of identify iug any precise tint 

 offered : again most of the experiments must be made by means of 

 pigments or coloured skeins of worsted or silk, and these are evidently 

 inferior to, and indeed may give totally different results from those 

 made with the corresponding homogeneous tints of the solar spectrum ; 

 so also, the nature of the light by which coloured objects are seen 

 powerfully affects the impression of tint conveyed to the eye : but 

 most of all, the difficulty lies in the want of a common language be- 



