200 COLOR BLINDNESS. 



the perception of complementary colors. He found that colors which 

 we regard as complementary, or such as when mingled together produce 

 white, do not appear as such to those affected' with abnormal vision. 

 They are not however insensible to accidental colors, but the feeling 

 which results from the fatigue of attempting to produce these appears to 

 be more painful in them than in us. 



Various hypotheses have been advanced by different persons for the 

 explanation of color-blindness. Mr. Dalton supposed that his peculiarity 

 of vision, as well as that of those whom he had examined, depended on 

 the fact that the vitreous or principal humour of the eye, in these cases, 

 instead of being colorless and transparent was tinged with a blue. After 

 his death, in obedience to his own instruction, his eyes were examined 

 by his medical attendant, Mr. Ransome, bat the vitreous humour was not 

 found to exhibit any tinge of blue; on the contrary, it was of a pale 

 yellow color. Objects viewed through it were not changed in color as 

 they should have been had the hypothesis been true. Indeed, were the 

 supposition correct, the same effect should be produced b}^ blue specta- 

 cles, which is known not to be the case. 



Stewart, Herschel and others are of the opinion that this malady of 

 vision is attributable to a defect in the sensorium itself, which renders 

 it incapable of appreciating the differences between the rays on which 

 the sensation of color depends. Sir David Brewster conceives that the 

 eye, in the case of color-blindness, is insensible to the colors at one end 

 of the spectrum, just as the ear of certain persons is insensible to sounds 

 at one extremity of the scale of musical notes, while it is perfectly sen- 

 sible to all other sounds. He knows nothing about the sensorium or its 

 connection with, or mode of operation upon, the nerves of sensation ; and 

 from the analogy of sight and hearing, he has no hesitation in predicting 

 that there may be found persons whose color-blindness is confined to 

 one eye, or at least is greater in one eye than in the other. Nor is this, 

 says he, wholly a conjecture from analogy, for my own right eye, though 

 not a better one than the left, which has no defect whatever, is more 

 sensible to red light than the left eye. The case is precisely analogous 

 with respect to his ears, for certain sounds; and no person, it is pre- 

 sumed, will maintain that there is a sensorium for each ear and each eye. 



Whatever may be the cause of the inferiority, there exists a very easy 

 means of rectifying it to a certain extent. This method, first used by Dr. 

 Seebeck, consists in viewing colored objects through colored media. 

 Suppose the medium to be a piece of red glass ; the impression of a red 

 body and of a green one on the eye of a person like Dr. Dalton, would 

 be different, although with the naked eye they would be the same. The 

 red glass would intercept much more of the light of the green object 

 than of the red one, and hence the two would be readily distinguishable 

 by a difference in the intensity of the illumination of the two objects. 

 [Nothing can equal the surprise, says Professor Wartmaun, of a Dalton- 

 ian when the errors which he commits every day in the appreciation of 

 colors are thus disclosed to him. 



