1 | L > ANM AL OF SCIKNTIFIC DISCOVKKY. 



All visible objects ei her reflect th; 1 same kind of li^ht as that which falls 

 on them. ;il>-.r1.iii- I"""' and reflecting the rest, or else they absorb more of 

 i,,iiie color-rays than others, and reflecl only a negative tint, made up of a 

 mixture <>f all the color-rays not absorbed. To a color-blind person, the 

 mixed li^ht, as it proceeds from the sun, is probably white, as seen by those 

 havinir perfect vision; for, as we have explained already, positive blue and 

 yellow (the color-rays when red is excluded) do not make green, and the 

 absence of the red ray is likely to produce only a slight darkening effect. 

 So far, then, there is no difference. But how must it be with regard to color? 



Hearing in mind what has been said above, it is evident that in withdrawing 

 the red rays from the spectrum, we affect all the colors. The orange is no 

 longer red and yellow, but darkened yellow; the yellow is purer, the green is 

 quite distinct, the bine purer, and the indigo and violet no longer red and 

 blue, but blue mingled with more or less of darkness, the violet being the 

 darkest, as containing least blue in proportion to red, while the red part 

 itself, though not seen as a color, is not absolutely black, inasmuch as its part 

 of the spectrum is faintly colored with the few mixed rays of blue and yellow 

 an. 1 white that escape from their proper place. The red then ought to be 

 seen as a gray neutral tint, the orange a dingy yellow, the indigo a dirty 

 indigo, and the violet a sickly, disagreeable tint of pale blue, darkened con- 

 siderably with black and gray. 



Next, let us take the case of an intelligent person affected with color-blind- 

 ness, but who is not yet aware of the fact. He has been taught from child- 

 hood that certain shades, some darker and some brighter, but all of neutral 

 tint, and not really presenting to him color at all, are to be called by various 

 names, scarlet, crimson, pale red, dark red, bright red, dark green, dark 

 purple, brown, and others. With all these lie can only associate an idea of 

 gray; nor can he possibly know that any one else sees more than he does. 

 Having been taught the names they are called by, he remembers the names, 

 with more or less accuracy, and thus passes muster. There is a real differ- 

 ence of tint, because each of these colors consists of more or less blue, 

 yellow, and white, mixed with the red; and our friend is enabled to recog- 

 nize and name them, more or less correctly, according to his aeuteness of 

 perception and accuracy of memory. 



If we desire to experiment on such a person, we must ask no names what- 

 ever, but simply place before him a number of similar objects differently 

 colored. Taking, for example, skeins of colored wools, let us select a com- 

 plete series of shades of tint, from red, through yellow and green to violet, 

 and request him to arrange them as Avell as he is able, placing the darkest 

 shades first, and putting those tints together that are most like each other. 

 It is curious then to watch the progress of the arrangement. In a case 

 lately tried by the writer of this article, the color-blind person first threw 

 a-idc at once a particular shade of pale green as undoubted white, and then 

 several dark blues, dark reds, dark greens, and browns, were put together 

 a~ black. The yellows and pure blues were placed correctly, as far as name 

 was concerned, by arranging several shades in order of brightness, but 

 the order was very different from that which another person would have 

 The greens were grouped, some with yellows, and some with blues. 



I h.- colors in this experiment were all negative and impure; but we may 



) obtain something like the same result with positive color, transmitted 



.1 of polarized light through plates of mica. In a case of this kind 



ascribed by Sir J. Ilerschel, the only colors seen were blue and yellow, 



