Report of the Committee on Colour- Vis ion. 377 



and then restore the whole to the pile, except the sample-skein. 

 As it would require too much time to examine every individual 

 in this way, it is advisable, when examining large numbers, to 

 instruct them all at once, and to ask them to attentively observe 

 the examination of those preceding them, so as to become 

 more familiar themselves with the process. This saves time 

 and there is no loss of security, for no one with a defective 

 chromatic sense will be able to find the correct skeins in the 

 pile the more easily from having a moment before seen others 

 looking for and arranging them. He will make the same 

 characteristic mistakes ; but the normal observer, on the other 

 hand, will generally accomplish his task much better and more 

 quickly after having seen how it has to be done. 



" The coloured plate {see Plate II) is for the purpose of assisting 

 the examiner in the choice of his colours, and to help him to 

 decide the character of the colour-blindness from the mistakes 

 made. The colours in the plates are of two characters : — 



" 1st. The colours for samples (test-colours); that is, those which 

 the examiner presents to the persons examined ; and 



• k 2nd. The * confusion colours;' 1 that is to say, those which 

 the colour-blind will select as matches with the sample. 



" The first are shown on the plate as horizontal bands, and are 

 distinguished by Roman numerals ; the second as vertical bands, 

 under the test-colours, and are distinguished by Arabic figures. 



" The coloured table is not intended to be used as a test ; it is 

 simply to assist the examiner in his choice of correct test-colours, 

 and to help him to diagnose the special form of colour-blindness. 



" As to the similarity between the confusion-colours of the 

 plate, and the wools which the colour-blind take from the 

 heap, reliance must be placed simply on the hue, and not on 

 their brightness or degree of colour saturation. In all cases 

 where we have to vary from this rule we must hold to the 

 relative rather than the absolute saturation. The confusion- 

 colours shown in the plate are only to illustrate the mistakes 

 which the colour-blind will make, and for this purpose they serve 

 perfectly. Having made this explanation, we can pass directly 

 to the test itself. The following are the directions for conduct- 

 ing it, and for making a diagnosis from, the results : — 



" Test I. — The green test-skein is presented. This sample 

 should be the palest shade (the lightest) of very pure green, 

 which is neither a yellow-green nor a blue-green to the normal 

 eye, but fairly intermediate between the two, or at least not 

 verging upon yellowish-green. 



" Rule. — The examination must continue until the examinee 

 has placed near the test-skein all the other skeins of the same 

 colour, or else, with these or separately, one or more skeins of 

 the class of ' confusion colours' (1-5), or until he has sufficiently 

 proved by his manner that he can easily and unerringly dis- 

 tinguish the confusion colours, or given unmistakable proof of- a 

 difficulty in accomplishing it. 



2 e 2 



