Report of the Committee on Colour- Vision. 349 



patient using the shutters until he is satisfied that he has 

 obtained the correct junction. 



Question — If you had say five points of difference, would they 

 always come exactly in the same place? — Yes; such a case 

 would not see orange as a definite colour. 



Question — Would a patient recognise no orange, supposing a 

 single colour was suitably chosen and distributed over a sensible 

 field, and beginning from the sodium line ? — A 5-unit case usually 

 objects to the term orange ; he would probably call it reddish- 

 yellow. 



I have not come across any 1-unit cases ; that is the 

 only one on the diagram that is not drawn from my own ex- 

 perience. I should explain that the diagrams are all drawn 

 the same lengths, to demonstrate the psychophysical diminution 

 of colour-perception and not the shortening of the spectrum, in 

 which case another effect is produced, viz., the junctions of all 

 colours are altered; a 2-unit, with shortening of the red end 

 of the spectrum, puts the junction of his two colours nearer the 

 blue than a 2-unit with an unshortened spectrum. 



Diagram No. 6 shows a transition from red to violet ; in such 

 cases there is no neutral band in any part of the spectrum. 

 The one colour passes into the other without any definite 

 intermediate point. 



In examining for scientific purposes the spectrum would be the 

 first test, afterwards wools, pigments, or lights, in accordance 

 with the spectrum examination. 



Question — Would it not be easy to coach a person for this ? — 

 No, because he would never be able to hit off the exact junctions 

 of the colours. 



Question — Which class of the colour-blind would you consider 

 as representing dangerous cases for signalling purposes ? — I. 

 Those who possess a psychophysical colour-perception with 

 three or less units. II. Those who, whilst being able to perceive 

 a greater number of units than three, have the red end of the 

 spectrum shortened to a degree incompatible with their recogni- 

 tion of a red light at a distance of two miles. III. Those who 

 are affected with central scotoma for red or green. The 3-unit 

 would be unsafe, for though he would always recognise red and 

 green, even to the lowest degree of luminosity, he would confuse 

 yellows, especially dark yellows, with reds and greens, and 

 generally call them reddish-greens ; in fact, yellow has been 

 described by such a patient as being of the same colour as a red 

 clover field in full blossom. The 2-unit cases and below are 

 absolutely dangerous. The 5-unit and 4-unit are safe. 



[The Witness here handed in his Pocket Test, and explained 

 its use, Captain Abney being asked to pick out all the shades 

 of orange.] 



Question— Would you describe a person as not having distinct 

 orange perception, who could not mark out the definite regions 

 on the spectrum bounded on one side by yellow and on the 



