1912.] Trichromic Vision and Anomalous Trichromatism. 165 



anomalous trichromat is a person who is supposed to have three fundamental 

 sensations but they have not the same proportions as in the normal-sighted. 

 Those are designated anomalous trichromats who, when making the equation 

 X 670 + A. 535 = X589, use proportions of red and green different from the 

 normal. At the same time the subjects of this abnormality object to the 

 normal equation. Those who put too much red in the mixed colour are 

 called red-anomalies and those who put too much green in the mixed colour 

 green-anomalies. 



• Anomalous trichromatism was discovered by Lord Eayleigh (6), who stated 

 that the colour vision is defective only in the sense that it differs from that 

 of the majority. In 1904 Guttmann (8) stated that the anomalous trichromats 

 were colour weak and described a number of symptoms similar to those given 

 by me as associated with trichromic vision. 



I then examined a number of persons with Kayleigh's apparatus (14) and 

 found that many colour-blind persons, both dichromic and trichromic, can 

 make a match which agrees in every particular with that of a normal sighted 

 person. 



I could find no evidence that colour weakness was necessarily associated 

 with anomalous trichromatism. I examined 15 students from Newnham 

 College on the same afternoon, the conditions being precisely the same for 

 each. There was considerable variation in the observations and those who 

 made an anomalous equation in every case strongly objected to the normal 

 match. I could find no evidence of colour-blindness in any of those 

 examined. All saw yellow in the spectrum. Of the 15 examined, five made 

 the normal match exactly and one required slightly more green, the others 

 more red in proportions varying in different cases ; there was considerable 

 difference between the two extremes, one requiring nearly twice as much red 

 as the other in the mixed colour. 



This year Lord Eayleigh kindly lent me his colour-mixing apparatus and I 

 examined 100 women students. 25 belonging to the London County Council 

 training college and 75 to University College. The last 75 were examined in 

 precisely similar conditions. The illumination was incandescent electric light 

 and the equation did not vary from day to day. All were examined with 

 Lord Kayleigh's colour-mixing apparatus ; 51 were examined by some kind 

 of test for colour-blindness, and 36 of these were examined by my lantern. 

 I have designated as " anomalies " those who, on an average of a number of 

 observations, had a deviation of more than one whole division from the normal 

 and did not agree with the normal equation. The colour-mixing instrument 

 of Eayleigh was arranged so that corresponded to full red and 25 to full 

 green. Then by the laws of double refraction the exact proportions of red 



