RESEARCHES BASED UPON THE THEORY 



229 



These results afford an explanation of the change in hue which 

 occurs when white light is added to the spectral colours. When this is 

 done the red becomes pinker, the scarlet orange, the orange yellow, 

 the yellow green. At SSN 48-7 (577-2 ;u//,) in the yellowish-green, no 

 change in hue occurs. Beyond this point, the green becomes yellowish, 

 the blue shows little change, and the violet becomes nearly salmon-pink. 

 Now SSN 48-7 is the point where the red and green sensation-values 

 are equal to their sensation-values in the white light. It therefore 

 seemed probable that the change in hue in lights of medium and long 

 wave-length was due to the addition of the red arid green sensation- 

 values of the white light, the value of the blue sensation being so small 



X 



1L 



00 



70 



60 



40 



30 



10 



10 



IS 



20 25 50 35 



55 



60 



65 



.Fig. 64. Abney's R, G, and B equal-area sensation curves. The sums of equal ordinates 

 of the three curves at any point represent the sensation of the unanalysed white 

 light. (Abney.) 



as to be negligible. This conjecture was fully borne out by experiment, 

 the matches being identical with those calculated, within the range of 

 experimental error. SSN 48-7 is easily found, since it is the comple- 

 mentary colour of the pure blue of the spectrum. 



In the colour triangle (Fig. 9) a mixture of white with any spectral 

 colour is represented by a point (a) on the line joining W with the 

 given point on the curve, the position of a being determined by the 

 relative amounts of the colour and white. The change in colour due 

 to the admixture with white is found by joining the points B and a and 

 producing Ba to meet the curve. The mixture will match the spectral 



