RESEARCHES BASED UPON THE THEORY 



239 



of the total areas of these curves^. Equation (4) shows that the wave- 

 length of the light corresponding to thepointof intersection is independent 

 of the amount or kind of the deficiency in colour sensation of the observer. 



" The curves given in Fig. 68 depend on : 



" (1) The accuracy of Abney's sensation curves. 



" (2) The correctness of Abney's theory that in the case of the 

 ordinary types of total or partial red or green colour blindness the 



120 



no 



100 

 90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



64 62 



7000' 



60 58 



56 54 52 



,1 



6000 



50 48 



I I 



46 

 I 



44 



55|oO 



42 



I 



40 38 



I 



36 



I 



34 



32 30 28 

 I I 



Fig. 68. Luminosity curves of persons having normal and reduced red and green sensa- 

 tions. Abscissae, wave-lengths of the prismatic spectrum of the arc light ; ordinates, 

 arbitrary scale. (Watson.) 



ordinates of one of the sensation curves are all reduced in the same 

 proportion, and 



" (3) The additive property which has been assumed and which 

 involves the corollary that the areas of the luminosity curves obtained 

 by normal and colour-deficient persons are the same. Thus, if it can 

 be shown that the observed luminosity curves of persons who are colour- 

 deficient agree with the calculated curves it is strong evidence in favour 

 of the correctness of the above three assumptions." 



1 The wave-length at which all the curves will intersect depends on the distribution 

 of lit^ht in the spectrum employed in the experiments, i.e. on the source of light. 



