EESEARCHES BASED UPON THE THEORY 



221 



from the same source of light. From the slit-widths he thus obtained 

 a standard equation : 



18-672 + 314 + 30-5 5= W. 



He then obtained 14 other equations for W , in each case mixing three 

 lights from different parts of the spectrum in suitable proportions. By 

 eliminating W from each of these equations he obtained the sensation- 

 values of 14 positions in the spectrum in terms of the sensation-values 

 of the three standard colours, R, G, B. Fig. 58 shows the curves plotted 

 from these values. It will be noticed that the R and B curves pass 

 below the base line. His standard colours were therefore not chosen 

 so as to eliminate negative values. 



Red,. 



Fig. 58. Clerk-Maxwell's sensation curves. The dotted line is the algebraical sum of 

 the ordinates at each point ; it is not a true luminosity curve. Abscissae, wave- 

 lengths of the prismatic spectrum of sunlight ; ordinates, arbitrary scale. (Clerk- 

 Maxwell.) 



Papers followed by J. J. Miiller 1 , Preyer 2 and Bonders 3 , but no 

 other researches on the three " sensation curves " were made until 

 Konig embarked upon his observations in 1883, continuing them until 

 his death in 1901. Almost simultaneously, Abney commenced the work 

 which he has recorded in a series of papers, culminating in his Researches 

 in Colour Vision (London, 1913), and which is happily still in progress. 

 Certain points on the sensation curves have also been worked out inde- 

 pendently by F. Exner 4 . 



1 Arch.f. Ophth. xv. 2, 208, 1869. 2 Arch.f. d. ges. Physiol. i. 299, 1869. 



3 Arch. f. Ophth. xxin. 4 : 282, 1877 ; xxvn. 1. 155, 1881 ; xxx. 1, 15, 1884 ; 

 OnderzoeJc. i. Lab. Utrecht. 1882. 



4 Sitz. d. Wiener Akad. cxi. i ; a, 1902. 



