and Flicker Photometer Speed, 



107 



In fig. 3 is shown the Koenig equal sensation triangle as 

 modified by the present writer *, in which are plotted the 

 spectrum, the white, the yellow-white, red and blue, above 

 mentioned, together with the lines giving the equal luminosity 

 mixture positions of the spectrum with each of these. 



Full line : spectrum in Koenig equal-sensation-sum triangle, as 

 modified by the writer. 



Heavy dots : equal hue steps in spectrum. 



Eg : approximate position of red comparison light used. 



Bg : approximate position of blue comparison light used. 



W: white. 



Y-W : Yellow-white of tungsten lamp. 



Dashed lines : loci of equal luminosity mixtures of each com- 

 parison light with spectrum. 



When it comes to the equal hue steps in this colour 

 triangle all that we have is the division of the spectrum into 

 equal hue steps by the just perceptible wave-length intervals 



* See footnote, p. 103. 



