80 



On Four Transition Points in the Spectrum. 



to the intersection of the green and red sensation curves. The- 

 transition point at X'420^ is shown by the curves to be 

 practically outside the influence of the red and green sen- 

 sations, and hence may be regarded as a region of a single* 



Fie-. 23. 



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Normal Sensation Curves. (Abney and Watson.) 

 (From Parsons's ' Colour Vision," p. 244.) 



Fio-. 24. 





























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 •60// -57// -Alfju -42/jl 



Sensation Curves. (Kouig and Dieterici.) 

 (From Parsons's ' Colour Vision/ p. 222.) 



pure-colour sensation. Similarly, the spectral region from 

 the transition point X -660 /u, to the end of the spectrum is 

 pure red free from the influence of the other two sensations. 

 The sensation curves of Konigand Dieterici, fig. 24, show 

 some differences. The ends of the green sensation curve 

 are the transition points X'660//, and X'420^, while the 

 transition point \ - 470/>6 is still the more refrangible end of 

 the sensation curve for red. The transition point \'570fi 



