Vision of Colours of Varying Intensity. 



87 



X'520 yit, A.'460/a, and \*430//<, show somewhat the same 

 characteristic relation . 



Fig-. 4. 



•025 05 



Cos z cc (kLumincsity). 9 



The lower portions of all the curves show the most striking: 

 differences. Those for X'665/i and X*725 fi are not far 

 from being continuous in direction with the upper portions 

 of the curves, while those for X "460/1, and X "430 /jl are quite 

 horizontal. The others lie at various inclinations between 

 these two extremes. Though in the curve for \ *460 jjl there is 

 but one point in the lower part, yet I have made that portion 

 horizontal since Ives obtained this result for the longer wave- 

 length \ "48 /j, and I for X *430 fju. 



These curves confirm similar results previously obtained 

 by Porter* and by Ivesj- Porter's results were for a disk 

 with white-light illumination, while those of Ives were for 

 five spectral colours. The latter found the curve for \ '65 fi 

 to be exactly a straight line. Considering the curves of Ives 



* Proc. Roy. Soc. lxx. p. 313 (1902). 

 t Phil. Mag. xxiv. p. 352 (1912). 



