74 Prof. F. Allen on Four Transition, Points in the 



Fiff. 18. 



•40//. 



•50 -60 



Wave Length. 



The three elevations of this curve are stron ply indicative of a* 

 trichromatic basis for the perception of colour. 



Table XL 



•400 /i 



•415 



■423 



•433 



•455 



•470 



The 



Mean 

 Ratio. 

 122 

 114 

 110 

 107 

 100 

 102-7 



•480 p 



•490 



•500 



•515 



•523 



•550 



Mean 

 Ratio. 

 104-7 

 106 

 107-5 

 109-5 

 112 

 109 



•566 n 



•600 



•620 



•630 



•640 



•650 



Mean 

 Ratio. 

 105 

 100-7 

 100-7 

 101-7 

 102-5 

 104 



\. 



Mean 



Ratio. 



663 n 



106 



677 



108 



695 



110 



715 



111 



733 



112 



•758 



110 



general 



results 

 in 



in this paper may be represented 

 diagrammatical^ as in fig. 21. In this diagram the indi- 

 cated wave-lengths mark the transition points and divide the 

 spectrum into five parts. It is evident that the fundamental 



