140 



EXPERIMENTS ON COLOUR, AS PERCEIVED BY THE EYE. 



By a similar calculation with respect to the point 8, between B and G, 



By measurement ............... '43 B + '57 G = '335 W + '665 Bk 



Observed by N. and X ....... '41 B + -59 G = '34 W + -66 Bk ...... (6). 



By X. alone ..................... '42 B+-58 G = '32 W + -68 Bk 



We may also observe, that the line GD crosses RY. At the point of inter- 

 section we have 



By calculation ........................ -87 R+'13 



Observed by N. and X .......... '86 R-K14 



X .......... -84R+-16 



X. . -90R + -10 



= '34 G + -66 Bk 1 

 = '40 G + -60 Bk 

 = -31 G + -69 Bk 

 = -27 G + 73 Bk 



(7). 



Here observations are at variance, owing to the decided colours produced 

 affecting the state of the retina, but the mean agrees well with calculation. 



Drawing the line BY, we find that it cuts lines through D drawn to every 

 colour. Hence all colours appear to the colour-blind as if composed of blue 

 and yellow. By measurement on the diagram, we find for red 



Measured -138 Y + -123 B + 749 Bk = 100 R" 



Observed by N.... -15 Y+'ll B+74 Bk = 100R[ (8). 



X....-13 Y + -11 B + 76 Bk = 100R 



For green we have in the same way 

 Measured ...... 705 Y + -295 



Observed by N.... 70 Y + -30 



X.... 70 Y + -30 



= '95 G + '05 Bk 

 = '86G + '14Bk 

 = -83 G + -17 Bk 



.(9). 



For white 



Measured ...... -407 Y + '593 B = '326 W + '674 Bk 



Observed by N.... -40 Y+'60 B = '33 W+'67 Bk 



X.... -44 Y+-56 B = '33 W+-G7 Bk 



The accuracy of these results shews that, whether the hypothesis of the 

 want of one element out of three necessary to perfect vision be actually true 

 or not, it affords a most trustworthy foundation on which to build a theory 

 of colour-blindness, as it expresses completely the observed facts of the case. 

 They also furnish us with a datum for our theory of perfect vision, namely, 

 the point D, which points out the exact nature of the colour-sensation, which 

 must be added to the colour-blind eye to render it perfect. I am not aware 



