2GG CAPTAIN W. DE W. ABNEY OX THE COLOUR 



(IX.) Method of Determining the Red and Green Sensations in tlie Yellow which is 



complementary to the Violet. 



We are now in a position to determine the US and GS, in that yellow is comple- 

 mentary to the violet, which, in this as in the previous case, we are assuming 

 to be a simple sensation. From the preliminary observations we know that the 

 amount of violet in the yellow is very minute, and is for our purpose here negligible. 

 If one slit be placed in this particular yellow and another in the red near the lithium 

 line, and the two colours be mixed to match the spectrum orange, we get 



c(Or) ....... (iv.), 



where Y signifies the yellow. But 



therefore 



n' 



and we have this particular yellow expressed in terms of the luminosity of the two 

 sensations. Measurements made with a mixture of yellow and violet give the 

 equation 



W ......... (vi.). 



Substituting from v. we get an equation of the form 



(US) + $ (GS) + y (V) = 100 (W) . '. ; i ; .. (vii.), 



and this becomes the standard equation for the particular white employed. 

 If we take another green which does not answer to A, fig. 1, we get 



. !'. .... (viii.). 

 From vii. and viii. we get 



100 (G) = ' (us) + ' (GS) + y (V), 



and this is the percentage composition in luminosities of this particular green. 



This method applies for every spectrum colour up to that which answers to D, 

 fig. 1, but it is not quite so well adapted for colours which lie on the blue side of 

 this point. 



