340 SIR W. DE W. ABNEY: MODIFIED APPARATUS FOR MEASUREMENT OF COLOUR 



As special accuracy was necessary between SSN's 48 to 50, a large series ot 

 measures was taken at this part of the spectrum. This necessity arose from the fact 

 that a great part of the complementary colours between the greenish-blue and the 

 violet lay in this part of the spectrum, ami their composition could only be accurately 

 determined when the exact percentage of RS and GS was known. 



(12.) Red and Green Sensations from SSN's 49 to 37'5. 



The equations were formed, as stated before, in the ordinary manner, keeping the 

 slits in the red and violet at the standard places and altering the position of the 

 green slit. 



As an example, the value of SSN 45"8 was found as follows : 



RS. (45-8.) V. 



38-8 + 16-8 + 2-03 = White, 

 or 



RS. 45-8. V. W. 



18-6 + 80-4 + 1 = 100, 

 but 



RS. GS. V. W. 



68 -4 + 30 '2 + 1-4 = 100 (standard equation), 



.L 1 L* ' 



therefore 



45-8. RS. GS. V. 



LOO = 6T9 + 37-6 + -5. 

 Similarly SSN's (40'5), (43), and (47 '5) were found 



(40-5.) RS. GS. V. 

 100 = 5 1-68 + 47 -49 + '83. 



(43.) RS. GS. V. 

 100 = 56-9 +42-5 +'60. 



(47-5.) RS. GS. V. 

 100 = 66-20 + 33-5 +'30. 



The more accurate values of the violet were determined as described by matching 

 the intermediate colours between SSN's 49 and (37 '5) of one spectrum by mixtures of 

 these standard colours. Using luminosities, we get 



SSN. R. G. (37-5.) 

 38 = 2-62 + 97-38 

 40= 9-66 + 90-34 

 42 = 17-16 + 82-84 

 44 = 24-45 + 75-55 

 46 = 31-31+68-69 

 48 = 39-41 + 60-59. 



