AND ITS APPLICATION TO THE DETERMINATION OF COLOUR SENSATIONS. 339 



(10.) The Standard Equation. 



Four separate series of 50 equations each were made with slits at the red lithium 

 line (37 '5) and (4) in the violet. The mean of each series gave the following results, 

 using 31 per cent, of GS in (37'5) : 



RS. GS. V. White. 

 68-48 + 30-16 + 1-36 = 100 

 6818 + 30-50 + 1-32 = 100 

 68-62 + 29-98 + 1-45 = 100 

 68-44 + 30-17 + 1-39 = 100. 



The mean taken to one place of decimals gave 



RS. GS. V. W. 



68-4 + 30-2 + 1-4 = 100, 



and this equation was adopted as the standard equation for white. It will be noticed 

 that this is somewhat different to the equation given in the former paper, but this 

 is accounted for by the fact that the white of the comparison lights in the two 

 cases are not quite identical, selective absorption by the glass used for reflection 

 being far greater in the former measures than in the latter. The percentage of white 

 in (37 '5) also differs. 



(11.) Red and Green Sensations from SSN's 58 to 49. 



The red and green sensations in this part of the spectrum were determined by 

 placing one slit in the red lithium colour and another in the yellow-orange of one 

 spectrum, and matching the intermediate colours thrown on the screen from the second 

 spectrum. The composition of the yellows and orange used had been previously 

 determined by mixing the colour of the red lithium with (37 '5) SSN : 



SSN. RS. GS. SSN. RS. GS. 



56-2 =95-6+ 4-4 56 = 96"5 + 3'5 



55-1 =92-6+ 7-4 55 = 93'!+ 6'9 



54-05 = 90 +10-0 54 = 90-5+ 9'5 



*54 =90-6+ 9-4 *54 = 90'6+ 9'4 



5275 = 86-8 + 13-2 52 = 84'2 + 15'8 



*52'6 =86 +14-0 *52 = 83-9 + 16-1 



51-6 = 80 +20-0 51 = 78-7 + 21-3 



*51'6 =80-2 + 19-8 *51 = 78-9 + 21-1 



50-9 = 79-3 + 207 50 = 75-0 + 25'! 



50-65 = 78-2 + 21-8 49 = 70'0 + 30'0 

 *50'55 = 78 +22 

 *497 = 75-7 + 24-3 

 *49'3 = 73-6 + 26-4 



49-25 = 7T5 + 28-5 



The numbers marked * were taken with a slit at D, the others at 49'0 SSN. 



2x2 



