AND ITS APPLICATION TO THE DETERMINATION OF COLOUR SENSATIONS. 347 



in the colours, but at 48 some small quantity of white is shown to exist, and it is 

 found to SSN 16. Taking SSN (40) as an example, in Table III. this colour has for 

 its components in the columns showing equal stimuli 



RS. GS x 2-3. BS x 178. 

 25-80, 55-40, 20. 



As equal ordinates make white, the smallest ordinate, 20 in that case, is deducted 



from the other two and we have 



RS. GS x 2-3. 



5-80 and 3 5 '40. 



35-40 

 2-3 



or 



Thus after deducting 28 '8 of white, the amount of ES is 5 '8 and of GS 



15'4, so that the colour at SSN (40) is given by the equation 



ES. GS. W. SSN (40). 

 5-8 + 15-4 + 28-8 = 50. 



In the same way the equations to the other colours of the different SN's were found, 

 and fig. 4 gives the curves of RS, GS, BS, and W. It will be seen that all the 



90 



80 



70 



fiO 



SO 





W 



30 



0.S (too r, 



V 



X 



20 



10 



20 



\ 



30 



35 



SCALE of 



45 



so 



55 



60 



Fig. 4. Luminosity curves of red, green, blue and white sensations of the prismatic spectrum of the 



crater (positive pole) of the arc light. 



curves are smooth, and not one is abrupt, which is the case where the old numbers in 

 my paper of 1898 for the BS are treated in the same way, more especially in the 

 green and white curves. 



Columns VI. , VII., and VIII., Table IV., give the percentage composition in terms 

 of RS and GS, GS and BS, and of RS and BS of the different colours. These 

 columns are useful when we are considering the accurate calculation of the colours of 

 pigments either reflected or transmitted. 



2 y 2 



