130 EXPERIMENTS ON COLOUR, AS PERCEIVED BY THE EYE. 



The apparent identity of the tints in these experiments is therefore not real, 

 but a consequence of a determinate constitution of the eye, and hence arises 

 the importance of the results, as indicating the laws of human vision. 



The first result which is worthy of notice is, that the equations, as observed 

 by different persons of ordinary vision, agree in a remarkable manner. If care 

 be taken to secure the same kind of light in all the experiments, the equations, 

 as determined by two independent observers, will seldom shew a difference of 

 more than three divisions in any part of the equation containing the bright 

 standard colours. As the duller colours are less active in changing the resultant 

 tint, their true proportions cannot be so well ascertained. The accuracy of vision 

 of each observer may be tested by repeating the same experiment at different 

 times, and comparing the equations so found. 



Experiments of this kind, made at Cambridge in November 1854, shew that 

 of ten observers, the best were accurate to within l division, and agreed 

 within 1 division of the mean of all ; and the worst contradicted themselves to 

 the extent of 6 degrees, but still were never more than 4 or 5 from the mean 

 of all the observations. 



We are thus led to conclude 



1st. That the human eye is capable of estimating the likeness of colours 

 with a precision which in some cases is very great. 



2nd. That the judgment thus formed is determined, not by the real identity 

 of the colours, but by a cause residing in the eye of the observer. 



3rd. That the eyes of different observers vary in accuracy, but agree with 

 each other so nearly as to leave no doubt that the law of colour-vision is 

 identical for all ordinary eyes. 



Investigation of the Law of the Perception of Colour. 



Before proceeding to the deduction of the elementary laws of the perception 

 of colour from the numerical results previously obtained, it will be desirable 

 to point out some general features of the experiments which indicate the form 

 which these laws must assume. 



Returning to experiment (1), in which a neutral gray was produced from 

 red, blue, and green, we may observe, that, while the adjustments were incom- 



