268 EXl'KIUMENTS ON THE PERCEPTION OF COLOUR. 



In Equation II. a mixture of red and green, represented in the diagram 

 by the point 2, is seen to be equivalent to a mixture of white and yellow, also 

 represented by 2, which is a pale yellow tint. 



Equation III. is between a mixture of blue and yellow and another of 

 white and red. The resulting tint is at the intersection of YU and WV ; that 

 is, at the point 3, which represents a pale pink grey. 



Equation IV. is between VG and UY, that is, at 4, a dirty yellow. 



Equation V. is between a mixture of white, red, and green, and a mixture 

 of blue and yellow at the point 5, a pale dirty yellow. 



Equation VI. has W. for its resulting tint. 



Blue, U. 



Bed, V^ -MA -^ O. Green. 



Y, Yellow. 



Of all the resulting tints, that of Equation IV. is the furthest from white ; 



and we find that the observations of this equation are affected with the greatest 



errors. Hence the importance of reducing the resultant tint to as nearly a 

 neutral colour as possible. 



It is hardly necessary for me to observe, that the whole of the numerical 

 results which I have given apply only to the coloured papers which I used, 

 and to them only when illuminated by daylight from the north at mid-day in 

 September, latitude 55*. In the evening, or in winter, or by candlelight, the 

 results are very different. I believe, however, that the results would differ far 

 less if observed by different persons, than if observed under different lights ; 

 for the apparatus of vision is wonderfully similar in different eyes, and even in 

 colour-blind eyes the system of perception is not different, but defective. 



