the Perception of Colour. 45 
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 wonder- 
fully similar in different eyes, and even in colour-blind eyes the 
system of perception is not different, but defective. 
Tasie I.—The observations arranged in groups. 
Equation I. v=0. +U. +G. —W. —B. +Y. 
1856, Sept. 3. 0 5A 12 34 66 34 
A. 0 58 14 dl 69 28 
ai 0 aD 12 32 68 33 
6. 0 54 14 382 68 32 
8. 0 5A 14 32 68 32 
9. 10) 53 15 32 68 32 
Mee AP ven s Se oy 1 oo a Sa ee ee 
Equation IT. —V. U=0. —G +W. +B. +Y. 
Sept. 3. 59 0) 4) 9 71 20 
4, 61 0 39 9 68 23 
5 61 0 39 9 67 24 
6 59 0 Al 10 66 24 
8 60 0) 40 9 69 22 
9 61 0) 39 9 68 23 
ee 
Equation III +V —U; G=0.  -+W. +B =—yY 
Equation IV. —V. +U.. —G. W=0. +B. +Y. 
