84 
OJiT THE THEOET OF COMPOOTD COLOEES. 
tions, calculated from the ordinary equations and consistent with them, supposing that 
the colour (D) is black to the colour-blind. 
The following Table is a comparison of the colour-bhnd equations deduced from 
Mr. Simpson’s observations alone, with those deduced fr'om my obseiwations and the 
value of D. 
Taple c. 
V. 
IJ. 
G. 
B. 
"W. 
Y. 
(15) Calculated . 
. -f96 
-1- 4 
-24 
-76 
0 
0 
By (19) .... 
. +93-9 
+ 6-1 
-21-7 
-78-3 
0 
0 
(14) Calculated . 
. -70 
+27 
+ 73 
0 
-30 
0 
By (17) and (19) . 
. -70 
+27-2 
-72-8 
0 
-30 
0 
(13) Calculated . 
. -19 
+40 
-81 
0 
0 
+60 
By (18) and (19) . 
. -13-6 
+ 38-5 
-86-4 
0 
0 
+61-5 
The average error here 
is 1-9, smaller than the average 
error of 
the individual colour- 
blind observations, showing that the theory of coloui’-blindness being the want of a cer- 
tain colour-sensation which is one of the three ordinary colour-sensations, agrees with 
observation to within the limits of error. 
In fig. 11, Plate II. I have laid down the chromatic relations of these colours accord- 
ing to Newton’s method. V (vermilion), U (ultramarine), and G (emerald -green) are 
assumed as standard colours, and placed at the angles of an equilateral triangle. The 
position of W (white) and Y (pale chrome-yellow) with respect to these are laid down 
from equations (17.) and (18.), deduced from my own observations. The positions of the 
defective colour, of white, and of yellow, as deduced from Mr. Simpson’s equations 
alone, are given at “ d” “ w,” and The positions of these points, as deduced from 
a combination of these equations with my own, are given at “ D,” “ W,” and “ Y.” 
The difference of these positions from those of “ “w,” and shows the amount 
of discrepancy between observation and theory. 
It will be observed that D is situated near V (vermilion), but that a line fr-om D to 
W cuts UV at C near to V. D is therefore a red colour, not scarlet, but fuidher from 
yellow. It may be called crimson, and may be imitated by a mixture of 86 vermilion 
and 14 ultramarine. This compound colour will be of the same hue as D ; but since C 
lies between D and W, C must be regarded as D diluted with a certain amount of white ; 
and therefore D must be imagined to be like C in hue, but without the intermixrure of 
white which is unavoidable in actual pigments, and which reduces the purity of the tmt. 
Lines drawn from D through “ W ” and “ Y,” the colour-blind positions of white and 
yellow, pass through W and Y, their positions in ordinary vision. The reason why they 
do not coincide with W and Y, is that the white and yellow papers are much brighter 
than the colours corresponding to the points W and Y of the triangle V, U, G ; and 
therefore lines from D, which represent them in intensity as well as in quality, must be 
longer than DW and DY in the proportion of their brightness. 
