THE THEOET OE COMPOUND COLOURS. 
83 
Table h (continued). 
V. 
U. 
G. 
B. 
W. 
Y. 
10. Observed . . . 
- 70 
+53 
0 
0 
-30 
+ 47 
= 0. 
Calculated . . 
- 73-5 +53 
0 
0 
-26*5 
+ 47 
= 0. 
11. Observed . . . 
-100 
+ 8 
0 
+ 71 
0 
+21 
= 0. 
Calculated . . 
-100 
+ 8 
0 
+ 74-5 
0 
+17-5 
= 0. 
12. Observed . . . 
+ 85 
+ 15 
0 
-88 
-12 
0 
= 0. 
Calculated . . 
+ 86 
+14 
0 
-88-5 
-11-5 
0 
=0. 
13. Observed . . . 
- 20 
+ .39 
- 80 
0 
0 
+ 61 
= 0. 
Calculated . . 
- 19 
+ 40 
- 81 
0 
0 
+ 60 
= 0. 
14. Observed . . . 
- 66 
+ 30 
+ 70 
0 
-34 
0 
= 0. 
Calculated . . 
- 70 
+27 
+ 73 
0 
-30 
0 
= 0. 
15. Observed . . . 
+ 100 
- 2 
- 27 
-71 
0 
0 
= 0. 
Calculated . . 
+ 96 
+ 4 
- 24 
-76 
0 
0 
= 0. 
But, according 
to our 
theory, colom’-blind vision 
is not only dichromic, 
but the two 
elements of colour are identical with two of the three elements of colour as seen by the 
ordinal*)" eye ; so that it differs from ordinary vision only in not perceiving a particular 
colour, the relation of which to known colours may be numerically defined. This colour 
may be expressed under the form 
«V+5U+cG=D, (16.) 
where V, U, and G are the standard colours used in the experiments, and D is the 
colour which is \’isible to the ordinary eye, but invisible to the colour-blind. If we 
know the value of D, we may always change an ordinary colour-equation into a colour- 
blind equation by subtracting from it riD [n being chosen so that one of the standard 
colours is eliminated), and adding n of black. 
In September 1856 I deduced, from thirty-six observations of my own, the chromatic 
relations of the same set of six coloured papers. These observations, with a comparison 
of them with the trichromic theory of vision, are to be found in the ‘ Philosophical 
Magazine’ for July 1857. The relations of the six colours may be deduced from two 
equations, of which the most convenient form is 
V. U. G. B. W. T. 
+ 39-7 +26-6 -1-33-7 -22-7 -77-3 0 =0. . . . (17.) 
-62-4 +18-6 -37-6 0 +45*7 +.35-7=0. . . . (18.) 
The value of D, as deduced from a comparison of these equations with the colour-blind 
equations, is 
l-198V+0-078U-0-276G=D (19.) 
By making D the same thing as black (B), and eliminating W and Y respectively from 
the two ordinary colour-equations by means of D, we obtain three colour-blind equa- 
