It seems impossible to believe that these mixtures, so dissimilar in colour, could ever form a satisfactory match. This last equation might have been derived from the two first, in which case it would have stood-- 137 G + 223 B = 342 R + 18 W. By a completely green-blind the following mixtures were made-- 251 R + 109 U = 62 W + 298 B, and 277 G + 83 U = 107 W + 253 B. In this case 363 Green are equivalent to 251 parts of Red mixed with 78 of White and 34 Black. The difference in the matches made by the two types of colour blindness is very evident. In the one case the amount of red required is much greater than the green, and in the other _vice versâ_. Another instance may be given of colour matches made, by means of discs, by a _partially_ green-blind person, whose case will be more fully described when we treat of the luminosity of the spectrum to the different classes of colour vision. His matches were as follows--1st, That of the normal vision. 2nd,-- 160 R + 80 G + 120 U = 72 W + 288 B. The green was then altered to 200, when the following made a match-- 65 R + 200 G + 95 U = 72 W + 288 B. Using these two equations, we have the following curious result--that 120 G was matched by 95 R + 25 U. As the green disc is nearly twice as luminous as the red to normal colour vision, this equation confirms the result otherwise obtained, that his blindness to colour is a deficiency in the green sensation. No mixtures of blue and red, or blue and green, would match a grey formed by the rotation of the black and white sectors.