We have now two systems of charting colour, in the first, the complete sensation is represented by a single point, as in Plate IV. In the second, each factor is represented by a separate point, and by connecting points of similar colours, a series of curves is established which represents a quantitative analysis of the progressive colour development, as in Plate V.
CHAPTER X.
Representations of Colour in Space of Three Dimensions.
The relations of the different colours to one another, and to neutral tint are, perhaps, best represented to the mind by a solid model, or by reference to three co-ordinate axes, as employed in solid geometry (see [Fig. 2]).
Fig. 2.
Let the three adjacent edges OR, OB, OY, of the above cube be three axes, along which are measured degrees of Red, Yellow and Blue respectively, starting from the origin O. Every point in space on the positive side of this origin will then represent a conceivable colour, the constituents of which in degrees of red, yellow and blue are measured by the three co-ordinates of the points. Pure reds lie all along the axis OR, pure yellows on the axis OY, and pure blues on the axis OB.
All normal oranges, normal greens, and normal violets lie on the diagonals of the faces of the cubes OO1, OG, OV respectively.