CHAPTER IV.
Derivation of Colour from White Light.
The method of analysing white light into its colour constituents by means of coloured glass absorbents of known intensity and purity, is illustrated by the set of nine circles in Plate II, which demonstrate that colour is developed by the absorption of the complementary colour rays. The ratios of transmission are equal.
In this set of illustrations the circles represent light of 20 units luminous intensity, and the absorptive value of the three glass colours is each of 20 units, therefore the whole of the light and colour energies are presumed to be dealt with.
In the first set of three circles, A represents a beam of normal white light. B a similar beam as divided into the six colour rays, Red, Orange, Yellow, Green, Blue and Violet in equal proportions, C as wholly absorbed by Red, Yellow, and Blue glasses, each of 20 units colour intensity.
Figures [1], [2] and [3] represent the specific action of Red, Yellow, and Blue glass on the white light.
Red absorbs Yellow, Green and Blue, transmitting Violet, Red and Orange, developing Red only.
Yellow absorbs Blue, Violet, and Red, transmitting Orange, Yellow and Green, developing Yellow only.
Blue absorbs Red, Orange and Yellow, transmitting Green, Blue, and Violet, developing Blue only.
By this method of development, Red, Yellow or Blue, when seen alone are visually monochromatic, although composite in structure, each containing a group of three rays, the middle ray alone exciting the colour sensation.