reacquaint, himself with the physiological phenomena which come liere into consideration. He will find in Figs. f and g, Plate II, dark outlines laid down in the one case upon a blue in the other case upon a red field. Viewing these outlines through the covering tissue paper,[1] it will be observed that they assume under the influence of the uncoloured light which radiates from this into the eye respectively a yellow and a green tint. In a similar manner, the dark margins of the glass filaments represented in Fig. k assume, when looked at through the covering tissue paper, a distinctly yellow tint. These are only illustrations of the general law that where we have disposed upon a coloured field a darker area, this area will, under the influence of uncoloured light reflected from its surface, assume in each case a tint complementary to that of the enveloping field.
- ↑ The office performed by the tissue paper is to render uniform the illumination all over the field. It will be realized that the tissue paper is made up of bright outstanding elements—the strands of the paper, and of sunken shaded elements—the fenestrae between the fibres. In accordance with this it spreads over the picture a network of lights and shadows which has the effect of lighting up the darker portions of the picture and of toning down the brighter portions.
Any other device, which will in similar manner equalize the brightness, will be equally effective in bringing out the colour contrast effects. Thus, when, on a blackboard, we cover an area with coloured chalk and leave in the centre of this area a vacant patch, the imposition of a film of chalk powder on this empty space will bring out the colour contrast upon it.
In external nature mist, and in certain circumstances snow, take upon themselves the office of lighting up the shadows of the landscape and of throwing up the colour contrast phenomena into prominence. (Vide Author's paper on "Colour Shadows," Nineteenth Century, 1897.)
