The Colour of a Body shadow'd by another Body, will never be pure in its shadow'd part, except the Colour of the Object whence the Shadow comes, be the same with that on which it is cast; for instance, if iu a Chamber the Walls of which are Green, be exposed, some Body whose Colour is Blue, and illumined by another Blue; in this case the enlighten'd side of the Object will be seen of a very beautiful Blue, the Shadow at the same time appearing foul and disagreeable; retaining nothing of the brightness of its original Azure, but mixing and debasing it with the Green reflected from the Walls; and the effect wou'd be still the worse were the Walls of a tann'd Colour.