Chap. CCLXXVIII.—Of the Colour of Lights and Reflexes.
When two lights strike upon an opake body, they can vary only in two ways; either they are equal in strength, or they are not. If they be equal, they may still vary in two other ways, that is, by the equality or inequality of their brightness; they will be equal, if their distance be the same; and unequal, if it be otherwise. The object placed at an equal distance, between two equal lights, in point both of colour and brightness, may still be enlightened by them in two different ways, either equally on each side, or unequally. It will be equally enlightened by them, when the space which remains round the lights shall be equal in colour, in degree of shade, and in brightness. It will be unequally enlightened by them when the spaces happen to be of different degrees of darkness.