When an Opake Body is found between two Lights, the effect will be as follows: These two Lights will be either equal to each other in force, or they will be unequal; if they be equal, they may yet differ two ways with regard to the brightness which they cast upon the Object, which will be either equal or unequal; equal when their distances are equal, and unequal, their distances being so: The Object placed at an equal distance, between two Lights equal both in brightness and Colour, may further be illumined by these Lights in two different manners; to wit, either equally on every side, or unequally; it will be equally enlighten'd, when the space remaining around the Lights is equal both in Colour, Shadow, and Brightness; and unequally when these spaces around the Lights are found to differ in their Colour, Brightness, or degree of obscurity.