The Reflex's of Light are more or less bright, that is, they are more or less apparent, in proportion as the Ground on which they are seen, is more or less obscure. When the Ground is darker than the Reflex, the latter will appear strong and sensible, the former serving as a Foil to it: so where the Reflex is found on a Ground brighter than it self, it must of Course appear the more Dim, by reason of the Whiteness surrounding it, becoming, by this means almost Imperceptible.