A Treatise on Painting/Chapter 220
Chap. CCXX.—Of double and treble Reflexions of Light.
Double reflexes are stronger than single ones, and the shadows which interpose between the common light and these reflexes are very faint. For instance, let A be the luminous body, A N, A S, are the direct rays, and S N the parts which receive the light from them. O and E are the places enlightened by the reflexion of that light in those parts. A N E is a single reflex, but A N O, A S O is the double reflex. The single reflex is that which proceeds from a single light, but the double reflexion is produced by two different lights. The single one E is produced by the light striking on B D, while the double one O proceeds from the enlightened bodies B D and D R co-operating together; and the shadows which are between N O and S O will be very faint.
