mon 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.

The only portion of air that will be seen reflected in the water, will be that which is reflected by the surface of the water to the eye between equal angles; that is to say, the angle of incidence must be equal to the angle of reflexion.