Of reflections: where shadow between lights is darkest
A body on a plane lit by s (r, h, p, m, n, o); why universal light hides reflections
This leaf of the Treatise on Painting continues the section on reflections. Chapter 780 explains that the shadow lying between incident and reflected light is very dark and looks darker still by contrast with the incident light beside it. Chapter 781, keyed to a small pen diagram of a rounded body resting on a plane and lit from above by a source s, argues where the reflection is darkest: the derivative shadow stamped on the pavement at m p rebounds into the body's part o p, and the derivative light m n rebounds into o r, so such bodies never carry a luminous reflection where they meet their pavement. Chapter 782 explains why reflections are scarcely seen in universal light, taking a body a lit by its hemisphere g c d and shadowed by the earth g f d.
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Shadow between incident and reflected light is darkest
Chapter 780 holds that the shadow interposed between the incident light and the reflected light is of great darkness and shows itself darker than it truly is, because of the comparison with the incident light that borders it. Contrast heightens the depth of the interposed shadow.
Where the reflection is darker: body r h p lit by source s
Chapter 781, with a small diagram, reasons that when light s illuminates the body r h p, the primitive shadow is brighter above toward the light than below where the body rests on the plane. The derivative shadow stamped on the pavement at m p rebounds into the body's part o p, and the derivative light m n rebounds into o r, so the body carries no luminous reflection where it meets its pavement.
Why reflections vanish in universal light
Chapter 782 explains that the reflections of shadowed bodies are seen little or not at all in universal lights, because such light surrounds and embraces much of each body, whose surface takes the colour of its objects. The example takes a body a illuminated by its hemisphere g c d and shadowed by the earth g f d.