SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
The diagram of c.1492 shows two large light sources of differing intensities close to two smaller objects. This diffuse lighting creates two shadows with ill-defined edges, one darker than the other, and which blend at one point. Leonardo explains that "it is impossible that from the blending of two complete shadows there should be a shadow darker in degree".
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