Open your eyes gradually. It takes a long time for me to see any details in illustration 6-8 because the illustration is all middle values rather than extreme lights and darks. One reason is that it is useful in directing our attention. We are creatures that are drawn to the light. Another reason is that each of us associates lightness and darkness with certain qualities.
Light is pure and honest and good.
Darkness is mysterious, dangerous, unknown. Value is another element of art that is often overlooked by people who have not been taught to look for it. In the painting by Mary Cassatt on page 47, there are extreme lights and darks. It is very light in the center and dark around the edges. The lightest point is the little girl and the water basin, but it is very close in value to the woman.