510. Why is there some amount of light even where shadows fall?
Because, as all objects reflect light, some of them throw their light into the field of the shadow.
511. Why are some substances opaque to light?
Because the arrangement of their particles will not admit of the vibrations of the luminous ether passing through them.
Opaque—impervious to rays of light.
512. Why do we see our faces reflected in mirrors?
Because the rays of light from our faces are reflected by the surface of the quicksilver at the back of the glass.
"The day is thine, the night also is thine: thou hast prepared the light and the sun."—Psalm lxxiv.