and cuts off the distribution of the dark and light rays.
And the eye can best distinguish the forms of objects when it is placed between the shaded and the illuminated parts.
129.
MEMORANDUM OF THINGS I REQUIRE TO HAVE GRANTED [AS AXIOMS] IN MY EXPLANATION OF PERSPECTIVE.
I ask to have this much granted me—to assert that every ray passing through air of equal density throughout, travels in a straight line from its cause to the object or place it falls upon.
FIRST BOOK ON LIGHT AND SHADE.
On the nature of light (130. 131).
130.
The reason by which we know that a light radiates from a single centre is this: We plainly see that a large light is often much broader than some small object which nevertheless—and although the rays [of the large light] are much more than twice the extent [of the small body]—always has its shadow cast on the nearest surface very visibly. Let c f be