THE RAYS WHETHER SHADED OR LUMINOUS HAVE GREATER STRENGTH AND EFFECT
AT THEIR POINTS THAN AT THEIR SIDES.

Although the points of luminous pyramids may extend into shaded
places and those of pyramids of shadow into illuminated places, and
though among the luminous pyramids one may start from a broader base
than another; nevertheless, if by reason of their various length
these luminous pyramids acquire angles of equal size their light
will be equal; and the case will be the same with the pyramids of
shadow; as may be seen in the intersected pyramids _a b c_ and _d e
f_, which though their bases differ in size are equal as to breadth
and light.

[Footnote: 51--55: This supplementary paragraph is indicated as being
a continuation of line 45, by two small crosses.]

The difference between light and lustre (132--135).