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obliquely and the blow will not tell.
[Footnote: See Pl. XXXI. No. 4; the sketch on the right hand side.]
5
75.
THE PROOF AND REASON WHY AMONG THE ILLUMINATED PARTS CERTAIN
PORTIONS ARE IN HIGHER LIGHT THAN OTHERS.
Since it is proved that every definite light is, or seems to be,
derived from one single point the side illuminated by it will have
its highest light on the portion where the line of radiance falls
perpendicularly; as is shown above in the lines a g, and also in
a h and in l a; and that portion of the illuminated side will be
least luminous, where the line of incidence strikes it between two
more dissimilar angles, as is seen at b c d. And by this means you
may also know which parts are deprived of light as is seen at m k.
Where the angles made by the lines of incidence are most equal there
will be the highest light, and where they are most unequal it will
be darkest.
I will make further mention of the reason of reflections.
[
Footnote: See Pl. XXXII. The text, here given complete, is on the
right hand side. The small circles above the beginning of lines 5
09
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