SECOND BOOK ON LIGHT AND SHADE.

Gradations of strength in the shadows (148. 149).

THAT PORTION OF A BODY IN LIGHT AND SHADE WILL BE LEAST LUMINOUS
WHICH IS SEEN UNDER THE LEAST AMOUNT OF LIGHT.

That part of the object which is marked _m_ is in the highest light
because it faces the window _a d_ by the line _a f_; _n_ is in the
second grade because the light _b d_ strikes it by the line _b e_;
_o_ is in the third grade, as the light falls on it from _c d_ by
the line _c h_; _p_ is the lowest light but one as _c d_ falls on it
by the line _d v_; _q_ is the deepest shadow for no light falls on
it from any part of the window.

In proportion as _c d_ goes into _a d_ so will _n r s_ be darker
than _m_, and all the rest is space without shadow.

[Footnote: The diagram belonging to this chapter is No. 1 on Plate
III. The letters _a b e d_ and _r_ are not reproduced in facsimile
of the original, but have been replaced by ordinary type in the
margin. 5-12. The original text of these lines is reproduced within
the diagram.--Compare No 275.]