mentioned. If the line _e f_ is to enter as an image into so small
an opening in the eye, you must confess that the smaller object
cannot enter into what is smaller than itself unless it is
diminished, and by diminishing it must take the form of a pyramid.

53.

PERSPECTIVE.

Perspective comes in where judgment fails [as to the distance] in
objects which diminish. The eye can never be a true judge for
determining with exactitude how near one object is to another which
is equal to it [in size], if the top of that other is on the level
of the eye which sees them on that side, excepting by means of the
vertical plane which is the standard and guide of perspective. Let
_n_ be the eye, _e f_ the vertical plane above mentioned. Let _a b c
d_ be the three divisions, one below the other; if the lines _a n_
and _c n_ are of a given length and the eye _n_ is in the centre,
then _a b_ will look as large as _b c. c d_ is lower and farther off
from _n_, therefore it will look smaller. And the same effect will
appear in the three divisions of a face when the eye of the painter
who is drawing it is on a level with the eye of the person he is
painting.

54.

TO PROVE HOW OBJECTS REACH THE EYE.

If you look at the sun or some other luminous body and then shut
your eyes you will see it again inside your eye for a long time.