WHY OF TWO OBJECTS OF EQUAL SIZE A PAINTED ONE WILL LOOK LARGER THAN
A SOLID ONE.

The reason of this is not so easy to demonstrate as many others.
Still I will endeavour to accomplish it, if not wholly, at any rate
in part. The perspective of diminution demonstrates by reason, that
objects diminish in proportion as they are farther from the eye, and
this reasoning is confirmed by experience. Hence, the lines of sight
that extend between the object and the eye, when they are directed
to the surface of a painting are all intersected at uniform limits,
while those lines which are directed towards a piece of sculpture
are intersected at various limits and are of various lengths. The
lines which are longest extend to a more remote limb than the others
and therefore that limb looks smaller. As there are numerous lines
each longer than the others--since there are numerous parts, each
more remote than the others and these, being farther off,
necessarily appear smaller, and by appearing smaller it follows that
their diminution makes the whole mass of the object look smaller.
But this does not occur in painting; since the lines of sight all
end at the same distance there can be no diminution, hence the parts
not being diminished the whole object is undiminished, and for this
reason painting does not diminish, as a piece of sculpture does.

On the choice of a position (536-537)