86.
A simple and natural method; showing how objects appear to the eye
without any other medium.
The object that is nearest to the eye always seems larger than
another of the same size at greater distance. The eye _m_, seeing
the spaces _o v x_, hardly detects the difference between them, and
the. reason of this is that it is close to them [Footnote 6: It is
quite inconceivable to me why M. RAVAISSON, in a note to his French
translation of this simple passage should have remarked: _Il est
clair que c'est par erreur que Leonard a ècrit_ per esser visino _au
lieu de_ per non esser visino. (See his printed ed. of MS. A. p.
38.)]; but if these spaces are marked on the vertical plane _n o_
the space _o v_ will be seen at _o r_, and in the same way the space
_v x_ will appear at _r q_. And if you carry this out in any place
where you can walk round, it will look out of proportion by reason
of the great difference in the spaces _o r_ and _r q_. And this
proceeds from the eye being so much below [near] the plane that the
plane is foreshortened. Hence, if you wanted to carry it out, you
would have [to arrange] to see the perspective through a single hole
which must be at the point _m_, or else you must go to a distance of
at least 3 times the height of the object you see. The plane _o p_
being always equally remote from the eye will reproduce the objects
in a satisfactory way, so that they may be seen from place to place.
87.
How every large mass sends forth its images, which may diminish
through infinity.
The images of any large mass being infinitely divisible may be
infinitely diminished.
88.
Objects of equal size, situated in various places, will be seen by
different pyramids which will each be smaller in proportion as the
object is farther off.
89.
Perspective, in dealing with distances, makes use of two opposite
pyramids, one of which has its apex in the eye and the base as
distant as the horizon. The other has the base towards the eye and
the apex on the horizon. Now, the first includes the [visible]
universe, embracing all the mass of the objects that lie in front of
the eye; as it might be a vast landscape seen through a very small
opening; for the more remote the objects are from the eye, the
greater number can be seen through the opening, and thus the pyramid
is constructed with the base on the horizon and the apex in the eye,
as has been said. The second pyramid is extended to a spot which is
smaller in proportion as it is farther from the eye; and this second
perspective [= pyramid] results from the first.
90.