Free The Notebooks of Leonardo Da Vinci by Leonardo Da Vinci

point and diverge
again beyond it to reproduce and re-magnify the real size of that
image. But their impressions will appear reversed—as is shown in
the first, above; where it is said that every image intersects as it
enters the narrow openings made in a very thin substance.
    Read the marginal text on the other side.
    In proportion as the opening is smaller than the shaded body, so
much less will the images transmitted through this opening intersect
each other. The sides of images which pass through openings into a
dark room intersect at a point which is nearer to the opening in
proportion as the opening is narrower. To prove this let a b be an
object in light and shade which sends not its shadow but the image
of its darkened form through the opening d e which is as wide as
this shaded body; and its sides a b , being straight lines (as has
been proved) must intersect between the shaded object and the
opening; but nearer to the opening in proportion as it is smaller
than the object in shade. As is shown, on your right hand and your
left hand, in the two diagrams a b c n m o where, the
right opening d e , being equal in width to the shaded object a b , the intersection of the sides of the said shaded object occurs
half way between the opening and the shaded object at the point c .
But this cannot happen in the left hand figure, the opening o being much smaller than the shaded object n m .
    It is impossible that the images of objects should be seen between
the objects and the openings through which the images of these
bodies are admitted; and this is plain, because where the atmosphere
is illuminated these images are not formed visibly.
    When the images are made double by mutually crossing each other they
are invariably doubly as dark in tone. To prove this let d e h be such a doubling which although it is only seen within the space
between the bodies in b and i this will not hinder its being
seen from f g or from f m ; being composed of the images a b i k which run together in d e h .
    [Footnote: 81. On the original diagram at the beginning of this
chapter Leonardo has written " azurro " (blue) where in the
facsimile I have marked A , and " giallo " (yellow) where B stands.]
    [Footnote: 15—23. These lines stand between the diagrams I and III.]
    [Footnote: 24—53. These lines stand between the diagrams I and II.]
    [Footnote: 54—97 are written along the left side of diagram I.]
    82.
    An experiment showing that though the pupil may not be moved from
its position the objects seen by it may appear to move from their
places.
    If you look at an object at some distance from you and which is
below the eye, and fix both your eyes upon it and with one hand
firmly hold the upper lid open while with the other you push up the
under lid—still keeping your eyes fixed on the object gazed at—you
will see that object double; one [image] remaining steady, and the
other moving in a contrary direction to the pressure of your finger
on the lower eyelid. How false the opinion is of those who say that
this happens because the pupil of the eye is displaced from its
position.
    How the above mentioned facts prove that the pupil acts upside down
in seeing.
    [Footnote: 82. 14—17. The subject indicated by these two headings is
fully discussed in the two chapters that follow them in the
original; but it did not seem to me appropriate to include them
here.]
    Demostration of perspective by means of a vertical glass plane
(83-85).
    83.
OF THE PLANE OF GLASS.
    Perspective is nothing else than seeing place [or objects] behind a
plane of glass, quite transparent, on the surface of which the
objects behind that glass are to be drawn. These can be traced in
pyramids to the point in the eye, and these pyramids are intersected
on the glass plane.
    84.
    Pictorial perspective can never make an object at the same distance,
look of the same size as it appears to the eye. You see that the
apex of the pyramid f c d is as far from the object c d as the
same point