There is another kind of perspective which I call Aerial
Perspective, because by the atmosphere we are able to distinguish
the variations in distance of different buildings, which appear
placed on a single line; as, for instance, when we see several
buildings beyond a wall, all of which, as they appear above the top
of the wall, look of the same size, while you wish to represent them
in a picture as more remote one than another and to give the effect
of a somewhat dense atmosphere. You know that in an atmosphere of
equal density the remotest objects seen through it, as mountains, in
consequence of the great quantity of atmosphere between your eye and
them--appear blue and almost of the same hue as the atmosphere
itself [Footnote 10: _quado il sole e per leuante_ (when the sun is
in the East). Apparently the author refers here to morning light in
general. H. LUDWIG however translates this passage from the Vatican
copy "_wenn namlich die Sonne (dahinter) im Osten steht_".] when the
sun is in the East [Footnote 11: See Footnote 10]. Hence you must
make the nearest building above the wall of its real colour, but the
more distant ones make less defined and bluer. Those you wish should
look farthest away you must make proportionately bluer; thus, if one
is to be five times as distant, make it five times bluer. And by
this rule the buildings which above a [given] line appear of the
same size, will plainly be distinguished as to which are the more
remote and which larger than the others.
296.
The medium lying between the eye and the object seen, tinges that
object with its colour, as the blueness of the atmosphere makes the
distant mountains appear blue and red glass makes objects seen
beyond it, look red. The light shed round them by the stars is
obscured by the darkness of the night which lies between the eye and
the radiant light of the stars.
297.
Take care that the perspective of colour does not disagree with the
size of your objects, hat is to say: that the colours diminish from
their natural [vividness] in proportion as the objects at various
distances dimmish from their natural size.
On the relative density of the atmosphere (298--290).
298.
WHY THE ATMOSPHERE MUST BE REPRESENTED AS PALER TOWARDS THE LOWER
PORTION.
Because the atmosphere is dense near the earth, and the higher it is
the rarer it becomes. When the sun is in the East if you look
towards the West and a little way to the South and North, you will
see that this dense atmosphere receives more light from the sun than
the rarer; because the rays meet with greater resistance. And if the
sky, as you see it, ends on a low plain, that lowest portion of the
sky will be seen through a denser and whiter atmosphere, which will
weaken its true colour as seen through that medium, and there the
sky will look whiter than it is above you, where the line of sight
travels through a smaller space of air charged with heavy vapour.
And if you turn to the East, the atmosphere will appear darker as
you look lower down because the luminous rays pass less freely
through the lower atmosphere.
299.