There are many birds in various regions of the world on whose
feathers we see the most splendid colours produced as they move, as
we see in our own country in the feathers of peacocks or on the
necks of ducks or pigeons, &c.
Again, on the surface of antique glass found underground and on the
roots of turnips kept for some time at the bottom of wells or other
stagnant waters [we see] that each root displays colours similar to
those of the real rainbow. They may also be seen when oil has been
placed on the top of water and in the solar rays reflected from the
surface of a diamond or beryl; again, through the angular facet of a
beryl every dark object against a background of the atmosphere or
any thing else equally pale-coloured is surrounded by these rainbow
colours between the atmosphere and the dark body; and in many other
circumstances which I will not mention, as these suffice for my
purpose.
_VI._
_'Prospettiva de' colri' (Perspective of Colour)_
_and_
_'Prospettiva aerea' (Aerial Perspective)._
_Leonardo distinctly separates these branches of his subject, as may
be seen in the beginning of No._ 295. _Attempts have been made to
cast doubts on the results which Leonardo arrived at by experiment
on the perspective of colour, but not with justice, as may be seen
from the original text of section_ 294.
_The question as to the composition of the atmosphere, which is
inseparable from a discussion on Aerial Perspective, forms a
separate theory which is treated at considerable length. Indeed the
author enters into it so fully that we cannot escape the conviction
that he must have dwelt with particular pleasure on this part of his
subject, and that he attached great importance to giving it a
character of general applicability._
General rules (289--291).
289.
The variety of colour in objects cannot be discerned at a great
distance, excepting in those parts which are directly lighted up by
the solar rays.
290.
As to the colours of objects: at long distances no difference is
perceptible in the parts in shadow.
291.