Volume Volume1\Perspective of Colour and Aerial
Entry# 300. On the colour of the atmosphere (300-307).
Contents: Vol. 1 | Vol. 2
OF THE COLOUR OF THE ATMOSPHERE.
I say that the blueness we see in the atmosphere is not intrinsic
colour, but is caused by warm vapour evaporated in minute and
insensible atoms on which the solar rays fall, rendering them
luminous against the infinite darkness of the fiery sphere which
lies beyond and includes it. And this may be seen, as I saw it by
any one going up Footnote 5: With regard to the place spoken of as
_M'oboso_ (compare No. 301 line 20) its identity will be discussed
under Leonardo's Topographical notes in Vol. II. Monboso, a peak of
the Alps which divide France from Italy. The base of this mountain
gives birth to the four rivers which flow in four different
directions through the whole of Europe. And no mountain has its base
at so great a height as this, which lifts itself almost above the
clouds; and snow seldom falls there, but only hail in the summer,
when the clouds are highest. And this hail lies unmelted there, so
that if it were not for the absorption of the rising and falling
clouds, which does not happen twice in an age, an enormous mass of
ice would be piled up there by the hail, and in the middle of July I
found it very considerable. There I saw above me the dark sky, and
the sun as it fell on the mountain was far brighter here than in the
plains below, because a smaller extent of atmosphere lay between the
summit of the mountain and the sun. Again as an illustration of the
colour of the atmosphere I will mention the smoke of old and dry
wood, which, as it comes out of a chimney, appears to turn very
blue, when seen between the eye and the dark distance. But as it
rises, and comes between the eye and the bright atmosphere, it at
once shows of an ashy grey colour; and this happens because it no
longer has darkness beyond it, but this bright and luminous space.
If the smoke is from young, green wood, it will not appear blue,
because, not being transparent and being full of superabundant
moisture, it has the effect of condensed clouds which take distinct
lights and shadows like a solid body. The same occurs with the
atmosphere, which, when overcharged with moisture appears white, and
the small amount of heated moisture makes it dark, of a dark blue
colour; and this will suffice us so far as concerns the colour of
the atmosphere; though it might be added that, if this transparent
blue were the natural colour of the atmosphere, it would follow that
wherever a larger mass air intervened between the eye and the
element of fire, the azure colour would be more intense; as we see
in blue glass and in sapphires, which are darker in proportion as
they are larger. But the atmosphere in such circumstances behaves in
an opposite manner, inasmuch as where a greater quantity of it lies
between the eye and the sphere of fire, it is seen much whiter. This
occurs towards the horizon. And the less the extent of atmosphere
between the eye and the sphere of fire, the deeper is the blue
colour, as may be seen even on low plains. Hence it follows, as I
say, that the atmosphere assumes this azure hue by reason of the
particles of moisture which catch the rays of the sun. Again, we may
note the difference in particles of dust, or particles of smoke, in
the sun beams admitted through holes into a dark chamber, when the
former will look ash grey and the thin smoke will appear of a most
beautiful blue; and it may be seen again in in the dark shadows of
distant mountains when the air between the eye and those shadows
will look very blue, though the brightest parts of those mountains
will not differ much from their true colour. But if any one wishes
for a final proof let him paint a board with various colours, among
them an intense black; and over all let him lay a very thin and
transparent coating of white. He will then see that this
transparent white will nowhere show a more beautiful blue than over
the black--but it must be very thin and finely ground.
Footnote 7: _reta_ here has the sense of _malanno_.
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