the
shadow on each other, they become darker by multiplying those shadows.

'The darker a mountain is in itself,' says Leonardo, 'the bluer it will
appear at a great distance. The highest part will be the darkest, being
more woody; because woods cover a great many shrubs and other plants,
which never receive the light. Near the tops of those mountains, where
the air is thinner and purer, the darkness of the woods will make it
appear of a deeper azure than at the bottom, where the air is thicker.'

'In general, all objects that are darker or lighter than the air are
discoloured by distance, which changes their quality, so that the
lighter appears darker, and the darker lighter.'

Colours are more or less _entirely_ lost at a great distance from the
eye, according to the purity or density of the air through which they
are revealed, or as they are more or less elevated from the earth,
merging as they retire into a general grey, occasioned by the quantity
of the intervening air. In countries where the air is thin, colours are
discernible at great distances, but still tinged with the colour of that
air.

The _darkest_ colours, in distance, will be most of all impregnated with
the colour of the air. So will the _strongest_ real or accidental
shadows.

Colours and outline are best defined on objects placed _out_ of the
strong light of the sun, and its reflexes. In sunshine, both are
operated on by refraction, which occasions that chaotic indistinctness
so painful for the eye to dwell on long together.

Every body, on which light falls, reflects a part of it back again. Any
thing red, held before a looking-glass, gives back a portion of its own
colour with great vividness; as a glass would throw the sun's ray on a
wall.

The real colour of polished surfaces are lost in the colour of the light
that falls on them. This likewise applies to all metals.

All smooth or shining surfaces repel the light they receive, throwing
their reflexes on any thing opposed to them.

Polished surfaces, as in plate or armour, do not show their real
colours. The reflected colours of the sun or air that shines on them
confuse their own. Rough surfaces, on the contrary, retain their natural
colours most.

Suppose the sun to equally illumine two sides of a street, as it passes
its centre, and on one side is a red house, and opposite to it a white
one, the white one would be impinged with the reflection from the action
of the light on the re