How Air Thickness Colours a Mountain's Peak and Base
The perspective of colours gives distance; the eye set high, and set low, sees mountain summits and bases differently
Leonardo argues that only the perspective of colours, not linear perspective alone, tells the eye the distance between an interposed object and another thing. When the eye is set high, a mountain's summit b is seen through thin air a b while its base d is seen through the thicker, shorter air a d, so the base appears more remote than the peak. A small landscape diagram of two peaks with rays converging to the eye illustrates the demonstration, and a further heading begins the converse case of the eye set low.
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Only the perspective of colours conveys interposed distance
The eye cannot, through linear perspective alone, know the distance between an object interposed between it and another thing except by means of the perspective of colours. The clause completes the precept carried over from the preceding page.
Eye set high: a mountain's base looks more remote than its peak
With the eye at height a, the summit b is seen through the thin air a b while the base d is seen through the shorter but thicker air a d. Because thicker air tinges an equal colour more, the base appears more distant from the eye than the summit, as the diagram of two peaks shows.
Eye set low: peaks and bases grow less distinct
When the eye is set low and sees the bases of mountains together with their summits, the colours of that mountain become much less known than in the previous case. This happens because summit and base are then seen through air of greater thickness, as the argument continues overleaf.