Aerial Perspective: Why a Field Looks Larger or Smaller
Crisp edges betray distance, and the thickness of interposed air changes the apparent size of the countryside.
This page of the Trattato continues Leonardo's rules for painting distance: sharp, well-defined boundaries make even the most remote view read as very near, and the angles of buildings in far-off cities should not be shown, since an angle is the meeting of two lines in a point that, having no part, is invisible. A new chapter then asks why one and the same countryside sometimes looks larger or smaller than it is, answering that denser or rarer air interposed between the horizon and the eye is the cause. Of two equally distant horizons, the one seen through thicker air appears more remote and the one through thinner air nearer. The text breaks off amid a worked example of a thing seen across a hundred miles of uniform thin air.
On this page
Do not draw the angles of buildings in distant cities
Leonardo warns the painter that rendering boundaries sharp and distinct, as is the custom, prevents any distance from reading as truly remote. The angles of buildings in far-off cities are the very things not to be shown, for an angle is the meeting of two lines in a point, and a point, having no part, is invisible.
Thicker or thinner air alters apparent size and distance
Air denser or rarer than usual, coming between the horizon and the eye, makes the same field appear larger or smaller than it is. Of two horizons at equal distance, the one seen through thicker air seems more remote, and the one seen through thinner air seems nearer.
The same countryside seen across a hundred miles of air
A single thing seen at equal distances looks larger or smaller in proportion as the interposed air is thicker or thinner. The chapter begins a quantitative case of a thing viewed at the limit of a hundred miles, first through uniform thin air and then through uniform thick air.