Fog, Buildings, and the Blue of Remote Landscapes
Why buildings darken in luminous fog, and why shadowed distances turn blue
Still within the sixth part of the Treatise on Painting, this page finishes the discussion of fog: mist between sun and eye glows the nearer it is to the sun, so city buildings set within brighter fog appear darker, and towers and bell-towers seem thinner toward their bases where the mist is densest and most luminous. Leonardo cross-refers the 32nd proposition of his own Perspective. Two short chapters follow, marked 'a' and 'b': the shadowed parts of remote landscapes take on more blue than their lit parts, and landscapes seen eastward in mist or at sunrise appear especially bright; the second chapter carries a marginal reference, 'Book A, folio 41.'
On this page
Buildings appear darker in more luminous fog near the sun
Fog between sun and eye partakes of the sun's splendor, the more so the closer it lies to the sun. City buildings set within brighter fog therefore look darker, since a dark body appears smaller and darker against more luminous air; and because the mist thickens toward the ground, parallel towers and bell-towers look thinnest near their bases. Leonardo refers the reason to the 32nd proposition of his Perspective.
Shadowed parts of remote landscapes turn blue
The shadowy parts of distant landscapes partake more of blue than their illuminated parts. This follows from the definition of the blue with which the colorless air is tinted: without darkness beyond it the air would stay white, for the blue of the air is itself compounded of light and darkness.
Landscapes in mist and at sunrise or sunset
Leonardo turns to landscapes lying to the east of the viewer: at sunrise, or when mists and thick vapors are interposed between sun and eye, such landscapes will appear much brighter. The passage, keyed to a marginal cross-reference ('Book A, folio 41'), breaks off as the observation is being stated.