Cast Shadows and the Blue of Distant Things
A dark object looks bluer with more air between it and the eye; why shadows change shape
The page opens with a note on aerial perspective: a dark object looks bluer the greater the mass of luminous air interposed between it and the eye, as the color of the sky demonstrates. Two large diagrams then examine cast shadows on a plane: the shadow-strike from a long shadowing body lit by a round source takes at one distance the shape of the shadowing body and at another the shape of the source. A third figure shows that even when the shadowing and luminous bodies are equal spheres, the derivative shadow becomes elongated rather than round if it falls between unequal angles.
On this page
Distance makes dark things appear blue
A dark object appears more blue the greater the sum of luminous air interposed between itself and the eye. Leonardo cites the color of the sky as the demonstration of this effect of the atmosphere.
A cast shadow takes the shape of body, then of source
The shadow-strike born of a long shadowing body and caused by a round luminous body has, at one distance, the figure of the shadowing body, and at another the figure of the source. The projected shadow thus changes shape as it travels away from the object.
Equal spheres can yield an elongated shadow
Even when the shadowing body and the luminous body are both spheres of equal size, the derivative shadow will not resemble the roundness of the body from which it springs. Instead it takes a long figure if it falls between unequal angles.