Shadows Cast by Four Lights and Four Bodies
Degrees of darkness ranked by how many of the lamps still reach a region
This page continues the notebook's study of light and shadow. The upper diagram sets four light sources (a, b, c, d) at the right, whose crossing beams fall on shadowy bodies and build up overlapping shadows, and the text ranks the darkness of each region by how many of the four lights it can still see. Leonardo states that among shadows of equal quality the one nearer the eye looks lighter, and imagines a room whose sieve-like ceiling sifts flour so that the falling dust would reveal the shadows hanging in the air. A closing note argues that simple derived shadows born of separate bodies but lit by a single light can never join or touch.
On this page
The nearer of two equal shadows appears lighter
Among shadows of equal quality, the one closest to the eye will appear of lesser darkness. Leonardo then imagines a room with four lamps and a ceiling turned into a bolting-sieve, so that sifted flour falling through the air would make the shadows evident, distinct and clear, as drawn.
Degrees of darkness by number of lights reaching a region
The darkest shadow is that derived from the more diverse shadowy and luminous bodies. At K f s the region still sees lights b c d, missing only a (a quarter of the number); at f S m po it sees only c d, half of all the lights; at m S p n no light reaches it, so it is the first degree of darkness.
Simple derived shadows from separate bodies cannot merge
It is impossible, Leonardo asserts, for the simple derivative shadows born of different bodies and caused by a single light ever to join together or touch one another.