Shadow Between Two Lights; Why a Cast Shadow Enlarges
Two equal lights make two equal shadows; a body near a small light throws a huge, blurred, disproportionate shadow
A text page from the fifth part of the Treatise on Painting on the behaviour of cast shadow relative to its light. A body set between two equal lights casts two shadows toward them; move it nearer one and the shadow thrown toward the nearer light grows lighter. It then explains why an object close to a small light casts an enormous shadow on the far wall, why such an over-large shadow is disproportionate to its cause, and why its edges are blurred by the bright air surrounding the light.
On this page
A body between two equal lights casts two shadows
A body placed between two equal lights sends out two shadows, which direct themselves in a line toward the two lights. Move the body nearer one light than the other, and the shadow directed toward the nearer light is less dark than the one directed toward the farther light.
Nearness to the light enlarges the cast shadow
An object set close before a single light casts a very large shadow on the opposite wall; and the farther the object is moved from the light, the more the form of that shadow diminishes.
Why the enlarged shadow is disproportionate and blurred
A shadow larger than its cause is of discordant proportion because the light, being smaller than the object, cannot lie equidistant from the object's extremities, so the more distant part grows more than the near. Its bounds are confused because the air surrounding the light is almost of the light's own nature and loses that likeness as it recedes.