The Science of Light and Shadow on Spherical Bodies
Ray diagrams, the pyramid of vision, and primary versus reflected light on spheres
The sheet (drawn with the page inverted) is covered with faint ray and cone diagrams studying how light and shadow fall upon spherical bodies and how the eye sees near and far. The accompanying notes treat the pyramid of vision, the angles at which luminous rays strike a sphere, the special brightness of a sphere's centre, and the way reflected light softens the boundaries of shadow. Several spheres are shown lit and cast into shade, with construction lines converging on eye-points. Further untranscribed notes appear in the tighter right-hand columns.
On this page
Why a thing seen too near, or too far, is not well made out
The note asks why the closer an object comes to the eye the less it is distinguished, and why the eye sees badly both near and far. Up close it fails because the origins of the transverse rays, converging toward the common meeting-point of the pyramid of vision, are too oblique.
Where the angles of the luminous pyramid are sharpest, the light is least
Where the base-angles made by the luminous pyramids upon a body are more acute and slender, there will be less light upon the spherical body. The idea governs how brightness grades across a curved lit surface.
The centre, noblest part of a sphere (f h S o n a X t z)
Beside the lettered figure f - h S - o n a - X t - z the note states that the centre is the most powerful and noble part of spherical bodies, because to it all the extremities of the body correspond equally, and the middles of the lights are the most luminous.
Primary and reflected light sharpen the edges of shadow
The boundaries of shadow on dense spherical bodies are more distinct at their edges than those of the reflected light. Primary light and derived reflected light surrounding the sphere make the edge of its primary shadow better known at one side than the other, in proportion as the primary light is brighter than the reflected.
Cones of rays converging on the eye and on lit spheres
Numerous faint pen diagrams show pyramids and cones of straight rays spreading between eye-points and small circles standing for spherical bodies. They are the geometric scaffolding for the light-and-shadow reasoning in the surrounding notes.