How a luminous body appears to the eye
Four observations on the apparent size and brightness of a light source with distance, aperture and one or two eyes.
This pen page, ruled into short paragraphs, sets down four rules about how a luminous body strikes the eye, with only a faint red-chalk sketch showing through the paper. An eye emerging from darkness sees a light as much larger at first than on continued looking, and the light seems larger and brighter with two eyes than with one. A body seen through a smaller aperture shows smaller, and an elongated light appears rounder the farther off it is.
On this page
A light seen on emerging from darkness looks larger
The eye that comes out of darkness and suddenly sees a luminous body finds it much larger at the first glance. As it continues to look, the body no longer appears so great.
Larger and brighter with two eyes than one
A luminous body appears larger and more luminous when seen with two eyes than with one alone. The note pairs binocular vision with an increase in apparent size and brightness.
Narrow aperture and distance alter apparent form
A luminous body shows itself smaller when seen through a smaller aperture of the eye. An elongated luminous body appears as a rounder body the farther it is set from the eye.