from Blackwater Quartet, selection 8

Mirror

A disk of metal, highly polished,
positions the image
at the centre of the imaginary sphere,
a line extending through the centre of curvature
at a point upon it.
This point is called the principal focus.
 
In 16th century Venice, the back
thins to a coating of tin
mixed with mercury— after 1840, silver,
small bits of silvered glass much used in the East
adorning, with little change in their character,
their relationship to one another in space.

The image is called the virtual image,
extensions of light rays appearing to intersect
behind the mirror, the image formed by it
always smaller than the object, never real,
reflected, diverging outward
from the face.