The Distorting Mirror
Opticians sometimes grind a glass mirror concave in one direction
only, or longitudinally; it is in fact a concave portion of a
cylinder, the breadth of which may be considered that of the mirror. A
person looking at his face in this mirror, in the direction of its
concavity, will see it curiously distorted in a very lengthened
appearance; and by turning the cylindrical mirror a quarter round, his
visage will appear distorted another way, by an apparent increase in
width only. If in a very near situation before it, you put your finger
on the right hand side of your nose, it will appear the same in the
mirror; but if in a distant situation, somewhat beyond the centre of
concavity, you again look at your face in the mirror, your finger will
appear to be removed to the other side of your nose.