STEREOGRAPH.

Democritus of Abdera, commonly known as the Laughing Philosopher,
probably because he did not consider the study of truth inconsistent
with a cheerful countenance, believed and taught that all bodies were
continually throwing off certain images like themselves, which subtile
emanations, striking on our bodily organs, gave rise to our sensations.
Epicurus borrowed the idea from him, and incorporated it into the famous
system, of which Lucretius has given us the most popular version. Those
who are curious on the matter will find the poet's description at the
beginning of his fourth book. Forms, effigies, membranes, or _films_,
are the nearest representatives of the terms applied to these
effluences. They are perpetually shed from the surfaces of solids, as
bark is shed by trees. _Cortex_ is, indeed, one of the names applied to
them by Lucretius.

These evanescent films may be seen in one of their aspects in any clear,
calm sheet of water, in a mirror, in the eye of an animal by one who
looks at it in front, but better still by the consciousness behind the
eye in the ordinary act of vision. They must be packed like the leaves
of a closed book; for suppose a mirror to give an image of an object a
mile off, it will give one at every point less than a mile, though this
were subdivided into a million parts. Yet the images will not be the
same; for the one taken a mile off will be very small, at half a mile as
large again, at a hundred feet fifty times as large, and so on, as long
as the mirror can contain the image.

Under the action of light, then, a body makes its superficial aspect
potentially present at a distance, becoming appreciable as a shadow or
as a picture. But remove the cause,--the body itself,--and the effect is
removed. The man beholdeth himself in the glass and goeth his way, and
straightway both the mirror and the mirrored forget what manner of man
he was. These visible films or membranous _exuviae_ of objects, which
the old philosophers talked about, have no real existence, separable
from their illuminated source, and perish instantly when it is
withdrawn.

If a man had handed a metallic speculum to Democritus of Abdera, and
told him to look at his face in it while his heart was beating thirty
or forty times, promising that one of the films his face was shedding
should stick there, so that neither he, nor it, nor anybody should
forget what manner of man he was, the Laughing Philosopher wo