Omaha daily bee., 1910-03-12
RANGE LIMIT OF NORMAL EYE
COlOrs Invisible to the Eye Repro
duced by Photographic
PlR2e.

Those of us who are fortunate enough
to possess normal eyes are apt to feel in
stinctively that we see things as they are.
This is a mistake. The appearance OF the
world at large is merely the result of the
circumstance that the human eye perceives
only a comparatively small part Of the
total radiation which comes from the sun
or is given out by a lamp.
To make this a little clearer, we nay
consider one of the oldest experiments in
optics, the passage of a ray OF light through
a prism. When a beam Of sunlight passes
through a prism Of glass such as is often
found on old-fsshioned chande RS, the rays
are spread out, forming a spectrum, which
we see as a rainbow-colored band upon
the wall. The colors Of the spectrum
merge into one another by insenslble grada-
lions, though the older physicists were In
the habit OF recognizing seven-red, orange.
yellow, green, blue, indigo and violet. These
colors which the eye perceiyes are by no
means the only ones present in the spec
trum. II we perform the experiment Il a
dark room, and place a Photographic plate
In such a position as to receive the image
Of the spectrum, we find that it extends TO
a considerable distance beyond the violet.
In other words, there is a region beyond
the violet which the eye cannot see, but
which the sensitive plate is able TO photo
graph, This region is termed the ultra
violet, and the light from virtually all
sources contains a greater or less amount
Of this ultraviolet ight.
The only difference between this ultra
violet Light and ordinary visible light Is
IN the length of the wave. which is. in fact.
the only difference between the diff
ferent colors of the visible spectrum. II,
. instead ~ YYefnu q gf.rg ,-g--, g. -
our spectrum, We use one cut from a
quartz crystal. We find that the ultra
violet spectrum is very much longer, which
shows US that the shortest waves OF light
are not transmitted ever by the c~learest
glass.
II our eyes were sensitive TO this region
OF the spectrum, instead OF TO the other.
The appearance Of things would appear
black our windows would be as opaque as
sheets Of iron, and polished silver would
resemble anthracite coal. In other words.
things appear as they do merely from the
circumstance that. in the process Of evolu-
ton. our eyes have developed a senslbihty
70 a certain region Of the total spectrum
OF the light which comes to Us from the
sun.
II we have used an ordinary Photographic
plate in our experiment.. we shall find
that it has received no impression from the
red and yellow parts OF the spectrum and
very little from the green. The plate. there
fore, suffers from the same defect as our
eye; 1t is sensitive only 70 a limited region.
Recently, however. means have been found
Of rendering plates sensitive TO the entire
visible spectrum. ard 70 a certain extent
TO the infra-red, or the extension beyond
the red analogous 10 the one beyond the
violet.
With a Photographic plate rendered SEN
sitive TO the entire spectrum we could OBJ
tain an idea Of how things would appear
II our eyes were sensitive 10 regions other
than the one adopted by nature. by ex-
Guiding from the lens OF the camera all
rays other than the ones with which we
wish 10 operate. This Is done to a limited
extent every day by an photographer who
employ color screens in their work. and Il
Is well known that increased contrast can
often be obtained IN this way.
II for example, We attempt to photograph
white clouds against a blue sky without the
use OF such a screen, we get scarcely any
trace Of the clouds at all whereas II We
place a yellow glass In front OF the lens.
the clouds come out snow white on a very
dark background.
We can see this same effect by view
ing the clouds first through a piece OF deem
blue glass. which Is what the photographs