The Randall County news. (Canyon City, Tex.) 1908-1926, 1910-03-04
LIGHT AND THE EYES
We Do Not Always See Things
as They Really Are.
col.0Rs WE CANNOT DISCERN

Normal Vision Is Not Able to Pene-
trate to the Regions Beyond the vio-
iet--Soms Results That Have Been
| Attained With the Camera.
Those OF us who are fortunate
enough to possess normal eyes are apt
to feel instinctively that we see things
as they are. This is mistake. The
appearance of the world at large Is
merely the result of the circumstance
that the human eye perceives only
comparatively small part Of the total
radiation which comes from the sun
or is given out by lamp.
To make this little clearer we may
consider one of the Oldest experiments
I'm optics. the passage of ray Of light
through prism.
When a beam OF sunlight passes
through prism Of glass such as is
often found on old fashioned chande-
lers the rays are spread out, forming
a spectrum. which we see as rain
bow cOlored band upon the wall. The
colOrs of the spectrum merge into ono
another by insensible gradations.
though the older physicists were in
the habit of recognizing seven-red.
orange, yellow. green, blue, indigo and
violet.
These colors which the eye perceives
are by no means the only ones present
i'm the spectrum: If we perform the
experiment i'm dark room and place
Photographic plate in such position
as to receive the image of the spec
trum we find that it extends to con
siderable distance beyond the violet.
In other words. there is a region be-
yond the violet which the eye cannot
see. but which the sensitive plate is
able TO photograph. This region is
termed the ultra violet and the light
from virtually all sources contains
greater or less amount of this ultra
violet light
The only difference between this ul-
ira violet light and ordinary visible
light is in the length Of the wave.
which is. in fact. the only difference
between the different colOrs of the
visible spectrum. II. instead Of using
glass prism for forming our spec
trum. we use one cut from 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 even by the
clearest glass.
II your eyes were sensitive to this
region Of the spectrum instead OF to
the other the appearance OF things
would appear black. our windows
would he rs Opaque as sheets OF iron.
and polished silver would resemble
anthracite coal. In other words. things
appear as they do merely from the cir
cumstance that in the process Of evo-
luton our eyes have developed a sensi-
bility to certain region OF the total
spectrum Of the light which comes to
us from the sun.
II we have used an ordinary photo
graphic plate In our experiment we
shall find that ii has received no i'm
preston from the red and yellow parts
Of the spectrum and very little from
the green. The plate therefore suffers
| lTOiu tuC SuIbC uStG't 10 ooh CyS' -
is sensitive only to limited region.
Recently. however. means have been
found of rendering plates sensitive to
the entire visible spectrum and to n
certain extent to the mira red or the
extension beyond the red analogous to
the one beyond the violet.
With Photographic plate rendered
sensitive to the entire spectrum we
could obtain an idea Of how things
would appear II our eyes were seh9i
tive to regions other than the one
adopted by nature by excluding from
the lens Of the camera all rays other
than the ones with which we wish to
operate. This is done to a limited ex'
. tent every day by all photographers
who employ color screens In their
work, and it is well known that In
creased contrast can often be obtained
in this way.
If. for example. we attempt to pho
:. tograph white clouds against a blue
:. sky without the use Of such a screer
we get scarcely any trace Of the
clouds at ALL whereas II we place 6
yellow glass in front of the lens tho
: clouds come out snow white on very
dark background.
. We can see this same effect by view
. ing the clouds first through piece o.
!, deep blue glass. which is what thu
: Photographic plate secs" and theI
, through the yellow plate.
At my laboratory at East Hampton
:, n. Y. I have pushed this principle Il
= the extreme and have obtained photo
!. graphs both by the mira red and tn
ultra violet invisible rays Robert WI
. liam Wood In Century.