The Daytona daily news. [volume] (Daytona, Fla.) 1903-1926, 1910-03-02
LIGHT AND THE EYES
We Do Not Always See Things
as They Really Are.
coLoRs WE CANNOT DISCERN

GULUhS WE CANNUI UlSGEnN
Normal Vision Is Not Able to Pene-
trate to the Regions Beyond the vio-
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 SUI
or is given out by a lamp
To make this little clearer we may
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 fashioned chande-
| liers 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 one
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
in the spectrum If we perform the
experiment in a dark room and place
a Photographic plate in such position
as to receive the image of the spec
trum we find that it extends to a 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 q
greater or less amount of this ultra
violet light
The only difference between this III
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. If, instead Of using
glass prism for forming our spec
trum, we use one cut from a quartz
crystal we find that the ultra viole
spectrum is very much longer. which
shows. US that the shortest waves Of
light are not transmitted even by the
clearest glass.
If your eyes were sensitive to thi:
region Of the spectrum instead Of t
the other the appearance Of thing.
would appear black. our Windows
would be as Opaque as sheets of iron
and polished silver would resemble
anthracite coal In other words. thing
appear as they do merely from the cir
cumstance that in the process of eve
luton our eyes have developed senSi
bility to certain region of the tota
spectrum of the light which comes t
us from the sun.
If we have used an ordinary photo
graphic plate in our experiment W
shall find that it has received no i'm
preston from the red and yellow part
of the spectrum and very little fror
the green. The plate therefore suffer
from the same defect as our eye.
is sensitive only to a limited region
Recently. however. means have bee
found of rendering plates sensitive
the entire visible spectrum and to
certain extent to the mira red or tt
extension beyond the red analogous
the one beyond the violet.
With a Photographic plate rendere
sensitive to the entire spectrum "
-
would appear if our eyes were sens
tive TO regions other than the OF
adopted by nature by excluding fro
the lens Of the camera all rays 9th
than the ones with which we wish
operate This is done TO a limited e
tent every day by all Photographic
who employ color screens in the
work. and it is we'll known that
creased contrast can often be obtain,
in this way.
If. for example. we attempt to pf
tograph white clouds against bl
sky without the use of such sore
we get scarcely any trace OF {
clouds at all. whereas If we place
yellow glass in front of the lens t
clouds come out snow white on a We
dark background.
We can see this same effect by vie
ing the clouds first through a piece
deep blue glass. which is what
Photographic plate "sees." and tn
through the yellow plate.
At my laboratory at East Fampt'
n. Y. have pushed this principle
the extreme and have obtained pho
graphs both by the mira red and
ultra violet invisible rays.-Robert v
liam Wood In Century.