Essex County herald. [volume] (Guildhall, Vt.) 1873-1964, 1910-03-04
LIGHT AND THE EYES
We Do Not Always See Things
as They Really Are.
CoLoRS WE CANNOT DISCERN
Normal Vision Is Not Able TO Pene-
trate to the Regions Beyond the VIC
Iet-Some Results That Have Been
Attained With the Camera.


trate to the Regions Beyond the VIC
Iet-Soms Results That Have Been
Attained With the Camera.
Those of us who are fortunate
enough tu possess normal eyes are APT
In feel instinctively that We see things
Rs they are This is n mistake, The
appearance of the world ut 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 llsh'
through prism.
When beam Of sunlight passes
through prism of glass such as Is
often found ON old fashioned chahde'
liers the rays are spread out. FORMING
spectrum. which we see as Il ram
how colored band upon the wall. The
colors of the spectrum merge into one
another by insensible gradauons.
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
eynariment In a dark room and place
a photographic plate in such position
In nf
trum we find that 1t extends to con
siderable distance beyond the. violet.
In other words there is II 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 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 violet
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 this
region of the spectrum instead of tC
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. thing:
appear as they do merely from the cir
cumstance that in the process of eyO
luton our eyes have developed a sensi
bility to a 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 froI
the green. The plate therefore suffer
from the same defect as our eye.
is sensitive only to a limited regior
Recently, however, means have bee
found of rendering plates sensitive t
the entire visible spectrum and to
certain extent to the infra red or tn
extension beyond the red analogous t
the one beyond tine violet.
With Photographic plate rendere
sensitive to the entire spectrum W
could obtain an idea Of how thing
would appear If our eyes were sens
tive to regions other than the on
adopted by nature by excluding frol
the lens Of the camera all rays othe
than the ones with which we wish [
operate. This Is done to limited e:
tent every day by all photographer
who employ color screens in the
work, and 1t is well known that il
creased contrast can often be obtaine
in this way.
If, for example. we attempt to phi
tograph white clouds against bl,
sky without the use Of such a scret
clouds at all, whereas If we place
yellow glass In front of the lens Il
clouds come out snow white on a vel
dark background.
We can see this same effect by vie'
ing the clouds first through piece
deep blue glass, which is what Il
Photographic plate secs" and thu
through the yellow plate.
At my labore tory at East Hampto
N. Y, have pushed this principle
the extreme and have obtained pilot
graphs both by the mira red and t
ultra violet invisible rays.-Robert W
liam Wood In Century.