The mirror., 1919-04-24
Phenomena of Light
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is, when we consider that if an inch we're
divided into exactly IS, 400, 900 equal parts,
each part would be one micro-millimetre in
length.
A physical law governing refraction,
tells us that the shorter the wave length of
light, the greater the refraction of that
wave, and vice versa. By permitting a
beam of light to pass through prism we
may produce an image of its spectrum. A
prism may be made of any transparent
refracting medium whose plane surfaces are
not parallel. The apex, base, and sides of
a prism are terms which explain them
selves. A ray of light entering prism,
obliquely, is. as we know, reflected towards
the perpendicular of that surface. On
emerging, it is refracted away from the per-
pendicular of the second surface. This
causes the rays always to be refracted
towards the base of the prism, the violet
rays being refracted the most, and the red
rays the least. So the beam of light on
emerging from the prism and being al
lowed to fall on white screen, will pre-
sent to our eyes an image OF spectrum of
the various colors existing in the original
beam. The beam is now decomposed or
separated into its various colors, in their
respective order; violet, indigo, blue, green,
yellow, orange and red.
To prove this, if we allow the decom-
posed light rays to pass through another
prism, whose base comedies to the apex of
the first prism, the decomposed light will
become recomposed and reassembled and
will emerge from the second prism as a
beam of white light.
1t is of interest to note that, through an
analysis of the spectra of luminous bodies,
scientists are able to determine the nature
and composition of that source of light.
The solar spectrum reveals to science the
knowledge of the various elements which
compose the body of the sun. By the
study and analysis of the spectra of light
emitted by distant stars we now know
what metals and minerals constitute the
structure of these stars. This seems more
wonderful still, when we consider that
some of these stars are so far disrant from
our earth, that it takes thousands of years
for their light to reach us, though this
light is continually travelling to our earth
at the rate of 186, 900 miles every second of
time.
By the formation of spectrum we can
also prove the existence of light rays which
do not stimulate the organs of vision, and
which, consequently we do not perceive.
There are light waves which are so long and
which vibrate so slowly that they fail to
affect the eye. Likewise are there waves
which are too short and which vibrate too
rapidly for US to perceive. The former
are known as infra-red, or heat rays; and
are below the visible red in the spectrum.
The latter are called ultraviolet rays and
are above the visible violet of the spec
trum. BY placing delicate thermometer
bulb just beyond the red of the spectrum,
the mercury will rise, proving the exis-
tence of the heat rays. The ultraviolet
rays, are detected by their action on var
ious chemicals. So we see that the word
sight does not always mean light, as there
are many light rays which are never seen
by the eye.
With our knowledge of the causation and
formation of the solar spectrum, it is sim.
pie matter to understand that phenomenon
of light known as the rainbow. Each sep
arate drop in a shower of rain or a curtain
of mist may be considered as tiny prism.
A round drop of water has prismatic ef-
feet on light as no two of its surfaces are
parallel. A rainbow is visible when
shower of rain or mist is before an OBJ
server, and the sun behind him. The rays
from the sun are all parallel and so effect
each separate drop alike. On entering the
drop of water the rays ara refracted by its
first surfas e, are reflected back by the Sec
ond surface, and on emerging, are again
refracted, but at different angle than at
which they entered. Reaching the eye Of
an observer they are projected backwards,
and the image being inverted, we see the
red on the outside of the bow, and the vi
olet on the inside, and the intermediate
colors in their respective order.