Re: [privacy] U.S. OMB: 'People are Losing Data'

["Brian Loe" <knobdy () gmail com>]

On 11/3/06, Drsolly <drsollyp () drsolly com> wrote:
> On Thu, 2 Nov 2006, Gadi Evron wrote:
>
> > On Thu, 2 Nov 2006, Fergie wrote:
> > > And in other news, scientists say the sky is blue. :-)
> >
> > I wonder what the real colour of the sky is. I am sure it is not blue!

Shine a narrow beam of light through fish tank or large beaker or
filled with water. Add drops of milk or powdered milk or acidified
sodium thiosulfate solution while stirring until you can see the beam
shining through the water. Look at the beam both from the side and
from the end, where the beam shines out of the container. Viewed from
the side, the beam appears blue. Viewed parallel to the direction of
the beam , the beam appears orange red or yellow. See the colour of
the beam change from blue-white to yellow orange along the length of
the beam. Let the light project onto a white card at the end of the
tank. The beam spreads so it is not so narrow as the source of light.
Particles in the milk scatter the light and so you can see the beam
from the side. Blue light is scattered much more than orange or red
light so we see more blue light from the side. Orange and red light is
scattered less so we see it at the end. The shorter wavelength blue
light has greater refractive index so it bends more than longer
wavelength red light with a smaller refractive index. Similarly,
atmospheric gases smaller than one wavelength scatter blue light so
the sky appears blue. This is called Rayleigh scattering. The sun is
white hot but it appear orange red because the white light from it has
lost some of the blue light. When the sun is on the horizon, its light
takes a longer path through the atmosphere to your eyes than when the
sun is directly overhead. So at sunset most of the blue light is lost
by scattering leaving the red orange light, i.e. white light minus
blue light. Only the longer wavelengths reach the eyes. If there were
no scattering, and all the from the sun travelled straight to the
earth, if not looking at the sun, the sky would look dark as it does
at night. Large particles, e.g. dust, smoke, pollen, scatter light
without breaking white light into component colours. This is called
Mie scattering. It is the cause of the whiteness of clouds, mist,
milk, latex paint and the white glare around the sun and moon during a
mist.
2. Place a lens from Polaroid sunglasses between the light source and
the fish tank. Hold the lens vertically and turn it while another
person observers the beam from above and another person observes the
beam from the side. When the person above observes a bright beam, the
person at the side person observes a dim beam, and vice versa. This is
the same effect when look through two parallel lenses from sunglasses
and you turn one of the lense. At a certain position no light or very
little light passes through both lenses. So the scattering in the fish
tank polarizes the light.
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