Mr Chabot
There is indeed a huge difference between the radiation absorption of
black and white surfaces. I first noticed this in a temple in Rangoon,
the black marble parts of the courtyard were too hot to stand on with
the required bare feet, whereas the white portions were quite cool. I
am not sure how this could be used in a practical sundial. Perhaps the
dial could be marked in relief and walked across with bare feet.
Everyone could be asked to remove their shoes.
I was an irrigation engineer in SE Asia before I retired, specializing
in rice. I proposed using the black absorption phenomena in drying
floors in SE Asia for the unhusked paddy. In some areas drying the
crop quickly is essential for successful rice cultivation.
Brian Albinson
now at 49.33,123.06
Th. Taudin Chabot wrote:
John,
When I red your experience with your feet I remembered the same
experience on a concrete pavement.
For a sundial my feelings would say: use for each quarter of an hour a
separate piece of stone separated by a thin thermal insulator. In that
way even the slightest heat differences might be able to feel.
Thibaud Chabot
At 18:34 02-07-2004, John Carmichael wrote:
Hello
All:
I've been meaning to tell you about an
experiment I did....
Several months ago, we recieved a photo
of a
sundial for the blind that used a glass sphere to focus sunlight on
metal
strips located around it. Each strip is a different hour. The
sun heats the strip and you feel the time. (The maker warns that
you have to be careful to avoid buring your fingers!) I thought it
was a neat idea then forgot about it.
Well, one day I was barefoot on on our
red
brick patio and my feet were on fire since the bricks were so hot.
But I had to cross the patio to get to the other side. Rather than
putting on shoes, I discovered if I walked along the shadow edge cast
from the roof eave, that it wasn't so hot. The temperature
difference of the brick between the shadow umbra and the full sun was
huge. Then I remembered the Sundial for the Blind. I wondered
how accurate a finger would be in finding out where the center of the
penumbra is. I was surprised that I was able to feel with my finger
within 2 cms. where the penumbral center was! This is just about as
precise as using a shadow sharpener!
So, you don't need the magnifying
effects of a
glass sphere in order to feel the temperature difference. The sun
alone is strong enough.
This implies that you could build
sundial for
the blind without having to magnify the sunlight. But I imagine
that it wouldn't work very well very early in the morning or very late
in
the afternoon since the sun is weak at these time. I don't know if
it would work in the winter. Also, you'd have to make the sundial
face out of some low thermo-cunductive material like stone, cement or
ceramics. I don't think you could make one out of any metal.
The gnomom would have to be a "sheet" gnomon and not a
cable or rod gnomon. Monumental large designs would problably work
best.
Not that anyone will ever make one. I
just thought you'd be interested in the concept.
John Carmichael
John L. Carmichael
Sundial Sculptures
925. E. Foothills Dr.
Tucson AZ 85718
USA
Tel: 520-6961709
Email:
[EMAIL PROTECTED]
My Websites:
Sundial Sculptures:
http://www.sundialsculptures.com
Stained Glass Sundials:
http://stainedglasssundials.com
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Th. Taudin Chabot, home email: [EMAIL PROTECTED]
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