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Dear Mike,
It shows that there is very
little new in the world! George Higgs made these dials with the assistance
of David Gulland in Dumfries for several years. And very nice they are
too. I have one in my SW window and it really is spot on time.
It hangs between the primary and secondary glazing spaced 1" from the outer
pane. The gnomon is a 'printed circuit' type round pad, (black crepe
tape), about 6mm dia with a central hole of about 1mm, stuck on the inside of
the outer pane. It is hence very easy to read, even at some
distance.
Regards,
Mike Cowham
Cambridge,
UK
----- Original Message -----
Sent: Sunday, July 28, 2002 7:53 PM
Subject: Double glazing dial
I have wondered for a while if it was possible to make use of
the two panes
of glass in double glazed units to make a window
sundial.
To try out the concept, I made a prototype dial using two
panes of glass,
clamped 44mm apart (I just happened to have some wood that
thickness).
The pane nearest to the sun carries a double arrow which acts
as the gnomon
nodus. The inner glass carries the dial
face.
The dial was designed for a site which declines 76 degrees West
of South -
the back of my house.
I used Francois Blateyron's Shadow
programme - Version 6.2.1
I have put a picture on my web page - follow the
link to "Double Glazing
Dial" - there is a link to Jim Tallman's single
glazing dial there as well.
The frosting was applied from a spray can,
and the clear areas were simply
masked off. For the lines, I used
"Magic" tape - the type that doesn't show
up on photocopiers, cut into thin
strips using a straight edge and craft
knife. The numbers were made
by removing the frosting using a stencil and
Dremel drill fitted with a
flexible drive shaft.
In this dial, I frosted both the "inside" faces,
so there is no glass
between the nodus and the dial face. Hence, no
refraction problems. But in
the "real thing" I would have to use the
"outside" surfaces, and account
would need to be taken of the refraction of
two panes of glass. The effect
would change throughout each day, and
through the seasons. The dial would
also be smaller, the gap between
the panes in my units is only 20mm.
A quick test (sticking OHP film on
the windows) shows that errors of about
15 minutes at the extremities - I
guess the varying error is related to the
changing angle of incidence of
the sunlight.
My mathematics isn't up to the three dimensions involved -
can anyone help?
Mike Shaw
mailto:[EMAIL PROTECTED]
http://homepage.ntlworld.com/jmikeshaw/
N
53º 21' 24"
W 03º 01' 47"
Wirral,
UK.
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