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Thad,
A ring dial (farmers ring) never works correct in
different latitudes. It just cannot be constructed for different
latitudes at the same time (except you put on its inner side 2 different scales
for different latitudes).
If ring dials are constructed in the correct
way than they work exactly and do not show any errors. But of course there is
the problem that you cannot read exactly the time displayed if the ring
diameter and/or the ring width is to small.
Helmut
----- Original Message -----
Sent: Friday, August 05, 2005 10:24
AM
Subject: Ring dial corrections between
latitudes
Dear Fellow Dialists:
To ensure I am not duplicating something that has already been done, has
anyone developed a formula for showing the error a ring dial (with a fixed
gnomon say 40N) will read when in different latitudes? I am trying to
express more detail than I have in bold below but I'm not sure such can be
easily done, considering the variation in sun altitude throughout a day in
different latitudes. Or have I already expressed the situation about as
well as it can be described to a general audience?
Also, what ring dial graphing programs are out there? I am just
aware of SONNE.
Thanks,
Thad Weakley
42.2N 83.8W
Ann Arbor, Michigan
RING DIAL:
The Ring Sundial is an instrument that gives you the current
time by casting a bead of light rather than a shadow.
- Hang the sundial from the chain to have the maximum exposure to
sunlight.
- Position the sundial to allow sunlight to shine through the hole on the
outer ring.
The bead of light that is cast on the
inner ring indicates the hour and the season.
Such dials are made for particular latitude. While these dials are
readable in other latitudes, there will be error as easy calibration isnt
available. In general in lower latitudes the dial will read fast in the a.m.
and slow in the p.m. In higher latitudes the dial will read slow in the a.m.
and fast in the p.m.
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