Hi,
Today a website called Vermont Free Press published an appallingly
confusing (to me) summary of types of sundials. If you can bear to look,
it's at https://www.vermontpressbureau.com/types-of-sundials/
However, there was one thing about it that piqued my interest: the photo
of an azimuth sundial (
https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg
).
From what I can make out, there is a metal flap at the end of the
alidade / sighting arm (the end at top in the photo). It must get turned
up to make a shadow-caster. I guess the arm has to be rotated so that
the shadow falls along it, and time is then read from where the
right-hand edge of the arm crosses the net of hour and declination
lines. But then, wouldn't the screws seen in the upper plate block the
arm from being turned to the required orientation?
Another bit I can't figure is the little circular scale just north of
the centre of the dial, with the pointer. Perhaps just an Equation of
Time scale? Or perhaps a cam connects it to the arm so that it can be
used to set the arm's length? (The slot in the arm suggests it can be
slid in and out to set the tip at the applicable declination circle,
which is a nifty feature.)
Cheers,
Steve
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