In a message dated 1/5/2003 12:43:11 PM Eastern Standard Time,
[EMAIL PROTECTED] writes:
> Here are the problematic ones for me-- Where should these be placed?
>
> Universal ring dials and crescent dials--these are self-aligning, and so
> must be more than simply directional equatorial dials. Are they
> combinations of hour-angle and altitude sundials, or something else?
I believe that these are purely specialized atltitude dials. They all
measure time solely from the sun's altitude, after being adjusted for a
specific date and latitude. They are self orienting because this adjustment
constrains sunlight from falling on the scale unless the orientation is
correct. i.e.; no reading can be made unless the orientation is correct for
a given adjustment.
> Oughtred-type dial (also called the "double horizontal dial") --a
> combination of a a horizontal plate dial with a polar gnomon and one with
a
> vertical-stick gnomon--self-aligning
> ?? is this a combo hour-angle and azimuth sundial??
Yes. And if I remember correclty, there is also a means for measuring the
sun's altitude, but this does not play a role in its time keeping or date
keeping.
> Analemmatic dial (modern form) with elliptical hour scale--is this an
> azimuth dial?
Yes.
> Heliochronometer--standard definition? A solar chronometer that uses the
> sun to find mean time directly. Where would this go in the
> classification? An equatorial dial with a date cam?
Well, all the ones I know measure hour angle, but they are not all
equatorial. John Carmichael's are horizontal, and mine are equatorial
(Renaissance) and horizontal (Saywer Equant).
Also, I favor the term "Right Ascension" or "Hour Angle" sundials to the term
"Directional" sundials.
Bill Gottesman
www.precisionsundials.com
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