Thank you to Joel, Fabio, and Bill.
Before I sent off my inquiry last night, I had got as far as deciding
the dial must be some kind of Foster-Lambert similar to the Herstmonceux
dial that Fabio mentioned, but I was still confused. I'm relieve to
learn that it's not related to an analemmatic dial at all, and Wikipedia
is simply wrong!
Steve
On 2019-05-31 5:14 a.m., Bill Gottesman wrote:
Hello Steve, I'll take a guess at this.
I think the dial is really a heliochronometer with an analemma, not an
analemmatic dial. I think the screws up top held a focusing lens or a
pinhole aperture that projected a beam on to an analemma on to the
lower plate. The analemma is not visible in that picture. The dial
is turned to make the beam align, so the hours go counter-clockwise,
and the time is read across from stationary indicator at the very top
of the dial, hidden from view in this photo.
Similar to the upper left dial seen at
https://equation-of-time.info/sundials-with-shaped-alidades . -Bill
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