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    Re: Agnostic gnomon and horary error
    From: Chuck Varney
    Date: 2024 Jun 1, 08:37 -0700

    Frank Reed,

    Albert Waugh, author of Sundials: Their Theory and Construction, neither designed nor built the armillary sphere at Mystic. At the end of The Armillary Sphere chapter of his book (which I have) he wrote: “ . . .Figure 17.4 [the photo that appears on the book cover] shows such a sphere, more ambitious, to be sure, than would ordinarily be made for a home garden, which was designed and built for the Old Mystic Seaport by Edwin Pugsley. . .”

    (Before I checked the book this morning I was going to refer to armillary spheres like the one at Mystic as ‘garden techno-art’.)

    If you’re really interested in the gnomon elevation angle of the Mystic sphere, you might start by photographing it yourself—perpendicularly, rather than obliquely as in the photo. (I calculate that photographing it from an azimuth of 129 degrees rather than from 90, would make a 41.36 degree angle look like 48.56 degrees, due to foreshortening of the horizontal dimension.)

    Rather than playing with photos, why not measure the gnomon angle with an inclinometer, or an Abney level? You could also use a clip board with a sheet of paper taped to it, a cheap 10-inch carpenters level, a pencil, and a protractor.

    Chuck V.

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