Wheatstone's Polarizing Dial An explanation of Wheatstone's invention is to be found in the Report of the meeting of the British Association for the Advancement of Science in Swansea held in 1848, although to be honest it's scientific foundation has me a little challenged! The report is available online at https://www.biodiversitylibrary.org/item/46637#page/188/mode/1up Should you have access to an original paper copy, the description of the Polarizing Dial begins on page 10. The numeral scale represents one complete day of 24 hours - it seems the device can work even without direct sunlight.
Best wishes, Patrick Vyvyan On Tue, 21 May 2019 at 16:07, Maes, F.W. <[email protected]> wrote: > Recently the Tesseract Catalogue 109 was announced on this list. Item nr. > 13 is a polarizing sundial by Charles Wheatstone. A virtually identical > dial is in the collection of the Greenwich museums, see: > https://collections.rmg.co.uk/collections/objects/265579.html. > I have never understood how this sundial works. The hour scale shows 2 x > 12 hour numbers in a semicircle. So whatever pattern is observed in the > black glass reflector, it is obviously supposed to rotate over 180° in 24 > hours, which is half the angular velocity of the sun itself. How does this > frequency division-by-two come out? Can anybody explain? > > Thanks! > Frans Maes > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > >
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