A modern version of a polarising sundial was described by Allan Mills in
the British Sundial Society's Bulletin in 2009. This article has a
large number of references to polarising dials.
"A NORTH-FACING POLARIZATION SUNDIAL OF VARYING HUE"
(BSS Bulletin Volume 21(i) March 2009 ).
Mike Isaacs
In message
<CAM6dci52LjiF6CHb_papM5eMiWjCSejjA9UP=1zxd4f7ntt...@mail.gmail.com>,
Patrick Vyvyan <[email protected]> writes
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
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