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Hi Frans et al,
Polarizing sundials have featured a number of times in the BSS Bulletin. In the
same issue (21(i), March 2009) as the article by the sadly-missed Allan Mills
that Mike Isaacs pointed to earlier, Allan had a second article, pp. 14-16, on
"An Electronic Polarization Sundial and Photometer" which shows background
experiments on the physics that Wheatstone's device is based on. The first of
these articles was one of the earliest we printed in colour, essential to see
the proper effect of Allan's dial.
Earlier articles in the Bulletin are by Allan Mills again ("The Sellotape
Sundial" 98(1) 3-9) and by David Colchester "A polarized light sundial" 96(3)
13-15.
I think reading these articles will fully explain Wheatstone's device, of which
several were evidently made.
Regards,
John----------------------------------
Dr J Davis
Flowton Dials http://www.flowton-dials.co.uk/
BSS Editor http://sundialsoc.org.uk/publications/the-bss-bulletin/
On Tuesday, 21 May 2019, 21:06:52 BST, 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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