Hi Steve et al,
It's usually just called a disc dial. I don't think the example shown is
latitude-adjustable: the suspension point is fixed. All the historical ones
I've seen are single latitude devices. Only the occulus is adjustable, for date
(declination). Earlier examples had the hour points set on a concentric circle
which meant that they were very inaccurate at some times of the year - the
extension lobe on this one is an empirical attempt to improve things. The
mathematics are dubious.
The earliest versions seem to be 16th century and there are quite a number from
the 17th. I have one along similar lines found by a metal detectorist in
Norfolk (UK).
Regards,
John
------------------------------------
Dr J Davis
Flowton Dials http://www.flowton-dials.co.uk/
BSS Editor http://www.sundialsoc.org.uk/bulletin.php
________________________________
From: Steve Lelievre <steve.lelievre.can...@gmail.com>
To: "sundial@uni-koeln.de" <sundial@uni-koeln.de>
Sent: Sunday, 1 June 2014, 23:13
Subject: Request for information about a type of altitude dial
Hi folks,
http://www.pinterest.com/pin/301178293801331061/
What type of dial is this; I realize it's a form of altitude dial, but is there
a specific name for it?
The accompanying note states that the dial can be adjusted for latitude by
moving "the attachment point". I don't understand which part of the mechanism
does that. Can anyone explain it for me?
Lastly, I'm appreciate references for articles or webpages that discuss these
dials - history and mathematics.
Thanks,
Steve
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