Re: Request for information about a type of altitude dial

[John Davis]

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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RE: Request for information about a type of altitude dial

[Schechner, Sara]

There has been some confusion in the discussion so far.  Here is my take:

The sundial pictured is called a “vertical disk dial.”  It is an altitude 
sundial.
The example pictured is similar to one at CHSI (inv. 7270) signed “I W” with a 
punch mark of a crown and date 1672.  It is for latitude 52° 35'.

Most of the vertical disk dials are for single latitudes, and have a single 
suspension point.  However, a few try to be adjustable for latitude.  At 
Harvard, an example is inv. 7264, which is signed and dated “ P. L. K. / 1755.”

I will tweet images of them and post them in this Dropbox:  
https://www.dropbox.com/sh/9qg1p0kejm3o842/AACoYez5bVtRU5JhPJuJgOK8a

Sara

Sara J. Schechner
Altazimuth Arts
42°36'N   71° 22'W
West Newton, MA 02465
http://www.altazimutharts.com/

Sara J. Schechner, Ph.D.
David P. Wheatland Curator of the Collection of Historical Scientific 
Instruments
Department of the History of Science, Harvard University
Science Center 251c, 1 Oxford Street, Cambridge, MA 02138
Tel: 617-496-9542   |   Fax: 617-496-5932   |   sche...@fas.harvard.edu
http://scholar.harvard.edu/saraschechner
http://chsi.harvard.edu/


On Sun, Jun 1, 2014 at 6:13 PM, Steve Lelievre 
steve.lelievre.can...@gmail.commailto:steve.lelievre.can...@gmail.com wrote:
Hi folks,

http://www.pinterest.com/pin/301178293801331061/https://urldefense.proofpoint.com/v1/url?u=http://www.pinterest.com/pin/301178293801331061/k=AjZjj3dyY74kKL92lieHqQ%3D%3D%0Ar=Y3uaNkd%2BN%2BBEMo7BAxbEQqOqpMk6uxYnCJsB4uxugzo%3D%0Am=izSTWMgNnFv8DfKU%2Bd249F%2B%2FyJSDHvIkXOyVUqkC8%2FU%3D%0As=7631973f481f1363e8d75a48591133eaed99295b1faf9d05a8f4a1ea4c25175d

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







---
https://lists.uni-koeln.de/mailman/listinfo/sundialhttps://urldefense.proofpoint.com/v1/url?u=https://lists.uni-koeln.de/mailman/listinfo/sundialk=AjZjj3dyY74kKL92lieHqQ%3D%3D%0Ar=Y3uaNkd%2BN%2BBEMo7BAxbEQqOqpMk6uxYnCJsB4uxugzo%3D%0Am=izSTWMgNnFv8DfKU%2Bd249F%2B%2FyJSDHvIkXOyVUqkC8%2FU%3D%0As=dcc654938564a18e96ec2bb9f94d253a409277009b33d3b5467c6486ffb43f43

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