Re: Classify sundials?

[john . davis]

Hi Sara,

Thanks for responding - I had remembered our previous discussions on the list 
re classifying dials, but I don't have a quotable reference to what you and 
your colleagues have produced that I, and the other dabblers at dialling, can 
refer to. Perhaps when you return home you could point us to the publication.

Re cylinder dials - whoops, I'm very red-faced at dropping that clanger!  What 
I should have said, of course, is that the gnomon always faces the Sun, not the 
south.

Re moving dial faces, I hadn't intended this to refer to portable dials, but to 
dials in which the dial face and its hour lines have to be specially aligned 
for every reading.  Thus a Butterfield dial, for example, is a portable dial 
but the dial is always set up just like a fixed dial, aligned horizontal & N/S. 
 However, Regiomontanus, Capuchin, quadrants etc have to be pointed at the Sun 
and tilted to align them.  I think this requires an entry in any classification 
scheme.

Re nonius - I agree with you in that the formal name of a "diagonal scale" is 
transversals - the Second Edition of the Glossay will contain both terms as the 
former is sometimes found in the literature.  The nonius gets a separate entry, 
together with a v. brief biog of Nonez.

Best regards,

John

Re: Classify sundials?

[Chris Lusby Taylor]

Sara Schechner wrote:
At 06:56 PM 10/15/01 +0100, Chris Lusby Taylor wrote:
By the way, John, could you please note in the BSS Glossary that the
correct term for a diagonal scale (used to interpolate the shadow edge
between successive hour lines) is a nonius, from Pedro Nuñez,
the
Portuguese inventor.
I do not think that this is right.  I think you are referring to
a
transversal rather than a nonius.
Happy dialling,
Sara
 
Sara is right. I was mistaken. Although in some countries 'nonius' is used
to refer to a vernier, it originally and correctly refers to a device consisting
of 45 concentric circular scales in a quadrant, each divided into between
46 and 90 parts, so an angle can be read as, say, 57/73 of a right angle.
See, for instance, < http://www.mhs.ox.ac.uk/epact/catalogue.asp?enumber=98558
>. This wouldn't seem very helpful for sundials.
A transversal is a diagonal scale. It appears to have been invented
by Tycho Brahe. He used it in a quadrant to allow stellar altitudes to
be read to 10 arc seconds (See ).
See also  
which has both a transversal scale and a grid that shows the sine and tangent
of the angle. In sundials, the diagonal scales are usually graduated in
minutes. I haven't been able to find a URL for one, but there's at least
one pictured in Cousins' book.
By coincidence, I visited Prague last month and climbed up the astronomy
tower in the Klementinum, which is where Tycho Brahe last worked. There
are two transit telescopes with quadrants, but I didn't notice if they
had transversals. In the same room, there is an unusual meridian line.
It consists of a fine wire strung about 5cm above a slab of marble. It
is illuminated by a small hole high in the wall. At noon, I presume one
sees the sun's disc on the marble bisected by the shadow of the wire. This
was used until the 1920s to give a noon signal by gun, flag and, latterly,
radio.
On the east and west sides of the tower there are painted sundials,
except that the westerly one has been totally obliterated. The gnomon is
all that remains. There are, apparently, 17 sundials in the Klementinum,
but I only spotted 8 of them, all painted on walls.
Chris Lusby Taylor
Newbury, England
51.4N 1.3W
 
 

Re: Classify sundials?

[Sara Schechner]

A brave attempt - there seem to be as many classification systems for 
dials as there are diallists.   
I believe that the professionals writing museum catalogues have their own 
classification system but I've not found out where it's written up - 
anyone know?


I can't respond very fully to this at this time, as I'm at a meeting of the 
Scientific Instrument Commission in Stockholm this week.  However, this 
topic has been discussed on this list before, and I would say that there 
are standards for dial classification, and these are published in works by 
myself and my colleagues.  More on this later.  For now:



1. The type of "hours" that the dial is intended to indicate is 
significant eg equal, temporary, Babylonian, Italian etc.


yes



2.  The dial plate may be movable, as in most of the card-dials etc.


By movable, I assume you mean portable as opposed to fixed dials.

 BTW, I note that you classify the shephers' (or cylinder) dial as having 
a movable gnomon, whereas I would say the gnomon is fixed - it always 
points south - whilst the dial plate rotates with the date behind it.


This is mistaken.  In a pillar dial, once the gnomon is set to the date, 
the instrument is turned until the gnomon points in the direction of the 
sun's azimuth at that moment.  It is only due south at solar 
noon.  Otherwise the gnomon is easterly or westerly.


At 06:56 PM 10/15/01 +0100, Chris Lusby Taylor wrote:
By the way, John, could you please note in the BSS Glossary that the 
correct term for a diagonal scale (used to interpolate the shadow edge 
between successive hour lines) is a nonius, from Pedro Nuñez, the 
Portuguese inventor.


I do not think that this is right.  I think you are referring to a 
transversal rather than a nonius.


Happy dialling,
Sara



Dr. Sara Schechner
David P. Wheatland Curator
Collection of Historical Scientific Instruments
Harvard University, Science Center B-6
Cambridge, MA 02138

Tel:  617-496-9542
Fax:  617-496-5932

Re: Classify sundials?

[Chris Lusby Taylor]

[EMAIL PROTECTED] wrote:

>
> I believe that the professionals writing museum catalogues have their own 
> classification system but I've not found out where it's written up - anyone 
> know?
>

The only museum catalogue I use that includes sundials is the Epact catalog 
. Unfortunately, it employs no discernable 
classification system, and the participating museums often use different terms 
for similar features, making searching very difficult.
However, it does have quite a good glossary.

By the way, John, could you please note in the BSS Glossary that the correct 
term for a diagonal scale (used to interpolate the shadow edge between 
successive hour lines) is a nonius, from Pedro Nuñez, the Portuguese inventor.

Sorry if this is in HTML. It should be plain text only, but I'm not confident 
in my settings.

Chris Lusby Taylor
Newbury, England
51.4N, 1.3W

Re: Classify sundials?

[john . davis]

Hi David,

A brave attempt - there seem to be as many classification systems for dials as 
there are diallists.  Your scheme is not unreasonable though I think you have 
missed a few things:

1. The type of "hours" that the dial is intended to indicate is significant eg 
equal, temporary, Babylonian, Italian etc.

2.  The dial plate may be movable, as in most of the card-dials etc.  BTW, I 
note that you classify the shephers' (or cylinder) dial as having a movable 
gnomon, whereas I would say the gnomon is fixed - it always points south - 
whilst the dial plate rotates with the date behind it.

3.  Gnomons can be multiple segments, as in bifilar dials, not to mention the 
shadow edge devices.

I believe that the professionals writing museum catalogues have their own 
classification system but I've not found out where it's written up - anyone 
know?

Regards,

John Davis

> Dear All,
> 
> Some time ago,  a list member gave the following definition of a 'singleton
> dial'  - "it's a horizontal dial with polar-pointing style and showing
> standard time on 12 date rings"  Also, in the BSS glossary of dials, key
> characteristics of dials physical construction are highlighted to explain
> the set of dials that belong to one dial type.
> 
> Classification of dials based on physical characteristics is a way of
> recognising basic types of dials.
> 
>  I am considering the question -
> "How many dimensions are necessary to classify the types of sundials?"
> 
> The following 4 dimensions (domains) come to mind quickly:
> 
> *dial principle
> shadow
> transmission (light beam through a hole)
> reflective
> diffraction
> 
> *dial plate
> -planar
> - horizontal
> - inclined
> - vertical
> -cylinder
> - polar
> - vertical
> -hemisphere
> -arbitary hollowed out surface
> 
> *gnomon
> -point
> - fixed
> - movable
>  -segment
> - polar
> - vertical
> - fixed
> - movable
> 
> *hour markers
> -point
>-segment
> - curve
>  -analemma
> -figure 8
> - half
>  - equation of time
> -unfolded "analemma"
> 
> Example classifications using the above 4 dimensions
> 
> Horizontal Dial: principle:shadow, dial:planar-horizontal, gnomon:
> segment-polar, hour markers: segment
> Analemmatic Dial: principle:shadow, dial:planar-horizontal, gnomon:
> segment-vertical(movable), hour markers: point
> Shepherd's Dial: principle:shadow, dial:cylinder-vertical, gnomon:
> point-movable, hour markers: solar altitude curve
> 
> Is 4 dimensions enough to separate all the various types of dial? Almost
> certainly not. What is the minimum set of other (semi) orthogonal dimensions
> can be added to classify known dial types?
> 
> Has any work been done on this by others?
> 
> In this endeavour, careful attention to separating 'classifying dimensions'
> from 'dial attributes'.  Attributes 'flow from' key classifying
> characteristics of the dial construction.  Eg. 'self aligning' is probably
> not a classifying dimension, as it arises as a consequence of the nature of
> construction, rather than being an observable classification dimension.
> 
> Thanks
> 
> David Pratten
> www.sunlitdesign.com
> 
> David Pratten
> 
> Phone:  7 (3272) 46 04 20
> Fax (auto forwarded):  1 (603) 676-1231
> Postal: PO Box 21, Almaty 480057, KAZAKHSTAN
> 
> 

Classify sundials?

[david]

Dear 
All,
 
Some time 
ago,  a list member gave the following definition of a 'singleton 
dial'  - "it's a 
horizontal dial with polar-pointing style and showing standard time on 12 date 
rings"  Also, in the BSS glossary of dials, key characteristics of dials 
physical construction are highlighted to explain the set of dials that belong to 
one dial type.
 
Classification of 
dials based on physical characteristics is a way of recognising basic types 
of dials. 
 
 I am 
considering the question - 
"How many 
dimensions are necessary to classify the types of sundials?"
 
The 
following 4 dimensions (domains) come to mind quickly:
 
*dial 
principle
    shadow
    transmission (light beam through a hole)
    reflective
    diffraction
 
*dial 
plate
    
-planar
    
- horizontal
    
- inclined
    
- vertical
    -cylinder 
    
- polar
    
- vertical
    -hemisphere
    -arbitary hollowed out surface
 
*gnomon
    
-point
    
- fixed
    
- movable
 -segment
    
- polar 
    
- vertical 
    
- fixed
    
- movable
 
*hour markers
    -point
   -segment
- curve
 -analemma 

    
-figure 8
    
- half
 
    - equation 
of time 
    
-unfolded "analemma"
 
Example 
classifications using the above 4 dimensions
 
Horizontal Dial: 
principle:shadow, dial:planar-horizontal, gnomon: segment-polar, hour markers: 
segment
Analemmatic Dial: 
principle:shadow, dial:planar-horizontal, gnomon: segment-vertical(movable), 
hour markers: point
Shepherd's Dial: 
principle:shadow, dial:cylinder-vertical, gnomon: point-movable, hour markers: 
solar altitude curve
 
Is 4 dimensions 
enough to separate all the various types of dial? Almost certainly 
not. What is the minimum set of other (semi) orthogonal dimensions can be 
added to classify known dial types?
 
Has any work been 
done on this by others?
 
In this endeavour, 
careful attention to separating 'classifying dimensions' from 'dial 
attributes'.  Attributes 'flow from' key classifying characteristics of the 
dial construction.  Eg. 'self aligning' is probably not a classifying 
dimension, as it arises as a consequence of the nature of construction, rather 
than being an observable classification dimension.
 
Thanks
David Pratten
www.sunlitdesign.com 
David PrattenPhone: 
+7 (3272) 46 04 20Fax (auto forwarded): +1 (603) 676-1231Postal: PO Box 
21, Almaty 480057, KAZAKHSTAN