Re: An unusual Polyhedron

[JOHN DAVIS]

Hi Frank,
   
  Thanks for your kind comments on the Bulletin cover.
   
  I think you are a little harsh on the Downing Site polyhedral dial: I don't 
know of many dials with a gnomon pierced with the outline of a camel (alluding 
to eye's of needles, perhaps?!) or which shows so well that the gnomons of 
dials on any plane are all parallel.
   
  I hadn't noticed that the polyhedron isn't one of the common ones used for 
dials. I wonder if there was a dialling reason for choosing it or whether it 
was just an in-joke reflecting the work of Cambridge mathematicians at the time.
   
  Regards,
   
  John D
-
Frank King [EMAIL PROTECTED] wrote:
  Dear John
CAMBRIDGE POLYHEDRAL DIAL

I have just received the June BSS Bulletin...

You are to be congratulated on the cover photograph.
Somehow, you have contrived to make what I regard as
one of the most unprepossessing dials in Britain seem
almost elegant!

For over 40 years my normal place of work has been
approximately half way between this dial and the Queens'
Dial and there could hardly be a more contrasting pair!

There is a curiosity about the polyhedron itself. Until
about 18 months ago I thought this was a straightforward
small rhombicuboctahedron, an Archimedean solid. This
incorporates three mutually perpendicular bands of eight
squares with the gaps filled with triangles.

Amongst other properties, three squares and one triangle
meet at each vertex. This is very clear in your photograph
as is the horizontal band of eight squares.

Rather late in the day, it suddenly dawned on me that this
is NOT a small rhombicuboctahedron. Have a look at your
photograph. You will see that there are NO vertical bands
of eight squares.

This is a pseudorhombicuboctahedron which is NOT an Archimedean
solid because it doesn't have octahedral symmetry. It won't
morph into itself when rotated about a horizontal axis. See:

http://en.wikipedia.org/wiki/Pseudorhombicuboctahedron

You correctly note that Sir William Ridgeway and his wife
Lucy were the donors of the dial. They had a daughter, also
called Lucy, who married John Archibald Venn who was at some
time President of Queens' College. I wonder which dial he
preferred!!

John Archibald Venn's father was the better known John Venn
whose name is forever linked with the well-known diagram.

Best wishes

Frank




Dr J Davis
Flowton Dials---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: An unusual Polyhedron

[Roger Bailey]

If others are interested in what the Cambridge Polyhedron dial looks like, I 
have posted my picture of it at www.walkingshadow.info. Click on Images and 
then CamPoly.jpg. The picture is compressed for the web, only about 103 kb.

I suppose the sundial is multifaceted to reflect Cambridge grads. But the 
sundial is also a bit odd, misshapen with some rough edges and sharp 
projections. If you look closely, you can see the camel in the eye of the 
top gnomon.

Roger Bailey
Walking Shadow Designs
N 48.6 W 123.4

- Original Message - 
From: Frank King [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Sent: Thursday, June 14, 2007 12:44 AM
Subject: An unusual Polyhedron


 Dear John
   CAMBRIDGE POLYHEDRAL DIAL

 I have just received the June BSS Bulletin...

 You are to be congratulated on the cover photograph.
 Somehow, you have contrived to make what I regard as
 one of the most unprepossessing dials in Britain seem
 almost elegant!


---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Rotating Sundials

[Edley McKnight]

Dear Dialers,

While we are on the subject of rotating dials around their gnomons or other 
lines parallel to the earth's axis ( Or not so very far off of the subject ) 
Other 
things can be accomplished by the rotation as well as EOT, Longitude and 
Daylight savings compensations.  For instance a Horizontal dial can be 
rotated a number of full hours, the hourlines renumbered and made viewable 
from a window or other site.  Instead of starting at say 6 AM, the dial might 
start at 9 AM for more civilized folks.  Some dials, such as the Cycloid Polar 
Sundial and the book dial derived from it typically have the Noon line buried 
down in a deep cleft.  Rotating them a few hours can put noon where it is 
easily read.  In fact other copies of the sundial, prerotated, can be placed 
above or below so that all of the hours are easily read.  Of course rotating 
several hours can be done to show the time in other time zones as well. An 
horizontal dial rotated a few hours and renumbered lets the rain and leaves 
run off better.

What other uses do polar axis rotated dials have?

Enjoy the Light!

Edley McKnight
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