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
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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
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