Patrick
Not quite right. Foster had many firsts, but he didn't discuss the
figure 8 Analemma. What I said in my article that seems to be your
source, was that Foster gave the first English treatment of the
analemmatic sundial.
Fred
Sent from my iPod
On Nov 15, 2009, at 3:10 AM, patrick_pow...@compuserve.com wrote:
The BSS Glossary (courtesy of John Davis) says:
The word analemma has had several other meanings in the history of
astronomy and dialling. In the first century BC, the Roman engineer
Vitruvius used the word to refer to a graphical construction,
equivalent to today's orthographic projection. In the second century
AD Ptolemy used analemma to mean an instrument acting as a nomograph
for defining the angles of a dial. The use of a modern analemma on a
dial dates to around 1640, and the first treatment in English was by
Samuel Foster in 1654.
Does this help?
Patrick
-----Original Message-----
From: Jack Aubert <jaub...@cpcug.org>
To: sundial@uni-koeln.de
Sent: Sat, Nov 14, 2009 11:18 pm
Subject: Origin of the Analemma figure?
I recently revised my notes for a sundial talk I was giving which
included a section on the EOT, and its connection with the
traditional figure 8 analemma. I wanted to explain its origin, or
at least be able to answer the question if asked, but have not been
able to find any believable references on how it emerged. I assume
that the source of the figure is simply a “connect the dots”
picture of what the sun, or a gnomon pointer will trace it out over
the course of the year projected onto a surface. But I do not see
how the dots can be generated without using an external non-solar so
urce of time.
The Wikipedia article on the EOT has a confusing statement to the
effect that Ptolomey was aware of the variation in the sun’s movemen
t and even devoted a chapter to the subject, but then says that he d
id not correctly account for the two sources of variation. Is there
any evidence that the Greeks or Romans ware aware of, and used, the
analemma representation, perhaps generated by reference to a clepsy
dra, or did it first appear when mechanical clocks became prevalent?
Jack
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