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Dale,
Ptolemy indeed installed a stone (column) with an inscription, containing the 
main parameters of the Solar system.
The column itself is lost, does not exist anymore.
But the contents of the inscription has been copied and preserved.

I suppose that Annapolis monument is inspired by this.

I would be interested in seeing a picture of this monument.
Ptolemy in his Almagest describes construction of several astronomical instruments,
one of them is the solstice ring for finding the moment of solstice (and using 
this, the length of the year and
length of the seasons).

But it consists of one ring, not two. It is a metal ring installed in the plane of the equator;
according to Ptolemy it existed in Alexandria for several centuries. Ptolemy did not make it
himself. The moment of solstice is found by observing the shade of one part of
the ring on another part.

Alex.

 

________________________________________
From: NavList@fer3.com [NavList@fer3.com] on behalf of Dale Lichtblau [NoReply_Lichtblau@fer3.com]
Sent: Wednesday, April 30, 2014 9:56 PM
To: eremenko@math.purdue.edu
Subject: [NavList] Ptolemy Stone...?

On the campus of St. John's College in Annapolis, Maryland, there is a 
so-called Ptolemy Stone. It apparently has something to do with the 
determination of the obliquity of the ecliptic (Almagest I.12). The two 
rings, one fixed, the other working like a sextant, are supposedly used in 
tandem. Anyone know anything about this?
Would attach a picture, but can't seem to get NavList to accept my posting 
code. Images are available on Google under "Ptolemy Stone."
Thanks,
Dale Lichtblau
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