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Wolfgang,
First I have to confess: I've never seen this armillary
sphere. I only read the description in Cotter,
and also remember seeing some ancient pictures where something
which looks like an armillary sphere in Cotter's description should look
is shown.

Is there a good antique description anywhere? (I mean of the
times BC, when it was really invented).

By the way, the Star Globe can be considered as a model of
Ptolemy system as well:-)

It shows how the sky rotates around the Earth, does not it?
It has no epicycles, however, so it is a simplified model
of Ptolemy system:-) Did armillary spheres show epicycles?

BTW, according to Cotter the armillary sphere was invented
by Erathosphenes, that is 4 centuries before Ptolemy lived.
On the other hand, as far as I understand, "Ptolemy system"
was not Prolemy's invention, the principle belongs to
Hypparchus, and Ptolemy could only modify or improve it.

On Thu, 28 Oct 2004, [iso-8859-1] Wolfgang K?berer wrote:

> Dear Alex,
>
> I always thought that the armillary sphere is a model of the Ptolemaic
> system; its only use was to demonstrate the celestial spheres and the
> "workings of the heavens". That seems to be a somewhat different task than
> that of a star globe. But correct me if I`m wrong.
>
> Regarding modern analogue devices you can turn to the 70`s edition of
> Bowditch which has a chapter on "Comparison of the different methods of
> Sight Reduction" and also discusses such machines. Willem M?rzer Bruyns, the
> former curator of the Nederlands Scheepvaart Museum at Amsterdam has
> published the following article on one of the analogue computers:
> The Willis Navigating Machine: A Forgotten Invention, in: Rittenhouse, Vol.
> 14 (2000), No. 51, 13 - 25.
>
> Regards, W. K?berer
>

   

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