An interesting question and more interesting history.
In J. L. Heilbron's book, The Sun in the Church, page 225 he describes
why the higher hole ( and lens) was placed. It seems it was more of a
way to get a larger midsummer image so that it was as good as the
midwinter one.
An interesting historical note on page 224 was that the fact that part
of the meridian ran behind the balustrade played a role in saving it
from destruction by revolutionaries in 1799.
On 4/3/2016 1:39 PM, Roger W. Sinnott wrote:
Dan,
I’m just guessing, but maybe the two holes and two spots are placed so
that, no matter what the Sun’s declination is, at least one of the
spots will fall on a smooth, uncluttered part of the floor.
Roger
*From:*sundial [mailto:[email protected]] *On Behalf Of
*Dan-George Uza
*Sent:* Sunday, April 03, 2016 3:23 PM
*To:* [email protected]
*Subject:* Gnomon of Saint-Sulpice
Hello,
Last week I visited the meridian line of Saint-Sulpice in Paris which
dates back to 1743. After the French Revolution the Republicans
chiseled out all references to royalty from the inscriptions. I don't
know why but they also erased some of the zodiac signs. Could it have
something to do with the new Republican Calendar? Also, there are two
holes for the light to enter with two spots forming on the ground and
I don't understand exactly why...
Dan Uza
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