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Glynn Reed
Hi- I have run across a gnomon built into a wall of an Italian church, and I’m extremely puzzled as to its name, origin, etc. it’s marked with Roman numerals from 16 to 24 and 4 astrological symbols, 2 straight lines horizontal and vertical, and marking lines that do not converge at the gnomon, rather to a point off the wall above and left of the gnomon. Can you help me identify this instrument and how to read it? Picture is available with a reply- thank you, Glynn Reed, NH USA
Frank H.King
Dear Glynn,
Many thanks for your posting about a puzzling sundial on the wall of an Italian Church.
This type of sundial is showing what are known as “Italian Hours”. There is no gnomon as such. What think of as a gnomon is really a horizontal support, probably with a small ball at its outer end.
To use the sundial, you note where the shadow of the ball falls in the hour lines and that gives you the number of hours since the last sunset. If the shadow falls on the hour line numbered 21 then this means 21 hours since sunset and, hence, it is 3 hours until the next sunset. You just subtract from 24.
The horizontal line is called the horizon line. When the shadow falls on this line it is sunrise or sunset. If the latter, the time will be 24.
The vertical line is for noon or midday. It may be labeled M (for mezzogiorno in Italian).
The four astrological symbols are probably for Aries, Cancer, Libra and Capricorn, which mark the solstices and equinoxes.
The should be a sloping straight line and two curved lines as well but they may have faded. I can explain more if you could let me have your e-mail address.
I should be most grateful if you can let me have a photograph. I am an enthusiast for Italian hours sundials!
Very best wishes
Frank
Frank H. King
Chairman
British Sundial Society
Anyone local to Newcastle upon Tyne?
We have had a wonderful donation of books about sundials so thought we’d let you know.
Oxfam Bookshop, Jesmond