Also known as a mass dial, although I seem to recall that strictly speaking there is a distinction. I came across this one by chance at St. Catherine's Church, Montacute, Somerset. It's a vertical sundial that surely pre-dates the Church clock of around A.D. 1400. The hole centre bottom would have held a horizontal gnomon to cast a shadow for telling the time.
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Originally, I wrote: There are 12 lines radiating from the gnomon hole for indicating the hours from 6 am to 6 pm, albeit inaccurately, as they are spaced regularly (15 degrees) and with no regard for latitude.
However, having read the section Medieval Times and Canonical Hours here on the excellent GAUDIUM SUB SOLE website, I was reminded that centuries ago, day and night were divided into 12 hours each, an hour in the day-time being longer than at night-time in the Summer, for example.
Then I wrote: There are 12 lines, spaced at 15 degrees, radiating from the gnomon hole for indicating the 12 daytime hours from sunrise to sunset, the length of the hour depending upon the time of year. While perhaps crude in execution, it and similar dials were sufficiently accurate for the needs of the period.
However, on further reflection, this is still only partially correct! These dials show sunrise and sunset only when the Sun is fully in the Southern sky, i.e. between the Autumn and Spring equinoxes. Between the Spring and Autumn equinoxes, for part of the day, after sunrise and before sunset, the Sun is in the Northern sky and such dials are in shadow. More to follow...
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The dial is unusual, being upside down, and hence unusable! Presumably the stone was re-used when the dial was no longer needed.
More info. on this dial from GAUDIUM SUB SOLE here, along with another dial at the church that I missed!
Note - the design was already ancient when it was made, being the same type as this Ancient Egyptian dial.
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