Medieval Stone Sundial

Post-excavation work on the finds recovered from St James’s Priory has lead to the discovery of what may be part of the earliest known ‘scientific’ sundial in Britain.

The sundial fragment was recovered from the rubble core of a Victorian extension to the church and is carved with medieval-style Arabic numerals.

It would appear that this sundial was originally positioned with its face at a 38.5° angle with a polar-orientated gnomon (rod) in the centre. Sundials set with their face at this angle are known as ‘equatorial’ sundials; these are the earliest form of ‘scientific’ sundial, the production of which requires a certain degree of astronomical knowledge. It is not known exactly when they were introduced to England, however the current best guess is that it occurred sometime in the early 15th century. Scientific sundials show equal hours, which were a new development in 14th-century Europe. Prior to this sundials were either horizontally or vertically mounted, and marked with evenly spaced ‘hour’ lines, the actual duration of which varied according to the height of the sun at different times of year.

medieval stone sundial

A fragment of a medieval sundial recovered from the site of St James’s Priory in Bristol

The earliest previously known British scientific sundial was made by Nicholas Kratzer in 1520, and was found in the garden of Acton Court near Bristol. Although the style of the numerals on the St James sundial suggests it could have been carved at any time between the late 13th and early 16th century, they are closest in style to those produced in the 15th century, which suggests it may be up to a century or so older than Nicholas Kratzer’s sundial.

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