Meridian Stone

This is a granite meridian stone erected in 1837 by the Royal Cornwall Polytechnic Society. It is a large, dressed block of granite with a narrow, chamfered step. The stone has four principal faces and a flat top with a small central hole. Each face is inscribed with a letter representing the principal points of the compass.

The stone was positioned on a meridian line running through the tower of St Keverne Church and served as a calibration tool for miners’ surveying compasses, known as dials. Magnetic north varies over time, and surveys reliant solely on magnetic readings would accumulate errors, which could be dangerous in a mining context. The Society erected this stone to mitigate these inaccuracies. Mining surveyors placed their dials in the hole in the stone’s centre and aligned them with the church tower to measure the difference between true north and magnetic north, thereby calibrating the dial. It was later discovered that magnetic variations also existed between the surface and underground, suggesting the stone may have been used for a relatively short period.

A plaque, formerly attached to the western face, read: "This pillar was erected in the Meridian of St Keverne by The Royal Polytechnic Society of Cornwall in the year 1837."