Equinoctial sun dial, c 1690.
© Science Museum / Science & Society Picture Library
The outer case of this instrument bears the monogram of William and Mary. It was made by M T Hager of Arnstadt, Germany. The compas needle was set to North and the latitude was indicated on the circular dial using an index finger which is now mising. The gnomon or pointer would then spring into the correct position and the time could be read from its shadow.