Magnetic Sundial, mid 18th century.
© Science Museum / Science & Society Picture Library
In this unusual dial the Sun's light is fixed and the compas points to the time. There are six silver hour rings, all engraved on both sides, with each side being correct for certain days of the year. The hour ring was placed around the compas, the strip of sunlight from a slit in the side of the case was made to fall on the 12 mark, and the compas needle pointed to the hour. The dial is engraved 'E W'. It is German and dates from about 1750.