Chalice sundial, 1596.
© Science Museum / Science & Society Picture Library
This ornate sundial was probably made in Germany but is designed for use in a latitude of 42 degrees (that of Rome, Italy). The gnomon consists of a pointed rod forming the axis of the chalice; the shadow of its tip falls on the hour-lines which are engraved on the inside of the vesel. The surface is marked with a scale of months, and before use, the chalice must be rotated until the shadow falls within the column corresponding to the present month. It shows Italian hours (1-24 starting from sunset), equal hours and 'planetary', or temporal, hours which divide the day into 12 daylight hours and 12 night hours, varying in length according to latitude and the changing seasons.