Column sundial, German, c 1550.
© Science Museum / Science & Society Picture Library
Pillar dials consist of a hollow tube with a gnomon fixed horizontally into a slot at the top so that it is in line with the correct month. The dial is then turned so that the shadow cast by the gnomon falls directly onto the pillar, the end of the shadow indicating the correct time on the hour scale. This gilt bronze sundial made in Augsburg, Germany, features the engraved figures of four of the astrological signs of the zodiac - Aries, Taurus, Virgo and Leo. Decorated zodiacal scales of this sort are relatively rare; one interesting example being the pillar dial depicted amongst the scientific instruments in Holbein's painting of 'The Ambasadors' in the National Gallery, London.