This column sundial has eight sides, each of which shows a time scale which has been calculated according to the amount of daylight during the different months of the year. To find the time a metal style, or gnomon, is inserted into a hole at the top of the stick in line with the correct month. The stick is then turned to face the sun until the shadow of the gnomon falls straight down on the scale. The time is indicated by the bottom edge of the shadow on the scale.
© Science Museum / Science & Society Picture Library