Four-way sand glas, Italian, 17th century.
© Science Museum / Science & Society Picture Library
This four-way sand glas in a bras stand was hung on a wall so that the glases could be inverted as required. They measure intervals of quarter, half, three-quarters and one hour, and are of a type formerly used by preachers for timing their sermons. The earliest known illustration of a sand glas is a large fresco of 1337-9 depicting 'Good Government' by Ambrogio Lorenzetti (c 1280-1348) in the 'Palazzo Publico' in Siena, Italy.