Drum clepsydra

At first, time was measured by observing heavenly bodies. Then, devices using water (the clepsydra) or sand (the hourglass), which were visible, were developed to show the passage of time. The use of water dates back to ancient Egypt ca. 1,800 BC. Much later, the clepsydra was perfected by adding a "drum" divided into compartments and suspended by two strings between two graduated scales. When water passed from one compartment to the other, it turned the drum, which gradually descended along the scales, indicating the passing time. The system was inaccurate, and as the development and miniaturisation of mechanics made progress it was replaced by spring-loaded clocks.