Water clocks were more reliable. Th

Water clocks were more reliable. The Greeks produced the most efficient, known as clepsydras (literally “water thieves”) around 325 BCE. These were small, consisting of an empty bowl with a precise hole at its base. This punctured bowl floated within a larger basin filled with water. Slowly, as the punctured bowl took on more water through the hole in its base, the water level gradually reached markers inscribed at different points on the inside of the bowl as it filled. Such a water clock could be emptied and reused repeatedly; for example, to mark the duration of an irrigation cycle on a farm. More elaborate water clocks relied on a small outflowing trickle of water from a large basin to fill a separate hollow cylinder in which a floating marker slowly rose, pointing out the hour on a measuring rod attached to the inside of the cylinder.