The clepsydra is an old instrument for time calculation, originating in the later part of the Neolithic Age.

The ancient people, upon finding that water in a pottery often leaked out drop by drop, made a pottery kettle with a small hole. Water filling the kettle would leak out through the hole, and another kettle was used to collect the leaking water.

A marked arrow, like the dial of today's watch, was placed inside the second kettle through the hole of the kettle lid, floating on top of the water with the support from a bamboo flake or a wooden plate. The kettle was known as an "arrow kettle." As the water level increased, the arrow also moved upwards, and people could know the xact time through looking at the marks on the arrow.

Author: Jessie