CLEPSYDRA

Form: Klepsydra.

A water-clock, or earthenware vessel filled with a certain measure of water, and having a hole in the bottom of a size to ensure the water running away within a definite space of time. Such water-clocks were used in the Athenian law courts, to mark the time allotted to the speakers. They were first introduced in Rome in 159 B.C., and used in the courts there in the same way. In the field they were used to mark the night-watches. The invention of the best kind of water-clock was attributed to Plato. In this the hours were marked by the height of the water flowing regularly into a vessel. This was done in one of two ways. (1) A dial was placed above the vessel, the band of which was connected by a wire with a cork floating on the top of the water. (2) The vessel was transparent, and had vertical lines drawn upon it, indicating certain typical days in the four seasons or in the twelve months. These lines were divided into twelve sections, corresponding to the position which the water was experimentally found to take at each of the twelve hours of night or day on each of these typical days. It must be remembered that the ancients always divided the night and day into twelve equal hours each, which involved a variation in the length of the hours corresponding to the varying length of the day and night.