They had but two measures of time—the clepsydra, or water-clock, and the sun-dial.
Like the sun-dial and the clepsydra, the hour-glass is older than we know.
The principle is the same as that of the simplest form of clepsydra.
The Djyotisha also teaches the art of constructing a clepsydra, or water-clock.
The water-clock, or clepsydra, has been known to the Chinese for centuries.