The clepsydra is an ancient water clock and serves as the primary metaphor for this examination of Jewish conceptions of time from antiquity to the present. Just as the flow of water is subject to a number of variables such as temperature and pressure, water clocks mark a time that is shifting and relative. Time is not a uniform phenomenon. It is a social construct made of beliefs, scientific knowledge, and political experiment. It is also a story told by theologians, historians, philosophers, ...