An hour glass is an obsolete time-keeping device. It is made up of two bulbs connected by a narrow passage, through which sand flows at a given rate. Hourglasses were probably invented in Alexandria, Egypt between 200 and 300 A.D. Though they are no longer used for the purpose of keeping time, they are sometimes used in lieu of electronic timers, for example, as egg timers.
- The Book of Days: A Miscellany of Popular Antiquities in Connection with the Calendar. W. & R. Chambers, Ltd..