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..