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An hourglass is a non-mechanical instrument that is used to keep time. It usually measures the passing of an hour, though individual ones can be designed to measure different units of time. Some measure just a few seconds, for example, while others measure minutes and some even measure days.
This timekeeping device is often constructed out of glass, as its name denotes, but it can also be made of plastic. An hourglass has two hollow bulbs connected by a narrow opening. The bulbs contain sand, which trickles through the opening between the top and bottom bulb. When all the sand has fallen to the bottom bulb, a particular amount of time has passed.
Hourglasses usually, but not always, have a stand that encases the glass bulbs. Suspending the device in a stand provides a stable base and is easily turned over to reset the time without leaving finger prints on the glass. Stands can be made of wood, glass, metal or plastic. The different designs of the stands are endless, ranging from simple to ornamental with everything in between.
The hourglass was invented sometime in the 14th century. Before the advent of mechanical clocks, they where commonly used for nautical purposes, cooking and the timing of church services, among other things. Because each marks only one period of time, we can imagine that our ancestors must have had a large collection of hourglasses. One notable one has achieved fame in the classic book and movie The Wizard of Oz. The suspense filled scenes in which the hourglass trickles away Dorothy's hope of a rescue makes the device familiar to many generations.
Today, hourglasses are often used in board games to mark a player's turn or the duration of a task. They can also be a fun way to time daily chores and other tasks. Well made ones can also make beautiful collector's pieces due to their elegant style and variations in design.