How does an Hourglass measure time?
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Answer: By using carefully calculated amounts of sand.
The hourglass is sometimes referred to as a sand clock or a sandglass. Like other timepieces, it needs to be carefully calibrated. The hourglass maker must test the instrument and fine tune it to measure the correct length of time.
There are many factors that contribute to the ability of an hourglass to accurately measure time. The type and quality of sand is key. It must have a rate of flow that does not fluctuate. Sand that is too coarse will wear away the glass, eventually making the neck too large. Most important is the ratio of the neck (the hole, or tube) width to the diameter of the sand particles.
History
The earliest hourglass appears in the 1338 fresco Allegory of Good Government by Ambrogio Lorenzetti. Written records from the same period mention the hourglass, and it appears in lists of ships stores. An early record is a sales receipt of Thomas de Stetesham, clerk of the English ship La George, in 1345.
Here are the other factors that affect the accuracy of an hourglass:
- The amount or volume of sand used
- The size and angle of the glass bulbs
- The quality of the sand or granular material. It must be fine, dry and consistently formed so it can flow smoothly. (Some substances used in the past were fine grain sand, powdered eggshells, and powdered marble.)
- The width of the neck
- A tight seal so no moisture can get into the chambers. Moisture can add weight to the sand or clog up the neck.
- A flat and level surface on which to rest the hourglass
Symbolic uses
Unlike most other methods of measuring time, the hourglass concretely represents the present as being between the past and the future, and this has made it an enduring symbol of time itself.
Modern Practical Uses
While they are no longer widely used for keeping time, some institutions do maintain them. Both houses of the Australian Parliament use three hourglasses to time certain procedures, such as divisions.
The sandglass is still widely used as the kitchen egg timer; for cooking eggs, a three minute timer is typical, hence the name "egg timer" for three minute hourglasses. Egg timers are sold widely as souvenirs.
Sand timers are also sometimes used in games such as Pictionary and Boggle to implement a time constraint on rounds of play.
We still use the hourglass to keep track of time. Just think of its many uses for cooking and for playing games!
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Black 10 Minute Hourglass Sand Timer
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