hourglass n : a sandglass that runs for sixty minutes
- Breton: eurier-traezh
- Czech: přesýpací hodiny f|p
- Dutch: zandloper
- Esperanto: sablohorloĝo
- Finnish: tiimalasi
- French: sablier
- German: Sanduhr
- Ido: sablo-horlojo
- Italian: clessidra
- Lithuanian: smėlio laikrodis
- Polish: klepsydra , zegar piaskowy
- Portuguese: ampulheta
- Russian: песочные часы (pesóčnyje časý) m|p
- Slovene: peščena ura
- Spanish: reloj de arena
- Swedish: timglas
- Turkish: kum saati
An hourglass, also known as a sandglass, sand timer or sand clock, is a device for the measurement of time. It consists of two glass bulbs placed one above the other which are connected by a narrow tube. One of the bulbs is usually filled with fine sand which flows through the narrow tube into the bottom bulb at a given rate. Once all the sand has run to the bottom bulb, the device can be inverted in order to measure time again. The hourglass is named for the most frequently used sandglass, where the sands have a running time of one hour.
Factors affecting the amount of time that the hourglass measures include: the volume of sand, the size and angle of the bulbs, the width of the neck, and the type and quality of the sand. Alternatives to sand that have been used are powdered eggshell and powdered marble. (Sources do not agree on the best internal material.)
Hourglasses are still in use, but typically only ornamentally or when a relatively approximate measurement of time is needed, as in egg timers for cooking or board games. Hourglass collecting has become a niche but avid hobby for some, with elaborate or antique hourglasses commanding high prices.
Hourglasses are said to have been invented at Alexandria about the middle of the third century, where they were sometimes carried around as people carry watches today. It is speculated that it was in use in the 11th century, where it would have complemented the magnetic compass as an aid to navigation. Glassmaking was brought to Europe in the thirteenth century by the Venetians, who created notable sandglasses. Recorded evidence of their existence is found no earlier than the 14th century, the earliest being an hourglass appearing 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. One of the earliest surviving records is a sales receipt of Thomas de Stetesham, clerk of the English ship La George, in 1345: The same Thomas accounts to have paid at Lescluse, in Flanders, for twelve glass horologes (" pro xii. orlogiis vitreis "), price of each 4½ gross', in sterling 9s. Item, For four horologes of the same sort (" de eadem secta "), bought there, price of each five gross', making in sterling 3s. 4d.
Practical usesHourglasses were the first dependable, reusable and reasonably accurate measure of time. The rate of flow of the sand is independent of the depth in the upper reservoir, and the instrument is not liable to freeze.
From the 15th century onwards, they were being used in a wide range of applications at sea, in the church, in industry and in cookery. During the voyage of Ferdinand Magellan around the globe, his vessels kept 18 hourglasses per ship. It was the job of a ship's page to turn the hourglasses and thus provide the times for the ship's log. Noon was the reference time for navigation, which did not depend on the glass, as the sun would be at its zenith. More than one hourglass was sometimes fixed in a frame, each with a different running time, for example 1 hour, 45 minutes, 30 minutes, and 15 minutes.
Modern practical usesWhile 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, and games such as Boggle also make use of it.
Symbolic usesUnlike 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.
The hourglass, sometimes with the addition of metaphorical wings, is often depicted as a symbol that human existence is fleeting, and that the "sands of time" will run out for every human life. It was used thus on pirate flags, to strike fear into the hearts of the pirates' victims. In England, hourglasses were sometimes placed in coffins, and they have graced gravestones for centuries.
Modern symbolic usesRecognition of the hourglass as a symbol of time has survived its obsolescence as a timekeeper. For example, the American television soap opera Days of our Lives, since its first broadcast in 1965, has displayed an hourglass in its opening credits, with the narration, "Like sands through the hourglass, so are the days of our lives."
Various computer programs and earlier versions of Windows may change the mouse cursor to an hourglass during a period when the program is in the middle of a task, and may not accept user input. During that period other programs, for example in different windows, may work normally. When a Windows hourglass does not disappear, it suggests a program is in an infinite loop and needs to be terminated, or is waiting for some external event (such as the user inserting a CD).
- Timewheel, a one-year hourglass