Hourglass
From Wikipedia, the free encyclopedia
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.[citation needed]
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.[1] (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.
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[edit] History
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.[2] 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.[3] 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.[4]
[edit] Practical uses
Hourglasses 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.[5]
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.[6] 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.
[edit] 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.[7]
The sandglass is still widely used as the kitchen egg timer; for cooking eggs, a three minute timer is typical,[8] hence the name "egg timer" for three minute hourglasses. Egg timers are sold widely as souvenirs,[citation needed] and games such as Boggle also make use of it.
[edit] Symbolic uses
Unlike most other methods of measuring time, the hourglass concretely represents the present as being between the past and the future,[citation needed] 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.[9] 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,[10] and they have graced gravestones for centuries.
[edit] Modern symbolic uses
Recognition 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).
[edit] See also
- Timewheel, a one-year hourglass
[edit] References
- ^ Madehow.com (2006). Hourglass. How Products Are Made, vol. 5. Madehow.com. Retrieved on 2008-02-04.
- ^ The Book of Days: A Miscellany of Popular Antiquities in Connection with the Calendar. W. & R. Chambers, Ltd..
- ^ Frugoni, Chiara (1988). Pietro et Ambrogio Lorenzetti. Scala Books, 83. ISBN 0935748806.
- ^ Nicolas, Nicholas Harris (1847). A history of the Royal navy, from the earliest times to the wars of the French revolution, vol. II. London: Richard Bentley, 476.
- ^ Mills, A.A.; Day, S. & Parkes, S. (1996), “Mechanics of the sandglass”, European Journal of Physics 17: 97-109, doi:10.1088/0143-0807/17/3/001, <http://www.iop.org/EJ/article/0143-0807/17/3/001/ej6301.pdf>
- ^ Bergreen, Laurence (2003). Over the Edge of the World: Magellan's Terrifying Circumnavigation of the Globe. William Morrow. ISBN 0066211735.
- ^ Senate of Australia (26 March 1997). "Official Hansard": 2472.
- ^ Herbst, Sharon Tyler (2001). The New Food Lover's Companion. Barron's Educational Series.
- ^ Room, Adrian (1999). Brewer's Dictionary of Phrase and Fable. New York: HarperCollinsPublishers. "Time is getting short; there will be little opportunity to do what you have to do unless you take the chance now. The phrase is often used with reference to one who has not much longer to live. The allusion is to the hourglass."
- ^ Ewbank, Thomas (1857). A Descriptive and Historical Account of Hydraulic and Other Machines for Raising Water, Ancient and Modern With Observations on Various Subjects Connected with the Mechanic Arts, Including the Progressive Development of the Steam Engine. Vol. 1. New York: Derby & Jackson, 547. "Hour-glasses were formerly placed in coffins and buried with the corpse, probably as symbols of mortality—the sands of life having run out. See Gent. Mag. vol xvi, 646, and xvii, 264."
[edit] Further reading
Books
- Branley, Franklyn M. (1993), Keeping time: From the beginning and into the twenty-first century, Boston: Houghton Mifflin Company
- Cowan, Harrison J. (1958), Time and its measurement: From the stone age to the nuclear age, New York: The World Publishing Company
- Guye, Samuel & Henri, Michel (1970), Time and space: Measuring instruments from the fifteenth to the nineteenth century, New York: Praeger Publishers
- Smith, Alan (1975), Clocks and watches: American, European and Japanese timepieces, New York: Crescent Books
Periodicals
- Morris, Scot (September 1992), “The floating hourglass”, Omni: 86
- Peterson, Ivars (September 11, 1993), “Trickling sand: how an hourglass ticks”, Science News
[edit] External links
- Brief History, a detailed history of the invention and construction of hourglasses at hourglasses.com
- Hourglass History, at the site of Tom Young, hourglass maker
- Allegory of Good Government at aiwaz.net
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