German half-hour sand glass, first quarter of the 16th century, bronze-gilt and silver-gilt, height: 8.3 cm, diameter: 8.4 cm,Metropolitan of Art (New York City)
Anhourglass (orsandglass,sand timer, orsand clock) is a device used to measure the passage oftime. It comprises twoglass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historicallysand) from the upper bulb to the lower one due togravity. Typically, the upper and lower bulbs are symmetric as they are usually manufactured by pinching a tube. The specific duration of time a given hourglass measures is determined by factors including the quantity and coarseness of the particulate matter and the neck width.
Depictions of an hourglass as a symbol of the passage of time are found in art, especially on tombstones or other monuments, from antiquity to the present day. The form of a winged hourglass has been used as a literal depiction of the Latin phrasetempus fugit ("time flies").
Sarcophagus dated c. 350, representing the wedding of Peleus and Thetis (with magnification of an hourglass held by Morpheus)
The origin of the hourglass is unclear. Its predecessor theclepsydra, orwater clock, is known to have existed inBabylon and Egypt as early as the 16th century BCE.[1]
The same Thomas accounts to have paid at Lescluse, in Flanders, for twelve glass horologes (" pro xii. orlogiis vitreis "), price of each 41⁄2 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.[6][4][5]
Marine sandglasses were popular aboard ships, as they were the most dependable measurement of time while at sea. Unlike the clepsydra, hourglasses using granular materials were not affected by the motion of a ship and less affected by temperature changes (which could cause condensation inside a clepsydra).[7] While hourglasses were insufficiently accurate to be compared againstsolar noon for the determination of a ship'slongitude (as an error of just four minutes would correspond to one degree of longitude),[7] they were sufficiently accurate to be used in conjunction with achip log to enable themeasurement of a ship's speed in knots.[citation needed]
The hourglass also found popularity on land as an inexpensive alternative to mechanical clocks.[7] Hourglasses were commonly seen in use in churches, homes, and work places to measure sermons, cooking time, and time spent on breaks from labor.[3] Because they were being used for more everyday tasks, the model of the hourglass began to shrink. The smaller models were more practical and very popular as they made timing more discreet.
After 1500, the hourglass was not as widespread as it had been. This was due to the development of the mechanical clock, which became more accurate, smaller and cheaper, and made keeping time easier.[citation needed] The hourglass, however, did not disappear entirely. Although they became relatively less useful as clock technology advanced, hourglasses remained desirable in their design. The oldest known surviving hourglass resides in theBritish Museum in London.[3]
Not until the 18th century didJohn Harrison come up with amarine chronometer that significantly improved on the stability of the hourglass at sea. Taking elements from the design logic behind the hourglass, he made a marine chronometer in 1761 that was able to accurately measure the journey from England to Jamaica accurate within five seconds.[8]: 13–14
Temperance bearing an hourglass; detail Lorenzetti'sAllegory of Good Government, 1338
Little written evidence exists to explain why its external form is the shape that it is. The glass bulbs used, however, have changed in style and design over time. While the main designs have always beenampoule in shape, the bulbs were not always connected. The first hourglasses were two separate bulbs with a cord wrapped at their union that was then coated in wax to hold the piece together and let sand flow in between.[9] It was not until 1760 that both bulbs were blown together to keep moisture out of the bulbs and regulate the pressure within the bulb that varied the flow.[7]
While some early hourglasses actually did usesilica sand as the granular material to measure time, many did not use sand at all. The material used in most bulbs was "powderedmarble,tin/lead oxides, [or] pulverized, burnt eggshell".[3] Over time, different textures of granule matter were tested to see which gave the most constant flow within the bulbs. It was later discovered that for the perfect flow to be achieved the ratio of granule bead to the width of the bulb neck needed to be 1/12 or more but not greater than 1/2 the neck of the bulb.[10]
Hourglasses were an early dependable and accurate measure of time. The rate of flow of the sand is independent of the depth in the upper reservoir, and the instrument will not freeze in cold weather.[3] From the 15th century onwards, hourglasses were being used in a range of applications at sea, in the church, in industry, and in cookery.
During the voyage ofFerdinand Magellan around the globe, 18 hourglasses from Barcelona were in the ship's inventory, after the trip had been authorized by KingCharles I of Spain.[11] 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 itszenith.[12] A number of sandglasses could be fixed in a common frame, each with a different operating time, e.g. as in a four-way Italian sandglass likely from the 17th century, in the collections of the Science Museum, in South Kensington, London, which could measure intervals of quarter, half, three-quarters, and one hour (and which were used in churches, for priests and ministers to measure lengths of sermons).[13]
Flag erroneously attributed to pirateChristopher MoodyA winged hourglass as a literal depiction of the Latin phrasetempus fugit ("time flies")
Unlike most other methods of measuring time, the hourglass concretely represents the present as being between thepast and thefuture, and this has made it an enduring symbol of time as a concept.[citation needed]
The hourglass, sometimes with the addition of metaphorical wings, is often used as a symbol that human existence is fleeting, and that the "sands of time" will run out for every human life.[15] It was used thus onpirate flags, to evoke fear through imagery associated with death. In England, hourglasses were sometimes placed in coffins,[16] and they have graced gravestones for centuries. The hourglass was also used inalchemy as a symbol forhour.[citation needed]
Recognition of the hourglass as a symbol of time has survived its obsolescence as a timekeeper. For example, the American television soap operaDays of Our Lives (1965–present) displays an hourglass in its opening credits, with narration byMacdonald Carey: "Like sands through the hourglass, so are the days of our lives."
Various computergraphical user interfaces may change thepointer to anhourglass while the program is in the middle of a task, and may not accept user input. During that period of time, other programs, such as those open in other windows, may work normally. When such an hourglass does not disappear, it suggests a program is in aninfinite loop and needs to be terminated, or is waiting for some external event (such as the user inserting a CD).
Diagram of "hourglass" motif from carved stone tablet,Solomon Islands
Because of its symmetry, graphic signs resembling an hourglass are seen in the art of cultures which never encountered such objects. Vertical pairs of triangles joined at the apex are common inNative American art; both in North America,[17] where it can represent, for example, the body of theThunderbird or (in more elongated form) an enemy scalp,[18][19] and in South America, where it is believed to represent aChuncho jungle dweller.[20] InZulu textiles they symbolise a married man, as opposed to a pair of triangles joined at the base, which symbolise a married woman.[21]Neolithic examples can be seen among Spanishcave paintings.[22][23] Observers have even given the name "hourglass motif" to shapes which have more complex symmetry, such as a repeating circle and cross pattern from theSolomon Islands.[24] Both the members of Project Tic Toc from the television seriesThe Time Tunnel and theChallengers of the Unknown use symbols of the hourglass, representing either time travel or time running out.
Hourglasses in art
17th century tombstone in the mausoleum of John Livingstone, "an apothecary in Edinburgh", who fell victim to the1645 plague
^abcdBalmer, R.T. "The Operation of Sand Clocks and Their Medieval Development." Technology and Culture, Vol. 19, No. 4 (Oct., 1978), pp. 615–632.
^Clowes, William Laird (1898).The Royal Navy: A History From the Earliest Times to the Present. Vol. 3. London: Sampson, Low, Marston and Company.OCLC645627800.
^Senate of Australia (26 March 1997),Official Hansard(PDF), p. 2472, archived fromthe original(PDF) on 29 April 1998
^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."
^Wilson, Lee AnnNature Versus Culture inTextile Traditions of Mesoamerica and the Andes: An Anthology (ed. Schevill, M.B. et al.), University of Texas Press (1996)ISBN0-292-77714-0
^Greenman, E.F.The Upper Palaeolithic and the New World inCurrent Anthropology Vol. 4, No. 1 (Feb., 1963), pp. 41-91 (NB: includes reviews disputing the central thesis and methodology)
Cowan, Harrison J. (1958). "Time and its measurement: From the stone age to the nuclear age".Cleveland.65. New York: The World Publishing Company.Bibcode:1958tmfs.book.....C.
Guye, Samuel; Henri, Michel; Dolan, D.; Mitchell, S. W. (1970).Time and space: Measuring Instruments from the Fifteenth to the Nineteenth century. New York: Praeger Publishers.Bibcode:1971tsmi.book.....G.
Smith, Alan (1975).Clocks and watches: American, European and Japanese timepieces. New York: Crescent Books.
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