Hourglass

The specific duration of time a given hourglass measures is determined by factors including the quantity and coarseness of the particulate matter, the bulb size, 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 phrase tempus fugit ("time flies").

[1] There are no records of the hourglass existing in Europe prior to the Late Middle Ages; the first documented example dates from the 14th century, a depiction in the 1338 fresco Allegory of Good Government by Ambrogio Lorenzetti.

The earliest recorded reference that can be said with certainty to refer to a marine sandglass dates from c. 1345, in a receipt of Thomas de Stetesham, clerk of the King's ship La George, in the reign of Edward III of England; translated from the Latin, the receipt says: in 1345:[4][5] The same Thomas accounts to have paid at Lescluse, in Flanders, for twelve glass horologes (" pro xii.

Item, For four horologes of the same sort (" de eadem secta "), bought there, price of each five gross', making in sterling 3s.

This was due to the development of the mechanical clock, which became more accurate, smaller and cheaper, and made keeping time easier.

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.

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.

During the voyage of Ferdinand Magellan around the globe, 18 hourglasses from Barcelona were in the ship's inventory, after the trip had been authorized by King Charles I of Spain.

[11] 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] Sand timers are sometimes included with boardgames such as Pictionary and Boggle that place time constraints on rounds of play.

When such an 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).

[21][22] Observers have even given the name "hourglass motif" to shapes which have more complex symmetry, such as a repeating circle and cross pattern from the Solomon Islands.