Hourglass in the context of "Memento mori"

The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have gradually improved through a series of new inventions, starting with measuring time by continuous processes, such as the flow of liquid in water clocks, to mechanical clocks, and eventually repetitive, oscillatory processes, such as the swing of pendulums. Oscillating timekeepers are used in modern timepieces. Sundials and water clocks were first used in ancient Egypt c. 1200 BC and later by the Babylonians, the Greeks and the Chinese. Incense clocks were being used in China by the 6th century. In the medieval period, Islamic water clocks were unrivalled in their sophistication until the mid-14th century. The hourglass, invented in Europe, was one of the few reliable methods of measuring time at sea.

In medieval Europe, purely mechanical clocks were developed after the invention of the bell-striking alarm, used to signal the correct time to ring monastic bells. The weight-driven mechanical clock controlled by the action of a verge and foliot was a synthesis of earlier ideas from European and Islamic science. Mechanical clocks were a major breakthrough, one notably designed and built by Henry de Vick in c. 1360, which established basic clock design for the next 300 years. Minor developments were added, such as the invention of the mainspring in the early 15th century, which allowed small clocks to be built for the first time.

A clock or chronometer is a device that measures and displays time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, and the year. Devices operating on several physical processes have been used over the millennia.

Some predecessors to the modern clock may be considered "clocks" that are based on movement in nature: A sundial shows the time by displaying the position of a shadow on a flat surface. There is a range of duration timers, a well-known example being the hourglass. Water clocks, along with sundials, are possibly the oldest time-measuring instruments. A major advance occurred with the invention of the verge escapement, which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.

Chronometry or horology (lit. 'the study of time') is the science studying the measurement of time and timekeeping. Chronometry enables the establishment of standard measurements of time, which have applications in a broad range of social and scientific areas. Horology usually refers specifically to the study of mechanical timekeeping devices, while chronometry is broader in scope, also including biological behaviours with respect to time (biochronometry), as well as the dating of geological material (geochronometry).

Horology is commonly used specifically with reference to the mechanical instruments created to keep time: clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. People interested in horology are called horologists. That term is used both by people who deal professionally with timekeeping apparatuses, as well as enthusiasts and scholars of horology. Horology and horologists have numerous organizations, both professional associations and more scholarly societies. The largest horological membership organisation globally is the NAWCC, the National Association of Watch and Clock Collectors, which is US based, but also has local chapters elsewhere.

Kvitøya (English: "White Island") is an island in the Svalbard archipelago in the Arctic Ocean, with an area of 682 square kilometres (263 sq mi). It is the easternmost part of the Kingdom of Norway. The closest Russian Arctic possession, Victoria Island, lies only 62 kilometres (39 mi) to the east of Kvitøya.

The island is almost completely covered by Kvitøyjøkulen, an ice cap with an area of 705 square kilometres (272 sq mi) with a classical, hourglass-shaped dome, which has given it its name. The few ice-free land areas are each only a few square kilometres large and very barren and rocky, the largest being Andréeneset on the southwest corner of the island. Kvitøya is a part of the Nordaust-Svalbard Nature Reserve.

Melencolia I is a large 1514 engraving by the German Renaissance artist Albrecht Dürer. Its central subject is an enigmatic and gloomy winged female figure thought to be a personification of melancholia – melancholy. Holding her head in her hand, she stares past the busy scene in front of her. The area is strewn with symbols and tools associated with craft and carpentry, including an hourglass, weighing scales, a hand plane, a claw hammer, and a saw. Other objects relate to alchemy, geometry or numerology. Behind the figure is a structure with an embedded magic square, and a ladder leading beyond the frame. The sky contains a rainbow, a comet or planet, and a bat-like creature bearing the text that has become the print's title.

Dürer's engraving is one of the most well-known extant old master prints, but, despite a vast art-historical literature, it has resisted any definitive interpretation. Dürer may have associated melancholia with creative activity; the woman may be a representation of a Muse, awaiting inspiration but fearful that it will not return. As such, Dürer may have intended the print as a veiled self-portrait. Other art historians see the figure as pondering the nature of beauty or the value of artistic creativity in light of rationalism, or as a purposely obscure work that highlights the limitations of allegorical or symbolic art.

Knight, Death and the Devil (German: Ritter, Tod und Teufel) is a large 1513 engraving by the German artist Albrecht Dürer, one of the three Meisterstiche (master prints) completed during a period when he almost ceased to work in paint or woodcuts to focus on engravings. The image is infused with complex iconography and symbolism, the precise meaning of which has been argued over for centuries.

A stolid armoured knight on a proud horse, accompanied by his faithful dog, rides through a wild narrow gorge flanked by a goat-headed devil and the figure of death riding a pale horse. Death's rotting corpse holds an hourglass, a reminder of the shortness of life. The rider moves through the scene looking away from the creatures lurking around him, and appears almost contemptuous of the threats, and is thus often seen as symbol of courage; the knight's armour, the horse which towers in size over the beasts, and the oak leaves are symbolic of the resilience of faith, while the knight's plight may represent Christians' earthly journey towards the Kingdom of Heaven symbolized by the city on the hill.