Markings on the inside surfaces measured the passage of 'hours' as the water level reached them. Other clepsydras were cylindrical or bowl-shaped containers designed to slowly fill with water coming in at a constant rate. Later named clepsydras ('water thieves') by the Greeks, who began using them about 325 BCE, these were stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the bottom. One of the oldest was found in the tomb of the Egyptian pharaoh Amenhotep I, buried around 1500 BCE. Water clocks were among the earliest timekeepers that didn't depend on the observation of celestial bodies. The history of timekeeping is the story of the search for ever more consistent actions or processes to regulate the rate of a clock. Our ways of keeping track of the passage of time include the position of clock hands and digital time displays.

a means of keeping track of the increments of time and displaying the result.

Modern clocks use a balance wheel, pendulum, vibrating crystal, or electromagnetic waves associated with the internal workings of atoms as their regulators. Early examples of such processes included the movement of the sun across the sky, candles marked in increments, oil lamps with marked reservoirs, sand glasses (hourglasses), and in the Orient, knotted cords and small stone or metal mazes filled with incense that would burn at a certain pace.

a regular, constant or repetitive process or action to mark off equal increments of time.

All clocks must have two basic components: By 30 BCE, Vitruvius could describe 13 different sundial styles in use in Greece, Asia Minor, and Italy.īefore we continue describing the evolution of ways to mark the passage of time, perhaps we should broadly define what constitutes a clock. The hemicycle, said to have been invented about 300 BCE, removed the useless half of the hemisphere to give an appearance of a half-bowl cut into the edge of a squared block. One version was the hemispherical dial, a bowl-shaped depression cut into a block of stone, carrying a central vertical gnomon (pointer) and scribed with sets of hour lines for different seasons. In the quest for better year-round accuracy, sundials evolved from flat horizontal or vertical plates to more elaborate forms.

They could then be used to mark off nighttime hours by determining when certain other stars crossed the meridian. A pair of merkhets was used to establish a north-south line (or meridian) by aligning them with the Pole Star. The merkhet, the oldest known astronomical tool, was an Egyptian development of around 600 BCE. At noon, the device was turned in the opposite direction to measure the afternoon 'hours.' When the long stem with 5 variably spaced marks was oriented east and west in the morning, an elevated crossbar on the east end cast a moving shadow over the marks. This device divided a sunlit day into 10 parts plus two 'twilight hours' in the morning and evening.

Later, additional markers around the base of the monument would indicate further subdivisions of time.Īnother Egyptian shadow clock or sundial, possibly the first portable timepiece, came into use around 1500 BCE. Obelisks also showed the year's longest and shortest days when the shadow at noon was the shortest or longest of the year. Their moving shadows formed a kind of sundial, enabling people to partition the day into morning and afternoon. Obelisks (slender, tapering, four-sided monuments) were built as early as 3500 BCE. The Sumerian culture was lost without passing on its knowledge, but the Egyptians were apparently the next to formally divide their day into parts something like our hours.

Old sand clock