On this day:
671 – Emperor Tenji of Japan introduces a water clock (clepsydra) called Rokoku. The instrument, which measures time and indicates hours, is placed in the capital of Ōtsu.
A water clock or clepsydra (Greek κλεψύδρα from κλέπτειν kleptein, ‘to steal’; ὕδωρ hydor, ‘water’) is any timepiece in which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel where the amount is then measured. Water clocks, along with sundials and hourglasses, are likely to be the oldest time-measuring instruments, with the only exceptions being the vertical gnomon and the day-counting tally stick. Where and when they were first invented is not known, and given their great antiquity it may never be. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century BCE. Other regions of the world, including India and China, also have early evidence of water clocks, but the earliest dates are less certain. Some authors, however, claim that water clocks appeared in China as early as 4000 BCE.
Some modern timepieces are called “water clocks” but work differently from the ancient ones. Their timekeeping is governed by a pendulum, but they use water for other purposes, such as providing the power needed to drive the clock by using a water wheel or something similar, or by having water in their displays.
The Greeks and Romans advanced water clock design to include the inflow clepsydra with an early feedback system, gearing, and escapement mechanism, which were connected to fanciful automata and resulted in improved accuracy. Further advances were made in Byzantium, Syria and Mesopotamia, where increasingly accurate water clocks incorporated complex segmental and epicyclic gearing, water wheels, and programmability, advances which eventually made their way to Europe. Independently, the Chinese developed their own advanced water clocks, incorporating gears, escapement mechanisms, and water wheels, passing their ideas on to Korea and Japan.
Some water clock designs were developed independently and some knowledge was transferred through the spread of trade. These early water clocks were calibrated with a sundial. While never reaching a level of accuracy comparable to today’s standards of timekeeping, the water clock was the most accurate and commonly used timekeeping device for millennia, until it was replaced by more accurate pendulum clocks in 17th-century Europe. A water clock uses a flow of water to measure time. If viscosity is neglected, the physical principle required to study such clocks is Torricelli’s law. There are two types of water clocks: inflow and outflow. In an outflow water clock, a container is filled with water, and the water is drained slowly and evenly out of the container. This container has markings that are used to show the passage of time. As the water leaves the container, an observer can see where the water is level with the lines and tell how much time has passed. An inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines and tell how much time has passed.
In China, as well as throughout eastern Asia, water clocks were very important in the study of astronomy and astrology. The oldest archaeological evidence of a water clock is around 4000 BCE. The oldest written reference dates the use of the water-clock in China to the 6th century BCE. From about 200 BCE onwards, the outflow clepsydra was replaced almost everywhere in China by the inflow type with an indicator-rod borne on a float.
Huan Tan (40 BCE – 30 CE), a Secretary at the Court in charge of clepsydrae, wrote that he had to compare clepsydrae with sundials because of how temperature and humidity affected their accuracy, demonstrating that the effects of evaporation, as well as of temperature on the speed at which water flows, were known at this time. In 976, Zhang Sixun addressed the problem of the water in clepsydrae freezing in cold weather by using liquid mercury instead. Again, instead of using water, the early Ming Dynasty engineer Zhan Xiyuan (c. 1360-1380) created a sand-driven wheel clock, improved upon by Zhou Shuxue (c. 1530-1558).
The use of clepsydrae to drive mechanisms illustrating astronomical phenomena began with Zhang Heng (78-139) in 117, who also employed a waterwheel. Zhang Heng was the first in China to add an extra compensating tank between the reservoir and the inflow vessel, which solved the problem of the falling pressure head in the reservoir tank. Zhang’s ingenuity led to the creation by Yi Xing (683–727) and Liang Lingzan in 725 of a clock driven by a waterwheel linkwork escapement mechanism. The same mechanism would be used by Su Song (1020–1101) in 1088 to power his astronomical clock tower, as well as a chain drive. Su Song’s clock tower, over 30 feet (9.1 m) tall, possessed a bronze power-driven armillary sphere for observations, an automatically rotating celestial globe, and five front panels with doors that permitted the viewing of changing mannequins which rang bells or gongs, and held tablets indicating the hour or other special times of the day. In the 2000s, in Beijing’s Drum Tower an outflow clepsydra is operational and displayed for tourists. It is connected to automata so that every quarter-hour a small brass statue of a man claps his cymbals.
Born on this day:
1825 – Sondre Norheim, Norwegian-American skier (d. 1897)
Sondre Norheim, born Sondre Auverson, (June 10, 1825 – March 9, 1897) was a Norwegian skier and pioneer of modern skiing. Sondre Norheim is known as the father of Telemark skiing.
Sondre Auverson was born at Øverbø, a little cotter’s farm and raised in Morgedal in the municipality of Kviteseid in Telemark, Norway. Skiing was a popular activity in Morgedal. Sondre took to downhill skiing as a recreational activity, rising to local fame for his skills. He made important innovations in skiing technology by designing new equipment, such as different bindings and shorter skis with curved sides to facilitate turns. He also designed the Telemark ski, which is the prototype of all those now produced. Sondre Norheim was regarded by his contemporaries as a master of the art of skiing. He combined ordinary skiing with jumping and slalom. In 1868 he won the first national skiing competition in Christiania, beating his younger competitors by a large margin. His reputation grew, and eventually made Norwegian words like ski and slalåm (slalom) known worldwide.
On January 15, 1854, Sondre Norheim married Rannei Åmundsdotter from a cotter’s farm at Øyfjell, a neighbouring village. In March 1854 their first daughter, Ingerid, was born. The next year little Hæge came, but she died at 15 weeks old. The next year Olav was born, and then another daughter they called Hæge, then Anne, Auver, Åmund and Talleiv. Sondre and Rannei lost a second child when Auver died at age 12. The family moved around to different places in Morgedal. Their last place was called “Norheim”, which Sondre took as a new family name. 
On May 30, 1884 Sondre and Rannei left Norway together with three of their children– Anne (21), Åmund (14) and Talleiv (12). Their son Olav and daughter Hæge had left home previously, and their eldest daughter Ingerid decided to stay back home. Norheim followed in the footsteps of many of his neighbors in Morgedal and emigrated from Norway to the United States. After having first settled in Minnesota, they moved to North Dakota, near Villard in McHenry County. He continued to ski when he could, though the climate and flat topography of the Dakota prairie offered few opportunities for downhill skiing. It was said he always had a pair of skis placed outside his door. Norheim grew more religious with age and helped build a Lutheran church in Villard. He died in 1897 and was buried in Denbigh, McHenry County, North Dakota.
Sondre Norheim was honored during opening ceremonies at the 1952 Winter Olympics in Oslo, at the 1960 Winter Olympics in Squaw Valley, California and at the 1994 Winter Olympics in Lillehammer, Norway. His grave was originally unmarked, but a memorial stone now marks its spot. During the week of Norsk Høstfest, held in Minot, N.D., groups visit the grave site and hold a commemorative service in memory of Sondre Norheim. 
The movie, Frikaren på ski – The history of Sondre Norheim, the Father of Modern Ski Sport was produced by NRK in 1970.  In 1984, Norheim was inducted into the Scandinavian-American Hall of Fame as the first class of inductees. A statue of Sondre Norheim by Norwegian sculptor Knut Skinnarland (1909-1993) was unveiled in 1987 in the Scandinavian Heritage Park, in Minot, North Dakota. During 1988, an identical statue was unveiled in Morgedal, Norway by King Olav V. During 1993, the Sondre Norheim Eternal Flame Monument was added to the Scandinavian Heritage Park. Lars Berge Haugan, a skier representing Morgedal, lit the flame.
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