sábado, 20 de abril de 2013

Keeping Time in History


 Obelisk in the Piazza del Popolo, Rome, Italy. 

For thousands of years, devices have been used to measure and keep track of time. The current sexagesimal system of time measurement dates to approximately 2000 BC, in Sumer. The Ancient Egyptians divided the day into two 12-hour periods, and used large obelisks to track the movement of the Sun.

Obelisk of Ramesses Ii and Pylons, 
Temple of Luxor, Thebes, Egypt

Stonehenge, England

They also developed water clocks, which were probably first used in the Precinct of Amun-Re, and later outside Egypt as well; they were employed frequently by the Ancient Greeks, who called them clepsydrae (literally water thief, and is the Greek word for water clock).


The Shang Dynasty is believed to have used the outflow water clock around the same time, devices which were introduced from Mesopotamia as early as 2000 BC.

Other ancient timekeeping devices include the candle clock, used in China, Japan, England and Iraq; the timestick (sundial), widely used in India and Tibet, as well as some parts of Europe; and the hourglass, which functioned similarly to a water clock.


The earliest clocks relied on shadows cast by the sun, and hence were not useful in cloudy weather or at night and required recalibration as the seasons changed (if the gnomon - the part of the sundial that casts the shadow - was not aligned with the Earth's axis).

hour glass                                    oil time keeper                candle clock