Pendulum Clock (ca. 1600–1670): The relationship between astronomical observations and timekeeping is an ancient one. Early civilizations found it important to be able to predict the passing of the seasons by the phases of the moon and the position of the sun in the sky. Today, massive stone structures called obelisks serve as reminders of early attempts to predict seasonal changes. These structures were often strategically placed in order to predict the longest and shortest days of the year. The most famous example is Stonehenge, located in southern Britain. The masonry that survives today was built around 2550 B.C.E., although there is evidence that the current structure was built on the foundations of older works. On a daily time scale, obelisks could be utilized as massive sundials to divide the day into smaller units of measurement. Obelisks, however, were practically useless for night-time astronomical observations. As cultures and religions became more advanced, there developed a need for more elaborate timekeeping mechanisms.
For many cultures, especially the Chinese and Arabic, water clocks were developed as a more accurate mechanism of keeping time. These instruments, called clepsydras, may have been in use as early as 1500 B.C.E. By the era of the ancient Greeks (ca. 325 B.C.E.), water clocks were a popular form of timekeeping. The construction of a water clock was relatively simple. A metal or stone bowl with a small hole in the bottom was placed in a pool of water. Incremental markings on the inside of the container recorded the passage of time as the container filled. The Chinese constructed elaborate clepsydras, one of which was over thirty feet in height, which included globes and other mechanisms for measuring astronomical time. Other water clocks functioned using
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Publication information: Book title: Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 17th Century. Contributors: Michael Windelspecht - Author. Publisher: Greenwood Press. Place of publication: Westport, CT. Publication year: 2002. Page number: 187.
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