A. The solar day, the lunar month, the astronomical year.
2. The great Chinese clocks.
A. Verge-and-foliot escapement.
The perception of time most likely arose through human observation of various natural phenomena. Repetitive occurrences such as the sunrise and the sunset eventually led to a delineation of specific time intervals. Among these, the earliest may have been the solar day, the lunar month, and the astronomical year. Perhaps it was the year's division into 12 months which led early societies to divide the day also into 12 equal parts. This original system was then supplanted by an hour based on the period of the nychthemeron: both night and day together were divided into 24 equal parts throughout the year.
These early delineations of time were used by astronomers, astrologers, and physicians; in addition, they most likely also had important uses in agriculture. However, the hour itself was not widely employed for ordering social life until about the 14th century.
The earliest device for time measurement was the sun-dial. In its simplest form, the day's progression was approximated through movement of the sun's shadow cast by a vertical rod--the gnonom. Eventually though, the sun-dial's inability to f
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