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horology(hōrŏl`əjē), science of measuring timetime,
sequential arrangement of all events, or the interval between two events in such a sequence. The concept of time may be discussed on several different levels: physical, psychological, philosophical and scientific, and biological.
..... Click the link for more information. and technology of constructing instruments for its measurement or recording. Early measurements of the passage of time were based on observations of seasonal cycles and of the apparent motion of celestial bodies. Shorter intervals were measured by observing the shadow cast by an upright object; the shadow clock and the sundialsundial,
instrument that indicates the time of day by the shadow, cast on a surface marked to show hours or fractions of hours, of an object on which the sun's rays fall.
..... Click the link for more information. were probably the first devices constructed. Later came the hourglasshourglass,
glass instrument for measuring time, usually consisting of two bulbs united by a narrow neck. One bulb is filled with fine sand that runs through the neck into the other bulb in an hour's time. The date of its invention is unknown, but it was in use in ancient times.
..... Click the link for more information. and the clepsydraclepsydra
or water clock,
ancient device for measuring time by means of the flow of water from a container. A simple form of clepsydra was an earthenware vessel with a small opening through which the water dripped; as the water level dropped, it exposed marks on the
..... Click the link for more information. and finally the clockclock,
instrument for measuring and indicating time. Predecessors of the clock were the sundial, the hourglass, and the clepsydra. See also watch. The Evolution of Mechanical Clocks
..... Click the link for more information. and the watchwatch,
small, portable timepiece usually designed to be worn on the person. Other kinds of timepieces are generally referred to as clocks. At one time it was generally believed that the first watches were made in Nuremburg, Germany, c.1500.
..... Click the link for more information. . The most accurate type of timekeeping device in existence today is the atomic clockatomic clock,
electric or electronic timekeeping device that is controlled by atomic or molecular oscillations. A timekeeping device must contain or be connected to some apparatus that oscillates at a uniform rate to control the rate of movement of its hands or the rate of
..... Click the link for more information. . Highly accurate time, which is necessary for such purposes as navigation and the tracking of artificial satellites, is provided throughout the world by time signals that are transmitted by certain radio stations.
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(science and technology)
The science of measuring time and the technology of constructing instruments for this measurement.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.