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History of Horology; Sundials to Atomic Clocks
Category: ScienceThis article explores the history of horology (the way we measure time).
Mankind
has always been preoccupied with measuring and recording the passage of time.
Timekeeping has been essential for the development of civilisations; from knowing when to plant or
harvest crops to identifying important events in the year.
Time has
historically been measured in relation to the movement of the Earth; a
day, is one revolution of the planet; while a year is an entire orbit of the
Sun. Calendars were developed
from as far back as 20,000 years ago when hunter-gatherers scratched
lines and gouged holes in sticks and bones to possibly count the days between
phases of the moon.
Civilizations from the Ancient Egyptians to the Roman Empire
have used differing methods to discover what day of the year it is. However,
measuring time as it passed throughout the day had always proved difficult to
early mankind. Sundials were perhaps the first time pieces and they can trace
their origin back over five thousand years; when obelisks were built, possibly
to allow the telling of time by the cast of their shadows.
However, the time told on a sundial was based on the
movement of the sun in the sky, which would differ throughout the seasons and
of course would not work on cloudy days or at night. Other methods such as
water clocks or the hourglass would simply act as crude timers. Telling the
time of day would prove difficult with people relying on comparisons as time
references such as: “As long as it would take a man to walk a
quarter mile.?
People were reliant on these methods and others such as bell
ringing to indicate important moments until the 14th century, when
mechanical clocks first appeared which were driven by weight and regulated by a
verge-and-foliot escapement (a system that advanced the gear train at regular
intervals or ‘ticks’). These clocks were far more reliable than sundials or
other methods allowing accurate and reliable telling of the time of day for the
first time in human history.
The next step forward in horology came in the 17th
century when the pendulum was developed to help clocks maintain their accuracy.
Clock making soon became widespread and it was not for another three hundred
years that the next revolutionary step in horology would take place; with the
development of electronic clocks. These were based on the movement of a vibrating
crystal (usually quartz) to create an electric signal with an exact frequency.
While electronic clocks were far more accurate than
mechanical clocks it wasn’t until the development of Atomic Clocks around fifty years ago that
modern technologies such as communication satellites, GPS and global computer
networks became possible.
Most atomic clocks use the resonance of the atom caesium-133
which vibrates exactly at a frequency of 9,192,631,770 every second. Since 1967
the International System of Units ( , allowing computer networks all over the
world to be synchronized to UTC.
About the author
Richard N Williams is a technical author and a
specialist in the telecommunications and network time synchronisation industry
helping to develop dedicated time server products. Please visit us for
more information about a GPS time server or other NTP
products.
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