A Chronicle of Timekeeping
Our conception of time depends on the way we measure it
According to the archaeological evidence, at least 5000 years ago,
and long before the advent of the Roman Empire, the Babylonians
began to measure time, introducing calendars to coordinate communal
activities, to plan the shipment of goods and, in particular, to regulate
planting and harvesting. They based their calendars on three natural
cycles: the solar year, defined by the changing seasons that accompany
our planets revolution around the sun.
Before the invention of artificial light, the moon had greater social
impact. And, for those living near the equator in particular, its waxing
and waning was more conspicuous than the passing of this seasons.
Hence the calendar is that were developed at the lower latitudes were
influenced more by the lunar cycle than by the solar year. In more
northern climes, however, where seasonal agriculture was practiced,
solar year became more crucial. As the Roman empire expanded
northward, but it organized its activity chart for the most part around
the solar year.
Centuries before the Roman empire, the Egyptians had
formulated a municipal calendar having 12 months of 30 days, with five
days added to approximate the solar year. Each period of 10 days was
marked by the appearance of special groups of stars called decans. At
the rise of the star Sirius just before sunrise, which occurred around the
all-important annual flooding of the Nile, 12 decans could be seen
scanning the heavens. The cosmic significance of the Egyptians placed
in the 12 decans led them to develop a system in which each interval of
darkness (and later, each interval of daylight) was divided into a dozen
equal parts. These periods became known as temporal hours because
the duration varied according to the changing length of days and nights
with the passing of this seasons. Summer hours were long, winter ones
short; only at the spring and autumn equinoxes were the hours of
daylight and darkness equal. Temporal hours, which were first
adopted by the Greeks and then the Romans, who disseminated them
through Europe, remained in use for more than 2500 years.
In order to track temporal hours during the day, inventors
created sundials, which indicate time by the length or direction of the
suns shadow. The sundials counterpart, the water clock, was designed
to measure temporal hours at night. One of the first water clocks was a
basin with a small hole near the bottom through which the water
dripped out. The falling water level denoted the passing hour as it
dipped below hour lines inscribed on the inner surface. Although
these devices performed satisfactorily around the Mediterranean, they
could not always be depended on in the cloudy and often freezing
weather of Northern Europe.
The advent of the mechanical clock meant that although it could
be adjusted to maintain temporal hours, it was naturally suited to
keeping equal ones. With these, however, arose the question of when
to begin counting, and so, in the early 14th century, a number of systems
evolved. This schemes that divided the day into 24 equal parts varied
according to the start of the count: Italian hours began at sunset,
Babylonian hours at sunrise, astronomical hour at midday and great
clock hours, used for some large public clocks in Germany, at
midnight for. Eventually these were superseded by small clocks, or
French, hours, which split the day into two 12 hour periods
commencing at midnight.
The earliest recorded weight driven mechanical clock was built in
1283 in Bedfordshire in England. The revolutionary aspect of this new
timekeeper was neither descending weight providing for its motive
force nor the gear wheels (which had been around for at least 1300
years) that transferred the power century; it was the part called the
escapement. In the early 1400s came the intention of the coiled spring
or fuse which maintained constant force to the gear wheels of the
timekeeper and despite the changing tension of its mainspring. By the
16th century, a pendulum clock had been devised, but the pendulum
swung in a large arc and thus was not very efficient.
To address this, a variation on the original escapement was
invented in 1670, in England. It was called the anchor escapement,
which was a lever based device shaped like a ships anchor. The
motion of a pendulum rocks this device so that catches and then
releases each tooth of the escape wheel, in turn allowing it to turn the
precise amount. Unlike the original form used in early pendulum
clocks, the anchor escapement permitted the pendulum to travel in a
smaller arc. Moreover, this invention allowed the use of a long
pendulum which could beat once a second and thus led to the
development of a new floor standing case design, which became known
as the grandfather clock.
Today, highly accurate timekeeping instruments set the beat for
most electronic devices. Nearly all computers contain a quartz crystal
clock to regulate their operation. Moreover, not only time signals
beamed down from Global Positioning System satellites calibrate the
functions of precision navigation equipment, they do so as well for
mobile phones, instant stock trading systems and nationwide power
distribution grids. So integral have these time based technologies
become to day to day existence that our dependency on them is
recognized only when they fail to work.
