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									                      Lesson 15—The Riddle of Time




Part Two




  W   B   T   L   E           ENTER
                                     Lesson 15—The Riddle of Time




Background Information


   I.        Development of Clocks

   II.       Biological Clock

   III.      Calendars



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                                                           Lesson 15—The Riddle of Time




I. Development of Clocks—Sun Clocks




   W   B   T   L   E   To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




I. Development of Clocks—Sun Clocks
  Not until somewhat recently (that is, in terms of
  human history) did people find a need for
  knowing the time of day. As best we know,
  5,000 to 6,000 years ago great civilizations in
  the Middle East and North Africa began to make
  clocks to augment their calendars. With their
  attendant bureaucracies, formal religions, and
  other burgeoning societal activities, these
  cultures apparently found a need to organize
  their time more efficiently.

    W   B   T   L   E          To be continued on the next page.
                                                                      Lesson 15—The Riddle of Time




I. Development of Clocks—Sun Clocks
  The Sumerian culture was lost without passing on its
  knowledge, but the Egyptians were apparently the
  next to formally divide their day into parts something
  like our hours. Obelisks (slender, tapering, four-sided
  monuments) were built as early as 3500 BC. Their
  moving shadows formed a kind of sundial, enabling
  people to partition the day into morning and
  afternoon. Obelisks also showed the year’s longest
  and shortest days when the shadow at noon was the
  shortest or longest of the year. Later, additional
  markers around the base of the monument would
  indicate further subdivisions of time.

    W    B   T   L   E            To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




I. Development of Clocks—Sun Clocks
  Another Egyptian shadow clock or sundial,
  possibly the first portable timepiece, came into
  use around 1500 BC. This device divided a sunlit
  day into 10 parts plus two “twilight hours” in the
  morning and evening. When the long stem with
  5 variably spaced marks was oriented east and
  west in the morning, an elevated crossbar on the
  east end cast a moving shadow over the marks.
  At noon, the device was turned in the opposite
  direction to measure the afternoon “hours”.

    W   B   T   L   E          To be continued on the next page.
                                                           Lesson 15—The Riddle of Time




I. Development of Clocks—Water Clocks




   W   B   T   L   E   To be continued on the next page.
                                                           Lesson 15—The Riddle of Time




I. Development of Clocks—Water Clocks




   W   B   T   L   E   To be continued on the next page.
                                                                     Lesson 15—The Riddle of Time




I. Development of Clocks—Water Clocks
   Water clocks were among the earliest timekeepers
   that didn’t depend on the observation of celestial
   bodies. One of the oldest was found in the tomb of
   the Egyptian pharaoh Amenhotep I, buried around
   1500 BC. Later named clepsydras (“water thieves”)
   by the Greeks, who began using them about 325
   BC, these were stone vessels with sloping sides
   that allowed water to drip at a nearly constant rate
   from a small hole near the bottom. Other
   clepsydras were cylindrical or bowl-shaped
   containers designed to slowly fill with water coming
   in at a constant rate.

   W    B   T   L   E            To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




I. Development of Clocks—Water Clocks

   Markings on the inside surfaces measured the
   passage of “hours” as the water level reached
   them. These clocks were used to determine
   hours at night, but may have been used in
   daylight as well. Another version consisted of
   a metal bowl with a hole in the bottom; when
   placed in a container of water the bowl would
   fill and sink in a certain time. These were still
   in use in North Africa in the 20th century.


   W   B   T   L   E           To be continued on the next page.
                                                                Lesson 15—The Riddle of Time




I. Development of Clocks—Water Clocks
   More elaborate and impressive mechanized
   water clocks were developed between 100 BC
   and 500 AD by Greek and Roman horologists
   and astronomers. The added complexity was
   aimed at making the flow more constant by
   regulating the pressure, and at providing
   fancier displays of the passage of time. Some
   water clocks rang bells and gongs; others
   opened doors and windows to show little
   figures of people, or moved pointers, dials,
   and astrological models of the universe.

   W   B   T   L   E        To be continued on the next page.
                                                                        Lesson 15—The Riddle of Time




I. Development of Clocks—Water Clocks
  In the Far East, mechanized astronomical/astrological
  clock making developed from 200 to 1300. Third-century
  Chinese clepsydras drove various mechanisms that
  illustrated astronomical phenomena. One of the most
  elaborate clock towers was built by Su Sung and his
  associates in 1088. Su Sung’s mechanism incorporated a
  water-driven escapement invented about 725. The Su
  Sung clock tower, over 30 feet tall, possessed a bronze
  power-driven armillary sphere for observations, an
  automatically rotating celestial globe, and five front
  panels with doors that permitted the viewing of changing
  manikins which rang bells or gongs, and held tablets
  indicating the hour or other special times of the day.

    W    B   T   L   E              To be continued on the next page.
                                                           Lesson 15—The Riddle of Time




I. Development of Clocks—Pendulum Clocks




   W   B   T   L   E   To be continued on the next page.
                                                                      Lesson 15—The Riddle of Time




I. Development of Clocks—Pendulum Clocks
  In Europe during most of the Middle Ages (roughly
  500 to 1500), technological advancement was at a
  virtual standstill. Sundial styles evolved, but didn’t
  move far from ancient Egyptian principles.
  During these times, simple sundials placed above
  doorways were used to identify midday and four
  “tides” of the sunlit day. By the 10th Century,
  several types of pocket sundials were used. One
  English model identified tides and even
  compensated for seasonal changes of the sun’s
  altitude.


    W   B   T   L   E             To be continued on the next page.
                                                                      Lesson 15—The Riddle of Time




I. Development of Clocks—Pendulum Clocks
   Then, in the early-to-mid-14th century, large
   mechanical clocks began to appear in the towers of
   several large Italian cities. There is no evidence or
   record of the working models preceding these public
   clocks that were weight-driven and regulated by a
   verge-and-foliot escapement. Verge-and-foliot
   mechanisms reigned for more than 300 years with
   variations in the shape of the foliot. All had the same
   basic problem: the period of oscillation of this
   escapement depended heavily on the amount of
   driving force and the amount of friction in the drive.
   Like water flow, the rate was difficult to regulate.


   W    B   T   L   E             To be continued on the next page.
                                                                  Lesson 15—The Riddle of Time




I. Development of Clocks—Pendulum Clocks
   Accurate Mechanical Clocks
   In 1656, Christian Huygens, a Dutch scientist,
   made the first pendulum clock, regulated by a
   mechanism with a “natural” period of oscillation.
   Although Galileo Galilei, sometimes credited
   with inventing the pendulum, studied its motion
   as early as 1582, Galileo’s design for a clock
   was not built before his death. Huygens’
   pendulum clock had an error of less than 1
   minute a day, the first time such accuracy had
   been achieved. His later refinements reduced
   his clock’s errors to less than 10 seconds a day.

    W   B   T   L   E         To be continued on the next page.
                                                                       Lesson 15—The Riddle of Time




I. Development of Clocks—Atomic Clocks
  The first atomic clock, Caesium I, was designed by
  Louis Essen and built at the National Physical
  Laboratory in Teddington in 1955. Although it was not
  the first machine to use atoms for timekeeping, it was
  the first to keep time better than the best pendulum
  or quartz clocks.
  It was also the first clock whose timekeeping was
  significantly more constant than the rotation of the
  Earth. Modern atomic clocks are even more accurate
  than Caesium I and time is now defined in terms of
  atoms rather than the Earth’s motion.

    W    B   T   L    E            To be continued on the next page.
                                                                     Lesson 15—The Riddle of Time




I. Development of Clocks—Atomic Clocks
 All mechanical clocks work by counting the vibrations
 of something which has a constant frequency such as a
 pendulum. Unfortunately, the frequency of a pendulum
 is not perfectly constant. It is affected by changes in
 temperature, air pressure and the strength of gravity.
 This causes the clock to run too quickly or too slowly.
 The frequencies measured by atomic clocks are much
 higher than those of a pendulum but vary much less,
 so atomic clocks keep time much better. Caesium I was
 so accurate that it would only gain or lose one second
 in three hundred years. Modern atomic clocks are even
 more accurate.


    W   B   T   L   E            To be continued on the next page.
                                                                 Lesson 15—The Riddle of Time




I. Development of Clocks—Atomic Clocks
   Modern Atomic Clocks

       Atomic clock technology continued to
       improve. Machines which are accurate to
       one second in 30,000 years, such as the
       HP5071A, are now commercially available
       and are often used by communications
       companies to obtain precise frequencies.




   W    B   T   L   E        To be continued on the next page.
                                                                 Lesson 15—The Riddle of Time




I. Development of Clocks—Atomic Clocks
  These clocks work on the same principle as Caesium I.
  The latest atomic clocks work in a slightly different
  way, which gives even greater accuracy. In 1993, the
  National Institute of Standards and Technology (NIST)
  in the U.S.A. (formerly the NBS) built NIST-7, a
  caesium atomic clock that uses lasers instead of
  magnets to separate the atoms before and after they
  pass through the beam tube. Initially, NIST-7 was
  accurate to one second in 800,000 years but has since
  been improved to one second in 6 million years. The
  next generation of atomic clocks will use other
  methods for controlling the movement of their atoms
  and will be even more reliable.

    W   B   T   L   E        The end of Development of Clocks.
                                                                   Lesson 15—The Riddle of Time




II. Biological Clock

  Molecular “clocks” in the brain create natural
  cycles in many body traits, such as blood
  pressure and temperature. Scientists have
  learned that these clocks, which can be reset by
  sunlight, are controlled by special genes.
  Knowledge of these clocks is leading to an
  improved understanding of biological cycles and
  new ways of treating disorders such as
  insomnia.


   W   B   T   L   E           To be continued on the next page.
                                                                        Lesson 15—The Riddle of Time




II. Biological Clock
  Are you a “night owl” or an “early bird”? The answer
  depends on a biological “clock” in your brain. This clock
  controls many natural body cycles—from the time you
  wake up each morning to rhythmic changes in body
  temperature and blood hormone levels.
  Nearly all organisms, from bacteria to plants to humans,
  have biological clocks that help maintain rhythms.
  By studying these clocks, scientists are beginning to
  understand:
  The biological foundations of behavior.
  Jet lag, insomnia, mental disorders, and how to treat
  them.
  Rhythmic changes in heart rate and other traits that
  affect the diagnosis and treatment of many disorders,
  including fever and high blood pressure.


    W   B    T   L   E              To be continued on the next page.
                                                                        Lesson 15—The Riddle of Time




II. Biological Clock
  During the mid-1900s, scientists began to examine
  biological cycles in several different organisms. By the
  early 1960s, they showed that daily, or circadian
  rhythms—“circa” means around and “dia” means day—
  are generated internally and synchronized to the 24-
  hour day. How are these cycles generated and altered?

  In mammals, including humans, a biological clock
  resides in a region of the brain’s hypothalamus, a
  quarter-sized structure that regulates hormone levels
  and plays a role in emotions. In some insects and
  snails the clocks are usually located in the retina of the
  eye. In birds the clocks can also be found in a brain
  region called the pineal gland or in the hypothalamus.


     W    B   T   L   E             To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




II. Biological Clock
  The clocks are almost always linked to some
  form of light-sensing cell called a photoreceptor.
  This type of cell responds to sunlight in ways
  that help synchronize the clock with the 24-hour
  day.

  Scientists have learned that exposure to light at
  certain times in the internal cycle can reset the
  clock in animals. In mammals, light turns on
  important genes and affects sleep patterns,
  alertness, and body temperature. In nature, this
  light sensitivity helps organisms synchronize
  their clock within the cycle of day and night.

    W   B   T   L   E          To be continued on the next page.
                                                                       Lesson 15—The Riddle of Time




II. Biological Clock
  Researchers have found that exposure to strong
  artificial light at certain times can reset the clock in
  ways that relieve insomnia, jet lag, and other
  problems. Light at the wrong time of the internal
  cycle, however, might contribute to or intensify these
  conditions.
  By studying mold, flies, mice, and other organisms,
  scientists have learned that the function of the
  biological clock is controlled by specific genes.
  Research in flies with disabled or altered clock genes
  shows that the proteins clock cells produce often work
  in a negative feedback cycle. When high levels of
  clock proteins are present, they block further
  production of these molecules until the levels fall
  again.

    W    B   T   L   E             To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




II. Biological Clock
  Some clock genes also regulate or stabilize other
  genes’ activity. The way these clock proteins
  affect body functions is not yet known. However,
  learning how normal cycles affect the body may
  improve the diagnosis of many disorders, such
  as fever and high blood pressure, by accounting
  for daily rhythmic variation in hormone levels,
  blood pressure, temperature, and other traits.

  Researchers believe only a few genes regulate
  circadian cycles in most organisms. Mutations in
  known clock genes usually create large changes
  in length of the cycle.

    W   B   T   L   E          To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




II. Biological Clock
  Organisms with some mutations are unable to
  maintain any normal rhythm at all. If mutations
  in human clock genes act in a similar way, they
  may prevent some people from synchronizing
  their cycles with the environment, causing sleep
  disturbances and other problems.

  Scientists have now uncovered several ways to
  treat clock-related disorders. Some studies
  suggest that the hormone melatonin, given at
  specific times, may be useful for resetting daily
  rhythms to help overcome the effects of jet lag
  and sleep disorders.

    W   B   T   L   E          To be continued on the next page.
                                                              Lesson 15—The Riddle of Time




II. Biological Clock

  Exposure to bright light at certain times in
  the cycle may also help people with
  depression and other disorders. These
  strategies, now being tested in humans,
  may brighten the lives of millions of people.




    W   B   T   L   E          The end of Biological Clock.
                                                                         Lesson 15—The Riddle of Time




III. Calendars—Solar Calendars
 The Julian Calendar was introduced by Julius Caesar in 45
 BCE and introduced a simple leap year rule: Insert an
 extra day every four years. The Julian Calendar eventually
 standardized on 21 March as the date of the vernal
 equinox. Although this leap year rule is a simple one, it is
 does not produce a precise match to the solar year. Over
 the centuries the date of the astronomical vernal equinox
 slowly drifted away from the date of 21 March. The
 ecclesiastical rules to compute the date of Easter defined
 21 March as the date of the vernal equinox. The
 Gregorian Calendar resulted from a perceived need to
 reform the calculation method for the dates of Easter.
 Nonetheless, the Julian Calendar and variations of it are
 still in use by some groups to set the dates for liturgical
 events.

    W    B   T    L   E              To be continued on the next page.
                                                                      Lesson 15—The Riddle of Time




III. Calendars—Solar Calendars
 The Gregorian Calendar has become the internationally
 accepted civil calendar. The leap year rule for the
 Gregorian Calendar differs slightly from one for the
 Julian Calendar. The Gregorian leap year rule is: Every
 year that is exactly divisible by four is a leap year,
 except for years that are exactly divisible by 100. For
 example, the year 1900 is not a leap year; the year
 2000 is a leap year. The centurial years that are exactly
 divisible by 400 are still leap years. The Gregorian
 dates for Easter are computed from a set of
 ecclesiastical rules and tables.


    W   B    T   L   E            To be continued on the next page.
                                                                     Lesson 15—The Riddle of Time




III. Calendars—Lunar Calendars
  The Islamic Calendar is a purely lunar calendar in
  which months correspond to the lunar phase cycle.
  Thus the twelve months of the Islamic Calendar
  systematically shift with respect to the months of
  the international civil calendar. The cycle of twelve
  months regresses through the seasons over a
  period of about 33 years. For religious purposes,
  Muslims begin each month with the first visibility
  of the lunar crescent after conjunction. For civil
  purposes a tabulated calendar that approximates
  the lunar phase cycle is often used.


    W    B   T   L   E           To be continued on the next page.
                                                                    Lesson 15—The Riddle of Time




III. Calendars—Lunisolar Calendars

   The Hebrew Calendar is a lunisolar calendar
   based on calculation rather than observation.
   Its current form dates from about 359CE. This
   calendar is the official calendar for the State of
   Israel, although variations on this calendar
   exist. The dates for Passover for this calendar
   are computed from a set of defined rules.




    W   B   T   L   E           To be continued on the next page.
                                                                   Lesson 15—The Riddle of Time




III. Calendars—Lunisolar Calendars
   The National Calendar of India is a formalized
   lunisolar calendar in which leap years coincide
   with those of the Gregorian Calendar. The
   Gregorian Calendar is used for administrative
   purposes. The Indian religious calendars require
   calculations of the motions of the Sun and the
   Moon. Tabulations of the religious holidays are
   prepared by the India Meteorological Department
   and published annually in The Indian
   Astronomical Ephemeris. Many local variations
   exist.


   W   B   T   L   E           To be continued on the next page.
                                                     Lesson 15—The Riddle of Time




III. Calendars—Lunisolar Calendars


  The Chinese Calendar is a lunisolar calendar
  based on calculations of the positions of the
  Sun and the Moon. Since this calendar uses
  the true positions of the Sun and the Moon, its
  accuracy depends on the accuracy of the
  astronomical theories and calculations.




   W   B   T   L   E         The end of Calendars.
                      Lesson 15—The Riddle of Time




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