Zhang Heng
Darani Vasudevan
Zhang Heng
(Biographies for children)
Darani Vasudevan
Preface, This is a Biography of the inventor of first seismometer. The words used are simple and suit people of all ages. Some of the important events happened in her life are listed in the succeeding pages. Hope you like it!! - V. Darani M.Sc., M.Phil., SET
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Name: Zhang Heng Born: 78 AD Place of Birth: Nanyang, China Died: 139 AD Place of Death: Luoyang, China
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Early Life and Education A Chinese astronomer, cartographer, mathematician, inventor, geographer, artist, poet, statesman and literary scholar- the one who own all these credits is Zhang Heng. He is also known as Chang Heng. The great man was born in a town North of modern Nanyang, China. During that time China was under the rule of Eastern Han dynasty and Chang-ti was the emperor at the time of his birth.
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Zhangâ€&#x;s grandfather served as a Governor
of
Unfortunately,
a
commandery.
Zhang
lost
. his
grandfather when he was 10 years old. This left Zhang to take care of his mother and grandmother. He left home at the age of 17 to pursue his studies in the ancient capitals of Changâ€&#x;an and Luoyang. He got educated in the moral and political philosophy of Confucianism. He studied literature for 10 years as well as trained himself as a writer. When he was 30 years old, his interest
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switched from literature to scientific matters especially astronomy. His published
works
and
Scientific
inventions adorned him with fame.
Minister and Astronomer Emperor Han appointed Zhang in his court in 112 AD after knowing his expertise in mathematics. In 116 AD Zhang was appointed as an official in the court of the Emperor in Luoyang. At Luoyang, he became a court gentleman
and
worked
for
the
imperial secretariat. Due to lack of
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ambition he failed to be successful as a official. He mentioned this in his biography “The History of the Eastern Han Dynasty.� So he spent several years away from the dynasty, sparing his time thinking about the nature of universe and several other scientific topics. He
was
Astronomer
promoted and
as
Chief
Minister
under
Emperor An-ti. He served during the reigns of Emperors An-ti (94- 125AD) and Shun-ti (125-144AD).
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During his time, there existed a belief that the organization of civil life was the reflection of and controlled by the heavens attention
which to
demanded events
careful
that
might
influence government. It was the responsibility of the Chief Astronomer
to
record
heavenly
observations, prepare calendar and report the auspicious days. Hence Zhang got the important function of creating and maintaining calendars, making predictions regarding celestial
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events and maintaining records of the events observed in heaven.
Armillary Sphere He was the first person in China to construct water powered equatorial armillary sphere. This instrument enabled Zhang to make more accurate star maps. Armillary Sphere is a bronze celestial globe. Zhang applied hydraulic motive power
(i.e.
by
employing
a
waterwheel and clepsydra or water clock) to rotate the armillary sphere.
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By turning waterwheel which was powered by the constant pressure from the head of water in the water clock tank rotated the sphere. This water powered
armillary
influenced the
design of later Chinese water clocks and led to the discovery of the escapement mechanism (8th century). It was constructed on the basis of a bamboo
model
which
Zhang
improved it by remapping over 2000 stars and powered it. It would make one rotation per year. A complicated gear system linked the armillary to a
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kettle clepsydra. As the water dripped from one pan to another the weight would drive the gears and the sphere would advance. He added a geardriven device which demonstrated the waxing and waning of moon. He named this instrument as Hunichu. Zhangâ€&#x;s description about his waterpowered armillary sphere: “The
equatorial ring goes around the
belly of the armillary sphere 91 and 5/19 away from the pole. The circle of the ecliptic also goes round the belly of
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the instrument at an angle of 24 with the
equator.
Thus
at
the
summer
solstice the ecliptic is 67 and a fraction away from the pole, while at the winter solstice it is 115 and a fraction away. Hence
where
the
ecliptic
and
the
equator intersect should give the north polar
distances
of
the
spring
and
autumn equinoxes. But now the spring equinox is 90 and ¼ away from the pole, and the autumn equinox is 92 and ¼ away. The former figure is adopted only because it agrees with the method of measuring solstitial sun shadows as embodied in the Xia calendar.”
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He described stars in his work Ling Xian as, “North are
and South of the equator there
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brightly
groups
which
shining,
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are
stars
always can
be
named. There are in all 2500, not including
those
which
the
sailors
observe. Of the very small stars there are 11520.”
He catalogued 2500 stars, which he placed
in
a
„brightly
shining‟
category, and he recognized 124 constellations. He noted the names of 320 brightest stars and also noted an additional 11520 small stars.
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Seismometer In 132 AD Zhang invented the first seismograph
for
measuring
earthquakes. During his time, people considered
earthquakes
as
punishments from the God for poor governance prevailing in the country. According
to
Zhang
Hang,
earthquakes were caused by wind and air, hence he wrote: “The chief cause of earthquake is air, an element naturally swift and shifting from place to place. As long as it is not
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stirred, but lurks in a vacant space, it reposes innocently, giving no trouble to objects around it. But any cause coming upon
it
from
without
ruses
it,
or
compresses it, and drives it into a narrow space....and when opportunity of escape is cut off, then „with deep murmur
of
the
mountain
it
roars
around the barriers‟ which after long battering it dislodges and tosses on high, growing more fierce the stronger the obstacle with which it is contended.”
Zhang named his seismometer “Hou Feng Di Dong Yi (meaning: an instrument for measuring seasonal winds and the movement of Earth).” It
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is of urn shaped and is made of copper. It consisted of eight dragon heads around the top, each with a copper ball in its mouth, and a pendulum in the centre of the urn shaped structure. Around the bottom were eight frogs each directly under a dragon head. When an earthquake occurred, a ball fell out of a dragonâ€&#x;s mouth into a frogâ€&#x;s mouth, making a noise.
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In 138 AD, Zhang reported of an earthquake more than a thousand
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kilometres northwest which reached the capital several days later. His
seismometer
discerned
the
cardinal direction of an earthquake 310 miles (500 Km) away.
Cartography Cartography
(map
making)
had
existed in China since 4th century BC. “The books of Later Han� hints that Zhang was the first to make a mathematical
grid
ancient china maps.
reference
on
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It states, “Cast a network of coordinates about heaven and earth, and reckoned on the basis of it.�
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He placed the horizontal and vertical lines on his charts based on the angle of arc.
Theories of Moon and Lunar & Solar Eclipse Zhang proposed theories on the moon and its relationship with the sun. He discussed the moonâ€&#x;s spherical nature, its illumination by reflected sunlight and the hidden nature of the other.
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He used the “radiating influence” theory to explain lunar and solar eclipses. In his writing “Ling Xian,” Zhang mentioned: “The sun is like fire and the moon like water. The fire gives out light and the water
reflects
brightness
is
it.
Thus
produced
the
moon‟s
from
the
radiance of the sun, and the moon‟s darkness
is
due
to
the
sun
being
obstructed. The side which fades the sun is fully lit, and the side which is away from it is dark. The planets have the nature of water and reflects light. The
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light pouring forth from the sun does not always reach the moon owing to the obstruction of the Earth itself – this is called „an-xu‟ (a lunar eclipse). When happens with a planet, an occupation; when the moon passes across then there is a solar eclipse.”
His View on Universe In 120 AD, in his “The spiritual constitution of the Universe,” Zhang theorized his observation of Universe as, “The
sky is like a hen‟s egg and is as
round as a crossbow pellet, the Earth is
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like the yolk of the egg, lying alone at the centre. The sky is large and the Earth small.�
Inflow clepsydra The outflow clepsydra (water clock) was used in China for ages. But the use of inflow clepsydra with and indicator rod on a float existed since the Han dynasty. The falling pressure head in the reservoir slowed the time keeping of the device as the inflow vessel was filled.
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Zhang was the one to address the problem.
He
compensating
added tank
an
between
extra the
reservoir and the inflow vessel. On the top, he mounted two statuettes of a Chinese immortal and a heavenly guard which guided the indicator rod with their left hand and pointed out the graduations with their right. His description about the inflow clepsydra is as follows: “Bronze vessels are made and placed one above the other at different levels; they are filled with pure water. Each
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has at the bottom a small opening in the form of a „jade dragon‟s neck.‟ The water
dripping
enters
two
inflow
receivers, the left one being for the night and the right one for the day. On the covers of each, there are small cast statuettes in bronze, the left one is an immortal policeman.
and
the
These
right
figures
one guide
is
a the
indicator rod with their left hands, and indicate the graduations on it with their right hands, thus giving the time.”
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Odometer and South Pointing Chariot
Zhang is often credited with the invention mechanical
of
odometer
device
called
and
a
South
pointing chariot. His south pointing
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chariot was a non-magnetic compass vehicle in the form of a two- wheeled chariot. Differential gears driven by the chariotâ€&#x;s wheels allowed a wooden figurine (shape of a Chinese state minister) to constantly point to the south.
Pi (ď °) Around 130 AD, Zhang compared the celestial circle to the diameter of the Earth, proportioning the former as 736 and the latter as 232. Based on his theoretical calculation he proposed
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that
ď °=
ďƒ–10
=3.162
which
is
practically not accurate. But still he rounded the value of pi to 3 which is accurate. He also studied 3 by 3 magical squares (a magic square is a set of integers arranged in a square in such a way that each row, each column and often the two diagonals as well sum to the same number)
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Other Contributions Historians believe that Zhang was well aware of the difference between rational and irrational numbers. He was well versed in the fields of mechanics and gears. His inventions stand as proofs for his knowledge in mechanics and gears. In his theory of cosmos, he proposed that the Earth is tilted so that the north is higher. He found that it was 26º5‟ which is just 3ºoff the modern measurement of 23º27‟.
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He also recorded the angular diameter of both the sun and the moon which is 1/736 of the celestial sphere or rather 29º21˝, a difference of 2˝ from the average value of 31˚5˝.
As a Poet Zhang was renowned for his fu (rhapsody) and shi poetry, which were highly regarded by later Chinese writers. As a poet and writer he had presented over 20 works to the world. His work Sichou shi (Four chapters of distressed poems) and Gui Tian Fu
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(To live in seclusion) are considered literary masterpieces. He composed 32 written works on literature, philosophy, science and mysticism. Here is the first stanza (translated) of his poem “The four stanzas of sorrow”: “In Taishan stays my dear Sweetheart, But Liangfu jeeps us long apart; Looking east, I find tears start. She gives me a sword to my
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Delight; A jade I give her as requite. Iâ€&#x;m at a loss as she is out of sight; Why should I trouble myself all Night?â€? (Source: Mac Tutor archieve)
Later life and Death Zhang retired from his position under Emperor Shun in 136 AD but he was appointed again as the Chancellor of Hejiang. He retired from his office in 138 AD and returned home to Nanyang. He composed rhapsody in
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his leisure time he got after retirement. Zhang was again appointed to serve under the Imperial Secretariat hence he travelled back to the capital. He died in 139 AD while serving in office. He was buried in his hometown Xiâ€&#x;e, in Nanyang and his friend Cui Yuan composed the inscription of his tomb. It is not that he faced appreciation all the time. Critics followed each and every time he invented something. But still he was strong enough to face them and he never gave up his next
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opportunity.
As
a
result,
critics
vanished with time and his inventions turned into objects of admiration. Now he stands as an icon in Chinese history as well as in the history of the world. WHATEVER HAPPENS IN LIFE ....NEVER GIVE UP. TRYING IS MORE WORTHY THAN GIVING UP. All the Best
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