and studied astronomy, geography, and the physics of earth-
quakes. A brilliant mapmaker, he created detailed render-
ings of the empire while relying on the magnetic compass,
which had allowed greater accuracy in maps and navigational
charts. As tools for military campaigns, these maps were of
vital importance to the emperor, who kept them a closely
guarded state secret.
By recording the locations and dates of earthquakes,
Zhang also took a scientifi c approach to understanding this
dangerous natural phenomenon. His ingenious seismograph,
known as the earth motion instrument, was a large bronze
bowl that held thin copper rods placed horizontally across its
mouth. Th e rods were attached to dragon’s heads, positioned
at the edge of the bowl at the eight major points of the com-
pass. Th e dragon’s heads held small copper balls and lay di-
rectly above small bronze frogs, cast with their mouths open
and directed upward. A tremor or earthquake caused the ball
to fall from the mouth of the dragon closest to the tremor into
the frog’s mouth, causing a small warning bell to ring. Th e
device was activated by the wave motion of earth tremors,
which move at great speed through the earth’s crust. In 138
c.e. the instrument successfully recorded an earthquake 310
miles west of the Han capital.
As an astronomer, Zhang correctly surmised that
eclipses were caused by the shadow of the moon passing over
the earth. Th e ability to predict eclipses was sought aft er by
the emperors, who thus gave themselves the aura of seers and
prophets who lived closer to the gods. Zhang also constructed
a model of the universe, showing the changing positions of
the stars. In the fi eld of mathematics he calculated the value
of pi (the ratio of the circumference of a circle to its diameter)
to 3.162, the most precise calculation of this number up to
that time.MATHEMATICS IN ANCIENT CHINA
Many historians also claim China as birthplace of the decimal
system, in which place values are used to express single digits,
10s, 100s, and so on. Th e earliest Chinese counting systems
used a system of rods placed in small boxes; the rods repre-
sented certain values depending on their position. No rods
meant a value of zero, a concept that was vital to mathemati-
cal calculations and which originated in China (though its
representation by a symbol came later and may have actually
been invented in Southeast Asia.) Later this physical system
of representing numbers developed into the abacus—a small,
portable counting device that is still in use throughout China
and the rest of Asia.
Th e Chinese also invented the concept of negative num-
bers, which in their counting system were represented by
black rods (as opposed to red, used for positive numbers). Th e
Chinese were the fi rst to use decimal fractions and algebraic
calculations for geometrical relationships. By the fi ft h cen-
tury c.e. Chinese mathematicians had calculated the value
of pi to 10 decimal places, putting them far ahead of Greek
mathematicians working out the same value at that time.Th e philosopher Mo Zi, who lived in the fi ft h century, ap-
plied himself to important questions in mathematics as well as
physics, including the nature of light and matter. His followers,
known as Mohists, lived in small communities and devoted
themselves to scientifi c experiment and theorizing. Th ey stud-
ied the force of gravity, the laws of motion, the nature of space
and time, the use of fulcrums, and the equilibrium of objects
fl oating in water. One of their inventions was a room-sized
camera that projected an image through a small hole bored
into a wall facing the sun. Mohists also carefully studied shad-
ows cast by animals and natural objects, and the refl ections in
convex and concave mirrors. Th ey were the fi rst in the world
to use experiments to draw conclusions about the nature of
light waves. Th eir ideas were compiled in a book known as
the Mo jing (Th e Mohist Canon), a work that has been closely
studied by Chinese scientists since the 18th century.SCIENCE IN INDIA
Th e civilization of the Indus River valley, in what is now
northwestern India and Pakistan, developed while the fi rst
large cities were also growing in Mesopotamia (along the Ti-
gris and Euphrates rivers in what is now Iraq) and the Yellow
R iver v a l le y of C h i na. Th e early cities of India developed a pre-
cise system of measurement and made several breakthroughs
in technology and engineering. Indus Valley cities, including
Harappa and Mohenjo Daro, had drainage and sewer sys-
tems, indoor toilets, and paved roads. Chemists applied their
knowledge to the craft of smelting molten metal ores to create
steel and other useful products. Indus Valley steel was in wide
use throughout Asia, the Middle East, and Europe by the fi rst
millennium b.c.e.
In later Vedic (or classical) times, Indian philosophers
divided the natural world into fi ve elements: earth, fi re, air,
water, and ether (or space). According to this philosophy, the
fi rst four elements are made of invisible small particles, the
smallest of which was called parmanu. Each element has a
corresponding sense in the human being: touch, sight, sound,
taste, and smell. Everything on earth was created by chance
combinations of the fi ve elements, while the earth itself is
a large round object under the control of the sun. Th e sun,
in fact, controls all the planets that wander through the sky
against the background of the fi xed stars. Th e earth is divided
into seven large islands, all surrounded by oceans of water.
Th e ancient texts known as the Upanishads delve into the
essential nature, or svabhāva, of the elements and all objects
in nature. Th ese objects are subject to the workings of chance,
or random occurrence, known as yadrccha. Th e philosopher
Kat.āda, writing in the sixth century b.c.e., is given credit by
some historians as the fi rst creator of the atomic theory—the
idea that all matter is composed of invisible, and indivisible,
atoms—in his work known as the Vaiśe S.ikasūtra of Kan.āda
(which precedes a similar theory of the Greek philosopher
Democritus). Kan.āda claimed that matter can never be cre-
ated or destroyed; atoms combine to form particles, which in
turn make up all objects in the universe.934 science: Asia and the Pacific0895-1194_Soc&Culturev4(s-z).i934 934 10/10/07 2:30:29 PM