science: Asia and the Pacific comprehensive star catalogue, plotting the position of more than 1,000 stars A tradition also records that Gan De made the first observation of Ganymede, a moon of Jupiter, without a telescope or artificial optics of any kind EARTH SCIENCE Geology and metallurgy made important advances in the early Chinese dynasties Geologists carefully recorded their discoveries while keeping the practical application of their knowledge foremost For example, they constantly compared rocks and soils above the ground with those found beneath it The Chinese discovered, for example, that the presence of hematite, or metallic stones, above ground indicates the existence of underground veins of iron ore and that the reddish mineral cinnabar is a good indicator of gold or mercury deposits These observations led to classification systems for minerals, one of which is found in the Shan hai jing (The Book of Mountains), a work of the fift h century b.c.e This book classified rocks according to their hardness, color, and shape, and guided metalsmiths in collecting mineral ores and smelting them into useful finished metals Ancient Chinese iron miners discovered magnetite, a rock with magnetic properties This discovery led to the navigational compass, one of the most important technological breakthroughs in history The Chinese built south-pointing compasses to guide themselves over land and sea The pointers on these devices were commonly spoons or representations of animals such as frogs Later the spoons were replaced by needles, which allowed the compass or pointer much greater accuracy The Chinese were also expert in the science of meteorology They were setting down weather records by the second millennium b.c.e and making daily calculations of temperature, rainfall amounts, and wind speed and direction This diligent record keeping brought them knowledge of the earth’s hydrologic cycle of precipitation and evaporation, which manifests in wind, clouds, and storms to keep the earth watered and fertile APPLIED SCIENCE In all scientific endeavors of ancient China, theory and observation had practical uses While observing the sun, an unknown Chinese inventor realized that the sun’s position can be measured by the length of its shadow He then created the gnomon, a simple vertical pole placed upright to cast the sun’s shadow The shadow shrinks to its smallest length at the summer solstice and to its greatest length at the winter solstice Thus, using the gnomon, the Chinese measured the length of the year and marked the beginning of the seasons The taller the gnomon, the more accurate the measurement; to raise large gnomons, the Chinese constructed massive brick structures, many of which still stand The scientist Zu Gengzhi took the gnomon a step further by adding a horizontal measuring scale and making the device small and light enough to be carried 933 Other Chinese breakthroughs include the making of cast iron and the forging of harder, more durable steel by blowing oxygen onto the cast iron and causing its carbon content to drop This process relies on another ancient Chinese invention, the double-action piston bellows, which forces air continuously into a forge or oven Chinese inventors also came up with gimbals—small iron rings that support an object and allow that object to remain upright no matter how the rings around it are turned The gimbal became an important component of marine compasses, which must function accurately aboard ships in constant motion, and the gyroscope, which was invented by the second century b.c.e The Chinese also invented, in the ancient period, umbrellas, stirrups, porcelain, hot-air balloons, iron plows, kites, and paper Chain pumps, which allow users to raise water from a canal or ditch into a field of crops, are still in use in rural China The southpointing carriage was used for navigation on land The device supported the figure of a man, pointing toward the horizon; no matter which way the carriage was turned, the figure always pointed south A complex series of gears governed the transfer of motion from the wheels to the figure One of the marvels of early Chinese science and engineering was the curious object known as the spouting bowl This large, precisely cast bronze bowl was filled with water When the bowl was carefully rubbed at the handles, the water within the bowl began to spout and the entire bowl began to hum The steady rubbing created a certain wavelength and frequency in the water’s motion that caused a standing wave—one that moves up and down, not sideways One of the most important scientific quests of ancient China was the search for an elixir of life Chinese alchemists sought to create gold and silver from baser elements and experimented with the properties of semiprecious stones such as jade One could be made immortal, it was believed, if one ingested an eternal substance, such as gold, which does not rust or burn Chinese alchemists undertook long and complex experiments, always basing their work on the five elements and the concept of yin and yang They heated and mixed chemicals derived from rocks, soil, and earth, as well as bones, teeth, and hair They dissolved them in water, vinegar, mercury, and saltpeter They studied the changes in the color and appearance of the elements, noting that different metals have different melting points and give off different colors when put in the fire Alchemists also studied the effect of these substances on the body when applied to the skin or when taken in through drinking or eating them Early chemical experimentation was held to be a great secret in ancient China and forbidden to common workers and peasants Chemists, astronomers, geologists, and other scientists worked diligently for the emperor and were kept within the palace quarters and the imperial capital, where they were closely watched One of the most important scientists of ancient China was Zhang Heng, a scholar of the Han dynasty, who was born in 78 c.e He served the dynasty as imperial historian