We have seen the first use of hydraulic energy in China under the Han Empire, at the beginning of the 1st century AD. The Chinese devices are quite complex from the very beginning, in contrast to the comparable but simpler devices developed at the same time in the Roman Empire. There, simple horizontal-axis mills are used to turn a grindstone. But in China there are complex devices powered by vertical-axis water wheels, according to all evidence. These wheels power batteries of pestles for agricultural or metallurgical use (21 AD). In the industrial center of Nanyang they power batteries of bellows to provide combustion air for the melting and casting of iron (31 AD).
It is probably in the 4th century that the direct use of rotating wheels to grind grain was developed, in response to depopulation resulting from the wars following the fall of the Han Empire. In the 7th century the technology of mills is exported from China toward Korea, Japan, and Tibet. In China of the 8th century one finds many large mills having up to five wheels, the property of rich merchants, Buddhist abbots, imperial concubines and palace eunuchs. Conflicts inevitably arise from competing uses of water: the industrial flour trade, navigation, and agriculture. The Confucian civil servants give priority to traditional uses of water for the general public good, and accordingly they issue edicts to limit the proliferation of mills. In 778, eighty mills are destroyed by order of the administration.[453]
Hydraulic energy is thoroughly assimilated into Chinese culture at the beginning of the Christian era, when the use of the water wheel is increasingly widespread. Such uses include the powering of batteries of hammers, forge bellows, mills, and also square-pallet chain pumps, and even merry-go-rounds of dolls (in 260), celestial spheres (slowly rotating astronomical models) in 590, and textile spinning machines (the first dating from 1313.[454] The noria should, however, be considered separately. As we have said earlier, it is probably a technique imported later from the Near East or India, independently of other uses of hydraulic energy.
Windmills, known in the Islamic world since the 7th century, are apparently introduced into China from Turkestan toward the 12th or 13th centuries:
“The people of the west use wind mills as the people of the south use water mills.”[455]
These are vertical-axis mills, as was the case in Persia. In China, the sails of the mills are improved through adoption of the technology of sails for junks.
