រាជវង្សហាន: Science, technology, and engineering

Science, technology, and engineering

thumb|The ruins of a Han-dynasty watchtower made of rammed earth at Dunhuang, Gansu province, the eastern edge of the Silk Road

The Han dynasty was a unique period in the development of premodern Chinese science and technology, comparable to the level of scientific and technological growth during the Song dynasty (960–1279).Jin, Fan, and Liu (1996), 178–179; Needham (1972), 111.

Writing materials
Typical ancient Chinese writing materials were bronzewares and animal bones. By the beginning of the Han dynasty, the chief writing materials were clay tablets, silk cloth, and rolled scrolls made from bamboo strips sewn together with hempen string; these were passed through drilled holes and secured with clay stamps.Loewe (1968), 89, 94–95; Tom (1989), 99; Cotterell (2004), 11–13.

The oldest known Chinese piece of hard, hempen wrapping paper dates to the 2nd century BC. The standard papermaking process was invented by Cai Lun (50–121 AD) in 105 AD.Buisseret (1998), 12; Needham and Tsien (1986), 1–2, 40–41, 122–123, 228; Day and McNeil (1996), 122. The oldest known surviving piece of paper with writing on it was found in the ruins of a Han watchtower that had been abandoned in 110 AD, in Inner Mongolia.Cotterell (2004), 11.

Metallurgy and agriculture
Evidence suggests that blast furnaces, that convert raw iron ore into pig iron, which can be remelted in a cupola furnace to produce cast iron by means of a cold blast and hot blast, were operational in China by the late Spring and Autumn period (722–481 BC).Wagner (2001), 7, 36–37, 64–68, 75–76; Pigott (1999), 183–184. The bloomery was nonexistent in ancient China; however, the Han-era Chinese produced wrought iron by injecting excess oxygen into a furnace and causing decarburization.Pigott (1999), 177, 191. Cast iron and pig iron could be converted into wrought iron and steel using a fining process.Wang (1982), 125; Pigott (1999), 186.

thumb|upright|left|A pair of Eastern-Han iron scissors

The Han-era Chinese used bronze and iron to make a range of weapons, culinary tools, carpenters' tools and domestic wares.Wagner (1993), 336; Wang (1982), 103–105, 122–124. A significant product of these improved iron-smelting techniques was the manufacture of new agricultural tools. The three-legged iron seed drill, invented by the 2nd century BC, enabled farmers to carefully plant crops in rows instead of casting seeds out by hand.Greenberger (2006), 12; Cotterell (2004), 24; Wang (1982), 54–55. The heavy moldboard iron plow, also invented during the Han dynasty, required only one man to control it, two oxen to pull it. It had three plowshares, a seed box for the drills, a tool which turned down the soil and could sow roughly 45,730 m2 (11.3 acres) of land in a single day.Nishijima (1986), 563–564; Ebrey (1986), 616–617.

To protect crops from wind and drought, the Grain Intendant Zhao Guo (趙過) created the alternating fields system (daitianfa 代田法) during Emperor Wu's reign. This system switched the positions of furrows and ridges between growing seasons.Nishijima (1986), 561–563. Once experiments with this system yielded successful results, the government officially sponsored it and encouraged peasants to use it. Han farmers also used the pit field system (aotian 凹田) for growing crops, which involved heavily fertilized pits that did not require plows or oxen and could be placed on sloping terrain.Hinsch (2002), 67–68; Nishijima (1986), 564–566. In southern and small parts of central Han-era China, paddy fields were chiefly used to grow rice, while farmers along the Huai River used transplantation methods of rice production.Nishijima (1986), 568–572.

Structural engineering
thumb|A stone-carved pillar-gate, or que (闕), 6 m (20 ft) in total height, located at the tomb of Gao Yi in Ya'an, Sichuan province, Eastern Han dynastyLiu (2002), 55.

Timber was the chief building material during the Han dynasty; it was used to build palace halls, multi-story residential towers and halls and single-story houses. Because wood decays rapidly, the only remaining evidence of Han wooden architecture is a collection of scattered ceramic roof tiles.Ebrey (1999) 76; Wang (1982), 1–40. The oldest surviving wooden halls in China date to the Tang dynasty (618–907 AD).Steinhardt (2004), 228–238. Architectural historian Robert L. Thorp points out the scarcity of Han-era archaeological remains, and claims that often unreliable Han-era literary and artistic sources are used by historians for clues about lost Han architecture.Thorp (1986), 360–378.

Though Han wooden structures decayed, some Han-dynasty ruins made of brick, stone, and rammed earth remain intact. This includes stone pillar-gates, brick tomb chambers, rammed-earth city walls, rammed-earth and brick beacon towers, rammed-earth sections of the Great Wall, rammed-earth platforms where elevated halls once stood, and two rammed-earth castles in Gansu.Wang (1982), 1, 30, 39–40, 148–;149; Chang (2007), 91–92; Morton and Lewis (2005), 56; see also Ebrey (1999), 76; see Needham (1972), Plate V, Fig. 15, for a photo of a Han-era fortress in Dunhuang, Gansu province that has rammed earth ramparts with defensive crenallations at the top. The ruins of rammed-earth walls that once surrounded the capitals Chang'an and Luoyang still stand, along with their drainage systems of brick arches, ditches, and ceramic water pipes.Wang (1982), 1–39. Monumental stone pillar-gates, twenty-nine of which survive from the Han period, formed entrances of walled enclosures at shrine and tomb sites.Steinhardt (2005), "Pleasure Tower Model," 279; Liu (2002), 55. These pillars feature artistic imitations of wooden and ceramic building components such as roof tiles, eaves, and balustrades.Steinhardt (2005), "Pleasure Tower Model," 279–280; Liu (2002), 55.

The courtyard house is the most common type of home portrayed in Han artwork.Ebrey (1999), 76. Ceramic architectural models of buildings, like houses and towers, were found in Han tombs, perhaps to provide lodging for the dead in the afterlife. These provide valuable clues about lost wooden architecture. The artistic designs found on ceramic roof tiles of tower models are in some cases exact matches to Han roof tiles found at archaeological sites.Steinhardt (2005), "Tower Model" 283–284.

thumb|left|An Eastern-Han vaulted tomb chamber at Luoyang made of small bricks

Over ten Han-era underground tombs have been found, many of them featuring archways, vaulted chambers, and domed roofs.Wang (1982), 175–178. Underground vaults and domes did not require buttress supports since they were held in place by earthen pits.Watson (2000), 108. The use of brick vaults and domes in aboveground Han structures is unknown.

From Han literary sources, it is known that wooden-trestle beam bridges, arch bridges, simple suspension bridges, and floating pontoon bridges existed in Han China.Needham (1986d), 161–188. However, there are only two known references to arch bridges in Han literature,Needham (1986c), 171–172. and only a single Han relief sculpture in Sichuan depicts an arch bridge.Liu (2002), 56.

Underground mine shafts, some reaching depths over , were created for the extraction of metal ores.Loewe (1968), 191–194; Wang (1982), 105. Borehole drilling and derricks were used to lift brine to iron pans where it was distilled into salt. The distillation furnaces were heated by natural gas funneled to the surface through bamboo pipelines.Loewe (1968), 191–194; Tom (1989), 103; Ronan (1994), 91. Dangerous amounts of additional gas were siphoned off via carburetor chambers and exhaust pipes.Temple (1986), 78–79.

Mechanical and hydraulic engineering
thumb|A Han-dynasty pottery model of two men operating a winnowing machine with a crank handle and a tilt hammer used to pound grain.

Evidence of Han-era mechanical engineering comes largely from the choice observational writings of sometimes disinterested Confucian scholars. Professional artisan-engineers (jiang 匠) did not leave behind detailed records of their work.Needham (1986c), 2, 9; see also Barbieri-Low (2007), 36. Han scholars, who often had little or no expertise in mechanical engineering, sometimes provided insufficient information on the various technologies they described.Needham (1986c), 2. Nevertheless, some Han literary sources provide crucial information. For example, in 15 BC the philosopher Yang Xiong described the invention of the belt drive for a quilling machine, which was of great importance to early textile manufacturing.Temple (1986), 54–55. The inventions of the artisan-engineer Ding Huan (丁緩) are mentioned in the Miscellaneous Notes on the Western Capital.Barbieri-Low (2007), 197. Around 180 AD, Ding created a manually operated rotary fan used for air conditioning within palace buildings.Needham (1986c), 99, 134, 151, 233. Ding also used gimbals as pivotal supports for one of his incense burners and invented the world's first known zoetrope lamp.Temple (1986), 87; Needham (1986b), 123, 233–234.

Modern archaeology has led to the discovery of Han artwork portraying inventions which were otherwise absent in Han literary sources. As observed in Han miniature tomb models, but not in literary sources, the crank handle was used to operate the fans of winnowing machines that separated grain from chaff.Temple (1986), 46; Needham (1986c), 116–119, PLATE CLVI. The odometer cart, invented during Han, measured journey lengths, using mechanical figures banging drums and gongs to indicate each distance traveled.Needham (1986c), 281–285. This invention is depicted in Han artwork by the 2nd century AD, yet detailed written descriptions were not offered until the 3rd century AD.Needham (1986c), 283–285. Modern archaeologists have also unearthed specimens of devices used during the Han dynasty, for example a pair of sliding metal calipers used by craftsmen for making minute measurements. These calipers contain inscriptions of the exact day and year they were manufactured. These tools are not mentioned in any Han literary sources.Temple (1986), 86–87; Loewe (1968), 195–196.

thumb|upright|left|A modern replica of Zhang Heng's seismometer

The waterwheel appeared in Chinese records during the Han. As mentioned by Huan Tan in about 20 AD, they were used to turn gears that lifted iron trip hammers, and were used in pounding, threshing and polishing grain.Needham (1986c), 183–184, 390–392. However, there is no sufficient evidence for the watermill in China until about the 5th century.Needham (1986c), 396–400. The Nanyang Commandery Administrator Du Shi (d. 38 AD) created a waterwheel-powered reciprocator that worked the bellows for the smelting of iron.de Crespigny (2007), 184; Needham (1986c), 370. Waterwheels were also used to power chain pumps that lifted water to raised irrigation ditches. The chain pump was first mentioned in China by the philosopher Wang Chong in his 1st-century-AD Balanced Discourse.Needham (1986c), 89, 110, 342–344.

The armillary sphere, a three-dimensional representation of the movements in the celestial sphere, was invented in Han China by the 1st century BC.Needham (1986a), 343. Using a water clock, waterwheel and a series of gears, the Court Astronomer Zhang Heng (78–139 AD) was able to mechanically rotate his metal-ringed armillary sphere.de Crespigny (2007), 1050; Needham (1986c), 30, 479 footnote e; Morton and Lewis (2005), 70; Bowman (2000), 595; Temple (1986), 37. To address the problem of slowed timekeeping in the pressure head of the inflow water clock, Zhang was the first in China to install an additional tank between the reservoir and inflow vessel.de Crespigny (2007), 1050; Needham (1986c), 479 footnote e. Zhang also invented a seismometer (Houfeng didong yi 候风地动仪) in 132 AD to detect the exact cardinal or ordinal direction of earthquakes from hundreds of kilometers away.de Crespigny (2007), 1050; Morton and Lewis (2005), 70. This employed an inverted pendulum that, when disturbed by ground tremors, would trigger a set of gears that dropped a metal ball from one of eight dragon mouths (representing all eight directions) into a metal toad's mouth.Needham (1986a), 626–631.

Mathematics
Three Han mathematical treatises still exist. These are the Book on Numbers and Computation, the Arithmetical Classic of the Gnomon and the Circular Paths of Heaven and the Nine Chapters on the Mathematical Art. Han-era mathematical achievements include solving problems with right-angle triangles, square roots, cube roots, and matrix methods,Dauben (2007), 212; Liu, Feng, Jiang, and Zheng (2003), 9–10. finding more accurate approximations for pi,Needham (1986a), 99–100; Berggren, Borwein and Borwein (2004), 27. providing mathematical proof of the Pythagorean theorem,Dauben (2007), 219–222; Needham (1986a), 22. use of the decimal fraction,Temple (1986), 139, 142–143 Gaussian elimination to solve linear equations,Shen, Crossley, and Lun (1999), 388; Straffin (1998), 166; Needham (1986a), 24–25, 121. and continued fractions to find the roots of equations.Temple (1986), 142.

One of the Han's greatest mathematical advancements was the world's first use of negative numbers. Negative numbers first appeared in the Nine Chapters on the Mathematical Art as black counting rods, where positive numbers were represented by red counting rods.Temple (1986), 141; Liu, Feng, Jiang, and Zheng (2003), 9–10. Negative numbers are used in the Bakhshali manuscript of ancient India, but its exact date of compilation is unknown.Teresi (2002), 65–66. Negative numbers were also used by the Greek mathematician Diophantus in about 275 AD, but were not widely accepted in Europe until the 16th century AD.Temple (1986), 141.

thumb|left|A Han-dynasty era mold for making bronze gear wheels (Shanghai Museum)

The Han applied mathematics to various diverse disciplines. In musical tuning, Jing Fang (78–37 BC) realized that 53 perfect fifths was approximate to 31 octaves while creating a musical scale of 60 tones, calculating the difference at 177147⁄176776 (the same value of 53 equal temperament discovered by the German mathematician Nicholas Mercator [1620–1687], i.e. 353/284).McClain and Ming (1979), 212; Needham (1986b), 218–219.

Astronomy
Mathematics were essential in drafting the astronomical calendar, a lunisolar calendar that used the Sun and Moon as time-markers throughout the year.Cullen (2006), 7; Lloyd (1996), 168. Use of the ancient Sifen calendar (古四分历), which measured the tropical year at 3651⁄4 days, was replaced in 104 BC with the Taichu calendar (太初历) that measured the tropical year at 365385⁄1539 days and the lunar month at 2943⁄81 days.Deng (2005), 67. However, Emperor Zhang later reinstated the Sifen calendar.de Crespigny (2007), 498.

Han Chinese astronomers made star catalogues and detailed records of comets that appeared in the night sky, including recording the 12 BC appearance of the comet now known as Halley's comet.Loewe (1994), 61, 69; Csikszentmihalyi (2006), 173–175; Sun and Kristemaker (1997), 5, 21–23; Balchin (2003), 27.

Han-era astronomers adopted a geocentric model of the universe, theorizing that it was shaped like a sphere surrounding the earth in the center.Dauben (2007), 214; Sun and Kistemaker (1997), 62; Huang (1988), 64. They assumed that the Sun, Moon, and planets were spherical and not disc-shaped. They also thought that the illumination of the Moon and planets was caused by sunlight, that lunar eclipses occurred when the Earth obstructed sunlight falling onto the Moon, and that a solar eclipse occurred when the Moon obstructed sunlight from reaching the Earth.Needham (1986a), 227, 414. Although others disagreed with his model, Wang Chong accurately described the water cycle of the evaporation of water into clouds.Needham (1986a), 468.

Cartography, ships, and vehicles
thumb|An early Western-Han silk map found in tomb 3 of Mawangdui, depicting the Kingdom of Changsha and Kingdom of Nanyue in southern China (note: the south direction is oriented at the top).
thumb|right|An Eastern-Han pottery ship model with a steering rudder at the stern and anchor at the bow

Evidence found in Chinese literature, and archaeological evidence, show that cartography existed in China before the Han.Hsu (1993), 90–93; Needham (1986a), 534–535. Some of the earliest Han maps discovered were ink-penned silk maps found amongst the Mawangdui Silk Texts in a 2nd-century-BC tomb.Hsu (1993), 90–93; Hansen (2000), 125. The general Ma Yuan created the world's first known raised-relief map from rice in the 1st century AD. This date could be revised if the tomb of Qin Shi Huang is excavated and the account in the Records of the Grand Historian concerning a model map of the empire is proven to be true.Temple (1986), 179.

Although the use of the graduated scale and grid reference for maps was not thoroughly described until the published work of Pei Xiu (224–271 AD), there is evidence that in the early 2nd century AD, cartographer Zhang Heng was the first to use scales and grids for maps.de Crespigny (2007), 1050; Hsu (1993), 90–93; Needham (1986a), 538–540; Nelson (1974), 359; Temple (1986), 30.

The Han-era Chinese sailed in a variety of ships differing from those of previous eras, such as the tower ship. The junk design was developed and realized during Han.  Junks featured a square-ended bow and stern, a flat-bottomed hull or carvel-shaped hull with no keel or sternpost, and solid transverse bulkheads in the place of structural ribs found in Western vessels.Turnbull (2002), 14; Needham (1986d), 390–391. Moreover, Han ships were the first in the world to be steered using a rudder at the stern, in contrast to the simpler steering oar used for riverine transport,  allowing them to sail on the high seas.Needham (1986d), 627–628; Chung (2005), 152; Tom (1989), 103–104; Adshead (2000), 156; Fairbank and Goldman (1998), 93; Block (2003), 93, 123.

Although ox-carts and chariots were previously used in China, the wheelbarrow was first used in Han China in the 1st century BC.Needham (1986c), 263–267; Greenberger (2006), 13. Han artwork of horse-drawn chariots shows that the Warring-States-Era heavy wooden yoke placed around a horse's chest was replaced by the softer breast strap. Later, during the Northern Wei (386–534 AD), the fully developed horse collar was invented.Needham (1986c), 308–312, 319–323.

Medicine
Han-era medical physicians believed that the human body was subject to the same forces of nature that governed the greater universe, namely the cosmological cycles of yin and yang and the five phases. Each organ of the body was associated with a particular phase. Illness was viewed as a sign that qi or "vital energy" channels leading to a certain organ had been disrupted. Thus, Han-era physicians prescribed medicine that was believed to counteract this imbalance.Csikszentmihalyi (2006), 181–182; Sun & Kistemaker (1997), 3–4; Hsu (2001), 75. For example, since the wood phase was believed to promote the fire phase, medicinal ingredients associated with the wood phase could be used to heal an organ associated with the fire phase.Csikszentmihalyi (2006), 181–182. To this end, the physician Zhang Zhongjing (c. 150–c. 219 AD) prescribed regulated diets rich in certain foods that were thought to curb specific illnesses. These are now known to be nutrition disorders caused by the lack of certain vitamins consumed in one's diet.Temple (1986), 131. Besides dieting, Han physicians also prescribed moxibustion, acupuncture, and calisthenics as methods of maintaining one's health.de Crespigny (2007) 332; Omura (2003), 15, 19–22; Loewe (1994), 65; Lo (2001), 23. When surgery was performed by the physician Hua Tuo (d. 208 AD), he used anesthesia to numb his patients' pain and prescribed a rubbing ointment that allegedly sped the process of healing surgical wounds.Crespigny (2007), 332.