Science and technology of the Han dynasty

The Han dynasty (206 BCE – 220 CE) of early imperial China, divided between the eras of Western Han (206 BCE – 9 CE, when the capital was at Chang'an), the Xin dynasty of Wang Mang (r. 9–23 CE), and Eastern Han (25–220 CE, when the capital was at Luoyang, and after 196 CE at Xuchang), witnessed some of the most significant advancements in premodern Chinese science and technology.

There were great innovations in metallurgy. In addition to Zhou-era China's (c. 1046 – 256 BCE) previous inventions of the blast furnace and cupola furnace to make pig iron and cast iron, respectively, the Han period saw the development of steel and wrought iron by use of the finery forge and puddling process. With the drilling of deep boreholes into the earth, the Chinese used not only derricks to lift brine up to the surface to be boiled into salt, but also set up bamboo-crafted pipeline transport systems which brought natural gas as fuel to the furnaces. Smelting techniques were enhanced with inventions such as the waterwheel-powered bellows; the resulting widespread distribution of iron tools facilitated the growth of agriculture. For tilling the soil and planting straight rows of crops, the improved heavy-moldboard plough with three iron plowshares and sturdy multiple-tube iron seed drill were invented in the Han, which greatly enhanced production yields and thus sustained population growth. The method of supplying irrigation ditches with water was improved with the invention of the mechanical chain pump powered by the rotation of a waterwheel or draft animals, which could transport irrigation water up elevated terrains. The waterwheel was also used for operating trip hammers in pounding grain and in rotating the metal rings of the mechanical-driven astronomical armillary sphere representing the celestial sphere around the Earth.

The Han Chinese had hempen-bound bamboo scrolls to write on, yet by the 2nd century CE had invented the papermaking process which created a writing medium that was both cheap and easy to produce. The invention of the wheelbarrow aided in the hauling of heavy loads. The maritime junk ship and stern-mounted steering rudder enabled the Chinese to venture out of calmer waters of interior lakes and rivers and into the open sea. The invention of the grid reference for maps and raised-relief map allowed for better navigation. In medicine, they used new herbal remedies to cure illnesses, calisthenics to keep physically fit, and regulated diets to avoid diseases. Authorities in the capital were warned ahead of time of the direction of sudden earthquakes with the invention of the seismometer that was tripped by a vibration-sensitive pendulum device. To mark the passing of the seasons and special occasions, the Han Chinese used two variations of the lunisolar calendar, which were established due to efforts in astronomy and mathematics. Han-era Chinese advancements in mathematics include the discovery of square roots, cube roots, the Pythagorean theorem, Gaussian elimination, the Horner scheme, improved calculations of pi, and negative numbers. Hundreds of new roads and canals were built to facilitate transport, commerce, tax collection, communication, and movement of military troops. The Han-era Chinese also employed several types of bridges to cross waterways and deep gorges, such as beam bridges, arch bridges, simple suspension bridges, and pontoon bridges. Han ruins of defensive city walls made of brick or rammed earth still stand today.