Science and technology of the Han dynasty

Many significant developments in the history of science and technology in China took place during the Han dynasty (202 BCE – 220 CE^[2]).

The Han period saw great innovations in metallurgy. Following the inventions of the blast furnace and cupola furnace during the Zhou dynasty (c. 1046 – 256 BCE) 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 initially wrote on hemp-bound bamboo scrolls; by the 2nd century CE, they 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 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.