Question: Where does the Great Wall end, in the country where the man who described the process of evaporation once lived?

Han-era astronomers adopted a geocentric model of the universe, theorizing that it was shaped like a sphere surrounding the earth in the center. Although others disagreed with his model, Wang Chong accurately described the water cycle of the evaporation of water into clouds. 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. <SEP> with the introduction of the blast furnace to europe in the middle ages, pig iron was able to be produced in much higher volumes than wrought iron. because pig iron could be melted, people began to develop processes of reducing the carbon in the liquid pig iron to create steel. puddling was introduced during the 1700s, where molten pig iron was stirred while exposed to the air, to remove the carbon by oxidation. in 1858, sir henry bessemer developed a process of steel-making by blowing hot air through liquid pig iron to reduce the carbon content. the bessemer process was able to produce the first large scale manufacture of steel. once the bessemer process began to gain widespread use, other alloys of steel began to follow. mangalloy, an alloy of steel and manganese exhibiting extreme hardness and toughness, was one of the first alloy steels, and was created by robert hadfield in 1882. <SEP> a system akin to the bessemer process has existed since the 11th century in east asia. economic historian robert hartwell writes that the chinese of the song dynasty innovated a ``partial decarbonization ''method of repeated forging of cast iron under a cold blast. sinologist joseph needham and historian of metallurgy theodore a. wertime have described the method as a predecessor to the bessemer process of making steel. this process was first described by the prolific scholar and polymath government official shen kuo (1031 -- 1095) in 1075, when he visited cizhou. hartwell states that perhaps the earliest center where this was practiced was the great iron - production district along the henan -- hebei border during the 11th century. <SEP> A comprehensive archaeological survey, using advanced technologies, has concluded that the Ming walls measure 8,850 km (5,500 mi). The Great Wall stretches from Dandong in the east to Lop Lake in the west, along an arc that roughly delineates the southern edge of Inner Mongolia. This is made up of 6,259 km (3,889 mi) sections of actual wall, 359 km (223 mi) of trenches and 2,232 km (1,387 mi) of natural defensive barriers such as hills and rivers. Another archaeological survey found that the entire wall with all of its branches measure out to be 21,196 km (13,171 mi). Today, the Great Wall is generally recognized as one of the most impressive architectural feats in history. <SEP> Wang Chong (; 27 – c. 100 AD), courtesy name Zhongren (仲任), was a Chinese meteorologist, astronomer, and philosopher active during the Han Dynasty. He developed a rational, secular, naturalistic and mechanistic account of the world and of human beings and gave a materialistic explanation of the origin of the universe. His main work was the "Lunheng" (論衡, "Critical Essays"). Wang also accurately described the process of the water cycle. This book contained many theories involving early sciences of astronomy and meteorology, and Wang Chong was even the first in Chinese history to mention the use of the square-pallet chain pump, which became common in irrigation and public works in China thereafter.