Science and technology Yi Xing

terrestrial-astronomical survey

in 8th century, tang court put yi xing in charge of terrestrial-astronomical survey. survey had many purposes. established in order obtain new astronomical data aid in prediction of solar eclipses. survey initiated flaws in calendar system corrected , new, updated calendar installed in place. survey essential in determining measurement of length of meridian arc. resolve confusion created earlier practice of using difference between shadow lengths of sun observed @ same time @ 2 places determine ground distance between them. same process used ancient greek eratosthenes (276–196 bc).

yi xing had thirteen test sites established throughout empire, extending jiaozhou in vietnam — @ latitude 17°n — region south of lake baikal — latitude 50°n. there 3 observations done each site, 1 height of polaris, 1 shadow lengths of summer, , 1 shadow lengths of winter. latitudes deciphered data, while tang calculation length of 1 degree of meridian accurate compared modern calculations. yi xing understood variations in length of degree of meridian, , criticized earlier scholars permanently fixed estimate shadow lengths duration of entire year.

the escapement , celestial globe

yi xing famed genius, known have calculated number of possible positions on go board game (though without symbol 0 had difficulties expressing number). he, along associate liang lingzan (a government official), best known applying earliest-known escapement mechanism water-powered celestial globe. however, yi xing s mechanical genius , achievements built upon knowledge , efforts of previous chinese mechanical engineers, such statesman , master of gear systems zhang heng (78–139) of han dynasty, equally brilliant engineer ma jun (200–265) of 3 kingdoms, , daoist li lan (c. 450) of southern , northern dynasties period.

it earlier chinese inventor zhang heng first apply hydraulic power (i.e. waterwheel , water clock) in mechanically-driving , rotating equatorial armillary sphere. arrangement followed model of water-wheel using drip of clepsydra (see water clock), exerted force on lug rotate toothed-gears on polar-axis shaft. this, slow computational movement rotated armillary sphere according recorded movements of planets , stars. yi xing owed scholarly followers of ma jun, had employed horizontal jack-wheels , other mechanical toys worked waterwheels. daoist li lan expert @ working water clocks, creating steelyard balances weighing water used in tank of clepsydra, providing more inspiration yi xing. earlier water-power employed zhang heng , later escapement mechanism in astronomical clock tower engineered , erected su song (1020–1101), yi xing s celestial globe employed water-power in order rotate , function properly. historian joseph needham states (wade–giles spelling):

when first escapement came, in +725 (ad), i-hsing , liang ling-tsan arranged 2 jacks strike hours, standing on horizon surface of sphere or globe.

in regards mercury instead of water (as noted in quote above), first apply liquid mercury motive power of armillary sphere zhang sixun in 979 ad (because mercury not freeze during winter). during age, song dynasty (960–1279) era historical text of song shi mentions yi xing , reason why armillary sphere did not survive ages after tang (wade–giles spelling):

a jade balancing mechanism (yu heng)(ie. escapement) erected behind (lit. outside) curtain, holding , resisting (chhih o) main scoops (shu tou). water pours down rotating wheel (chu shui chi lun). lower, there cog-wheel (chi lun) 43 (teeth). there hooks, pins, , interlocking rods 1 holding (kou chien chiao tsho hsiang chhih). each (wheel) moves next without reliance on human force. fastest wheel turns round each day through 2928 teeth (chhih), slowest 1 moves 1 tooth in every 5 days. such great difference there between speed of wheels, yet of them depend on 1 single driving mechanism. in precision, engine can compared nature (lit. maker of things; tsao wu che). rest, same apparatus made (long ago) i-hsing. old design employed bronze , iron, corroded , rusted machine ceased able move automatically. modern plan substitutes hard wood these parts, beautiful jade...

earlier tang era historical texts of 9th century have of yi xing s work in astronomical instruments in 8th century (wade–giles spelling):

one (of these) made in image of round heavens (yuan thien chih hsiang) , on shown lunar mansions (hsiu) in order, equator , degrees of heavenly circumference. water, flowing (into scoops), turned wheel automatically (chu shui chi lun, ling chhi tzu chuan), rotating (the sphere) 1 complete revolution in 1 day , night. besides this, there 2 rings (lit. wheels) fitted round celestial (sphere) outside, having sun , moon threaded on them, , there made move in circling orbit (ling te yun hsing). each day celestial (sphere) turned 1 revolution westwards, sun made way 1 degree eastwards, , moon 13 , 7/19 degrees (eastwards). after 29 , fraction rotations (of celestial sphere) sun , moon met. after made 365 rotations sun accomplished complete circuit. , made wooden casing surface of represented horizon, since instrument half sunk in it. permitted exact determinations of times of dawns , dusks, full , new moons, tarrying , hurrying. there 2 wooden jacks standing on horizon surface, having 1 bell , other drum in front of it, bell being struck automatically indicate hours, , drum being beaten automatically indicate quarters.

all these motions brought (by machinery) within casing, each depending on wheels , shafts (lun chu), hooks, pins , interlocking rods (kou chien chiao tsho), coupling devices , locks checking mutually (kuan hsiang chhih)(ie. escapement). since (the clock) showed agreement tao of heaven, @ time praised ingenuity. when completed (in +725) called water-driven spherical bird s-eye-view map of heavens (shui yun hun thien fu shih thu) or celestial sphere model water-engine , set in front of wu chheng hall (of palace) seen multitude of officials. candidates in imperial examinations (in +730) asked write essay on new armillary (clock). not long afterwards mechanism of bronze , iron began corrode , rust, instrument no longer rotate automatically. therefore relegated (museum of the) college of sages (chi hsien yuan) , went out of use.