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1、ReadingThefourbasicinstrumentsfornavigation:Sinan,InchAstrolabe,Sextantandnauticalmap.Sinan,theancientChinesecompass.ItwasinventedbyZhangHengintheHandynasty.Itismadeupofabronzefoundation(青铜地盘)andmagneticspoon(磁勺)whichismadeofnaturalmagnet,positionedrightinthecentralofthefounda
2、tion.Thehandleofthespoonpointstothesouth,whiletheothersidepointstothenorth.WhentheSinanisinthestill,thehandleofthespoonpointstothesouthbecauseofinfluenceoftheterrestrialmagnetism(地磁).Ithas17starslistedaswellasamapoftheskyoverhead(for37degrees)andtheecliptic(黄道).Thetimeofdayorn
3、ightisontheoutsideedgewithnoonatthetopoftheAstrolabeandmidnightatthebottom.Itcomeswithacarryingchain,apouch,andabookonitsuse.Thereversesidehasasightformeasuringtheelevationsoftheheavenlybodies.astrolabesextantThesextantisanavigationalinstrumentformeasuringtheanglebetweenthehor
4、izonandsomeobjectinthesky.Firstasailorlooksatthehorizonthroughaneyepiece.Atthesametimehecanseelightfromthesunorastarreflectedoffasmallmirrorontopoftheinstrument,ontoasecondmirrorandintotheeyepiece.Thenavigatorcanthenseetwoimages,thehorizonandthesunsidebyside.Hecanthenmeasureth
5、eanglebetweenthemonascaleatthebottomoftheinstrument.Thescalegoesfrom0to120degrees.Anearlierinstrument,calledaquadrant,measuredinangleinthesamewaybutitcouldonlymeasureanglesfrom0to90degrees.nauticalchartNauticalchartsaremapsofthedepthoftheseaandthecurrentsoftheoceans.Theyprovid
6、emodernsailorswithroutesthroughtheseas,ratherlikeroadsthroughthecountryside.Theinformationbegantobecollectedinthenineteenthcenturyandhascontinuedtobeupdatedeversince.ThesechartswerenotavailabletoCaptainBlighorZhengHe.Discuss1.Howdoyouthinkseamenfoundtheirwaybeforemodernaccurat
7、emethodsofnavigationwereinvented?Keptclosetotheshore,usednaturesuchasthesun,wind,birds,tide,etc,tohelpthem,andusedsomeoftheinstrumentsincludingacompass,astrolabe,etc.2.Whichdoyouthinkwaseasiertoworkout:latitudeorlongitude?Latitude,becauseitwasusedtomeasurehowfaryouhadtraveledf
8、romlandonastraightline.Itwasdiscoveredalongtimebeforelongitud
