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1、ERWINSCHRÖDINGERThefundamentalideaofwavemechanicsNobelLecture,December12,1933Onpassingthroughanopticalinstrument,suchasatelescopeoracameralens,arayoflightissubjectedtoachangeindirectionateachrefractingorreflectingsurface.Thepathoftherayscanbeconstructedifweknowthetwosimplelawswhichgovernthechangesin
2、direction:thelawofrefrac-tionwhichwasdiscoveredbySnelliusafewhundredyearsago,andthelawofreflectionwithwhichArchimedeswasfamiliarmorethan2,000yearsago.Asasimpleexample,Fig.1showsarayA-BwhichissubjectedtorefractionateachofthefourboundarysurfacesoftwolensesinaccordancewiththelawofSnellius.Fig.1.Fermatd
3、efinedthetotalpathofarayoflightfromamuchmoregeneralpointofview.Indifferentmedia,lightpropagateswithdifferentvelocities,andtheradiationpathgivestheappearanceasifthelightmustarriveatitsdestinationasquicklyaspossible.(Incidentally,itispermissibleheretocon-sideranytwopointsalongtherayasthestarting-anden
4、d-points.)Theleastdeviationfromthepathactuallytakenwouldmeanadelay.Thisisthefa-mousFermatprincipleoftheshortestlighttime,whichinamarvellousmannerdeterminestheentirefateofarayoflightbyasinglestatementandalsoincludesthemoregeneralcase,whenthenatureofthemediumvariesnotsuddenlyatindividualsurfaces,butgr
5、aduallyfromplacetoplace.Theat-mosphereoftheearthprovidesanexample.Themoredeeplyarayoflightpenetratesintoitfromoutside,themoreslowlyitprogressesinanincreas-inglydenserair.Althoughthedifferencesinthespeedofpropagationare3061933E.SCHRÖDINGERinfinitesimal,Fermat’sprincipleinthesecircumstancesdemandsthat
6、thelightrayshouldcurveearthward(seeFig.2),sothatitremainsalittlelongerinthehigher"faster"layersandreachesitsdestinationmorequicklythanbytheshorterstraightpath(brokenlineinthefigure;disregardthesquare,Fig.2.11WWWWforthetimebeing).Ithink,hardlyanyofyouwillhavefailedtoobservethatthesunwhenitisdeeponthe
7、horizonappearstobenotcircularbutflattened:itsverticaldiameterlookstobeshortened.Thisisaresultofthecurvatureoftherays.Accordingtothewavetheoryoflight,thelightrays,strictlyspeaking,haveonlyfictitioussig