WhenwepasstothatthirdgreatAthenianteacher，Aristotle，thecaseisfardifferent。HerewasamanwhosenamewastobereceivedasalmostasynonymforGreekscienceformorethanathousandyearsafterhisdeath。AllthroughtheMiddleAgeshiswritingsweretobeacceptedasvirtuallythelastwordregardingtheproblemsofnature。Weshallseethathisfollowersactuallypreferredhismandatetothetestimonyoftheirownsenses。Weshallsee，further，thatmodernscienceprogressedsomewhatinproportionasitoverthrewtheAristoteliandogmas。Butthetraditionsofseventeenoreighteencenturiesarenoteasilysetaside，anditisperhapsnottoomuchtosaythatthenameofAristotlestands，eveninourowntime，asvaguelyrepresentativeinthepopularmindofallthatwashighestandbestinthescienceofantiquity。Yet，perhaps，itwouldnotbegoingtoofartoassertthatsomethinglikeareversalofthisjudgmentwouldbenearerthetruth。Aristotledid，indeed，bringtogetheragreatmassoffactsregardinganimalsinhisworkonnaturalhistory，which，beingpreserved，hasbeendeemedtoentitleitsauthortobecalledthe\"fatherofzoology。\"Butthereisnoreasontosupposethatanyconsiderableportionofthisworkcontainedmatterthatwasnovel，orrecordedobservationsthatwereoriginalwithAristotle；andtheclassificationsthereoutlinedareatbestbutavagueforeshadowingoftheelaborationofthescience。Suchasitis，however，thenaturalhistorystandstothecreditoftheStagirite。Hemustbecredited，too，withaclearenunciationofonemostimportantscientificdoctrine——namely，thedoctrineofthesphericalfigureoftheearth。WehavealreadyseenthatthistheoryoriginatedwiththePythagoreanphilosophersoutinItaly。Wehaveseen，too，thatthedoctrinehadnotmadeitswayinAtticainthetimeofAnaxagoras。Butintheinterveningcenturyithadgainedwidecurrency，elsesoessentiallyconservativeathinkerasAristotlewouldscarcelyhaveacceptedit。Hedidacceptit，however，andgavethedoctrineclearestandmostpreciseexpression。Herearehiswords:[2]
\"Astothefigureoftheearthitmustnecessarilybespherical……Ifitwerenotso，theeclipsesofthemoonwouldnothavesuchsectionsastheyhave。Forintheconfigurationsinthecourseofamonththedeficientparttakesalldifferentshapes；itisstraight，andconcave，andconvex；butineclipsesitalwayshasthelineofdivisionsconvex；wherefore，sincethemooniseclipsedinconsequenceoftheinterpositionoftheearth，theperipheryoftheearthmustbethecauseofthisbyhavingasphericalform。Andagain，fromtheappearanceofthestarsitisclear，notonlythattheearthisround，butthatitssizeisnotverylarge；forwhenwemakeasmallremovaltothesouthorthenorth，thecircleofthehorizonbecomespalpablydifferent，sothatthestarsoverheadundergoagreatchange，andarenotthesametothosethattravelinthenorthandtothesouth。ForsomestarsareseeninEgyptoratCyprus，butarenotseeninthecountriestothenorthofthese；andthestarsthatinthenortharevisiblewhiletheymakeacompletecircuit，thereundergoasetting。Sothatfromthisitismanifest，notonlythattheformoftheearthisround，butalsothatitisapartofanotverylargesphere；forotherwisethedifferencewouldnotbesoobvioustopersonsmakingsosmallachangeofplace。WhereforewemayjudgethatthosepersonswhoconnecttheregionintheneighborhoodofthepillarsofHerculeswiththattowardsIndia，andwhoassertthatinthiswaytheseaisone，donotassertthingsveryimprobable。Theyconfirmthisconjecturemoreoverbytheelephants，whicharesaidtobeofthesamespeciestowardseachextreme；asifthiscircumstancewasaconsequenceoftheconjunctionoftheextremes。Themathematicianswhotrytocalculatethemeasureofthecircumference，makeitamounttofourhundredthousandstadia；
whencewecollectthattheearthisnotonlyspherical，butisnotlargecomparedwiththemagnitudeoftheotherstars。\"
ButingivingfullmeedofpraisetoAristotleforthepromulgationofthisdoctrineofthesphericityoftheearth，itmustunfortunatelybeaddedthattheconservativephilosopherpausedwithouttakingoneotherimportantstep。Hecouldnotaccept，but，onthecontrary，heexpresslyrepudiated，thedoctrineoftheearth’smotion。WehaveseenthatthisideaalsowasapartofthePythagoreandoctrine，andweshallhaveoccasiontodwellmoreatlengthonthispointinasucceedingchapter。IthasevenbeencontendedbysomecriticsthatitwastheadverseconvictionofthePeripateticphilosopherwhich，morethananyothersingleinfluence，tendedtoretardtheprogressofthetruedoctrineregardingthemechanismoftheheavens。
Aristotleacceptedthesphericityoftheearth，andthatdoctrinebecameacommonplaceofscientificknowledge，andsocontinuedthroughoutclassicalantiquity。ButAristotlerejectedthedoctrineoftheearth’smotion，andthatdoctrine，thoughpromulgatedactivelybyafewcontemporariesandimmediatesuccessorsoftheStagirite，wasthendoomedtosinkoutofviewformorethanathousandyears。IfitbeacorrectassumptionthattheinfluenceofAristotlewas，inalargemeasure，responsibleforthisresult，thenweshallperhapsnotbefarastrayinassumingthatthegreatfounderofthePeripateticschoolwas，onthewhole，moreinstrumentalinretardingtheprogressofastronomicalsciencethatanyotheronemanthateverlived。