THEBEGINNINGSOFMODERNSCIENCE
ThestudiesofthepresentbookcovertheprogressofsciencefromthecloseoftheRomanperiodinthefifthcenturyA。D。toaboutthemiddleoftheeighteenthcentury。Intracingthecourseofeventsthroughsolongaperiod，adifficultybecomesprominentwhicheverywherebesetsthehistorianinlessdegree——adifficultyduetotheconflictbetweenthestrictlychronologicalandthetopicalmethodoftreatment。Wemustholdascloselyaspossibletotheactualsequenceofevents，since，asalreadypointedout，onediscoveryleadsontoanother。But，ontheotherhand，progressivestepsaretakencontemporaneouslyinthevariousfieldsofscience，andifweweretoattempttointroducetheseinstrictchronologicalorderweshouldloseallsenseoftopicalcontinuity。
Ourmethodhasbeentoadoptacompromise，followingthecourseofasinglescienceineachgreatepochtoaconvenientstopping-point，andthenturningbacktobringforwardthestoryofanotherscience。Thus，forexample，wetellthestoryofCopernicusandGalileo，bringingtherecordofcosmicalandmechanicalprogressdowntoaboutthemiddleoftheseventeenthcentury，beforeturningbacktotakeupthephysiologicalprogressofthefifteenthandsixteenthcenturies。Oncethelatterstreamisentered，however，wefollowitwithoutinterruptiontothetimeofHarveyandhiscontemporariesinthemiddleoftheseventeenthcentury，whereweleaveittoreturntothefieldofmechanicsasexploitedbythesuccessorsofGalileo，whowerealsothepredecessorsandcontemporariesofNewton。
Ingeneral，itwillaidthereadertorecallthat，sofaraspossible，weholdalwaystothesamesequencesoftopicaltreatmentofcontemporaryevents；asarulewetreatfirstthecosmical，thenthephysical，thenthebiologicalsciences。Thesameorderoftreatmentwillbeheldtoinsucceedingvolumes。
Severaloftheverygreatestofscientificgeneralizationsaredevelopedintheperiodcoveredbythepresentbook:forexample，theCopernicantheoryofthesolarsystem，thetruedoctrineofplanetarymotions，thelawsofmotion，thetheoryofthecirculationoftheblood，andtheNewtoniantheoryofgravitation。Thelaborsoftheinvestigatorsoftheearlydecadesoftheeighteenthcentury，terminatingwithFranklin’sdiscoveryofthenatureoflightningandwiththeLinnaeanclassificationofplantsandanimals，bringustothecloseofoursecondgreatepoch；or，toputitotherwise，tothethresholdofthemodernperiod，I。SCIENCEINTHEDARKAGE
Anobviousdistinctionbetweentheclassicalandmediaevalepochsmaybefoundinthefactthattheformerproduced，whereasthelatterfailedtoproduce，afewgreatthinkersineachgenerationwhowereimbuedwiththatscepticismwhichisthefoundationoftheinvestigatingspirit；whothoughtforthemselvesandsuppliedmoreorlessrationalexplanationsofobservedphenomena。Couldweeliminatetheworkofsomescoreorsoofclassicalobserversandthinkers，theclassicalepochwouldseemasmuchadarkageasdoestheepochthatsucceededit。
Butimmediatelywearemetwiththequestion:Whydonogreatoriginalinvestigatorsappearduringalltheselatercenturies？
Wehavealreadyofferedapartexplanationinthefactthatthebordersofcivilization，whereracialminglingnaturallytookplace，werepeopledwithsemi-barbarians。Butwemustnotforgetthatinthecentresofcivilizationallalongthereweremanymenofpowerfulintellect。Indeed，itwouldviolatetheprincipleofhistoricalcontinuitytosupposethattherewasanysuddenchangeinthelevelofmentalityoftheRomanworldatthecloseoftheclassicalperiod。Wemustassume，then，thatthedirectioninwhichthegreatmindsturnedwasforsomereasonchanged。Newtonissaidtohaveallegedthathemadehisdiscoveriesby\"intending\"hismindinacertaindirectioncontinuously。Itisprobablethatthesameexplanationmaybegivenofalmosteverygreatscientificdiscovery。Anaxagorascouldnothavethoughtoutthetheoryofthemoon’sphases；Aristarchuscouldnothavefoundoutthetruemechanismofthesolarsystem；Eratosthenescouldnothavedevelopedhisplanformeasuringtheearth，hadnoteachoftheseinvestigators\"intended\"hismindpersistentlytowardstheproblemsinquestion。
Norcanwedoubtthatmenlivedineverygenerationofthedarkagewhowerecapableofcreativethoughtinthefieldofscience，badtheychosensimilarlyto\"intend\"theirmindsintherightdirection。Thedifficultywasthattheydidnotsochoose。Theirmindshadaquitedifferentbent。Theywereunderthespellofdifferentideals；alltheirmentaleffortsweredirectedintodifferentchannels。Whatthesedifferentchannelswerecannotbeindoubt——theywerethechannelsoforientalecclesiasticism。Oneall-significantfactspeaksvolumeshere。Itisthefactthat，asProfessorRobinson[1]pointsout，fromthetimeofBoethiusdied524or525A。D。tothatofDante1265-1321A。D。therewasnotasinglewriterofrenowninwesternEuropewhowasnotaprofessionalchurchman。Allthelearningofthetime，then，centredinthepriesthood。WeknowthatthesameconditionofthingspertainedinEgypt，whensciencebecamestaticthere。But，contrariwise，wehaveseenthatinGreeceandearlyRomethescientificworkerswerelargelyphysiciansorprofessionalteachers；therewasscarcelyaprofessionaltheologianamongthem。
Similarly，asweshallseeintheArabicworld，wherealonetherewasprogressinthemediaevalepoch，thelearnedmenwere，forthemostpart，physicians。Nowthemeaningofthismustbeself-evident。Thephysiciannaturally\"intends\"hismindtowardsthepracticalities。Hisprofessionalstudiestendtomakehimaninvestigatoroftheoperationsofnature。Heisusuallyasceptic，withaspontaneousinterestinpracticalscience。Butthetheologian\"intends\"hismindawayfrompracticalitiesandtowardsmysticism。Heisaprofessionalbelieverinthesupernatural；hediscountsthevalueofmerely\"natural\"
phenomena。Hiswholeattitudeofmindisunscientific；thefundamentaltenetsofhisfaitharebasedonallegedoccurrenceswhichinductivesciencecannotadmit——namely，miracles。Andsotheminds\"intended\"towardsthesupernaturalachievedonlythehazymysticismofmediaevalthought。Insteadofinvestigatingnaturallaws，theypaidheedas，forexample，ThomasAquinasdoesinhisSummaTheologiatothe\"actsofangels，\"the\"speakingofangels，\"the\"subordinationofangels，\"the\"deedsofguardianangels，\"andthelike。Theydisputedsuchimportantquestionsas，Howmanyangelscanstanduponthepointofaneedle？TheyarguedproandconastowhetherChristwerecoevalwithGod，orwhetherhehadbeenmerelycreated\"inthebeginning，\"perhapsagesbeforethecreationoftheworld。Howcoulditbeexpectedthatscienceshouldflourishwhenthegreatestmindsoftheagecouldconcernthemselveswithproblemssuchasthese？
Despiteourpreconceptionsorprejudices，therecanbebutoneanswertothatquestion。Orientalsuperstitioncastitsblightuponthefairfieldofscience，whatevercompensationitmayormaynothavebroughtinotherfields。Butwemustbeonourguardlestweoverestimateorincorrectlyestimatethisinfluence。
Posterity，inglancingbackward，isalwayspronetostampanygivenageofthepastwithoneidea，andtodesiretocharacterizeitwithasinglephrase；whereasinrealityallagesarediversified，andanygeneralizationregardinganepochissuretodothatepochsomethinglessorsomethingmorethanjustice。Wemaybesure，then，thattheidealofecclesiasticismisnotsolelyresponsibleforthescientificstasisofthedarkage。Indeed，therewasanotherinfluenceofatotallydifferentcharacterthatistoopatenttobeoverlooked——theinfluence，namely，oftheeconomicconditionofwesternEuropeduringthisperiod。AsIhaveelsewherepointedout，[2]Italy，thecentreofwesterncivilization，wasatthistimeimpoverished，andhencecouldnotprovidethemonetarystimulussoessentialtoartisticandscientificnolessthantomaterialprogress。TherewerenopatronsofscienceandliteraturesuchasthePtolemiesofthatelderAlexandrianday。Therewerenogreatlibraries；nocollegestosupplyopportunitiesandaffordstimulitotherisinggeneration。Worstofall，itbecameincreasinglydifficulttosecurebooks。
Thisphaseofthesubjectisoftenoverlooked。Yetamoment’sconsiderationwillshowitsimportance。Howshouldwefareto-dayifnonewscientificbookswerebeingproduced，andiftherecordsofformergenerationsweredestroyed？ThatiswhatactuallyhappenedinEuropeduringtheMiddleAges。Atanearlierdaybooksweremadeanddistributedmuchmoreabundantlythanissometimessupposed。Bookmakinghad，indeed，beenanimportantprofessioninRome，theactualmakersofbooksbeingslaveswhoworkedunderthedirectionofapublisher。ItwasthroughtheeffortsoftheseworkersthattheclassicalworksinGreekandLatinweremultipliedanddisseminated。UnfortunatelytheclimateofEuropedoesnotconducetotheindefinitepreservationofabook；henceveryfewremnantsofclassicalworkshavecomedowntousintheoriginalfromaremoteperiod。Therareexceptionsarecertainpapyrusfragments，foundinEgypt，someofwhichareGreekmanuscriptsdatingfromthethirdcenturyB。C。Evenfromthesesourcestheoutputismeagre；andtheonlyotherrepositoryofclassicalbooksisasingleroomintheburiedcityofHerculaneum，whichcontainedseveralhundredmanuscripts，mostlyinacharredcondition，aconsiderablenumberofwhich，however，havebeenunrolledandfoundmoreorlesslegible。Thislibraryintheburiedcitywaschieflymadeupofphilosophicalworks，someofwhichwerequiteunknowntothemodernworlduntildiscoveredthere。
Butthisfind，interestingasitwasfromanarchaeologicalstand-point，hadnoveryimportantbearingonourknowledgeoftheliteratureofantiquity。Ourchiefdependenceforourknowledgeofthatliteraturemuststillbeplacedinsuchcopiesofbooksasweremadeinthesuccessivegenerations。
Comparativelyfewoftheextantmanuscriptsareolderthanthetenthcenturyofourera。Itrequiresbutamomentaryconsiderationoftheconditionsunderwhichancientbookswereproducedtorealizehowslowanddifficulttheprocesswasbeforetheinventionofprinting。Thetasteofthebook-buyingpublicdemandedaclearlywrittentext，andintheMiddleAgesitbecamecustomarytoproducearichlyornamentedtextaswell。Thescriptemployedbeingtheprototypeofthemodernprintedtext，itwillbeobviousthatascribecouldproducebutafewpagesatbestinaday。Alargeworkwouldthereforerequirethelaborofascribeformanymonthsorevenforseveralyears。Wemayassume，then，thatitwouldbeaveryflourishingpublisherwhocouldproduceahundredvolumesalltoldperannum；andprobablytherewerenotmanypublishersatanygiventime，evenintheperiodofRome’sgreatestglory，whohadanythinglikethisoutput。
Astherewasalargenumberofauthorsineverygenerationoftheclassicalperiod，itfollowsthatmostoftheseauthorsmusthavebeenobligedtocontentthemselveswitheditionsnumberingveryfewcopies；anditgoeswithoutsayingthatthegreaternumberofbookswereneverreproducedinwhatmightbecalledasecondedition。Evenbooksthatretainedtheirpopularityforseveralgenerationswouldpresentlyfailtoarousesufficientinteresttobecopied；andinduecoursesuchworkswouldpassoutofexistencealtogether。Doubtlessmanyhundredsofbookswerethuslostbeforethecloseoftheclassicalperiod，thenamesoftheirauthorsbeingquiteforgotten，orpreservedonlythroughachancereference；andofcoursetheworkofeliminationwentonmuchmorerapidlyduringtheMiddleAges，whentheinterestinclassicalliteraturesanktosolowanebbintheWest。SuchcollectionsofreferencesandquotationsastheGreekAnthologyandthefamousanthologiesofStobaeusandAthanasiusandEusebiusgiveusglimpsesofahostofwriters——morethansevenhundredarequotedbyStobaeus——averylargeproportionofwhomarequiteunknownexceptthroughthesebriefexcerptsfromtheirlostworks。
Quitenaturallythescientificworkssufferedatleastaslargelyasanyothersinanagegivenovertoecclesiasticaldreamings。
Yetinsomeregardsthereismatterforsurpriseastotheworkspreserved。Thus，aswehaveseen，theveryextensiveworksofAristotleonnaturalhistory，andtheequallyextensivenaturalhistoryofPliny，whichwerepreservedthroughoutthisperiod，andarestillextant，makeuprelativelybulkyvolumes。TheseworksseemtohaveinterestedthemonksoftheMiddleAges，whilemanymuchmoreimportantscientificbookswereallowedtoperish。
AconsiderablebulkofscientificliteraturewasalsopreservedthroughthecuriouschannelsofArabicandArmeniantranslations。
ReferencehasalreadybeenmadetotheAlmagestofPtolemy，which，aswehaveseen，wastranslatedintoArabic，andwhichwasatalaterdaybroughtbytheArabsintowesternEuropeandattheinstanceofFrederickIIofSicilytranslatedoutoftheirlanguageintomediaevalLatin。
Itremainstoinquire，however，throughwhatchannelstheGreekworksreachedtheArabsthemselves。TogainananswertothisquestionwemustfollowthestreamofhistoryfromitsRomancourseeastwardtothenewseatoftheRomanempireinByzantium。
HerecivilizationcentredfromaboutthefifthcenturyA。D。，andheretheEuropeancameincontactwiththecivilizationoftheSyrians，thePersians，theArmenians，andfinallyoftheArabs。
TheByzantinesthemselves，unliketheinhabitantsofwesternEurope，didnotignoretheliteratureofoldGreece；theGreeklanguagebecametheregularspeechoftheByzantinepeople，andtheirwritersmadeastrenuousefforttoperpetuatetheidiomandstyleoftheclassicalperiod。Naturallytheyalsomadetranscriptionsoftheclassicalauthors，andthusagreatmassofliteraturewaspreserved，whilethecorrespondingworkswerequiteforgotteninwesternEurope。
MeantimemanyoftheseworksweretranslatedintoSyriac，Armenian，andPersian，andwhenlaterontheByzantinecivilizationdegenerated，manyworksthatwerenolongertobehadintheGreekoriginalscontinuedtobewidelycirculatedinSyriac，Persian，Armenian，and，ultimately，inArabictranslations。WhentheArabsstartedoutintheirconquests，whichcarriedthemthroughEgyptandalongthesoutherncoastoftheMediterranean，untiltheyfinallyinvadedEuropefromthewestbywayofGibraltar，theycarriedwiththemtheirtranslationsofmanyaGreekclassicalauthor，whowasintroducedanewtothewesternworldthroughthisstrangechannel。
Wearetold，forexample，thatAverrhoes，thefamouscommentatorofAristotle，wholivedinSpaininthetwelfthcentury，didnotknowawordofGreekandwasobligedtogainhisknowledgeofthemasterthroughaSyriactranslation；or，asothersallegeddenyingthatheknewevenSyriac，throughanArabicversiontranslatedfromtheSyriac。Weknow，too，thatthefamouschronologyofEusebiuswaspreservedthroughanArmeniantranslation；andreferencehasmorethanoncebeenmadetotheArabictranslationofPtolemy’sgreatwork，towhichwestillapplyitsArabictitleofAlmagest。
ThefamiliarstorythatwhentheArabsinvadedEgypttheyburnedtheAlexandrianlibraryisnowregardedasaninventionoflatertimes。ItseemsmuchmoreprobablethatthelibrarybadbeenlargelyscatteredbeforethecomingoftheMoslems。Indeed，ithasevenbeensuggestedthattheChristiansofanearlierdayremovedtherecordsofpaganthought。Bethatasitmay，thefamousAlexandrianlibraryhaddisappearedlongbeforetherevivalofinterestinclassicallearning。Meanwhile，aswehavesaid，theArabs，farfromdestroyingthewesternliterature，wereitschiefpreservers。Partlyatleastbecauseoftheirregardfortherecordsofthecreativeworkofearliergenerationsofalienpeoples，theArabswereenabledtooutstriptheircontemporaries。
Foritcannotbeindoubtthat，duringthatlongstretchoftimewhenthewesternworldwasignoringsciencealtogetheroratmostcontentingitselfwiththecasualreadingofAristotleandPliny，theArabshadtheuniquedistinctionofattemptingoriginalinvestigationsinscience。TothemweredueallimportantprogressivestepswhichweremadeinanyscientificfieldwhateverforaboutathousandyearsafterthetimeofPtolemyandGalen。TheprogressmadeevenbytheArabsduringthislongperiodseemsmeagreenough，yetithassomesignificantfeatures。
Thesewillnowdemandourattention。
II。MEDIAEVALSCIENCEAMONGTHEARABIANS
ThesuccessorsofMohammedshowedthemselvescuriouslyreceptiveoftheideasofthewesternpeoplewhomtheyconquered。TheycameincontactwiththeGreeksinwesternAsiaandinEgypt，and，ashasbeensaid，becametheirvirtualsuccessorsincarryingforwardthetorchoflearning。Itmustnotbeinferred，however，thattheArabianscholars，asaclass，werecomparabletotheirpredecessorsincreativegenius。Onthecontrary，theyretainedmuchoftheconservativeorientalspirit。Theywereunderthespelloftradition，and，inthemain，whattheyacceptedfromtheGreekstheyregardedasalmostfinalinitsteaching。Therewere，however，afewnotableexceptionsamongtheirmenofscience，andtothesemustbeascribedseveraldiscoveriesofsomeimportance。
ThechiefsubjectsthatexcitedtheinterestandexercisedtheingenuityoftheArabianscholarswereastronomy，mathematics，andmedicine。Thepracticalphasesofallthesesubjectsweregivenparticularattention。Thusitiswellknownthatourso-calledArabiannumeralsdatefromthisperiod。Therevolutionaryeffectofthesecharacters，asappliedtopracticalmathematics，canhardlybeoverestimated；butitisgenerallyconsidered，andinfactwasadmittedbytheArabsthemselves，thatthesenumeralswerereallyborrowedfromtheHindoos，withwhomtheArabscameincontactontheeast。CertainoftheHindooalphabets，notablythatoftheBattaksofSumatra，giveusclewstotheoriginalsofthenumerals。Itdoesnotseemcertain，however，thattheHindoosemployedthesecharactersaccordingtothedecimalsystem，whichistheprimeelementoftheirimportance。Knowledgeisnotforthcomingastojustwhenorbywhomsuchapplicationwasmade。IfthiswasanArabicinnovation，itwasperhapsthemostimportantonewithwhichthatnationistobecredited。Anothermathematicalimprovementwastheintroductionintotrigonometryofthesine——thehalf-chordofthedoublearc——insteadofthechordofthearcitselfwhichtheGreekastronomershademployed。ThisimprovementwasduetothefamousAlbategnius，whoseworkinotherfieldsweshallexamineinamoment。
AnotherevidenceofpracticalitywasshownintheArabianmethodofattemptingtoadvanceuponEratosthenes’measurementoftheearth。Insteadoftrustingtothemeasurementofangles，theArabsdecidedtomeasuredirectlyadegreeoftheearth’ssurface——orrathertwodegrees。SelectingalevelplaininMesopotamiafortheexperiment，onepartyofthesurveyorsprogressednorthward，anotherpartysouthward，fromagivenpointtothedistanceofonedegreeofarc，asdeterminedbyastronomicalobservations。Theresultfoundwasfifty-sixmilesforthenortherndegree，andfifty-sixandtwo-thirdmilesforthesouthern。Unfortunately，wedonotknowthepreciselengthofthemileinquestion，andthereforecannotbeassuredastotheaccuracyofthemeasurement。Itisinterestingtonote，however，thatthetwodegreeswerefoundofunequallengths，suggestingthattheearthisnotaperfectsphere——asuggestionthevalidityofwhichwasnottobeputtothetestofconclusivemeasurementsuntilaboutthecloseoftheeighteenthcentury。TheArabmeasurementwasmadeinthetimeofCaliphAbdallahal-Mamun，thesonofthefamousHarun-al-Rashid。Bothfatherandsonwerefamousfortheirinterestinscience。Harun-al-Rashidwas，itwillberecalled，thefriendofCharlemagne。Itissaidthathesentthatruler，asatokenoffriendship，amarvellousclockwhichletfallametalballtomarkthehours。Thismechanism，whichisallegedtohaveexcitedgreatwonderintheWest，furnishesyetanotherinstanceofArabianpracticality。
PerhapsthegreatestoftheArabianastronomerswasMohammedbenJabirAlbategnius，orEl-batani，whowasbornatBatan，inMesopotamia，abouttheyear850A。D。，anddiedin929。
AlbategniuswasastudentofthePtolemaicastronomy，buthewasalsoapracticalobserver。Hemadetheimportantdiscoveryofthemotionofthesolarapogee。Thatistosay，hefoundthatthepositionofthesunamongthestars，atthetimeofitsgreatestdistancefromtheearth，wasnotwhatithadbeeninthetimeofPtolemy。TheGreekastronomerplacedthesuninlongitude65
degrees，butAlbategniusfounditinlongitude82degrees，adistancetoogreattobeaccountedforbyinaccuracyofmeasurement。Themoderninferencefromthisobservationisthatthesolarsystemismovingthroughspace；butofcoursethisinferencecouldnotwellbedrawnwhiletheearthwasregardedasthefixedcentreoftheuniverse。
IntheeleventhcenturyanotherArabiandiscoverer，Arzachel，observingthesuntobelessadvancedthanAlbategniushadfoundit，inferredincorrectlythatthesunhadrecededinthemeantime。ThemodernexplanationofthisobservationisthatthemeasurementofAlbategniuswassomewhatinerror，sinceweknowthatthesun’smotionissteadilyprogressive。Arzachel，however，acceptingthemeasurementofhispredecessor，drewthefalseinferenceofanoscillatorymotionofthestars，theideaofthemotionofthesolarsystemnotbeingpermissible。Thisassumedphenomenon，whichreallyhasnoexistenceinpointoffact，wasnamedthe\"trepidationofthefixedstars，\"andwasforcenturiesacceptedasanactualphenomenon。Arzachelexplainedthissupposedphenomenonbyassumingthattheequinoctialpoints，orthepointsofintersectionoftheequatorandtheecliptic，revolveincirclesofeightdegrees’radius。ThefirstpointsofAriesandLibraweresupposedtodescribethecircumferenceofthesecirclesinabouteighthundredyears。Allofwhichillustrateshowadifficultandfalseexplanationmaytaketheplaceofasimpleandcorrectone。Theobservationsoflatergenerationshaveshownconclusivelythatthesun’sshiftofpositionisregularlyprogressive，hencethatthereisno\"trepidation\"ofthestarsandnorevolutionoftheequinoctialpoints。
IftheArabswerewrongasregardsthissupposedmotionofthefixedstars，theymadeatleastonecorrectobservationastotheinequalityofmotionofthemoon。Twoinequalitiesofthemotionofthisbodywerealreadyknown。Athird，calledthemoon’svariation，wasdiscoveredbyanArabianastronomerwholivedatCairoandobservedatBagdadin975，andwhoboretheformidablenameofMohammedAboulWefaal-Bouzdjani。Theinequalityofmotioninquestion，invirtueofwhichthemoonmovesquickestwhensheisatneworfull，andslowestatthefirstandthirdquarter，wasrediscoveredbyTychoBrahesixcenturieslater；afactwhichinitselfevidencestheneglectoftheArabianastronomer’sdiscoverybyhisimmediatesuccessors。
IntheninthandtenthcenturiestheArabiancityofCordova，inSpain，wasanotherimportantcentreofscientificinfluence。
Therewasalibraryofseveralhundredthousandvolumeshere，andacollegewheremathematicsandastronomyweretaught。Granada，Toledo，andSalamancawerealsoimportantcentres，towhichstudentsflockedfromwesternEurope。ItwastheproximityoftheseArabiancentresthatstimulatedthescientificinterestsofAlfonsoX。ofCastile，atwhoseinstancethecelebratedAlfonsinetableswereconstructed。AfamiliarstoryrecordsthatAlfonso，ponderingthecomplicationsofthePtolemaiccyclesandepicycles，wasledtoremarkthat，hadhebeenconsultedatthetimeofcreation，hecouldhavesuggestedamuchbetterandsimplerplanfortheuniverse。SomecenturiesweretoelapsebeforeCopernicuswastoshowthatitwasnottheplanoftheuniverse，butman’sinterpretationofit，thatwasatfault。
AnotherroyalpersonagewhocameunderArabianinfluencewasFrederickII。ofSicily——the\"WonderoftheWorld，\"ashewascalledbyhiscontemporaries。TheAlmagestofPtolemywastranslatedintoLatinathisinstance，beingintroducedtotheWesternworldthroughthiscuriouschannel。AtthistimeitbecamequiteusualfortheItalianandSpanishscholarstounderstandArabicalthoughtheyweretotallyignorantofGreek。
InthefieldofphysicalscienceoneofthemostimportantoftheArabianscientistswasAlhazen。Hiswork，publishedabouttheyear1100A。D。，hadgreatcelebritythroughoutthemediaevalperiod。TheoriginalinvestigationsofAlhazenhadtodolargelywithoptics。Hemadeparticularstudiesoftheeyeitself，andthenamesgivenbyhimtovariouspartsoftheeye，asthevitreoushumor，thecornea，andtheretina，arestillretainedbyanatomists。ItisknownthatPtolemyhadstudiedtherefractionoflight，andthathe，incommonwithhisimmediatepredecessors，wasawarethatatmosphericrefractionaffectstheapparentpositionofstarsnearthehorizon。Alhazencarriedforwardthesestudies，andwasledthroughthemtomakethefirstrecordedscientificestimateofthephenomenaoftwilightandoftheheightoftheatmosphere。Thepersistenceofaglowintheatmosphereafterthesunhasdisappearedbeneaththehorizonissofamiliaraphenomenonthattheancientphilosophersseemnottohavethoughtofitasrequiringanexplanation。Yetamoment’sconsiderationmakesitclearthat，iflighttravelsinstraightlinesandtheraysofthesunwereinnowisedeflected，thecompletedarknessofnightshouldinstantlysucceedtodaywhenthesunpassesbelowthehorizon。Thatthissuddenchangedoesnotoccur，Alhazenexplainedasduetothereflectionoflightbytheearth’satmosphere。
Alhazenappearstohaveconceivedtheatmosphereasasharplydefinedlayer，and，assumingthattwilightcontinuesonlysolongasraysofthesunreflectedfromtheoutersurfaceofthislayercanreachthespectatoratanygivenpoint，hehituponameansofmeasurementthatseemedtosolvethehithertoinscrutableproblemastotheatmosphericdepth。LikethemeasurementsofAristarchusandEratosthenes，thiscalculationofAlhazenissimpleenoughintheory。Itsdefectconsistslargelyinthedifficultyoffixingitstermswithprecision，combinedwiththefurtherfactthattheraysofthesun，intakingtheslantingcoursethroughtheearth’satmosphere，arereallydeflectedfromastraightlineinvirtueoftheconstantlyincreasingdensityoftheairneartheearth’ssurface。Alhazenmusthavebeenawareofthislatterfact，sinceitwasknowntothelaterAlexandrianastronomers，buthetakesnoaccountofitinthepresentmeasurement。ThediagramwillmakethemethodofAlhazenclear。
Hisimportantpremisesaretwo:first，thewell-recognizedfactthat，whenlightisreflectedfromanysurface，theangleofincidenceisequaltotheangleofreflection；and，second，themuchmoredoubtfulobservationthattwilightcontinuesuntilsuchtimeasthesun，accordingtoasimplecalculation，isnineteendegreesbelowthehorizon。Referringtothediagram，lettheinnercirclerepresenttheearth’ssurface，theoutercirclethelimitsoftheatmosphere，Cbeingtheearth’scentre，andRR
radiioftheearth。ThentheobserveratthepointAwillcontinuetoreceivethereflectedraysofthesununtilthatbodyreachesthepointS，whichis，accordingtothehypothesis，nineteendegreesbelowthehorizonlineoftheobserveratA。
Thishorizonline，beingrepresentedbyAH，andthesun’sraybySM，theangleHMSisanangleofnineteendegrees。ThecomplementaryangleSMAis，obviously，anangleof180-19onehundredandsixty-onedegrees。ButsinceMisthereflectingsurfaceandtheangleofincidenceequalstheangleofreflection，theangleAMCisanangleofone-halfofonehundredandsixty-onedegrees，oreightydegreesandthirtyminutes。NowthisangleAMC，beingknown，theright-angledtriangleMACiseasilyresolved，sincethesideACofthattriangle，beingtheradiusoftheearth，isaknowndimension。ResolutionofthistrianglegivesusthelengthofthehypotenuseMC，andthedifferencebetweenthisandtheradiusAC，orCD，isobviouslytheheightoftheatmosphereh，whichwasthemeasurementdesired。AccordingtothecalculationofAlhazen，thish，ortheheightoftheatmosphere，representsfromtwentytothirtymiles。
Themoderncomputationextendsthistoaboutfiftymiles。But，consideringthevariousambiguitiesthatnecessarilyattendedtheexperiment，theresultwasaremarkablycloseapproximationtothetruth。
Turningfromphysicstochemistry，wefindasperhapsthegreatestArabiannamethatofGeber，whotaughtintheCollegeofSevilleinthefirsthalfoftheeighthcentury。Themostimportantresearchesofthisreallyremarkableexperimenterhadtodowiththeacids。Theancientworldhadhadnoknowledgeofanyacidmorepowerfulthanacetic。Geber，however，vastlyincreasedthepossibilitiesofchemicalexperimentbythediscoveryofsulphuric，nitric，andnitromuriaticacids。Hemadeusealsooftheprocessesofsublimationandfiltration，andhisworksdescribethewaterbathandthechemicaloven。Amongtheimportantchemicalswhichhefirstdifferentiatedisoxideofmercury，andhisstudiesofsulphurinitsvariouscompoundshavepeculiarinterest。Inparticularisthistrueofhisobservationthat，tindercertainconditionsofoxidation，theweightofametalwaslessened。
Fromtherecordofthesestudiesinthefieldsofastronomy，physics，andchemistry，weturntoasomewhatextendedsurveyoftheArabianadvancesinthefieldofmedicine。
ARABIANMEDICINE
TheinfluenceofArabianphysiciansrestedchieflyupontheiruseofdrugsratherthanuponanatomicalknowledge。LikethemediaevalChristians，theylookedwithhorrorondissectionofthehumanbody；yettherewerealwaysamongtheminvestigatorswhoturnedconstantlytonatureherselfforhiddentruths，andwerereadytoupholdthesuperiorityofactualobservationtomerereading。ThusthephysicianAbdel-Letif，whileinEgypt，madecarefulstudiesofamoundofbonescontainingmorethantwentythousandskeletons。Whileexaminingtheseboneshediscoveredthatthelowerjawconsistsofasinglebone，notoftwo，ashadbeentaughtbyGalen。HealsodiscoveredseveralotherimportantmistakesinGalenicanatomy，andwassoimpressedwithhisdiscoveriesthathecontemplatedwritingaworkonanatomywhichshouldcorrectthegreatclassicalauthority’smistakes。
ItwastheArabswhoinventedtheapothecary，andtheirpharmacopoeia，issuedfromthehospitalatGondisapor，andelaboratedfromtimetotime，formedthebasisforWesternpharmacopoeias。Justhowmanydrugsoriginatedwiththem，andhowmanywereborrowedfromtheHindoos，Jews，Syrians，andPersians，cannotbedetermined。Itiscertain，however，thatthroughthemvariousnewandusefuldrugs，suchassenna，aconite，rhubarb，camphor，andmercury，werehandeddownthroughtheMiddleAges，andthattheyareresponsiblefortheintroductionofalcoholinthefieldoftherapeutics。
InmediaevalEurope，Arabiansciencecametoberegardedwithsuperstitiousawe，andtheworksofcertainArabianphysicianswereexaltedtoapositionabovealltheancientwriters。Inmoderntimes，however，therehasbeenareactionandatendencytodepreciationoftheirwork。BysometheyareheldtobemerecopyistsortranslatorsofGreekbooks，andinnosenseoriginalinvestigatorsinmedicine。YettherecanbelittledoubtthatwhiletheArabiansdidcopyandtranslatefreely，theyalsooriginatedandaddedconsiderablytomedicalknowledge。ItiscertainthatinthetimewhenChristianmonarchsinwesternEuropewerepayinglittleattentiontoscienceoreducation，thecaliphsandvizirswereencouragingphysiciansandphilosophers，buildingschools，anderectinglibrariesandhospitals。Theymadeatleastacreditableefforttoupholdandadvanceuponthescientificstandardsofanearlierage。
ThefirstdistinguishedArabianphysicianwasHaretsbenKaladah，whoreceivedhiseducationintheNestonianschoolatGondisapor，aboutthebeginningoftheseventhcentury。NotwithstandingthefactthatHaretswasaChristian，hewaschosenbyMohammedashischiefmedicaladviser，andrecommendedassuchtohissuccessor，theCaliphAbuBekr。Thus，attheveryoutset，thescienceofmedicinewasdivorcedfromreligionamongtheArabians；foriftheprophethimselfcouldemploytheservicesofanunbeliever，surelyothersmightfollowhisexample。AndthatthisexamplewasfollowedisshowninthefactthatmanyChristianphysicianswereraisedtohonorablepositionsbysucceedinggenerationsofArabianmonarchs。Thisbroad-mindedviewofmedicinetakenbytheArabsundoubtedlyassistedasmuchasanyonesinglefactorinupbuildingthescience，justasthenarrowandsuperstitiousviewtakenbyWesternnationshelpedtodestroyit。
TheeducationoftheArabiansmadeitnaturalforthemtoassociatemedicinewiththenaturalsciences，ratherthanwithreligion。AnArabiansavantwassupposedtobeequallywelleducatedinphilosophy，jurisprudence，theology，mathematics，andmedicine，andtopractiselaw，theology，andmedicinewithequalskilluponoccasion。Itiseasytounderstand，therefore，whythesereligiousfanaticswerewillingtoemployunbelievingphysicians，andtheirphysiciansthemselvestoturntothescientificworksofHippocratesandGalenformedicalinstruction，ratherthantoreligiousworks。EvenMohammedhimselfprofessedsomeknowledgeofmedicine，andoftenrelieduponthisknowledgeintreatingailmentsratherthanuponprayersorincantations。Heissaid，forexample，tohaverecommendedandappliedthecauteryinthecaseofafriendwho，whensufferingfromangina，hadsoughthisaid。
ThelistofeminentArabianphysiciansistoolongtobegivenhere，butsomeofthemareofsuchimportanceintheirinfluenceuponlatermedicinethattheycannotbeentirelyignored。OneofthefirstofthesewasHonainbenIsaac809-873A。D。，aChristianArabofBagdad。HemadetranslationsoftheworksofHippocrates，andpractisedtheartalongthelinesindicatedbyhisteachingsandthoseofGalen。Heisconsideredthegreatesttranslatoroftheninthcenturyandoneofthegreatestphilosophersofthatperiod。
AnothergreatArabianphysician，whoseworkwasjustbeginningasHonain’swasdrawingtoaclose，wasRhazes850-923A。D。，whoduringhislifewasnolessnotedasaphilosopherandmusicianthanasaphysician。HecontinuedtheworkofHonain，andadvancedtherapeuticsbyintroducingmoreextensiveuseofchemicalremedies，suchasmercurialointments，sulphuricacid，andaquavitae。Heisalsocreditedwithbeingthefirstphysiciantodescribesmall-poxandmeaslesaccurately。
WhileRhazeswasstillaliveanotherArabian，HalyAbbasdiedabout994，waswritinghisfamousencyclopaediaofmedicine，calledTheRoyalBook。ButthenamesofallthesegreatphysicianshavebeenconsiderablyobscuredbythereputationofAvicenna980-1037，theArabian\"PrinceofPhysicians，\"thegreatestnameinArabicmedicine，andoneofthemostremarkablemeninhistory。Leclercsaysthat\"hewasperhapsneversurpassedbyanymaninbrilliancyofintellectandindefatigableactivity。\"Hiscareerwasamostvariedone。Hewasatalltimesaboisterousreveller，butwhetherflauntinggaylyamongtheguestsofanemirorbidinginsomeobscureapothecarycellar，hisworkofphilosophicalwritingwascarriedonsteadily。Whenafriendlyemirwasinpower，hetaughtandwroteandcarousedatcourt；butbetweentimes，whensomeunfriendlyrulerwassupreme，hewashidingawayobscurely，stillpouringouthisgreatmassofmanuscripts。Inthiswayhisentirelifewasspent。
ByhisextensivewritingsherevivedandkeptalivethebestoftheteachingsoftheGreekphysicians，addingtothemsuchobservationsashehadmadeinanatomy，physiology，andmateriamedica。Amonghisdiscoveriesisthatofthecontagiousnessofpulmonarytuberculosis。Hisworksforseveralcenturiescontinuedtobelookeduponasthehigheststandardbyphysicians，andheshouldundoubtedlybecreditedwithhavingatleastretardedthedeclineofmediaevalmedicine。
ButitwasnottheEasternArabsalonewhowereactiveinthefieldofmedicine。Cordova，thecapitalofthewesterncaliphate，becamealsoagreatcentreoflearningandproducedseveralgreatphysicians。Oneofthese，Albucasisdiedin1013A。D。，iscreditedwithhavingpublishedthefirstillustratedworkonsurgery，thisbookbeingremarkableinstillanotherway，inthatitwasalsothefirstbook，sinceclassicaltimes，writtenfromthepracticalexperienceofthephysician，andnotamerecompilationofancientauthors。AcenturyafterAlbucasiscamethegreatphysicianAvenzoar1113-1196，withwhomhedividesaboutequallythemedicalhonorsofthewesterncaliphate。AmongAvenzoar’sdiscoverieswasthatofthecauseof\"itch\"——alittleparasite，\"sosmallthatheishardlyvisible。\"Thediscoveryofthecauseofthiscommondiseaseseemsofminorimportancenow，butitisofinterestinmedicalhistorybecause，hadAvenzoar’sdiscoverybeenrememberedahundredyearsago，\"itchstruckin\"
couldhardlyhavebeenconsideredthecauseofthree-fourthsofalldiseases，asitwasbythefamousHahnemann。
TheillustriouspupilofAvenzoar，Averrhoes，whodiedin1198
A。D。，wasthelastofthegreatArabianphysicianswho，byrationalconceptionofmedicine，attemptedtostemthefloodofsuperstitionthatwasoverwhelmingmedicine。Foratimehesucceeded；butatlasttheMoslemtheologiansprevailed，andhewasdegradedandbanishedtoatowninhabitedonlybythedespisedJews。
ARABIANHOSPITALS
ToearlyChristiansbelongthecreditofhavingestablishedthefirstcharitableinstitutionsforcaringforthesick；buttheireffortsweresooneclipsedbybothEasternandWesternMohammedans。AsearlyastheeighthcenturytheArabshadbegunbuildinghospitals，buttheflourishingtimeofhospitalbuildingseemstohavebegunearlyinthetenthcentury。LadySeidel，in918A。D。，openedahospitalatBagdad，endowedwithanamountcorrespondingtoaboutthreehundredpoundssterlingamonth。
Othersimilarhospitalswereerectedintheyearsimmediatelyfollowing，andin977theEmirAdad-adaulaestablishedanenormousinstitutionwithastaffoftwenty-fourmedicalofficers。ThegreatphysicianRhazesissaidtohaveselectedthesiteforoneofthesehospitalsbyhangingpiecesofmeatinvariousplacesaboutthecity，selectingthesiteneartheplaceatwhichputrefactionwasslowestinmakingitsappearance。BythemiddleofthetwelfthcenturythereweresomethinglikesixtymedicalinstitutionsinBagdadalone，andtheseinstitutionswerefreetoallpatientsandsupportedbyofficialcharity。
TheEmirNureddin，abouttheyear1160，foundedagreathospitalatDamascus，asathank-offeringforhisvictoriesovertheCrusaders。ThisgreatinstitutioncompletelyovershadowedalltheearlierMoslemhospitalsinsizeandinthecompletenessofitsequipment。Itwasfurnishedwithfacilitiesforteaching，andwasconductedforseveralcenturiesinalavishmanner，regardlessofexpense。Butlittleoveracenturyafteritsfoundationthefameofitsmethodsoftreatmentledtotheestablishmentofalargerandstillmoreluxuriousinstitution——theMansurihospitalatCairo。Itseemsthatacertainsultan，havingbeencuredbymedicinesfromtheDamascenehospital，determinedtobuildoneofhisownatCairowhichshouldeclipseeventhegreatDamasceneinstitution。
Inasingleyear1283-1284thishospitalwasbegunandcompleted。Noeffortsweresparedinhurryingonthegoodwork，andnoonewasexemptfromperforminglaboronthebuildingifhechancedtopassoneoftheadjoiningstreets。Itwastheorderofthesultanthatanypersonpassingnearcouldbeimpressedintothework，andthisorderwascarriedouttotheletter，noblemenandbeggarsalikebeingforcedtolendahand。Verynaturally，theadjacentthoroughfaresbecameunpopularandpracticallydeserted，butstilltheholyworkprogressedrapidlyandwasshortlycompleted。
Thisimmensestructureissaidtohavecontainedfourcourts，eachhavingafountaininthecentre；lecture-halls，wardsforisolatingcertaindiseases，andadepartmentthatcorrespondedtothemodernhospital’s\"out-patient\"department。Theyearlyendowmentamountedtosomethingliketheequivalentofonehundredandtwenty-fivethousanddollars。Anovelfeaturewasahallwheremusiciansplayeddayandnight，andanotherwherestory-tellerswereemployed，sothatpersonstroubledwithinsomniawereamusedandmelancholiacscheered。ThoseofareligiousturnofmindcouldlistentoreadingsoftheKoran，conductedcontinuouslybyastaffofsomefiftychaplains。Eachpatientonleavingthehospitalreceivedsomegoldpieces，thatheneednotbeobligedtoattempthardlaboratonce。
InconsideringtheastonishingtalesofthesesumptuousArabianinstitutions，itshouldbeborneinmindthatouraccountsofthemare，forthemostpart，fromMohammedansources。
Nevertheless，therecanbelittlequestionthattheywereenormousinstitutions，farsurpassinganysimilarinstitutionsinwesternEurope。Theso-calledhospitalsintheWestwere，atthistime，branchesofmonasteriesundersupervisionofthemonks，anddidnotcomparefavorablywiththeArabianhospitals。
ButwhilethemedicalscienceoftheMohammedansgreatlyovershadowedthatoftheChristiansduringthisperiod，itdidnotcompletelyobliterateit。Abouttheyear1000A。D。cameintoprominencetheChristianmedicalschoolatSalerno，situatedontheItaliancoast，somethirtymilessoutheastofNaples。Justhowlongthisschoolhadbeeninexistence，orbywhomitwasfounded，cannotbedetermined，butitsperiodofgreatestinfluencewastheeleventh，twelfth，andthirteenthcenturies。
ThemembersofthisschoolgraduallyadoptedArabicmedicine，makinguseofmanydrugsfromtheArabicpharmacopoeia，andthisformedoneofthestepping-stonestotheintroductionofArabianmedicineallthroughwesternEurope。
ItwasnottheadoptionofArabianmedicines，however，thathasmadetheschoolatSalernofamousbothinrhymeandprose，butratherthefactthatwomentherepractisedthehealingart。
GreatestamongthemwasTrotula，wholivedintheeleventhcentury，andwhoselearningisreputedtohaveequalledthatofthegreatestphysiciansoftheday。SheisaccreditedwithaworkonDiseasesofWomen，stillextant，andmanyofherwritingsongeneralmedicalsubjectswerequotedthroughtwosucceedingcenturies。Ifwemayjudgefromthesewritings，sheseemedtohavehadmanyexcellentideasastothepropermethodsoftreatingdiseases，butitisdifficulttodeterminejustwhichofthewritingscreditedtoherareinrealityhers。Indeed，theuncertaintyisevengreaterthanthisimplies，for，accordingtosomewriters，\"Trotula\"ismerelythetitleofabook。SuchanauthorityasMalgaigne，however，believedthatsuchawomanexisted，andthattheworksaccreditedtoherareauthentic。Thetruthofthemattermayperhapsneverbefullyestablished，butthisatleastiscertain——thetraditioninregardtoTrotulacouldneverhavearisenhadnotwomenheldafardifferentpositionamongtheArabiansofthisperiodfromthataccordedthemincontemporaryChristendom。
III。MEDIAEVALSCIENCEINTHEWEST
WehavepreviouslyreferredtotheinfluenceoftheByzantinecivilizationintransmittingthelearningofantiquityacrosstheabysmofthedarkage。Itmustbeadmitted，however，thattheimportanceofthatcivilizationdidnotextendmuchbeyondthetaskofthecommoncarrier。TherewerenogreatcreativescientistsinthelaterRomanempireoftheEastanymorethaninthecorrespondingempireoftheWest。Therewas，however，onefieldinwhichtheByzantinemaderespectableprogressandregardingwhichtheireffortsrequireafewwordsofspecialcomment。Thiswasthefieldofmedicine。
TheByzantinesofthistimecouldboastoftwogreatmedicalmen，AetiusofAmidaabout502-575A。D。andPaulofAeginaabout620-690。TheworksofAetiuswereofvaluelargelybecausetheyrecordedtheteachingsofmanyofhiseminentpredecessors，buthewasnotentirelylackinginoriginality，andwasperhapsthefirstphysiciantomentiondiphtheria，withanallusiontosomeobservationsoftheparalysisofthepalatewhichsometimesfollowsthisdisease。
PaulofAegina，whocamefromtheAlexandrianschoolaboutacenturylater，wasoneofthoseremarkablemenwhoseideasarecenturiesaheadoftheirtime。ThiswasparticularlytrueofPaulinregardtosurgery，andhisattitudetowardsthesupernaturalinthecausationandtreatmentofdiseases。Hewasessentiallyasurgeon，beingparticularlyfamiliarwithmilitarysurgery，andsomeofhisdescriptionsofcomplicatedanddifficultoperationshavebeenlittleimproveduponeveninmoderntimes。Inhisbookshedescribessuchoperationsastheremovalofforeignbodiesfromthenose，ear，andesophagus；andherecognizesforeigngrowthssuchaspolypiintheair-passages，andgivesthemethodoftheirremoval。Suchoperationsastracheotomy，tonsellotomy，bronchotomy，staphylotomy，etc。，wereperformedbyhim，andheevenadvocatedanddescribedpunctureoftheabdominalcavity，givingcarefuldirectionsastothelocationinwhichsuchpuncturesshouldbemade。Headvocatedamputationofthebreastforthecureofcancer，anddescribedextirpationoftheuterus。
Justhowsuccessfulthislastoperationmayhavebeenasperformedbyhimdoesnotappear；buthewouldhardlyhaverecommendeditifithadnotbeensometimes，atleast，successful。Thathementionsitatall，however，issignificant，asthisdifficultoperationisconsideredoneofthegreattriumphsofmodernsurgery。
ButPaulofAeginaisastrikingexceptiontotheruleamongByzantinesurgeons，andashewastheirgreatest，sohewasalsotheirlastimportantsurgeon。TheenergiesofallByzantiumweresoexpendedinreligiouscontroversiesthatmedicine，liketheothersciences，wassoonrelegatedtoaplaceamongtheothersuperstitions，andtheinfluenceoftheByzantineschoolwaspresentlyreplacedbythatoftheconqueringArabians。
THIRTEENTH-CENTURYMEDICINE
Thethirteenthcenturymarksthebeginningofagradualchangeinmedicine，andatendencytoleavethetime-wornrutofsuperstitiousdogmasthatsolongretardedtheprogressofscience。ItisthoughtthatthegreatepidemicswhichragedduringtheMiddleAgesactedpowerfullyindivertingthemedicalthoughtofthetimesintonewandentirelydifferentchannels。ItwillberememberedthattheteachingsofGalenwerehandedthroughmediaevaltimesasthehighestandbestauthorityonthesubjectofalldiseases。When，however，thegreatepidemicsmadetheirappearance，themedicalmenappealedtotheworksofGaleninvainforenlightenment，astheseworks，havingbeenwrittenseveralcenturiesbeforethetimeoftheplagues，naturallycontainednoinformationconcerningthem。Itwasevident，therefore，thatonthissubject，atleast，Galenwasnotinfallible；anditwouldnaturallyfollowthat，onefalliblepointhavingbeenrevealed，otherswouldbesoughtfor。Inotherwords，scepticisminregardtoacceptedmethodswouldbearoused，andwouldleadnaturally，assuchscepticismusuallydoes，toprogress。Thedevastatingeffectsoftheseplagues，despiteprayersandincantations，wouldarousedoubtinthemindsofmanyastotheefficacyofsuperstitiousritesandceremoniesincuringdiseases。Theyhadseenthousandsandtensofthousandsoftheirfellow-beingssweptawaybytheseawfulscourges。Theyhadseentheravagesoftheseepidemicscontinueformonthsorevenyears，notwithstandingthefactthatmultitudesofGod-fearingpeopleprayedhourlythatsuchravagesmightbechecked。Andtheymusthaveobservedalsothatwhenevenverysimplerulesofcleanlinessandhygienewerefollowedtherewasadiminutionintheravagesoftheplague，evenwithouttheaidofincantations。
Suchobservationsasthesewouldhaveatendencytoawakenasuspicioninthemindsofmanyofthephysiciansthatdiseasewasnotamanifestationofthesupernatural，butanaturalphenomenon，tobetreatedbynaturalmethods。
But，bethecauseswhattheymay，itisafactthatthethirteenthcenturymarksaturning-point，orthebeginningofanattitudeofmindwhichresultedinbringingmedicinetoamuchmorerationalposition。Amongthethirteenth-centuryphysicians，twomenaredeservingofspecialmention。TheseareArnaldofVillanova1235-1312andPeterofAbano1250-1315。Boththesemensufferedpersecutionforexpressingtheirbeliefinnatural，asagainstthesupernatural，causesofdisease，andatonetimeArnaldwasobligedtofleefromBarcelonafordeclaringthatthe\"bulls\"ofpopeswerehumanworks，andthat\"actsofcharityweredearertoGodthanhecatombs。\"Hewasalsoaccusedofalchemy。
Fleeingfrompersecution，hefinallyperishedbyshipwreck。
ArnaldwasthefirstgreatrepresentativeoftheschoolofMontpellier。Hedevotedmuchtimetothestudyofchemicals，andwasactiveinattemptingtore-establishtheteachingsofHippocratesandGalen。Hewasoneofthefirstofalonglineofalchemistswho，forseveralsucceedingcenturies，expendedsomuchtimeandenergyinattemptingtofindthe\"elixiroflife。\"
TheArabdiscoveryofalcoholfirstdeludedhimintothebeliefthatthe\"elixir\"hadatlastbeenfound；butlaterhediscardeditandmadeextensiveexperimentswithbrandy，employingitinthetreatmentofcertaindiseases——thefirstrecordoftheadministrationofthisliquorasamedicine。Arnaldalsorevivedthesearchforsomeanaestheticthatwouldproduceinsensibilitytopaininsurgicaloperations。Thisideawasnotoriginalwithhim，forsinceveryearlytimesphysicianshadattemptedtodiscoversuchananaesthetic，andevensoearlyawriterasHerodotustellshowtheScythians，byinhalationofthevaporsofsomekindofhemp，producedcompleteinsensibility。ItmayhavebeenthesewritingsthatstimulatedArnaldtosearchforsuchananaesthetic。Inabookusuallycreditedtohim，medicinesarenamedandmethodsofadministrationdescribedwhichwillmakethepatientinsensibletopain，sothat\"hemaybecutandfeelnothing，asthoughheweredead。\"Forthispurposeamixtureofopium，mandragora，andhenbaneistobeused。Thismixturewasheldatthepatient’snostrilsmuchasetherandchloroformareadministeredbythemodernsurgeon。ThemethodwasmodifiedbyHugoofLuccadiedin1252or1268，whoaddedcertainothernarcotics，suchashemlock，tothemixture，andboiledanewspongeinthisdecoction。Afterboilingforacertaintime，thisspongewasdried，andwhenwantedforusewasdippedinhotwaterandappliedtothenostrils。
Justhowfrequentlypatientsrecoveredfromtheadministrationofsuchacombinationofpowerfulpoisonsdoesnotappear，butthepercentageofdeathsmusthavebeenveryhigh，asthepracticewasgenerallycondemned。Insensibilitycouldhavebeenproducedonlybyswallowinglargequantitiesoftheliquid，whichdrippedintothenoseandmouthwhenthespongewasapplied，andalethalquantitymightthusbeswallowed。Themethodwasrevived，withvariousmodifications，fromtimetotime，butasoftenfellintodisuse。Aslateas1782itwassometimesattempted，andinthatyeartheKingofPolandissaidtohavebeencompletelyanaesthetizedandtohaverecovered，afterapainlessamputationhadbeenperformedbythesurgeons。
PeterofAbanowasoneofthefirstgreatmenproducedbytheUniversityofPadua。HisfatewouldhavebeenevenmoretragicthanthatoftheshipwreckedArnaldhadhenotcheatedthepurifyingfagotsofthechurchbydyingopportunelyontheeveofhisexecutionforheresy。Butifhisspirithadcheatedthefanatics，hisbodycouldnot，andhisboneswereburnedforhisheresy。Hehaddaredtodenytheexistenceofadevil，andhadsuggestedthatthecaseofapatientwholayinatranceforthreedaysmighthelptoexplainsomemiracles，liketheraisingofLazarus。
HisgreatworkwasConciliatorDifferentiarum，anattempttoreconcilephysiciansandphilosophers。Buthisresearcheswerenotconfinedtomedicine，forheseemstohavehadaninklingofthehithertounknownfactthatairpossessesweight，andhiscalculationofthelengthoftheyearatthreehundredandsixty-fivedays，sixhours，andfourminutes，isexceptionallyaccuratefortheageinwhichhelived。HewasprobablythefirstoftheWesternwriterstoteachthatthebrainisthesourceofthenerves，andtheheartthesourceofthevessels。Fromthisitisseenthathewasgropinginthedirectionofanexplanationofthecirculationoftheblood，asdemonstratedbyHarveythreecenturieslater。
TheworkofArnaldandPeterofAbanoin\"reviving\"medicinewascontinuedactivelybyMondino1276-1326ofBologna，the\"restorerofanatomy，\"andbyGuyofChauliac:bornabout1300，the\"restorerofsurgery。\"AllthroughtheearlyMiddleAgesdissectionsofhumanbodieshadbeenforbidden，andevendissectionoftheloweranimalsgraduallyfellintodisreputebecausephysiciansdetectedinsuchpracticesweresometimesaccusedofsorcery。Beforethecloseofthethirteenthcentury，however，areactionhadbegun，physicianswereprotected，anddissectionswereoccasionallysanctionedbytherulingmonarch。
ThusEmperorFrederickH。1194-1250A。D。——whoseservicestosciencewehavealreadyhadoccasiontomention——orderedthatatleastonehumanbodyshouldbedissectedbyphysiciansinhiskingdomeveryfiveyears。BythetimeofMondinodissectionswerebecomingmorefrequent，andhehimselfisknowntohavedissectedanddemonstratedseveralbodies。HiswritingsonanatomyhavebeencalledmerelyplagiarismsofGalen，butinallprobabilitybemademanydiscoveriesindependently，andonthewhole，hisworkmaybetakenasmoreadvancedthanGalen’s。Hisdescriptionoftheheartisparticularlyaccurate，andheseemstohavecomenearertodeterminingthecourseofthebloodinitscirculationthananyofhispredecessors。Inthisquesthewasgreatlyhandicappedbytheprevailingbeliefintheideathatblood-vesselsmustcontainairaswellasblood，andthisledhimtoassumethatoneofthecavitiesoftheheartcontained\"spirits，\"orair。Itisprobable，however，thathisaccurateobservations，sofarastheywent，werehelpfulstepping-stonestoHarveyinhisdiscoveryofthecirculation。
GuyofChauliac，whoseinnovationsinsurgeryreestablishedthatscienceonafirmbasis，wasnotonlyoneofthemostcultured，butalsothemostpracticalsurgeonofhistime。HehadgreatreverencefortheworksofGalen，Albucasis，andothersofhisnotedpredecessors；butthisreverencedidnotblindhimtotheirmistakesnorpreventhimfromusingrationalmethodsoftreatmentfarinadvanceoftheirs。Hispracticalityisshowninsomeofhissimplebutusefulinventionsforthesick-room，suchasthedeviceofarope，suspendedfromtheceilingoverthebed，bywhichapatientmaymovehimselfaboutmoreeasily；andinsomeofhisimprovementsinsurgicaldressings，suchasstiffeningbandagesbydippingtheminthewhiteofaneggsothattheyareheldfirmly。Hetreatedbrokenlimbsinthesuspendedcradlestillinuse，andintroducedthemethodofmaking\"traction\"onabrokenlimbbymeansofaweightandpulley，topreventdeformitythroughshorteningofthemember。Hewasoneofthefirstphysicianstorecognizetheutilityofspectacles，andrecommendedthemincasesnotamenabletotreatmentwithlotionsandeye-waters。Insomeofhissurgicaloperations，suchastrephiningforfractureoftheskull，histechniquehasbeenlittleimproveduponeveninmoderntimes。Inoneoftheseoperationshesuccessfullyremovedaportionofaman’sbrain。
Surgerywasundoubtedlystimulatedgreatlyatthisperiodbytheconstantwars。Layphysicians，asaclass，hadbeenlookeddownuponduringtheDarkAges；butwiththebeginningofthereturntorationalism，theservicesofsurgeonsonthebattle-field，toremovemissilesfromwounds，andtocareforwoundsandapplydressings，cametobemorefullyappreciated。Inreturnforhislaborsthesurgeonwasthusaffordedbetteropportunitiesforobservingwoundsanddiseases，whichlednaturallytoagradualimprovementinsurgicalmethods。
FIFTEENTH-CENTURYMEDICINE
Thethirteenthandfourteenthcenturieshadseensomeslightadvancementinthescienceofmedicine；atleast，certainsurgeonsandphysicians，ifnotthegenerality，hadmadeadvances；butitwasnotuntilthefifteenthcenturythatthegeneralrevivalofmedicallearningbecameassured。Inthismovement，naturally，theprinting-pressplayedanall-importantpart。Medicalbooks，hithertopracticallyinaccessibletothegreatmassofphysicians，nowbecamecommon，andthisoutputofreprintsofGreekandArabictreatisesrevealedthefactthatmanyofthesupposedtruecopieswerespurious。Thesediscoveriesverynaturallyarousedallmannerofdoubtandcriticism，whichinturnhelpedinthedevelopmentofindependentthought。
AcertainmanuscriptofthegreatCorneliusCelsus，theDeMedicine，whichhadbeenlostformanycenturies，wasfoundinthechurchofSt。Ambrose，atMilan，in1443，andwasatonceputintoprint。Theeffectofthepublicationofthisbook，whichhadlaininhidingforsomanycenturies，wasarevelation，showingthemedicalprofessionhowfarmostoftheirsupposedtruecopiesofCelsushaddriftedawayfromtheoriginal。Theindisputableauthenticityofthismanuscript，discoveredandvouchedforbythemanwhoshortlyafterbecamePopeNicholasV。，madeitspublicationthemoreimpressive。Theoutputinbookformofotherauthoritiesfollowedrapidly，andthemanifestdiscrepanciesbetweensuchteachersasCelsus，Hippocrates，Galen，andPlinyheightenedstillmorethegrowingspiritofcriticism。
Thesedoubtsresultedingreatcontroversiesastothepropertreatmentofcertaindiseases，somephysiciansfollowingHippocrates，othersGalenorCelsus，stillotherstheArabianmasters。Oneofthemostbitterofthesecontestswasoverthequestionof\"revulsion，\"and\"derivation\"——thatis，whetherincasesofpleurisytreatedbybleeding，thevenesectionshouldbemadeatapointdistantfromtheseatofthedisease，asheldbythe\"revulsionists，\"oratapointnearerandonthesamesideofthebody，aspractisedbythe\"derivationists。\"Thatanygreatpointfordiscussioncouldberaisedinthefifteenthorsixteenthcenturiesonsosimpleamatterasitseemsto-dayshowshownecessarytotheprogressofmedicinewasthediscoveryofthecirculationofthebloodmadebyHarveytwocenturieslater。AfterHarvey’sdiscoverynosuchdiscussioncouldhavebeenpossible，becausethisdiscoverymadeitevidentthatasfarasthegeneraleffectuponthecirculationisconcerned，itmadelittledifferencewhetherthebleedingwasdonenearadiseasedpartorremotefromit。Butinthesixteenthcenturythisquestionwastheall-absorbingoneamongthedoctors。AtonetimethefacultyofPariscondemned\"derivation\"；butthesupportersofthismethodcarriedthewarstillhigher，andEmperorCharlesV。himselfwasappealedto。HereversedthedecisionoftheParisfaculty，anddecidedinfavorof\"derivation。\"HisdecisionwasfurthersupportedbyPopeClementVII。，althoughthediscussiondraggedonuntilcutshortbyHarvey’sdiscovery。
Butanewformofinjurynowclaimedtheattentionofthesurgeons，somethingthatcouldbedecidedbyneitherGreeknorArabianauthors，asthetreatmentofgun-shotwoundswas，forobviousreasons，notgivenintheirwritings。Aboutthistime，also，camethegreatepidemics，\"thesweatingsickness\"andscurvy；anduponthesesubjects，also，theGreeksandArabiansweresilent。JohnofVigo，inhisbook，thePracticaCopiosa，publishedin1514，andrepeatedinmanyeditions，becamethestandardauthorityonallthesesubjects，andthussupplantedtheworksoftheancientwriters。
AccordingtoVigo，gun-shotwoundsdifferedfromthewoundsmadebyordinaryweapons——thatis，spear，arrow，sword，oraxe——inthatthebullet，beinground，bruisedratherthancutitswaythroughthetissues；itburnedtheflesh；and，worstofall，itpoisonedit。Vigolaidespecialstressupontreatingthislastcondition，recommendingtheuseofthecauteryortheoilofelder，boilinghot。Itislittlewonderthatgun-shotwoundsweresolikelytoprovefatal。Yet，afterall，herewasthegermoftheideaofantisepsis。
NEWBEGINNINGSINGENERALSCIENCE
Wehavedweltthusatlengthonthesubjectofmedicalscience，becauseitwaschieflyinthisfieldthatprogresswasmadeintheWesternworldduringthemediaevalperiod，andbecausethesestudiesfurnishedthepointofdeparturefortherevivalallalongtheline。Itwillbeunderstood，however，fromwhatwasstatedintheprecedingchapter，thattheArabianinfluencesinparticularweretosomeextentmakingthemselvesfeltalongotherlines。TheopportunityaffordedaportionoftheWesternworld——notablySpainandSicily——togainaccesstothescientificideasofantiquitythroughArabictranslationscouldnotfailofinfluence。Oflikecharacter，andperhapsevenmorepronouncedindegree，wastheinfluencewroughtbytheByzantinerefugees，who，whenConstantinoplebegantobethreatenedbytheTurks，migratedtotheWestinconsiderablenumbers，bringingwiththemaknowledgeofGreekliteratureandalargenumberofpreciousworkswhichforcenturieshadbeenquiteforgottenorabsolutelyignoredinItaly。NowWesternscholarsbegantotakeaninterestintheGreeklanguage，whichhadbeenutterlyneglectedsincethebeginningoftheMiddleAges。InterestingstoriesaretoldoftheeffortsmadebysuchmenasCosmode’
Medicitogainpossessionofclassicalmanuscripts。Therevivaloflearningthusbroughtabouthaditsfirstpermanentinfluenceinthefieldsofliteratureandart，butitseffectonsciencecouldnotbelongdelayed。QuiteindependentlyoftheByzantineinfluence，however，thestrivingforbetterintellectualthingshadmanifesteditselfinmanywaysbeforethecloseofthethirteenthcentury。Anillustrationofthisisfoundinthealmostsimultaneousdevelopmentofcentresofteaching，whichdevelopedintotheuniversitiesofItaly，France，England，and，alittlelater，ofGermany。
Theregularlistofstudiesthatcametobeadoptedeverywherecomprisedsevennominalbranches，dividedintotwogroups——theso-calledquadrivium，comprisingmusic，arithmetic，geometry，andastronomy；andthetriviumcomprisinggrammar，rhetoric，andlogic。Thevaguenessofimplicationofsomeofthesebranchesgaveopportunitytotheteacherforthepromulgationofalmostanyknowledgeofwhichhemightbepossessed，buttherecanbenodoubtthat，ingeneral，sciencehadbutmeagreshareinthecurriculum。Insofarasitwasgivenrepresentation，itschieffieldmusthavebeenPtolemaicastronomy。Theutterlackofscientificthoughtandscientificmethodisillustratedmostvividlyintheworksofthegreatestmenofthatperiod——suchmenasAlbertusMagnus，ThomasAquinas，Bonaventura，andthehostsofotherscholasticsoflesserrank。Yetthementalawakeningimpliedintheireffortswassuretoextendtootherfields，andinpointoffacttherewasatleastonecontemporaryofthesegreatscholasticswhosemindwasintendedtowardsscientificsubjects，andwhoproducedwritingsstrangelyatvarianceintoneandincontentwiththeothers。ThisanachronisticthinkerwastheEnglishmonk，RogerBacon。
ROGERBACON
Baconwasbornin1214anddiedin1292。Bysomeitisheldthathewasnotappreciatedinhisowntimebecausehewasreallyamodernscientistlivinginanagetwocenturiesbeforemodernscienceormethodsofmodernscientificthinkingwereknown。Suchanestimate，however，isamanifestexaggerationofthefacts，althoughthereisprobablyagrainoftruthinitwithal。Hislearningcertainlybroughthimintocontactwiththegreatthinkersofthetime，andhiswritingscausedhimtobeimprisonedbyhisfellow-churchmenatdifferenttimes，fromwhichcircumstanceswemaygatherthathewasadvancedthinker，evenifnotamodernscientist。
AlthoughBaconwasatvarioustimesindurance，orundersurveillance，andforbiddentowrite，hewasneverthelessamarvellouslyprolificwriter，asisshownbythenumerousbooksandunpublishedmanuscriptsofhisstillextant。Hismaster-productionwastheOpusMajus。InPartIV。ofthisworkheattemptstoshowthatallsciencesrestultimatelyonmathematics；butPartV。，whichtreatsofperspective，isofparticularinteresttomodernscientists，becauseinthishediscussesreflectionandrefraction，andthepropertiesofmirrorsandlenses。Inthispart，also，itisevidentthatheismakinguseofsuchArabianwritersasAlkindiandAlhazen，andthisisofespecialinterest，sinceithasbeenusedbyhisdetractors，whoaccusehimoflackoforiginality，toprovethathisseeminginventionsanddiscoverieswereinrealityadaptationsoftheArabscientists。Itisdifficulttodeterminejusthowfullysuchcriticismsarejustified。Itiscertain，however，thatinthisparthedescribestheanatomyoftheeyewithgreataccuracy，anddiscussesmirrorsandlenses。
ThemagnifyingpowerofthesegmentofaglassspherehadbeennotedbyAlhazen，whohadobservedalsothatthemagnificationwasincreasedbyincreasingthesizeofthesegmentused。Bacontookupthediscussionofthecomparativeadvantagesofsegments，andinthisdiscussionseemstoshowthatheunderstoodhowtotracetheprogressoftheraysoflightthroughasphericaltransparentbody，andhowtodeterminetheplaceoftheimage。Healsodescribedamethodofconstructingatelescope，butitisbynomeansclearthathehadeveractuallyconstructedsuchaninstrument。Itisalsoamootedquestionastowhetherhisinstructionsastotheconstructionofsuchaninstrumentwouldhaveenabledanyonetoconstructone。ThevagariesofthenamesoftermsasheusesthemallowsuchlatitudeininterpretationthatmodernscientistsarenotagreedastothepracticabilityofBacon’ssuggestions。Forexample，heconstantlyreferstoforceundersuchnamesasvirtus，species，imago，agentis，andascoreofothernames，andthisnaturallygivesrisetothegreatdifferencesintheinterpretationsofhiswritings，withcorrespondingdifferencesinestimatesofthem。
TheclaimthatBaconoriginatedtheuseoflenses，intheformofspectacles，cannotbeproven。Smithhasdeterminedthatasearlyastheopeningyearsofthefourteenthcenturysuchlenseswereinuse，butthisprovesnothingasregardsBacon’sconnectionwiththeirinvention。Theknowledgeoflensesseemstobeveryancient，ifwemayjudgefromtheconvexlensofrockcrystalfoundbyLayardinhisexcavationsatNimrud。Thereisnothingtoshow，however，thattheancientseverthoughtofusingthemtocorrectdefectsofvision。Neither，apparently，isitfeasibletodeterminewhethertheideaofsuchanapplicationoriginatedwithBacon。
AnothermechanicaldiscoveryaboutwhichtherehasbeenagreatdealofdiscussionisBacon’ssupposedinventionofgunpowder。Itappearsthatinacertainpassageofhisworkhedescribestheprocessofmakingasubstancethatis，ineffect，ordinarygunpowder；butitismorethandoubtfulwhetherheunderstoodthepropertiesofthesubstancehedescribes。Itisfairlywellestablished，however，thatinBacon’stimegunpowderwasknowntotheArabs，sothatitshouldnotbesurprisingtofindreferencesmadetoitinBacon’swork，sincethereisreasontobelievethatheconstantlyconsultedArabianwritings。
ThegreatmeritofBacon’swork，however，dependsontheprinciplestaughtasregardsexperimentandtheobservationofnature，ratherthanonanysingleinvention。Hehadtheall-importantideaofbreakingwithtradition。Hechampionedunfetteredinquiryineveryfieldofthought。Hehadtheinstinctofascientificworker——arareinstinctindeedinthatage。Norneedwedoubtthattothebestofhisopportunitieshewashimselfanoriginalinvestigator。