ButtherearemanyothercircumstanceswhichevincethatwhatIhaveallegedisthetruecauseofthemotionoftheblood：thus，inthefirstplace，thedifferencethatisobservedbetweenthebloodwhichflowsfromtheveins，andthatfromthearteries，canonlyarisefromthis，thatbeingrarefied，and，asitwere，distilledbypassingthroughtheheart，itisthinner，andmorevivid，andwarmerimmediatelyafterleavingtheheart，inotherwords，wheninthearteries，thanitwasashorttimebeforepassingintoeither，inotherwords，whenitwasintheveins；andifattentionbegiven，itwillbefoundthatthisdifferenceisverymarkedonlyintheneighborhoodoftheheart；andisnotsoevidentinpartsmoreremotefromit。Inthenextplace，theconsistencyofthecoatsofwhichthearterialveinandthegreatarteryarecomposed，sufficientlyshowsthatthebloodisimpelledagainstthemwithmoreforcethanagainsttheveins。Andwhyshouldtheleftcavityoftheheartandthegreatarterybewiderandlargerthantherightcavityandthearterialvein，wereitnotthatthebloodofthevenousartery，havingonlybeeninthelungsafterithaspassedthroughtheheart，isthinner，andrarefiesmorereadily，andinahigherdegree，thanthebloodwhichproceedsimmediatelyfromthehollowvein？Andwhatcanphysiciansconjecturefromfeelingthepulseunlesstheyknowthataccordingasthebloodchangesitsnatureitcanberarefiedbythewarmthoftheheart，inahigherorlowerdegree，andmoreorlessquicklythanbefore？Andifitbeinquiredhowthisheatiscommunicatedtotheothermembers，mustitnotbeadmittedthatthisiseffectedbymeansoftheblood，which，passingthroughtheheart，isthereheatedanew，andthencediffusedoverallthebody？Whenceithappens，thatifthebloodbewithdrawnfromanypart，theheatislikewisewithdrawnbythesamemeans；andalthoughtheheartwereas—hotasglowingiron，itwouldnotbecapableofwarmingthefeetandhandsasatpresent，unlessitcontinuallysentthithernewblood。Welikewiseperceivefromthis，thatthetrueuseofrespirationistobringsufficientfreshairintothelungs，tocausethebloodwhichflowsintothemfromtherightventricleoftheheart，whereithasbeenrarefiedand，asitwere，changedintovapors，tobecomethick，andtoconvertitanewintoblood，beforeitflowsintotheleftcavity，withoutwhichprocessitwouldbeunfitforthenourishmentofthefirethatisthere。Thisreceivesconfirmationfromthecircumstance，thatitisobservedofanimalsdestituteoflungsthattheyhavealsobutonecavityintheheart，andthatinchildrenwhocannotusethemwhileinthewomb，thereisaholethroughwhichthebloodflowsfromthehollowveinintotheleftcavityoftheheart，andatubethroughwhichitpassesfromthearterialveinintothegrandarterywithoutpassingthroughthelung。Inthenextplace，howcoulddigestionbecarriedoninthestomachunlesstheheartcommunicatedheattoitthroughthearteries，andalongwiththiscertainofthemorefluidpartsoftheblood，whichassistinthedissolutionofthefoodthathasbeentakenin？Isnotalsotheoperationwhichconvertsthejuiceoffoodintobloodeasilycomprehended，whenitisconsideredthatitisdistilledbypassingandrepassingthroughtheheartperhapsmorethanoneortwohundredtimesinaday？Andwhatmoreneedbeadducedtoexplainnutrition，andtheproductionofthedifferenthumorsofthebody，beyondsaying，thattheforcewithwhichtheblood，inbeingrarefied，passesfromthehearttowardstheextremitiesofthearteries，causescertainofitspartstoremaininthemembersatwhichtheyarrive，andthereoccupytheplaceofsomeothersexpelledbythem；
　　andthataccordingtothesituation，shape，orsmallnessoftheporeswithwhichtheymeet，someratherthanothersflowintocertainparts，inthesamewaythatsomesievesareobservedtoact，which，bybeingvariouslyperforated，servetoseparatedifferentspeciesofgrain？And，inthelastplace，whataboveallishereworthyofobservation，isthegenerationoftheanimalspirits，whicharelikeaverysubtlewind，orratheraverypureandvividflamewhich，continuallyascendingingreatabundancefromthehearttothebrain，thencepenetratesthroughthenervesintothemuscles，andgivesmotiontoallthemembers；sothattoaccountforotherpartsofthebloodwhich，asmostagitatedandpenetrating，arethefittesttocomposethesespirits，proceedingtowardsthebrain，itisnotnecessarytosupposeanyothercause，thansimply，thatthearterieswhichcarrythemthitherproceedfromtheheartinthemostdirectlines，andthat，accordingtotherulesofmechanicswhicharethesamewiththoseofnature，whenmanyobjectstendatoncetothesamepointwherethereisnotsufficientroomforall（asisthecasewiththepartsofthebloodwhichflowforthfromtheleftcavityoftheheartandtendtowardsthebrain），theweakerandlessagitatedpartsmustnecessarilybedrivenasidefromthatpointbythestrongerwhichaloneinthiswayreachitI
　　hadexpoundedallthesematterswithsufficientminutenessinthetreatisewhichIformerlythoughtofpublishing。Andafterthese，Ihadshownwhatmustbethefabricofthenervesandmusclesofthehumanbodytogivetheanimalspiritscontainedinitthepowertomovethemembers，aswhenweseeheadsshortlyaftertheyhavebeenstruckoffstillmoveandbitetheearth，althoughnolongeranimated；whatchangesmusttakeplaceinthebraintoproducewaking，sleep，anddreams；howlight，sounds，odors，tastes，heat，andalltheotherqualitiesofexternalobjectsimpressitwithdifferentideasbymeansofthesenses；howhunger，thirst，andtheotherinternalaffectionscanlikewiseimpressuponitdiversideas；whatmustbeunderstoodbythecommonsense（sensuscommunis）inwhichtheseideasarereceived，bythememorywhichretainsthem，bythefantasywhichcanchangetheminvariousways，andoutofthemcomposenewideas，andwhich，bythesamemeans，distributingtheanimalspiritsthroughthemuscles，cancausethemembersofsuchabodytomoveinasmanydifferentways，andinamannerassuited，whethertotheobjectsthatarepresentedtoitssensesortoitsinternalaffections，ascantakeplaceinourowncaseapartfromtheguidanceofthewill。Norwillthisappearatallstrangetothosewhoareacquaintedwiththevarietyofmovementsperformedbythedifferentautomata，ormovingmachinesfabricatedbyhumanindustry，andthatwithhelpofbutfewpiecescomparedwiththegreatmultitudeofbones，muscles，nerves，arteries，veins，andotherpartsthatarefoundinthebodyofeachanimal。SuchpersonswilllookuponthisbodyasamachinemadebythehandsofGod，whichisincomparablybetterarranged，andadequatetomovementsmoreadmirablethanisanymachineofhumaninvention。AndhereIspeciallystayedtoshowthat，weretheresuchmachinesexactlyresemblingorgansandoutwardformanapeoranyotherirrationalanimal，wecouldhavenomeansofknowingthattheywereinanyrespectofadifferentnaturefromtheseanimals；butifthereweremachinesbearingtheimageofourbodies，andcapableofimitatingouractionsasfarasitismorallypossible，therewouldstillremaintwomostcertaintestswherebytoknowthattheywerenotthereforereallymen。Ofthesethefirstisthattheycouldneverusewordsorothersignsarrangedinsuchamannerasiscompetenttousinordertodeclareourthoughtstoothers：forwemayeasilyconceiveamachinetobesoconstructedthatitemitsvocables，andeventhatitemitssomecorrespondenttotheactionuponitofexternalobjectswhichcauseachangeinitsorgans；forexample，iftouchedinaparticularplaceitmaydemandwhatwewishtosaytoit；ifinanotheritmaycryoutthatitishurt，andsuchlike；butnotthatitshouldarrangethemvariouslysoasappositelytoreplytowhatissaidinitspresence，asmenofthelowestgradeofintellectcando。Thesecondtestis，thatalthoughsuchmachinesmightexecutemanythingswithequalorperhapsgreaterperfectionthananyofus，theywould，withoutdoubt，failincertainothersfromwhichitcouldbediscoveredthattheydidnotactfromknowledge，butsolelyfromthedispositionoftheirorgans：forwhilereasonisanuniversalinstrumentthatisalikeavailableoneveryoccasion，theseorgans，onthecontrary，needaparticulararrangementforeachparticularaction；whenceitmustbemorallyimpossiblethatthereshouldexistinanymachineadiversityoforganssufficienttoenableittoactinalltheoccurrencesoflife，inthewayinwhichourreasonenablesustoact。Again，bymeansofthesetwotestswemaylikewiseknowthedifferencebetweenmenandbrutes。Foritishighlydeservingofremark，thattherearenomensodullandstupid，notevenidiots，astobeincapableofjoiningtogetherdifferentwords，andtherebyconstructingadeclarationbywhichtomaketheirthoughtsunderstood；andthatontheotherhand，thereisnootheranimal，howeverperfectorhappilycircumstanced，whichcandothelike。Nordoesthisinabilityarisefromwantoforgans：forweobservethatmagpiesandparrotscanutterwordslikeourselves，andareyetunabletospeakaswedo，thatis，soastoshowthattheyunderstandwhattheysay；inplaceofwhichmenborndeafanddumb，andthusnotless，butrathermorethanthebrutes，destituteoftheorganswhichothersuseinspeaking，areinthehabitofspontaneouslyinventingcertainsignsbywhichtheydiscovertheirthoughtstothosewho，beingusuallyintheircompany，haveleisuretolearntheirlanguage。
　　Andthisprovesnotonlythatthebruteshavelessreasonthanman，butthattheyhavenoneatall：forweseethatverylittleisrequiredtoenableapersontospeak；andsinceacertaininequalityofcapacityisobservableamonganimalsofthesamespecies，aswellasamongmen，andsincesomearemorecapableofbeinginstructedthanothers，itisincrediblethatthemostperfectapeorparrotofitsspecies，shouldnotinthisbeequaltothemoststupidinfantofitskindoratleasttoonethatwascrack—brained，unlessthesoulofbruteswereofanaturewhollydifferentfromours。Andweoughtnottoconfoundspeechwiththenaturalmovementswhichindicatethepassions，andcanbeimitatedbymachinesaswellasmanifestedbyanimals；normustitbethoughtwithcertainoftheancients，thatthebrutesspeak，althoughwedonotunderstandtheirlanguage。Forifsuchwerethecase，sincetheyareendowedwithmanyorgansanalogoustoours，theycouldaseasilycommunicatetheirthoughtstousastotheirfellows。Itisalsoveryworthyofremark，that，thoughtherearemanyanimalswhichmanifestmoreindustrythanweincertainoftheiractions，thesameanimalsareyetobservedtoshownoneatallinmanyothers：sothatthecircumstancethattheydobetterthanwedoesnotprovethattheyareendowedwithmind，foritwouldthencefollowthattheypossessedgreaterreasonthananyofus，andcouldsurpassusinallthings；onthecontrary，itratherprovesthattheyaredestituteofreason，andthatitisnaturewhichactsinthemaccordingtothedispositionoftheirorgans：thusitisseen，thataclockcomposedonlyofwheelsandweightscannumberthehoursandmeasuretimemoreexactlythanwewithallourskin。
　　Ihadafterthisdescribedthereasonablesoul，andshownthatitcouldbynomeansbeeducedfromthepowerofmatter，astheotherthingsofwhichIhadspoken，butthatitmustbeexpresslycreated；andthatitisnotsufficientthatitbelodgedinthehumanbodyexactlylikeapilotinaship，unlessperhapstomoveitsmembers，butthatitisnecessaryforittobejoinedandunitedmorecloselytothebody，inordertohavesensationsandappetitessimilartoours，andthusconstitutearealman。
　　Ihereentered，inconclusion，uponthesubjectofthesoulatconsiderablelength，becauseitisofthegreatestmoment：foraftertheerrorofthosewhodenytheexistenceofGod，anerrorwhichIthinkI
　　havealreadysufficientlyrefuted，thereisnonethatismorepowerfulinleadingfeeblemindsastrayfromthestraightpathofvirtuethanthesuppositionthatthesoulofthebrutesisofthesamenaturewithourown；andconsequentlythatafterthislifewehavenothingtohopefororfear，morethanfliesandants；inplaceofwhich，whenweknowhowfartheydifferwemuchbettercomprehendthereasonswhichestablishthatthesoulisofanaturewhollyindependentofthebody，andthatconsequentlyitisnotliabletodiewiththelatterand，finally，becausenoothercausesareobservedcapableofdestroyingit，wearenaturallyledthencetojudgethatitisimmortal。
　　PARTVI
　　ThreeyearshavenowelapsedsinceIfinishedthetreatisecontainingallthesematters；andIwasbeginningtoreviseit，withtheviewtoputitintothehandsofaprinter，whenIlearnedthatpersonstowhomIgreatlydefer，andwhoseauthorityovermyactionsishardlylessinfluentialthanismyownreasonovermythoughts，hadcondemnedacertaindoctrineinphysics，publishedashorttimepreviouslybyanotherindividualtowhichIwillnotsaythatIadhered，butonlythat，previouslytotheircensureIhadobservedinitnothingwhichIcouldimaginetobeprejudicialeithertoreligionortothestate，andnothingthereforewhichwouldhavepreventedmefromgivingexpressiontoitinwriting，ifreasonhadpersuadedmeofitstruth；andthisledmetofearlestamongmyowndoctrineslikewisesomeonemightbefoundinwhichIhaddepartedfromthetruth，notwithstandingthegreatcareIhavealwaystakennottoaccordbelieftonewopinionsofwhichIhadnotthemostcertaindemonstrations，andnottogiveexpressiontoaughtthatmighttendtothehurtofanyone。Thishasbeensufficienttomakemealtermypurposeofpublishingthem；foralthoughthereasonsbywhichIhadbeeninducedtotakethisresolutionwereverystrong，yetmyinclination，whichhasalwaysbeenhostiletowritingbooks，enabledmeimmediatelytodiscoverotherconsiderationssufficienttoexcusemefornotundertakingthetask。
　　Andthesereasons，ononesideandtheother，aresuch，thatnotonlyisitinsomemeasuremyinterestheretostatethem，butthatofthepublic，perhaps，toknowthem。
　　Ihavenevermademuchaccountofwhathasproceededfrommyownmind；andsolongasIgatherednootheradvantagefromthemethodIemploybeyondsatisfyingmyselfonsomedifficultiesbelongingtothespeculativesciences，orendeavoringtoregulatemyactionsaccordingtotheprinciplesittaughtme，Ineverthoughtmyselfboundtopublishanythingrespectingit。Forinwhatregardsmanners，everyoneissofullofhisownwisdom，thattheremightbefoundasmanyreformersasheads，ifanywereallowedtotakeuponthemselvesthetaskofmendingthem，exceptthosewhomGodhasconstitutedthesupremerulersofhispeopleortowhomhehasgivensufficientgraceandzealtobeprophets；andalthoughmyspeculationsgreatlypleasedmyself，Ibelievedthatothershadtheirs，whichperhapspleasedthemstillmore。ButassoonasIhadacquiredsomegeneralnotionsrespectingphysics，andbeginningtomaketrialoftheminvariousparticulardifficulties，hadobservedhowfartheycancarryus，andhowmuchtheydifferfromtheprinciplesthathavebeenemployeduptothepresenttime，IbelievedthatIcouldnotkeepthemconcealedwithoutsinninggrievouslyagainstthelawbywhichweareboundtopromote，asfarasinuslies，thegeneralgoodofmankind。ForbythemIperceivedittobepossibletoarriveatknowledgehighlyusefulinlife；andinroomofthespeculativephilosophyusuallytaughtintheschools，todiscoverapractical，bymeansofwhich，knowingtheforceandactionoffire，water，airthestars，theheavens，andalltheotherbodiesthatsurroundus，asdistinctlyasweknowthevariouscraftsofourartisans，wemightalsoapplytheminthesamewaytoalltheusestowhichtheyareadapted，andthusrenderourselvesthelordsandpossessorsofnature。Andthisisaresulttobedesired，notonlyinordertotheinventionofaninfinityofarts，bywhichwemightbeenabledtoenjoywithoutanytroublethefruitsoftheearth，andallitscomforts，butalsoandespeciallyforthepreservationofhealth，whichiswithoutdoubt，ofalltheblessingsofthislife，thefirstandfundamentalone；forthemindissointimatelydependentupontheconditionandrelationoftheorgansofthebody，thatifanymeanscaneverbefoundtorendermenwiserandmoreingeniousthanhitherto，Ibelievethatitisinmedicinetheymustbesoughtfor。Itistruethatthescienceofmedicine，asitnowexists，containsfewthingswhoseutilityisveryremarkable：butwithoutanywishtodepreciateit，I
　　amconfidentthatthereisnoone，evenamongthosewhoseprofessionitis，whodoesnotadmitthatallatpresentknowninitisalmostnothingincomparisonofwhatremainstobediscovered；andthatwecouldfreeourselvesfromaninfinityofmaladiesofbodyaswellasofmind，andperhapsalsoevenfromthedebilityofage，ifwehadsufficientlyampleknowledgeoftheircauses，andofalltheremediesprovidedforusbynature。ButsinceIdesignedtoemploymywholelifeinthesearchaftersonecessaryascience，andsinceIhadfalleninwithapathwhichseemstomesuch，thatifanyonefollowithemustinevitablyreachtheenddesired，unlesshebehinderedeitherbytheshortnessoflifeorthewantofexperiments，IjudgedthattherecouldbenomoreeffectualprovisionagainstthesetwoimpedimentsthanifIwerefaithfullytocommunicatetothepublicallthelittleImightmyselfhavefound，andincitemenofsuperiorgeniustostrivetoproceedfarther，bycontributing，eachaccordingtohisinclinationandability，totheexperimentswhichitwouldbenecessarytomake，andalsobyinformingthepublicofalltheymightdiscover，sothat，bythelastbeginningwherethosebeforethemhadleftoff，andthusconnectingthelivesandlaboursofmany，wemightcollectivelyproceedmuchfartherthaneachbyhimselfcoulddo。
　　Iremarked，moreover，withrespecttoexperiments，thattheybecomealwaysmorenecessarythemoreoneisadvancedinknowledge；for，atthecommencement，itisbettertomakeuseonlyofwhatisspontaneouslypresentedtooursenses，andofwhichwecannotremainignorant，providedwebestowonitanyreflection，howeverslight，thantoconcernourselvesaboutmoreuncommonandreconditephenomena：thereasonofwhichis，thatthemoreuncommonoftenonlymisleadussolongasthecausesofthemoreordinaryarestillunknown；andthecircumstancesuponwhichtheydependarealmostalwayssospecialandminuteastobehighlydifficulttodetect。ButinthisIhaveadoptedthefollowingorder：first，Ihaveessayedtofindingeneraltheprinciples，orfirstcausesofallthatisorcanbeintheworld，withouttakingintoconsiderationforthisendanythingbutGodhimselfwhohascreatedit，andwithouteducingthemfromanyothersourcethanfromcertaingermsoftruthsnaturallyexistinginourmindsInthesecondplace，Iexaminedwhatwerethefirstandmostordinaryeffectsthatcouldbededucedfromthesecauses；anditappearstomethat，inthisway，Ihavefoundheavens，stars，anearth，andevenontheearthwater，air，fire，minerals，andsomeotherthingsofthiskind，whichofallothersarethemostcommonandsimple，andhencetheeasiesttoknow。AfterwardswhenIwishedtodescendtothemoreparticular，somanydiverseobjectspresentedthemselvestome，thatI
　　believedittobeimpossibleforthehumanmindtodistinguishtheformsorspeciesofbodiesthatareupontheearth，fromaninfinityofotherswhichmighthavebeen，ifithadpleasedGodtoplacethemthere，orconsequentlytoapplythemtoouruse，unlesswerisetocausesthroughtheireffects，andavailourselvesofmanyparticularexperiments。
　　Thereupon，turningoverinmymindItheobjectsthathadeverbeenpresentedtomysensesIfreelyventuretostatethatIhaveneverobservedanywhichIcouldnotsatisfactorilyexplainbytheprincipleshaddiscovered。Butitisnecessaryalsotoconfessthatthepowerofnatureissoampleandvast，andtheseprinciplessosimpleandgeneral，thatIhavehardlyobservedasingleparticulareffectwhichIcannotatoncerecognizeascapableofbeingdeducedinmandifferentmodesfromtheprinciples，andthatmygreatestdifficultyusuallyistodiscoverinwhichofthesemodestheeffectisdependentuponthem；foroutofthisdifficultycannototherwiseextricatemyselfthanbyagainseekingcertainexperiments，whichmaybesuchthattheirresultisnotthesame，ifitisintheoneofthesemodesatwemustexplainit，asitwouldbeifitweretobeexplainedintheother。Astowhatremains，Iamnowinapositiontodiscern，asIthink，withsufficientclearnesswhatcoursemustbetakentomakethemajoritythoseexperimentswhichmayconducetothisend：butIperceivelikewisethattheyaresuchandsonumerous，thatneithermyhandsnormyincome，thoughitwereathousandtimeslargerthanitis，wouldbesufficientforthemall；sothataccordingashenceforwardI
　　shallhavethemeansofmakingmoreorfewerexperiments，Ishallinthesameproportionmakegreaterorlessprogressintheknowledgeofnature。
　　ThiswaswhatIhadhopedtomakeknownbythetreatiseIhadwritten，andsoclearlytoexhibittheadvantagethatwouldthenceaccruetothepublic，astoinduceallwhohavethecommongoodofmanatheart，thatis，allwhoarevirtuousintruth，andnotmerelyinappearance，oraccordingtoopinion，aswelltocommunicatetometheexperimentstheyhadalreadymade，astoassistmeinthosethatremaintobemade。
　　Butsincethattimeotherreasonshaveoccurredtome，bywhichIhavebeenledtochangemyopinion，andtothinkthatIoughtindeedtogooncommittingtowritingalltheresultswhichIdeemedofanymoment，assoonasIshouldhavetestedtheirtruth，andtobestowthesamecareuponthemasIwouldhavedonehaditbeenmydesigntopublishthem。Thiscoursecommendeditselftome，aswellbecauseIthusaffordedmyselfmoreampleinducementtoexaminethemthoroughly，fordoubtlessthatisalwaysmorenarrowlyscrutinizedwhichwebelievewillbereadbymany，thanthatwhichiswrittenmerelyforourprivateuse（andfrequentlywhathasseemedtometruewhenIfirstconceivedit，hasappearedfalsewhenI
　　havesetaboutcommittingittowriting），asbecauseIthuslostnoopportunityofadvancingtheinterestsofthepublic，asfarasinmelay，andsincethuslikewise，ifmywritingspossessanyvalue，thoseintowhosehandstheymayfallaftermydeathmaybeabletoputthemtowhatusetheydeemproper。ButIresolvedbynomeanstoconsenttotheirpublicationduringmylifetime，lesteithertheoppositionsorthecontroversiestowhichtheymightgiverise，oreventhereputation，suchasitmightbe，whichtheywouldacquireforme，shouldbeanyoccasionofmylosingthetimethatIhadsetapartformyownimprovement。Forthoughitbetruethateveryoneisboundtopromotetotheextentofhisabilitythegoodofothers，andthattobeusefultonooneisreallytobeworthless，yetitislikewisetruethatourcaresoughttoextendbeyondthepresent，anditisgoodtoomitdoingwhatmightperhapsbringsomeprofittotheliving，whenwehaveinviewtheaccomplishmentofotherendsthatwillbeofmuchgreateradvantagetoposterity。Andintruth，I
　　amquitewillingitshouldbeknownthatthelittleIhavehithertolearnedisalmostnothingincomparisonwiththatofwhichIamignorant，andtotheknowledgeofwhichIdonotdespairofbeingabletoattain；
　　foritismuchthesamewiththosewhograduallydiscovertruthinthesciences，aswiththosewhowhengrowingrichfindlessdifficultyinmakinggreatacquisitions，thantheyformerlyexperiencedwhenpoorinmakingacquisitionsofmuchsmalleramount。Ortheymaybecomparedtothecommandersofarmies，whoseforcesusuallyincreaseinproportiontotheirvictories，andwhoneedgreaterprudencetokeeptogethertheresidueoftheirtroopsafteradefeatthanafteravictorytotaketownsandprovinces。Forhetrulyengagesinbattlewhoendeavorstosurmountallthedifficultiesanderrorswhichpreventhimfromreachingtheknowledgeoftruth，andheisovercomeinfightwhoadmitsafalseopiniontouchingamatterofanygeneralityandimportance，andherequiresthereaftermuchmoreskilltorecoverhisformerpositionthantomakegreatadvanceswhenonceinpossessionofthoroughlyascertainedprinciples。Asformyself，ifIhavesucceededindiscoveringanytruthsinthesciences（andItrustthatwhatiscontainedinthisvolume1willshowthatIhavefoundsome），IcandeclarethattheyarebuttheconsequencesandresultsoffiveorsixprincipaldifficultieswhichIhavesurmounted，andmyencounterswithwhichIreckonedasbattlesinwhichvictorydeclaredforme。Iwillnothesitateeventoavowmybeliefthatnothingfurtheriswantingtoenablemefullytorealizemydesignsthantogaintwoorthreesimilarvictories；andthatIamnotsofaradvancedinyearsbutthat，accordingtotheordinarycourseofnature，Imaystillhavesufficientleisureforthisend。ButIconceivemyselfthemoreboundtohusbandthetimethatremainsthegreatermyexpectationofbeingabletoemployitaright，andIshoulddoubtlesshavemuchtorobmeofit，wereItopublishtheprinciplesofmyphysics：foralthoughtheyarealmostallsoevidentthattoassenttothemnomoreisneededthansimplytounderstandthem，andalthoughthereisnotoneofthemofwhichIdonotexpecttobeabletogivedemonstration，yet，asitisimpossiblethattheycanbeinaccordancewithallthediverseopinionsofothers，IforeseethatI
　　shouldfrequentlybeturnedasidefrommygranddesign，onoccasionoftheoppositionwhichtheywouldbesuretoawaken。
　　Itmaybesaid，thattheseoppositionswouldbeusefulbothinmakingmeawareofmyerrors，and，ifmyspeculationscontainanythingofvalue，inbringingotherstoafullerunderstandingofit；andstillfarther，asmanycanseebetterthanone，inleadingotherswhoarenowbeginningtoavailthemselvesofmyprinciples，toassistmeinturnwiththeirdiscoveries。ButthoughIrecognizemyextremeliabilitytoerror，andscarceevertrusttothefirstthoughtswhichoccurtome，yet—theexperienceIhavehadofpossibleobjectionstomyviewspreventsmefromanticipatinganyprofitfromthem。ForIhavealreadyhadfrequentproofofthejudgments，aswellofthoseIesteemedfriends，asofsomeotherstowhomIthoughtIwasanobjectofindifference，andevenofsomewhosemalignancyandenvywould，Iknew，determinethemtoendeavortodiscoverwhatpartialityconcealedfromtheeyesofmyfriends。ButithasrarelyhappenedthatanythinghasbeenobjectedtomewhichIhadmyselfaltogetheroverlooked，unlessitweresomethingfarremovedfromthesubject：sothatIhavenevermetwithasinglecriticofmyopinionswhodidnotappeartomeeitherlessrigorousorlessequitablethanmyself。
　　Andfurther，Ihaveneverobservedthatanytruthbeforeunknownhasbeenbroughttolightbythedisputationsthatarepractisedintheschools；
　　forwhileeachstrivesforthevictory，eachismuchmoreoccupiedinmakingthebestofmereverisimilitude，thaninweighingthereasonsonbothsidesofthequestion；andthosewhohavebeenlonggoodadvocatesarenotafterwardsonthataccountthebetterjudges。
　　Asfortheadvantagethatotherswouldderivefromthecommunicationofmythoughts，itcouldnotbeverygreat；becauseIhavenotyetsofarprosecutedthemasthatmuchdoesnotremaintobeaddedbeforetheycanbeappliedtopractice。AndIthinkImaysaywithoutvanity，thatifthereisanyonewhocancarrythemoutthatlength，itmustbemyselfratherthananother：notthattheremaynotbeintheworldmanymindsincomparablysuperiortomine，butbecauseonecannotsowellseizeathingandmakeitone’sown，whenithasbeenlearnedfromanother，aswhenonehashimselfdiscoveredit。Andsotrueisthisofthepresentsubjectthat，thoughIhaveoftenexplainedsomeofmyopinionstopersonsofmuchacuteness，who，whilstIwasspeaking，appearedtounderstandthemverydistinctly，yet，whentheyrepeatedthem，IhaveobservedthattheyalmostalwayschangedthemtosuchanextentthatIcouldnolongeracknowledgethemasmine。Iamglad，bytheway，totakethisopportunityofrequestingposteritynevertobelieveonhearsaythatanythinghasproceededfrommewhichhasnotbeenpublishedbymyself；andIamnotatallastonishedattheextravagancesattributedtothoseancientphilosopherswhoseownwritingswedonotpossess；whosethoughts，however，Idonotonthataccountsupposetohavebeenreallyabsurd，seeingtheywereamongtheablestmenoftheirtimes，butonlythatthesehavebeenfalselyrepresentedtous。Itisobservable，accordingly，thatscarcelyinasingleinstancehasanyoneoftheirdisciplessurpassedthem；andIamquitesurethatthemostdevotedofthepresentfollowersofAristotlewouldthinkthemselveshappyiftheyhadasmuchknowledgeofnatureashepossessed，wereitevenundertheconditionthattheyshouldneverafterwardsattaintohigher。Inthisrespecttheyareliketheivywhichneverstrivestoriseabovethetreethatsustainsit，andwhichfrequentlyevenreturnsdownwardswhenithasreachedthetop；foritseemstomethattheyalsosink，inotherwords，renderthemselveslesswisethantheywouldbeiftheygaveupstudy，who，notcontentedwithknowingallthatisintelligiblyexplainedintheirauthor，desireinadditiontofindinhimthesolutionofmanydifficultiesofwhichhesaysnotaword，andneverperhapssomuchasthought。Theirfashionofphilosophizing，however，iswellsuitedtopersonswhoseabilitiesfallbelowmediocrity；fortheobscurityofthedistinctionsandprinciplesofwhichtheymakeuseenablesthemtospeakofallthingswithasmuchconfidenceasiftheyreallyknewthem，andtodefendallthattheysayonanysubjectagainstthemostsubtleandskillful，withoutitsbeingpossibleforanyonetoconvictthemoferror。Inthistheyseemtometobelikeablindman，who，inordertofightonequaltermswithapersonthatsees，shouldhavemadehimdescendtothebottomofanintenselydarkcave：andImaysaythatsuchpersonshaveaninterestinmyrefrainingfrompublishingtheprinciplesofthephilosophyofwhichImakeuse；for，sincetheseareofakindthesimplestandmostevident，Ishould，bypublishingthem，domuchthesameasifIweretothrowopenthewindows，andallowthelightofdaytoenterthecaveintowhichthecombatantshaddescended。Butevensuperiormenhavenoreasonforanygreatanxietytoknowtheseprinciples，forifwhattheydesireistobeabletospeakofallthings，andtoacquireareputationforlearning，theywillgaintheirendmoreeasilybyremainingsatisfiedwiththeappearanceoftruth，whichcanbefoundwithoutmuchdifficultyinallsortsofmatters，thanbyseekingthetruthitselfwhichunfoldsitselfbutslowlyandthatonlyinsomedepartments，whileitobligesus，whenwehavetospeakofothers，freelytoconfessourignorance。If，however，theyprefertheknowledgeofsomefewtruthstothevanityofappearingignorantofnone，assuchknowledgeisundoubtedlymuchtobepreferred，and，iftheychoosetofollowacoursesimilartomine，theydonotrequireforthisthatI
　　shouldsayanythingmorethanIhavealreadysaidinthisdiscourse。ForiftheyarecapableofmakinggreateradvancementthanIhavemade，theywillmuchmorebeableofthemselvestodiscoverallthatIbelievemyselftohavefound；sinceasIhaveneverexaminedaughtexceptinorder，itiscertainthatwhatyetremainstobediscoveredisinitselfmoredifficultandrecondite，thanthatwhichIhavealreadybeenenabledtofind，andthegratificationwouldbemuchlessinlearningitfrommethanindiscoveringitforthemselves。Besidesthis，thehabitwhichtheywillacquire，byseekingfirstwhatiseasy，andthenpassingonwardslowlyandstepbysteptothemoredifficult，willbenefitthemmorethanallmyinstructions。Thus，inmyowncase，IampersuadedthatifIhadbeentaughtfrommyyouthallthetruthsofwhichIhavesincesoughtoutdemonstrations，andhadthuslearnedthemwithoutlabour，Ishouldnever，perhaps，haveknownanybeyondthese；atleast，IshouldneverhaveacquiredthehabitandthefacilitywhichIthinkIpossessinalwaysdiscoveringnewtruthsinproportionasIgivemyselftothesearch。
　　And，inasingleword，ifthereisanyworkintheworldwhichcannotbesowellfinishedbyanotherasbyhimwhohascommencedit，itisthatatwhichIlabour。
　　Itistrue，indeed，asregardstheexperimentswhichmayconducetothisend，thatonemanisnotequaltothetaskofmakingthemall；butyethecanadvantageouslyavailhimself，inthiswork，ofnohandsbesideshisown，unlessthoseofartisans，orpartiesofthesamekind，whomhecouldpay，andwhomthehopeofgain（ameansofgreatefficacy）mightstimulatetoaccuracyintheperformanceofwhatwasprescribedtothem。Forastothosewho，throughcuriosityoradesireoflearning，oftheirownaccord，perhaps，offerhimtheirservices，besidesthatingeneraltheirpromisesexceedtheirperformance，andthattheysketchoutfinedesignsofwhichnotoneiseverrealized，theywill，withoutdoubt，expecttobecompensatedfortheirtroublebytheexplicationofsomedifficulties，or，atleast，bycomplimentsanduselessspeeches，inwhichhecannotspendanyportionofhistimewithoutlosstohimself。Andasfortheexperimentsthatothershavealreadymade，evenalthoughthesepartiesshouldbewillingofthemselvestocommunicatethemtohim（whichiswhatthosewhoesteemthemsecretswillneverdo），theexperimentsare，forthemostpart，accompaniedwithsomanycircumstancesandsuperfluouselements，astomakeitexceedinglydifficulttodisentanglethetruthfromitsadjuncts—besides，hewillfindalmostallofthemsoilldescribed，orevensofalse（becausethosewhomadethemhavewishedtoseeinthemonlysuchfactsastheydeemedconformabletotheirprinciples），that，ifintheentirenumberthereshouldbesomeofanaturesuitedtohispurpose，stilltheirvaluecouldnotcompensateforthetimewhatwouldbenecessarytomaketheselection。Sothatifthereexistedanyonewhomweassuredlyknewtobecapableofmakingdiscoveriesofthehighestkind，andofthegreatestpossibleutilitytothepublic；
　　andifallothermenwerethereforeeagerbyallmeanstoassisthiminsuccessfullyprosecutinghisdesigns，Idonotseethattheycoulddoaughtelseforhimbeyondcontributingtodefraytheexpensesoftheexperimentsthatmightbenecessary；andfortherest，preventhisbeingdeprivedofhisleisurebytheunseasonableinterruptionsofanyone。ButbesidesthatIneitherhavesohighanopinionofmyselfastobewillingtomakepromiseofanythingextraordinary，norfeedonimaginationssovainastofancythatthepublicmustbemuchinterestedinmydesigns；
　　Idonot，ontheotherhand，ownasoulsomeanastobecapableofacceptingfromanyoneafavorofwhichitcouldbesupposedthatIwasunworthy。
　　Theseconsiderationstakentogetherwerethereasonwhy，forthelastthreeyears，IhavebeenunwillingtopublishthetreatiseIhadonhand，andwhyIevenresolvedtogivepublicityduringmylifetonootherthatwassogeneral，orbywhichtheprinciplesofmyphysicsmightbeunderstood。Butsincethen，twootherreasonshavecomeintooperationthathavedeterminedmeheretosubjoinsomeparticularspecimens，andgivethepublicsomeaccountofmydoingsanddesigns。Oftheseconsiderations，thefirstis，thatifIfailedtodoso，manywhowerecognizantofmypreviousintentiontopublishsomewritings，mighthaveimaginedthatthereasonswhichinducedmetorefrainfromsodoing，werelesstomycreditthantheyreallyare；foralthoughIamnotimmoderatelydesirousofglory，oreven，ifImayventuresotosay，althoughIamaversefromitinsofarasIdeemithostiletoreposewhichIholdingreateraccountthanaughtelse，yet，atthesametime，Ihaveneversoughttoconcealmyactionsasiftheywerecrimes，normadeuseofmanyprecautionsthatImightremainunknown；andthispartlybecauseIshouldhavethoughtsuchacourseofconductawrongagainstmyself，andpartlybecauseitwouldhaveoccasionedmesomesortofuneasinesswhichwouldagainhavebeencontrarytotheperfectmentaltranquillitywhichIcourt。
　　Andforasmuchas，whilethusindifferenttothethoughtalikeoffameorofforgetfulness，Ihaveyetbeenunabletopreventmyselffromacquiringsomesortofreputation，Ihavethoughtitincumbentonmetodomybesttosavemyselfatleastfrombeingill—spokenof。Theotherreasonthathasdeterminedmetocommittowritingthesespecimensofphilosophyis，thatIambecomingdailymoreandmorealivetothedelaywhichmydesignofself—instructionsuffers，forwantoftheinfinityofexperimentsI
　　require，andwhichitisimpossibleformetomakewithouttheassistanceofothers：and，withoutflatteringmyselfsomuchastoexpectthepublictotakealargeshareinmyinterests，IamyetunwillingtobefoundsofarwantinginthedutyIowetomyself，astogiveoccasiontothosewhoshallsurvivemetomakeitmatterofreproachagainstmesomeday，thatI
　　mighthaveleftthemmanythingsinamuchmoreperfectstatethanIhavedone，hadInottoomuchneglectedtomakethemawareofthewaysinwhichtheycouldhavepromotedtheaccomplishmentofmydesigns。
　　AndIthoughtthatitwaseasyformetoselectsomematterswhichshouldneitherbeobnoxioustomuchcontroversy，norshouldcompelmetoexpoundmoreofmyprinciplesthanIdesired，andwhichshouldyetbesufficientclearlytoexhibitwhatIcanorcannotaccomplishinthesciences。
　　WhetherornotIhavesucceededinthisitisnotformetosay；andIdonotwishtoforestallthejudgmentsofothersbyspeakingmyselfofmywritings；butitwillgratifymeiftheybeexamined，and，toaffordthegreaterinducementtothisIrequestallwhomayhaveanyobjectionstomaketothem，totakethetroubleofforwardingthesetomypublisher，whowillgivemenoticeofthem，thatImayendeavortosubjoinatthesametimemyreply；andinthiswayreadersseeingbothatoncewillmoreeasilydeterminewherethetruthlies；forIdonotengageinanycasetomakeprolixreplies，butonlywithperfectfranknesstoavowmyerrorsifIamconvincedofthem，orifIcannotperceivethem，simplytostatewhatI
　　thinkisrequiredfordefenseofthemattersIhavewritten，addingtheretonoexplicationofanynewmattethatitmaynotbenecessarytopasswithoutendfromonethingtoanother。
　　IfsomeofthemattersofwhichIhavespokeninthebeginningofthe"Dioptrics"and"Meteorics"shouldoffendatfirstsight，becauseIcallthemhypothesesandseemindifferentaboutgivingproofofthem，Irequestapatientandattentivereadingofthewhole，fromwhichIhopethosehesitatingwillderivesatisfaction；foritappearstomethatthereasoningsaresomutuallyconnectedinthesetreatises，that，asthelastaredemonstratedbythefirstwhicharetheircauses，thefirstareintheirturndemonstratedbythelastwhicharetheireffects。NormustitbeimaginedthatIherecommitthefallacywhichthelogicianscallacircle；forsinceexperiencerendersthemajorityoftheseeffectsmostcertain，thecausesfromwhichIdeducethemdonotservesomuchtoestablishtheirrealityastoexplaintheirexistence；butonthecontrary，therealityofthecausesisestablishedbytherealityoftheeffects。NorhaveIcalledthemhypotheseswithanyotherendinviewexceptthatitmaybeknownthatIthinkIamabletodeducethemfromthosefirsttruthswhichIhavealreadyexpounded；andyetthatIhaveexpresslydeterminednottodoso，topreventacertainclassofmindsfromthencetakingoccasiontobuildsomeextravagantphilosophyuponwhattheymaytaketobemyprinciples，andmybeingblamedforit。Irefertothosewhoimaginethattheycanmasterinadayallthatanotherhastakentwentyyearstothinkout，assoonashehasspokentwoorthreewordstothemonthesubject；orwhoarethemoreliabletoerrorandthelesscapableofperceivingtruthinveryproportionastheyaremoresubtleandlively。Astotheopinionswhicharetrulyandwhollymine，Ioffernoapologyforthemasnew，——persuadedasIamthatiftheirreasonsbewellconsideredtheywillbefoundtobesosimpleandsoconformed，tocommonsenseastoappearlessextraordinaryandlessparadoxicalthananyotherswhichcanbeheldonthesamesubjects；nordoIevenboastofbeingtheearliestdiscovererofanyofthem，butonlyofhavingadoptedthem，neitherbecausetheyhadnorbecausetheyhadnotbeenheldbyothers，butsolelybecausereasonhasconvincedmeoftheirtruth。
　　Thoughartisansmaynotbeableatoncetoexecutetheinventionwhichisexplainedinthe"Dioptrics，"Idonotthinkthatanyoneonthataccountisentitledtocondemnit；forsinceaddressandpracticearerequiredinordersotomakeandadjustthemachinesdescribedbymeasnottooverlookthesmallestparticular，Ishouldnotbelessastonishediftheysucceededonthefirstattemptthanifapersonwereinonedaytobecomeanaccomplishedperformerontheguitar，bymerelyhavingexcellentsheetsofmusicsetupbeforehim。AndifIwriteinFrench，whichisthelanguageofmycountry，inpreferencetoLatin，whichisthatofmypreceptors，itisbecauseIexpectthatthosewhomakeuseoftheirunprejudicednaturalreasonwillbebetterjudgesofmyopinionsthanthosewhogiveheedtothewritingsoftheancientsonly；andasforthosewhounitegoodsensewithhabitsofstudy，whomaloneIdesireforjudges，theywillnot，Ifeelassured，besopartialtoLatinastorefusetolistentomyreasoningsmerelybecauseIexpoundtheminthevulgartongue。
　　Inconclusion，IamunwillingheretosayanythingveryspecificoftheprogresswhichIexpecttomakeforthefutureinthesciences，ortobindmyselftothepublicbyanypromisewhichIamnotcertainofbeingabletofulfill；butthisonlywillIsay，thatIhaveresolvedtodevotewhattimeImaystillhavetolivetonootheroccupationthanthatofendeavoringtoacquiresomeknowledgeofNature，whichshallbeofsuchakindastoenableustherefromtodeducerulesinmedicineofgreatercertaintythanthoseatpresentinuse；andthatmyinclinationissomuchopposedtoallotherpursuits，especiallytosuchascannotbeusefultosomewithoutbeinghurtfultoothers，thatif，byanycircumstances，Ihadbeenconstrainedtoengageinsuch，IdonotbelievethatIshouldhavebeenabletosucceed。OfthisIheremakeapublicdeclaration，thoughwellawarethatitcannotservetoprocureformeanyconsiderationintheworld，which，however，Idonotintheleastaffect；andIshallalwaysholdmyselfmoreobligedtothosethroughwhosefavorIampermittedtoenjoymyretirementwithoutinterruptionthantoanywhomightoffermethehighestearthlypreferments。