69。Farther，theairbeingvariouslyimpregnated，sometimesmoreandsometimesless，withvapoursandexhalationsfittedtoretundandintercepttheraysoflight，itfollowsthattheappearanceofthehorizontalmoonhathnotalwaysanequalfaintness，andbyconsequencethatluminary，thoughintheverysamesituation，isatonetimejudgedgreaterthanatanother。
70。Thatwehaveheregiventhetrueaccountofthephenomenaofthehorizontalmoonwill，Isuppose，befartherevidenttoanyonefromthefollowingconsiderations。First，itisplainthatwhichinthiscasesuggeststheideaofgreatermagnitudemustbesomethingwhichisitselfperceived；forthatwhichisunperceivedcannotsuggesttoourperceptionanyotherthing。Secondly，itmustbesomethingthatdoesnotconstantlyremainthesame，butissubjecttosomechangeorvariation，sincetheappearanceofthehorizontalmoonvaries，beingatonetimegreaterthanatanother。Andyet，thirdly，itcannotbethevisiblefigureormagnitude，sincethatremainsthesame，orisratherlesser，byhowmuchthemoonisnearertothehorizon。Itremainsthereforethatthetruecauseisthataffectionoralterationofthevisibleappearancewhichproceedsfromthegreaterpaucityofraysarrivingattheeye，andwhichItermfaintness：sincethisanswersalltheforementionedconditions，andIamnotconsciousofanyotherperceptionthatdoth。
71。Addtothisthatinmistyweatheritisacommonobservationthattheappearanceofthehorizontalmoonisfarlargerthanusual，whichgreatlyconspireswithandstrengthensouropinion。Neitherwoulditproveintheleastirreconcilablewithwhatwehavesaid，ifthehorizontalmoonshouldchancesometimestoseemenlargedbeyonditsusualextent，eveninmoresereneweather。Forwemustnotonlyhaveregardtothemistwhichhappenstobeintheplacewherewestand；weoughtalsototakeintoourthoughtsthewholesumofvapoursandexhalationswhichliebetwixttheeyeandthemoon：allwhichcooperatingtorendertheappearanceofthemoonmorefaint，andtherebyincreaseitsmagnitude，itmaychancetoappeargreaterthanitusuallydoes，eveninthehorizontalposition，atatimewhen，thoughtherebenoextraordinaryfogorhaziness，justintheplacewherewestand，yettheairbetweentheeyeandthemoon，takenalltogether，maybeloadedwithagreaterquantityofinterspersedvapoursandexhalationsthanatothertimes。
72。Itmaybeobjectedthatinconsequenceofourprinciplestheinterpositionofabodyinsomedegreeopaque，whichmayinterceptagreatpartoftheraysoflight，shouldrendertheappearanceofthemooninthemeridianaslargeaswhenitisviewedinthehorizon。TowhichIanswer，itisnotfaintnessanyhowappliedthatsuggestsgreatermagnitude，therebeingnonecessarybutonlyanexperimentalconnexionbetweenthosetwothings。
Itfollowsthatthefaintnesswhichenlargestheappearancemustbeappliedinsuchsort，andwithsuchcircumstances，ashavebeenobservedtoattendthevisionofgreatmagnitudes。Whenfromadistancewebeholdgreatobjects，theparticlesoftheintermediateairandvapours，whicharethemselvesunperceivable，dointerrupttheraysoflight，andtherebyrendertheappearancelessstrongandvivid：now，faintnessofappearancecausedinthissorthathbeenexperiencedtocoexistwithgreatmagnitude。Butwhenitiscausedbytheinterpositionofanopaquesensiblebody，thiscircumstancealtersthecase，sothatafaintappearancethiswaycauseddothnotsuggestgreatermagnitude，becauseithathnotbeenexperiencedtocoexistwithit。
73。Faintness，aswellasallotherideasorperceptionswhichsuggestmagnitudeordistance，dothitinthesamewaythatwordssuggestthenotionstowhichtheyareannexed。Now，itisknownawordpronouncedwithcertaincircumstances，orinacertaincontextwithotherwords，hathnotalwaysthesameimportandsignificationthatithathwhenpronouncedinsomeothercircumstancesordifferentcontextofwords。Theverysamevisibleappearanceastofaintnessandallotherrespects，ifplacedonhigh，shallnotsuggestthesamemagnitudethatitwouldifitwereseenatanequaldistanceonalevelwiththeeye。Thereasonwhereofisthatwearerarelyaccustomedtoviewobjectsatagreatheight；ourconcernslieamongthingssituatedratherbeforethanaboveus，andaccordinglyoureyesarenotplacedonthetopofourheads，butinsuchapositionasismostconvenientforustoseedistantobjectsstandinginourway。Andthissituationofthembeingacircumstancewhichusuallyattendsthevisionofdistantobjects，wemayfromhenceaccountfor（whatiscommonlyobserved）anobject’sappearingofdifferentmagnitude，evenwithrespecttoitshorizontalextension，onthetopofasteeple，forexample，anhundredfeethightoonestandingbelow，fromwhatitwouldifplacedatanhundredfeetdistanceonalevelwithhiseye。Forithathbeenshewnthatthejudgmentwemakeonthemagnitudeofathingdependsnotonthevisibleappearancealone，butalsoondiversothercircumstances，anyoneofwhichbeingomittedorvariedmaysufficetomakesomealterationinourjudgment。Hence，thecircumstancesofviewingadistantobjectinsuchasituationasisusual，andsuitswiththeordinarypostureoftheheadandeyesbeingomitted，andinsteadthereofadifferentsituationoftheobject，whichrequiresadifferentpostureoftheheadtakingplace，itisnottobewonderedatifthemagnitudebejudgeddifferent：
butitwillbedemandedwhyanhighobjectshouldconstantlyappearlessthananequidistantlowobjectofthesamedimensions，forsoitisobservedtobe：itmayindeedbegrantedthatthevariationofsomecircumstancesmayvarythejudgmentmadeonthemagnitudeofhighobjects，whichwearelessusedtolookat：butitdoesnothenceappearwhytheyshouldbejudgedlessratherthangreater？Ianswerthatincasethemagnitudeofdistantobjectswassuggestedbytheextentoftheirvisibleappearancealone，andthoughtproportionalthereto，itiscertaintheywouldthenbejudgedmuchlessthannowtheyseemtobe（videsect。79）·；Butseveralcircumstancesconcurringtoformthejudgmentwemakeonthemagnitudeofdistantobjects，bymeansofwhichtheyappearfarlargerthanothers，whosevisibleappearancehathanequalorevengreaterextension；itfollowsthatuponthechangeoromissionofanyofthosecircumstanceswhicharewonttoattendthevisionofdistantobjects，andsocometoinfluencethejudgmentsmadeontheirmagnitude，theyshallproportionablyappearlessthanotherwisetheywould。Foranyofthosethingsthatcausedanobjecttobethoughtgreaterthaninproportiontoitsvisibleextensionbeingeitheromittedorappliedwithouttheusualcircumstances，thejudgmentdependsmoreentirelyonthevisibleextension，andconsequentlytheobjectmustbejudgedless。Thusinthepresentcasethesituationofthethingseenbeingdifferentfromwhatitusuallyisinthoseobjectswehaveoccasiontoview，andwhosemagnitudeweobserve，itfollowsthattheverysameobject，beinganhundredfeethigh，shouldseemlessthanifitwasanhundredfeetoffon（ornearlyon）alevelwiththeeye。Whathasbeenheresetforthseemstometohavenosmallshareincontributingtomagnifytheappearanceofthehorizontalmoon，anddeservesnottobepassedoverintheexplicationofit。
74。Ifweattentivelyconsiderthephenomenonbeforeus，weshallfindthenotdiscerningbetweenthemediateandimmediateobjectsofsighttobethechiefcauseofthedifficultythatoccursintheexplicationofit。Themagnitudeofthevisiblemoon，orthatwhichistheproperandimmediateobjectofvision，isnotgreaterwhenthemoonisinthehorizonthanwhenitisinthemeridian。Howcomesit，therefore，toseemgreaterinonesituationthantheother？Whatisitcanputthischeatontheunderstanding？
Ithasnootherperceptionofthemoonthanwhatitgetsbysight：andthatwhichisseenisofthesameextent，Isay，thevisibleappearancehaththesame，orratheraless，magnitudewhenthemoonisviewedinthehorizontalthanwheninthemeridionalposition：andyetitisesteemedgreaterintheformerthaninthelatter。Hereinconsiststhedifficulty，whichdothvanishandadmitofamosteasysolution，ifweconsiderthatasthevisiblemoonisnotgreaterinthehorizonthaninthemeridian，soneitherisitthoughttobeso。Ithathbeenalreadyshewnthatinanyactofvisionthevisibleobjectabsolutely，orinitself，islittletakennoticeof，themindstillcarryingitsviewfromthattosometangibleideaswhichhavebeenobservedtobeconnectedwithit，andbythatmeanscometobesuggestedbyit。Sothatwhenathingissaidtoappeargreatorsmall，orwhateverestimatebemadeofthemagnitudeofanything，thisismeantnotofthevisiblebutofthetangibleobject。Thisdulyconsidered，itwillbenohardmattertoreconciletheseemingcontradictionthereis，thatthemoonshouldappearofadifferentbigness，thevisiblemagnitudethereofremainingstillthesame。Forbysect。56theverysamevisibleextension，withadifferentfaintness，shallsuggestadifferenttangibleextension。Whenthereforethehorizontalmoonissaidtoappeargreaterthanthemeridionalmoon，thismustbeunderstoodnotofagreatervisibleextension，butaofgreatertangibleorrealextension，whichbyreasonofthemorethanordinaryfaintnessofthevisibleappearance，issuggestedtothemindalongwithit。
75。Manyattemptshavebeenmadebylearnedmentoaccountforthisappearance。Gassendus，Descartes，Hobbes，andseveralothershaveemployedtheirthoughtsonthatsubject；buthowfruitlessandunsatisfactorytheirendeavourshavebeenissufficientlyshewninThePhilosophicalTransactions，[4]
whereyoumayseetheirseveralopinionsatlargesetforthandconfuted，notwithoutsomesurprizeatthegrossblundersthatingeniousmenhavebeenforcedintobyendeavouringtoreconcilethisappearancewiththeordinaryPrinciplesofoptics。SincethewritingofwhichtherehathbeenpublishedintheTransactions[5]anotherpaperrelatingtothesameaffairbythecelebratedDr。Wallis，whereinheattemptstoaccountforthatphenomenonwhich，thoughitseemsnottocontainanythingnewordifferentfromwhathadbeensaidbeforebyothers，Ishallneverthelessconsiderinthisplace。
76。Hisopinion，inshort，isthis；wejudgenotofthemagnitudeofanobjectbythevisualanglealone，butbythevisualangleinconjunctionwiththedistance。Hence，thoughtheangleremainthesame，orevenbecomeless，yetifwithalthedistanceseemtohavebeenincreased，theobjectshallappeargreater。Now，onewaywherebyweestimatethedistanceofanythingisbythenumberandextentoftheintermediateobjects：whenthereforethemoonisseeninthehorizon，thevarietyoffields，houses，etc。，togetherwiththelargeprospectofthewideextendedlandorseathatliesbetweentheeyeandtheutmostlimbofthehorizon，suggestuntothemindtheideaofgreaterdistance，andconsequentlymagnifytheappearance。
Andthis，accordingtoDr。Wallis，isthetrueaccountoftheextraordinarylargenessattributedbythemindtothehorizontalmoonatatimewhentheanglesubtendedbyitsdiameterisnotonejotgreaterthanitusedtobe。
77。Withreferencetothisopinion，nottorepeatwhathathbeenalreadysaidconcerningdistance，Ishallonlyobserve，first，thatiftheprospectofinterjacentobjectsbethatwhichsuggeststheideaoffartherdistance，andthisideaoffartherdistancebethecausethatbringsintothemindtheideaofgreatermagnitude，itshouldhencefollowthatifonelookedatthehorizontalmoonfrombehindawall，itwouldappearnobiggerthanordinary。Forinthatcasethewallinterposingcutsoffallthatprospectofseaandland，etc。whichmightotherwiseincreasetheapparentdistance，andtherebytheapparentmagnitudeofthemoon。Norwillitsufficetosaythememorydotheventhensuggestallthatextentofland，etc。，whichlieswithinthehorizon；whichsuggestionoccasionsasuddenjudgmentofsensethatthemoonisfartheroffandlargerthanusual。Foraskanymanwho，fromsuchastationbeholdingthehorizontalmoon，shallthinkhergreaterthanusual，whetherhehathatthattimeinhismindanyideaoftheintermediateobjects，orlongtractoflandthatliesbetweenhiseyeandtheextremeedgeofthehorizon？Andwhetheritbethatideawhichisthecauseofhismakingtheaforementionedjudgment？
Hewill，Isuppose，replyinthenegative，anddeclarethehorizontalmoonshallappeargreaterthanthemeridional，thoughheneverthinksofalloranyofthosethingsthatliebetweenhimandit。Secondly，itseemsimpossiblebythishypothesistoaccountforthemoon’sappearingintheverysamesituationatonetimegreaterthanatanother；whichneverthelesshasbeenshewntobeveryagreeabletotheprincipleswehavelaiddown，andreceivesamosteasyandnaturalexplicationfromthem。Forthefurtherclearing’upofthispointitistobeobservedthatwhatweimmediatelyandproperlyseeareonlylightsandcoloursinsundrysituationsandshadesanddegreesoffaintnessandclearness，confusionanddistinctness。Allwhichvisibleobjectsareonlyinthemind，nordotheysuggestoughtexternal，whetherdistanceormagnitude，otherwisethanbyhabitualconnexionaswordsdothings。Wearealsotoremarkthat，besidethestrainingoftheeyes，andbesidethevividandfaint，thedistinctandconfusedappearances（which，bearingsomeproportiontolinesandangles，havebeensubstitutedinsteadofthemintheforegoingpartofthistreatise），thereareothermeanswhichsuggestbothdistanceandmagnitude；particularlythesituationofvisiblepointsofobjects，asupperorlower；theonesuggestingafartherdistanceandgreatermagnitude，theotheranearerdistanceandlessermagnitude：allwhichisaneffectonlyofcustomandexperience；therebeingreallynothingintermediateinthelineofdistancebetweentheuppermostandlowermost，whicharebothequidistant，orratheratnodistancefromtheeye，asthereisalsonothinginupperorlower，whichbynecessaryconnexionshouldsuggestgreaterorlessermagnitude。Now，asthesecustomary，experimentalmeansofsuggestingdistancedolikewisesuggestmagnitude，sotheysuggesttheoneasimmediatelyastheother。Isaytheydonot（videsect。53）firstsuggestdistance，andthenleavethemindfromthencetoinferorcomputemagnitude，jutsuggestmagnitudeasimmediatelyanddirectlyastheysuggestdistance。
78。Thisphenomenonofthehorizontalmoonisaclearinstanceoftheinsufficiencyoflinesandanglesforexplainingthewaywhereinthemindperceivesandestimatesthemagnitudeofoutwardobjects。Thereisneverthelessauseofcomputationbytheminordertodeterminetheapparentmagnitudeofthings，sofarastheyhaveaconnexionwith，andareproportionalto，thoseotherideasorperceptionswhicharethetrueandimmediateoccasionsthatsuggesttothemindtheapparentmagnitudeofthings。Butthisingeneralmay，Ithink，beobservedconcerningmathematicalcomputationinoptics：thatitcanneverbeverypreciseandexactsincethejudgmentswemakeofthemagnitudeofexternalthingsdooftendependonseveralcircumstances，whicharenotproportionableto，orcapableofbeingdefinedby，linesandangles。
79。Fromwhathasbeensaidwemaysafelydeducethisconsequence；towit，thatamanbornblindandmadetoseewould，atfirstopeningofhiseyes，makeaverydifferentjudgmentofthemagnitudeofobjectsintromittedbythemfromwhatothersdo。Hewouldnotconsidertheideasofsightwithreferenceto，orashavinganyconnexionwith，theideasoftouch：hisviewofthembeingentirelyterminatedwithinthemselves，hecannootherwisejudgethemgreatorsmallthanastheycontainagreaterorlessernumberofvisiblepoints。Now，itbeingcertainthatanyvisiblepointcancoverorexcludefromviewonlyoneothervisiblepoint，itfollowsthatwhateverobjectinterceptstheviewofanotherhathanequalnumberofvisiblepointswithit；andconsequentlytheyshallbothbethoughtbyhimtohavethesamemagnitude。Henceitisevidentoneinthosecircumstanceswouldjudgehisthumb，withwhichhemighthideatowerorhinderitsbeingseen，equaltothattower，orhishand，theinterpositionwhereofmightconcealexperimentalmeansthefirmamentfromhisview，equaltothefirmament：howgreataninequalitysoevertheremayinourapprehensionsseemtobebetwixtthosetwothings，becauseofthecustomaryandcloseconnexionthathasgrownupinourmindsbetweentheobjectsofsightandtouch；wherebytheverydifferentanddistinctideasofthosetwosensesaresoblendedandconfoundedtogetherastobemistakenforoneandthesamething；outofwhichprejudicewecannoteasilyextricateourselves。
80。Forthebetterexplainingthenatureofvision，andsettingthemannerwhereinweperceivemagnitudesinaduelight，Ishallproceedtomakesomeobservationsconcerningmattersrelatingthereto，whereofthewantofreflexion，anddulyseparatingbetweentangibleandvisibleideas，isapttocreateinusmistakenandconfusednotions。Andfirst，Ishallobserve·；thattheminimumvisibileisexactlyequalinallbeingswhatsoeverthatareendowedwiththevisivefaculty。
Noexquisiteformationoftheeye，nopeculiarsharpnessofsight，canmakeitlessinonecreaturethaninanother；foritnotbeingdistinguishableintoparts，norinanywiseaconsistingofthem，itmustnecessarilybethesametoall。Forsupposeitotherwise，andthattheminimumvisibileofamite，forinstance，belessthantheminimumvisibileofaman：thelatterthereforemaybydetractionofsomepartbemadeequaltotheformer：itdoththereforeconsistofparts，whichisinconsistentwiththenotionofaminimumvisibileorpoint。
81。Itwillperhapsbeobjectedthattheminimumvisibileofamandothreallyandinitselfcontainpartswherebyitsurpassesthatofamite，thoughtheyarenotperceivablebytheman。TowhichIanswer，theminimumvisibilehaving（inlikemannerasallothertheproperandimmediateobjectsofsight）beenshewnnottohaveanyexistencewithoutthemindofhimwhoseesit，itfollowstherecannotbeanypanofitthatisnotactuallyperceived，andthereforevisible。Nowforanyobjecttocontaindistinctvisibleparts，andatthesametimetobeaminimumvisibile，isamanifestcontradiction。
82。Ofthesevisiblepointsweseeatalltimesanequalnumber。Itiseverywhitasgreatwhenourviewiscontractedandboundedbynearobjectsaswhenitisextendedtolargerandremoter。Foritbeingimpossiblethatoneminimumvisibileshouldobscureorkeepoutofsightmotethanoneother，itisaplainconsequencethatwhenmyviewisonallsidesboundedbythewallsofmystudyseejustasmanyvisiblepointsasIcould，incasethatbytheremovalofthestudy—wallsandallotherobstructions，Ihadafullprospectofthecircumjacentfields，mountains，sea，andopenfirmament：forsolongasIamshutupwithinthewalls，bytheirinterpositioneverypointoftheexternalobjectsiscoveredfrommyview：buteachpointthatisseenbeingabletocoverorexcludefromsightoneonlyothercorrespondingpoint，itfollowsthatwhilstmysightisconfinedtothosenarrowwallsIseeasmanypoints，orminimavisibilia，asIshouldwerethosewallsaway，bylookingonalltheexternalobjectswhoseprospectisinterceptedbythem。Wheneverthereforewearesaidtohaveagreaterprospectatonetimethananother，thismustbeunderstoodwithrelation，nottotheproperandimmediate，butthesecondaryandmediateobjectsofvision，which，ashathbeenshewn，properlybelongtothetouch。
83。Thevisivefacultyconsideredwithreferencetoitsimmediateobjectsmaybefoundtolabouroftwodefects。First，inrespectoftheextentornumberofvisiblepointsthatareatonceperceivablebyit，whichisnarrowandlimitedtoacertaindegree。Itcantakeinatoneviewbutacertaindeterminatenumberofminimavisibilia，beyondwhichitcannotextenditsprospect。Secondly，oursightisdefectiveinthatitsviewisnotonlynarrow，butalsoforthemostpartconfused：
ofthosethingsthatwetakeinatoneprospectwecanseebutafewatonceclearlyandunconfusedly：andthemorewefixoursightonanyoneobject，bysomuchthedarkerandmoreindistinctshalltherestappear。
84。Correspondingtothesetwodefectsofsight，wemayimagineasmanyperfections，towit，1st，thatofcomprehendinginoneviewagreaternumberofvisiblepoints。2dly，ofbeingabletoviewthemallequallyandatoncewiththeutmostclearnessanddistinction。Thatthoseperfectionsarenotactuallyinsomeintelligencesofadifferentorderandcapacityfromoursitisimpossibleforustoknow。
85。Inneitherofthosetwowaysdomicroscopescontributetotheimprovementofsight；forwhenwelookthroughamicroscopeweneitherseemorevisiblepoints，norarethecollateralpointsmoredistinctthanwhenwelookwiththenakedeyeatobjectsplacedinaduedistance。Amicroscopebringsus，asitwere，intoanewworld：itpresentsuswithanewsceneofvisibleobjectsquitedifferentfromwhatwebeholdwiththenakedeye。Buthereinconsiststhemostremarkabledifference，towit，thatwhereastheobjectsperceivedbytheeyealonehaveacertainconnexionwithtangibleobjects，wherebywearetaughttoforeseewhatwillensueupontheapproachorapplicationofdistantobjectstothepartsofourownbody，whichmuchconducethtoitspreservation，thereisnotthelikeconnexionbetweenthingstangibleandthosevisibleobjectsthatareperceivedbyhelpofafinemicroscope。
86。Henceitisevidentthatwereoureyesturnedintothenatureofmicroscopes，weshouldnotbemuchbenefitedbythechange；weshouldbedeprivedoftheforementionedadvantageweatpresentreceivebythevisivefaculty，andhaveleftusonlytheemptyamusementofseeing，withoutanyotherbenefitarisingfromit。Butinthatcase，itwillperhapsbesaid，oursightwouldbeenduedwithafargreatersharpnessandpenetrationthanitnowhath。Butitiscertainfromwhatwehavealreadyshewnthattheminimumvisibileisnevergreaterorlesser，butinallcasesconstantlythesame：andinthecaseofmicroscopicaleyesIseeonlythisdifference，towit，thatupontheceasingofacertainobservableconnexionbetwixtthediversperceptionsofsightandtouch，whichbeforeenabledustoregulateouractionsbytheeye，itwouldnowberenderedutterlyunserviceabletothatpurpose。
87。Uponthewholeitseemsthatifweconsidertheuseandendofsight，togetherwiththepresentstateandcircumstancesofourbeing，weshallnotfindanygreatcausetocomplainofanydefectorimperfectioninit，oreasilyconceivehowitcouldbemended。Withsuchadmirablewisdomisthatfacultycontrived，bothforthepleasureandconvenienceoflife。
88。HavingfinishedwhatIintendedtosayconcerningthedistanceandmagnitudeofobjects，Icomenowtotreatofthemannerwhereinthemindperceivesbysighttheirsituation。Amongthediscoveriesofthelastage，itisreputednoneoftheleastthatthemannerofvisionhathbeenmoreclearlyexplainedthaneverithadbeenbefore。Thereisatthisdaynooneignorantthatthepicturesofexternalobjectsarepaintedontheretina，orfundoftheeye：thatwecanseenothingwhichisnotsopainted：andthat，accordingasthepictureismoredistinctorconfused，soalsoistheperceptionwehaveoftheobject：buttheninthisexplicationofvisionthereoccursonemightydifficulty。Theobjectsarepaintedinaninvertedorderonthebottomoftheeye：theupperpartofanyobjectbeingpaintedonthelowerpartoftheeye，andthelowerpartoftheobjectontheupperpartoftheeye：andsoalsoastorightandleft。Sincethereforethepicturesarethusinverted，itisdemandedhowitcomestopassthatweseetheobjectserectandintheirnaturalposture？
89。Inanswertothisdifficultywearetoldthatthemind，perceivinganimpulseofarayoflightontheupperpartoftheeye，considersthisrayascominginadirectlinefromthelowerpartoftheobject；andinlikemannertracingtheraythatstrikesonthelowerpartoftheeye，itisdirectedtotheupperpartoftheobject。Thusintheadjacentfigure，C，thelowerpointoftheobjectABC，isprojectedonctheupperpartoftheeye。SolikewisethehighestpointAisprojectedonathelowestpartoftheeye，whichmakestherepresentationcbainverted：
butthemindconsideringthestrokethatismadeoncascominginthestraightlineCcfromthelowerendoftheobject；andthestrokeorimpulseonaascominginthelineAafromtheupperendoftheobject，isdirectedtomakearightjudgmentofthesituationoftheobjectABC，notwithstandingthepictureofitisinverted。Thisisillustratedbyconceivingablindmanwho，holdinginhishandstwosticksthatcrosseachother，dothwiththemtouchtheextremitiesofanobject，placedinaperpendicularsituation。Itiscertainthismanwilljudgethattobetheupperpartoftheobjectwhichhetoucheswiththestickheldintheundermosthand，andthattobethelowerpartoftheobjectwhichhetoucheswiththestickinhisuppermosthand。Thisisthecommonexplicationoftheerectappearanceofobjects，whichisgenerallyreceivedandacquiescedin，being（asMr。Molyneuxtellsus[6]）’allowedbyallmenassatisfactory’。
90。Butthisaccounttomedoesnotseeminanydegreetrue。DidIperceivethoseimpulses，decussations，anddirectionsoftheraysoflightinlikemannerashathbeensetforth，thenindeeditwouldnotbealtogethervoidofprobability。Andtheremightbesomepretenceforthecomparisonoftheblindmanandhiscrosssticks。Butthecaseisfarotherwise。IknowverywellthatIperceivenosuchthing。AndofconsequenceIcannottherebymakeanestimateofthesituationofobjects。Iappealtoanyone’sexperience，whetherhebeconscioustohimselfthathethinksontheintersectionmadebytheradious[sic]pencils，orpursuestheimpulsestheygiveinrightlines，wheneverheperceivesbysightthepositionofanyobject？
Tomeitseemsevidentthatcrossingandtracingoftheraysisneverthoughtonbychildren，idiots，orintruthbyanyother，saveonlythosewhohaveappliedthemselvestothestudyofoptics。Andforthemindtojudgeofthesituationofobjectsbythosethingswithoutperceivingthem，ortoperceivethemwithoutknowingit，isequallybeyondmycomprehension。Addtothisthattheexplainingthemannerofvisionbytheexampleofcrosssticksandhuntingfortheobjectalongtheaxesoftheradiouspencils，dothsupposetheproperobjectsofsighttobeperceivedatadistancefromus，contrarytowhathathbeendemonstrated。
91。Itremains，therefore，thatwelookforsomeotherexplicationofthisdifficulty：andIbelieveitnotimpossibletofindone，providedweexamineittothebottom，andcarefullydistinguishbetweentheideasofsightandtouch；whichcannotbetoooftinculcatedintreatingofvision：
butmoreespeciallythroughouttheconsiderationofthisaffairweoughttocarrythatdistinctioninourthoughts：forthatfromwantofarightunderstandingthereofthedifficultyofexplainingerectvisionseemschieflytoarise。
92。Inordertodisentangleourmindsfromwhateverprejudiceswemayentertainwithrelationtothesubjectinhand，nothingseemsmoreappositethanthetakingintoourthoughtsthecaseofonebornblind，andafterwards，whengrownup，madetosee。Andthough，perhaps，itmaynotbeaneasytasktodivestourselvesentirelyoftheexperiencereceivedfromsight，soastobeabletoputourthoughtsexactlyinthepostureofsuchaone’s，wemust，nevertheless，asfaraspossible，endeavourtoframetrueconceptionsofwhatmightreasonablybesupposedtopassinhismind。
93。Itiscertainthatamanactuallyblind，andwhohadcontinuedsofromhisbirth，wouldbythesenseoffeelingattaintohaveideasofupperandlower。BythemotionofhishandhemightdiscernthesituationofanytangibleobjectplacedwithinhisFIreach。Thatpartonwhichhefelthimselfsupported，ortowardswhichheperceivedhisbodytogravitate，hewouldtermlower，andthecontrarytothisupper；andaccordinglydenominatewhatsoeverobjectshetouched。
94。Butthen，whateverjudgmentshemakesconcerningthesituationofobjectsareconfinedtothoseonlythatareperceivablebytouch。Allthosethingsthatareintangibleandofaspiritualnature，histhoughtsanddesires，hispassions，andingeneralallthemodificationsofthesoul，tothesehewouldneverapplythetermsupperandlower，exceptonlyinametaphoricalsense。Hemay，perhaps，bywayofallusion，speakofhighorlowthoughts：butthosetermsintheirpropersignificationwouldneverbeappliedtoanythingthatwasnotconceivedtoexistwithoutthemind。Foramanbornblind，andremaininginthesamestate，couldmeannothingelsebythewordshigherandlowerthanagreaterorlesserdistancefromtheearth；whichdistancehewouldmeasurebythemotionorapplicationofhishandorsomeotherpartofhisbody。Itisthereforeevidentthatallthosethingswhich，inrespectofeachother，wouldbyhimbethoughthigherorlower，mustbesuchaswereconceivedtoexistwithouthismind，intheambientspace。
95。Whenceitplainlyfollowsthatsuchaone，ifwesupposehimmadetosee，wouldnotatfirstsightthinkanythinghesawwashighorlow，erectorinverted；forithathbeenalreadydemonstratedinsect。41thathewouldnotthinkthethingsheperceivedbysighttobeatanydistancefromhim，orwithouthismind。Theobjectstowhichhehadhithertobeenusedtoapplythetermsupanddown，highandlow，weresuchonlyasaffectedorweresomewayperceivedbyhiscouch：buttheproperobjectsofvisionmakeanewsetofideas，perfectlydistinctanddifferentfromtheformer，andwhichcaninnosortmakethemselvesperceivedbytouch。Thereis，therefore，nothingatallthatcouldinducehimtothinkthosetermsapplicabletothem：norwouldheeverthinkittillsuchtimeashehadobservedtheirconnexionwithtangibleobjects，andthesameprejudicebegantoinsinuateitselfintohisunderstanding，whichfromtheirinfancyhadgrownupintheunderstandingsofothermen。
96。TosetthismatterinaclearerlightIshallmakeuseofanexample。
Supposetheabove—mentionedblindpersonbyhistouchperceivesamantostanderect。Letusinquireintothemannerofthis。Bytheapplicationofhishandtotheseveralpartsofahumanbodyhehadperceiveddifferenttangibleideas，whichbeingcollectedintosundrycomplexones，havedistinctnamesannexedtothem。Thusonecombinationofacertaintangiblefigure，bulk，andconsistencyofpartsiscalledthehead，anotherthehand，athirdthefoot，andsooftherest：allwhichcomplexideascould，inhisunderstanding，bemadeuponlyofideasperceivablebytouch。Hehadalsobyhistouchobtainedanideaofearthorground，towardswhichheperceivesthepartsofhisbodytohaveanaturaltendency。Now，byerectnothingmorebeingmeantthanthatperpendicularpositionofamanwhereinhisfeetarenearesttotheearth，iftheblindpersonbymovinghishandoverthepartsofthemanwhostandsbeforehimperceivesthetangibleideasthatcomposetheheadtobefarthestfrom，andthosethatcomposethefeettobenearestto，thatothercombinationoftangibleideaswhichhecallsearth，hewilldenominatethatmanerect。Butifwesupposehimonasuddentoreceivehissight，andthathebeholdamanstandingbeforehim，itisevidentinthatcasehewouldneitherjudgethemanheseestobeerectnorinverted；forheneverhavingknownthosetermsappliedtoanyothersavetangiblethings，orwhichexistedinthespacewithouthim，andwhatheseesneitherbeingtangiblenorperceivedasexistingwithout，hecouldnotknowthatinproprietyoflanguagetheywereapplicabletoit。
97。Afterwards，whenuponturninghisheadoreyesupanddowntotherightandleftheshallobservethevisibleobjectstochange，andshallalsoattaintoknowthattheyarecalledbythesamenames，andconnectedwiththeobjectsperceivedbytouch；thenindeedhewillcometospeakofthemandtheirsituation，inthesametermsthathehasbeenusedtoapplytotangiblethings；andthosethatheperceivesbyturninguphiseyeshewillcallupper，andthosethatbyturningdownhiseyeshewillcalllower。
98。Andthisseemstomethetruereasonwhyheshouldthinkthoseobjectsuppermostthatarepaintedonthelowerpartofhiseye：forbyturningtheeyeuptheyshallbedistinctlyseen；aslikewisethosethatarepaintedonthehighestpartoftheeyeshallbedistinctlyseenbyturningtheeyedown，andareforthatreasonesteemedlowest；forwehaveshewnthattotheimmediateobjectsofsightconsideredinthemselves，hewouldnotattributethetermshighandlow。Itmustthereforebeonaccountofsomecircumstanceswhichareobservedtoattendthem：andthese，itisplain，aretheactionsofturningtheeyeupanddown，whichsuggestaveryobviousreasonwhythemindshoulddenominatetheobjectsofsightaccordinglyhighorlow。Andwithoutthismotionoftheeye，thisturningitupanddowninordertodiscerndifferentobjects，doubtlesserect，inverse，andothertheliketermsrelatingtothepositionoftangibleobjects，wouldneverhavebeentransferred，orinanydegreeapprehendedtobelongtotheideasofsight：themereactofseeingincludingnothinginittothatpurpose；whereasthedifferentsituationsoftheeyenaturallydirectthemindtomakeasuitablejudgmentofthesituationofobjectsintromittedbyit。
99。Farther，whenhehasbyexperiencelearnedtheconnexionthereisbetweentheseveralideasofsightandtouch，hewillbeable，bytheperceptionhehasofthesituationofvisiblethingsinrespectofoneanother，tomakeasuddenandtrueestimateofthesituationofoutward，tangiblethingscorrespondingtothem。Andthusitisheshallperceivebysightthesituationofexternalobjectswhichdonotproperlyfallunderthatsense。
100。Iknowweareverypronetothinkthat，ifjustmadetosee，weshouldjudgeofthesituationofvisiblethingsaswedonow：butwearealsoaspronetothinkthat，atfirstsight，weshouldinthesamewayapprehendthedistanceandmagnitudeofobjectsaswedonow：whichhathbeenshewntobeafalseandgroundlesspersuasion。Andforthelikereasonsthesamecensuremaybepassedonthepositiveassurancethatmostmen，beforetheyhavethoughtsufficientlyofthematter，mighthaveoftheirbeingabletodeterminebytheeyeatfirstview，whetherobjectswereerectorinverse。
l01。Itwill，perhaps，beobjectedcoouropinionthataman，forinstance，beingthoughterectwhenhisfeetarenexttheearth，andinvertedwhenhisheadisnexttheearth，itdothhencefollowthatbythemereactofvision，withoutanyexperienceoralteringthesituationoftheeye，weshouldhavedeterminedwhetherhewereerectorinverted：forboththeearthitself，andthelimbsofthemanwhostandsthereon，beingequallyperceivedbysight，onecannotchooseseeingwhatpartofthemanisnearesttheearth，andwhatpartfarthestfromit，i。e。whetherhebeerectorinverted。
I02。TowhichIanswer，theideaswhichconstitutethetangibleearthandmanareentirelydifferentfromthosewhichconstitutethevisibleearthandman。Norwasitpossible，byvirtueofthevisivefacultyalone，withoutsuperaddinganyexperienceoftouch，oralteringthepositionoftheeye，evertohaveknown，orsomuchassuspected，therehadbeenanyrelationorconnexionbetweenthem。Henceamanatfirstviewwouldnotdenominateanythinghesawearth，orhead，orfoot；andconsequentlyhecouldnottellbythemereactofvisionwhethertheheadorfeetwerenearesttheearth：nor，indeed，wouldwehavetherebyanythoughtofearthorman，erectorinverse，atall：whichwillbemadeyetmoreevidentifwenicelyobserve，andmakeaparticularcomparisonbetween，theideasofbothsenses。
103。ThatwhichIseeisonlyvarietyoflightandcolours。ThatwhichIfeelishardorsoft，hotorcold，roughorsmooth。Whatsimilitude，whatconnexionhavethoseideaswiththese？Orhowisitpossiblethatanyoneshouldseereasontogiveoneandthesamenametocombinationsofideassoverydifferentbeforehehadexperiencedtheircoexistence？
Wedonotfindthereisanynecessaryconnexionbetwixtthisorthattangiblequalityandanycolourwhatsoever。Andwemaysometimesperceivecolourswherethereisnothingtobefelt。Allwhichdothmakeitmanifestthatnoman，atfirstreceivingofhissight，wouldknowtherewasanyagreementbetweenthisorthatparticularobjectofhissightandanyobjectoftouchhehadbeenalreadyacquaintedwith：thecolours，therefore，oftheheadwouldtohimnomoresuggesttheideaofheadthantheywouldtheideaoffoot。
104。Farther，wehaveatlargeshewn（vid。sect。63and64）thereisnodiscoverablenecessaryconnexionbetweenanygivenvisiblemagnitudeandanyoneparticulartangiblemagnitude；butthatitisentirelytheresultofcustomandexperience，anddependsonforeignandaccidentalcircumstancesthatwecanbytheperceptionofvisibleextensioninformourselveswhatmaybetheextensionofanytangibleobjectconnectedwithit。Henceitiscertainthatneitherthevisiblemagnitudeofheadorfootwouldbringalongwiththemintothemind，atfirstopeningoftheeyes，therespectivetangiblemagnitudesofthoseparts。
105。Bytheforegoingsectionitisplainthevisiblefigureofanypartofthebodyhathnonecessaryconnexionwiththetangiblefigurethereof，soasatfirstsighttosuggestittothemind。Forfigureistheterminationofmagnitude；whenceitfollowsthatnovisiblemagnitudehavinginitsownnatureanaptnesstosuggestanyoneparticulartangiblemagnitude，soneithercananyvisiblefigurebeinseparablyconnectedwithitscorrespondingtangiblefigure：soasofitselfandinawaypriortoexperience，itmightsuggestittotheunderstanding。Thiswillbefartherevidentifweconsiderthatwhatseemssmoothandroundtothetouchmaytosight，ifviewedthroughamicroscope，seemquiteotherwise。
106。Fromallwhichlaidtogetheranddulyconsidered，wemayclearlydeducethisinference。Inthefirstactofvisionnoideaenteringbytheeyewouldhaveaperceivableconnexionwiththeideastowhichthenamesearth，man，head，foot，etc。，wereannexedintheunderstandingofapersonblindfromhisbirth；soasinanysorttointroducethemintohismind，ormakethemselvesbecalledbythesamenames，andreputedthesamethingswiththem，asafterwardstheycometobe。
107。Theredoth，nevertheless，remainonedifficulty，whichperhapsmayseemtopresshardonouropinion，anddeservenottobepassedover：
forthoughitbegrantedthatneitherthecolour，size，norfigureofthevisiblefeethaveanynecessaryconnexionwiththeideasthatcomposethetangiblefeet，soastobringthematfirstsightintomymind，ormakemeindangerofconfoundingthembeforeIhadbeenusedto，andforsometimeexperiencedtheirconnexion：yetthusmuchseemsundeniable，namely，thatthenumberofthevisiblefeetbeingthesamewiththatofthetangiblefeet，Imayfromhencewithoutanyexperienceofsightreasonablyconcludethattheyrepresentorareconnectedwiththefeetratherthanthehead。
Isay，itseemstheideaoftwovisiblefeetwillsoonersuggesttothemindtheideaoftwotangiblefeetthanofonehead；sothattheblindmanuponfirstreceptionofthevisivefacultymightknowwhichwerethefeetortwo，andwhichtheheadorone。
108。Inordertogetclearofthisseemingdifficultyweneedonlyobservethatdiversityofvisibleobjectsdothnotnecessarilyinferdiversityoftangibleobjectscorrespondingtothem。Apicturepaintedwithgreatvarietyofcoloursaffectsthetouchinoneuniformmanner；itisthereforeevidentthatIdonotbyanynecessaryconsecution，independentofexperience，judgeofthenumberofthingstangiblefromthenumberofthingsvisible。
Ishouldnot，therefore，atfirstopeningmyeyesconcludethatbecauseIseetwoIshallfeeltwo。How，therefore，canI，beforeexperienceteachesme，knowthatthevisiblelegs，becausetwo，areconnectedwiththetangiblelegs，orthevisiblehead，becauseone，isconnectedwiththetangiblehead？Thetruthis，thethingsIseearesoverydifferentandheterogeneousfromthethingsIfeelthattheperceptionoftheonewouldneverhavesuggestedtheothertomythoughts，orenabledmetopasstheleastjudgmentthereon，untilIhadexperiencedtheirconnexion。
109。Butforafullerillustrationofthismatteritoughttobeconsideredthatnumber（howeversomemayreckonitamongsttheprimaryqualities）
isnothingfixedandsettled，reallyexistinginthingsthemselves。Itisentirelythecreatureofthemind，consideringeitheranideabyitself，oranycombinationofideastowhichitgivesonename，andsomakesitpassforanunit。Accordingasthemindvariouslycombinesitsideastheunitvaries：andastheunit，sothenumber，whichisonlyacollectionofunits，dothalsovary。Wecallawindowone，achimneyone，andyetahouseinwhichtherearemanywindowsandmanychimneyshathanequalrighttobecalledone，andmanyhousesgotothemakingofthecity。Intheseandthelike，instancesitisevidenttheunitconstantlyrelatestotheparticulardraughtsthemindmakesofitsideas，towhichitaffixesnames，andwhereinitincludesmoreorlessasbestsuitsitsownendsandpurposes。Whatever，therefore，themindconsidersasone，thatisanunit。Everycombinationofideasisconsideredasonethingbythemind，andintokenthereofismarkedbyonename。Now，thisnamingandcombiningtogetherofideasisperfectlyarbitrary，anddonebythemindinsuchsortasexperienceshewsittobemostconvenient：withoutwhichourideashadneverbeencollectedintosuchsundrydistinctcombinationsastheynoware。
110。Henceitfollowsthatamanbornblindandafterwards，whengrownup，madetosee，wouldnotinthefirstactofvisionparcelouttheideasofsightintothesamedistinctcollectionsthatothersdo，whohaveexperiencedwhichdoregularlycoexistandarepropertobebundleduptogetherunderonename。Hewouldnot，forexample，makeintoonecomplexidea，andtherebyesteemanunit，allthoseparticularideaswhichconstitutethevisibleheadorfoot。Fortherecanbenoreasonassignedwhyheshoulddoso，barelyuponhisseeingamanstanduprightbeforehim。Therecrowdintohismindtheideaswhichcomposethevisibleman，incompanywithalltheotherideasofsightperceivedatthesametime：butalltheseideasofferedatoncetohisview，hewouldnotdistributeintosundrydistinctcombinationstillsuchtimeasbyobservingthemotionofthepartsofthemanandotherexperienceshecomestoknowwhicharetobeseparatedandwhichtobecollectedtogether。
111。Fromwhathathbeenpremiseditisplaintheobjectsofsightandtouchmake，ifImaysosay，twosetsofideaswhicharewidelydifferentfromeachother。Toobjectsofeitherkindweindifferentlyattributethetermshighandlow，rightandleft，andsuchlike，denotingthepositionorsituationofthings：butthenwemustwellobservethatthepositionofanyobjectisdeterminedwithrespectonlytoobjectsofthesamesense。
Wesayanyobjectoftouchishighorlow，accordingasitismoreorlessdistantfromthetangibleearth：andinlikemannerwedenominateanyobjectofsighthighorlowinproportionasitismoreorlessdistantfromthevisibleearth：buttodefinethesituationofvisiblethingswithrelationtothedistancetheybearfromanytangiblething，orviceversa，thiswereabsurdandperfectlyunintelligible。Forallvisiblethingsareequallyinthemind，andtakeupnopartoftheexternalspace：andconsequentlyareequidistantfromanytangiblethingwhichexistswithoutthemind。
112。Orrather，tospeaktruly，theproperobjectsofsightareatnodistance，neithernearnorfar，fromanytangiblething。Forifweinquirenarrowlyintothematterweshallfindthatthosethingsonlyarecomparedtogetherinrespectofdistancewhichexistafterthesamemanner，orappertainuntothesamesense。Forbythedistancebetweenanytwopointsnothingmoreismeantthanthenumberofintermediatepoints：ifthegivenpointsarevisiblethedistancebetweenthemismarkedoutbythenumberoftheinterjacentvisiblepoints：iftheyaretangible，thedistancebetweenthemisalineconsistingoftangiblepoints；butiftheyareonetangibleandtheothervisible，thedistancebetweenthemdothneitherconsistofpointsperceivablebysightnorbytouch，i。e。itisutterlyinconceivable。
This，perhaps，willnotfindaneasyadmissionintoallmen’sunderstanding：
however，Ishouldgladlybeinformedwhetheritbenottruebyanyonewhowillbeatthepainstoreflectalittleandapplyithometohisthoughts。
113。Thenotobservingwhathasbeendeliveredinthetwolastsectionsseemstohaveoccasionednosmallpartofthedifficultythatoccursinthebusinessoferectappearances。Thehead，whichispaintednearesttheearth，seemstobefarthestfromit：andontheotherhandthefeet，whicharepaintedfarthestfromtheearth，arethoughtnearesttoit。Hereinliesthedifficulty，whichvanishesifweexpressthethingmoreclearlyandfreefromambiguity，thus：howcomesitthattotheeyethevisibleheadwhichisnearestthetangibleearthseemsfarthestfromtheearth，andthevisiblefeet，whicharefarthestfromthetangibleearthseemnearesttheearth？Thequestionbeingthusproposed，whoseesnotthedifficultyisfoundedonasuppositionthattheeye，orvisivefaculty，orratherthesoulbymeansthereof，shouldjudgeofthesituationofvisibleobjectswithreferencetotheirdistancefromthetangibleearth？Whereasitisevidentthetangibleearthisnotperceivedbysight：andithathbeenshewninthetwolastprecedingsectionsthatthelocationofvisibleobjectsisdeterminedonlybythedistancetheybearfromoneanother；andthatitisnonsensetotalkofdistance，farornear，betweenavisibleandtangiblething。
114。Ifweconfineourthoughtstotheproperobjectsofsight，thewholeisplainandeasy。Theheadispaintedfarthestfrom，andthefeetnearestto，thevisibleearth；andsotheyappeartobe。Whatistherestrangeorunaccountableinthis？Letussupposethepicturesinthefundoftheeyetobetheimmediateobjectsofthesight。Theconsequenceisthatthingsshouldappearinthesameposturetheyarepaintedin；andisitnotso？Theheadwhichisseenseemsfarthestfromtheearthwhichisseen；andthefeetwhichareseenseemnearesttotheearth，whichisseen；andjustsotheyarepainted。
115。But，sayyou，thepictureofthemanisinverted，andyettheappearanceiserect：Iask，whatmeanyoubythepictureoftheman，or，whichisthesamething，thevisibleman’sbeinginverted？Youtellmeitisinverted，becausetheheelsareuppermostandtheheadundermost？Explainmethis。
Yousaythatbythehead’sbeingundermostyoumeanthatitisnearesttotheearth；andbytheheelsbeinguppermostthattheyarefarthestfromtheearth。Iaskagainwhatearthyoumean？Youcannotmeantheearththatispaintedontheeye，orthevisibleearth：forthepictureoftheheadisfarthestfromthepictureoftheearth，andthepictureofthefeetnearesttothepictureoftheearth；andaccordinglythevisibleheadisfarthestfromthevisibleearth，andthevisiblefeetnearesttoit。Itremains，therefore，thatyoumeanthetangibleearth，andsodeterminethesituationofvisiblethingswithrespecttotangiblethings；contrarytowhathathbeendemonstratedinsect。111and112。Thetwodistinctprovincesofsightandtouchshouldbeconsideredapart，andasiftheirobjectshadnointercourse，nomannerofrelationonetoanother，inpointofdistanceorposition。
116。Farther，whatgreatlycontributestomakeusmistakeinthismatteristhatwhenwethinkofthepicturesinthefundoftheeye，weimagineourselveslookingonthefundofanother’seye，oranotherlookingonthefundofourowneye，andbeholdingthepicturespaintedthereon。SupposetwoeyesAandB：AfromsomedistancelookingonthepicturesinBseestheminverted，andforthatreasonconcludestheyareinvertedinB：butthisiswrong。ThereareprojectedinlittleonthebottomofAtheimagesofthepicturesof，suppose，man，earth，etc。，whicharepaintedonB。
AndbesidesthesetheeyeBitself，andtheobjectswhichenvironit，togetherwithanotherearth，areprojectedinalargersizeonA。Now，bytheeyeAtheselargerimagesaredeemedthetrueobjects，andthelesseronlypicturesinminiature。Anditiswithrespecttothosegreaterimagesthatitdeterminesthesituationofthesmallerimages：sothatcomparingthelittlemanwiththegreatearth，Ajudgeshiminverted，orthatthefeetarefarthestfromandtheheadnearesttothegreatearth。Whereas，ifAcomparethelittlemanwiththelittleearth，thenhewillappearerect，i。e。hisheadshallseemfarthestfrom，andhisfeetnearestto，thelittleearth。ButwemustconsiderthatBdoesnotseetwoearthsasAdoes：itseesonlywhatisrepresentedbythelittlepicturesinA，andconsequentlyshalljudgethemanerect。For，intruth，themaninBisnotinverted，fortherethefeetarenexttheearth；butitistherepresentationofitinAwhichisinverted，fortheretheheadoftherepresentationofthepictureofthemaninBisnexttheearth，andthefeetfarthestfromtheearth，meaningtheearthwhichiswithouttherepresentationofthepicturesinB。ForifyoutakethelittleimagesofthepicturesinB，andconsiderthembythemselves，andwithrespectonlytooneanother，theyareallerectandintheirnaturalposture。
117。Farther，thereliesamistakeinourimaginingthatthepicturesofexternalobjectsarepaintedonthebottomoftheeye。Ithathbeenshewnthereisnoresemblancebetweentheideasofsightandthingstangible。Ithathlikewisebeendemonstratedthattheproperobjectsofsightdonotexistwithoutthemind。Whenceitclearlyfollowsthatthepicturespaintedonthebottomoftheeyearenotthepicturesofexternalobjects。Letanyoneconsulthisownthoughts，andthensaywhataffinity，whatlikenessthereisbetweenthatcertainvarietyanddispositionofcolourswhichconstitutethevisibleman，orpictureofaman，andthatothercombinationoffardifferentideas，sensiblebytouch，whichcomposethetangibleman。Butifthisbethecase，howcometheytobeaccountedpicturesorimages，sincethatsupposesthemtocopyorrepresentsomeoriginalsorother？
118。TowhichIanswer：intheforementionedinstancetheeyeAtakesthelittleimages，includedwithintherepresentationoftheothereyeB，tobepicturesorcopies，whereofthearchetypesarenotthingsexistingwithout，butthelargerpicturesprojectedonitsownfund：andwhichbyAarenotthoughtpictures，buttheoriginals，ortruethingsthemselves。
ThoughifwesupposeathirdeyeCfromaduedistancetobeholdthefundofA，thenindeedthethingsprojectedthereonshall，toC，seempicturesorimagesinthesamesensethatthoseprojectedonBdotoA。
119。Rightlytoconceivethispointwemustcarefullydistinguishbetweentheideasofsightandtouch，betweenthevisibleandtangibleeye；forcertainlyonthetangibleeyenothingeitherisorseemstobepainted。
Again，thevisibleeye，aswellasallothervisibleobjects，hathbeenshewntoexistonlyinthemind，whichperceivingitsownideas，andcomparingthemtogether，callssomepicturesinrespectofothers。Whathathbeensaid，beingrightlycomprehendedandlaidtogether，doth，Ithink，affordafullandgenuineexplicationoftheerectappearanceofobjects；
whichphenomenon，Imustconfess，Idonotseehowitcanbeexplainedbyanytheoriesofvisionhithertomadepublic。
120。Intreatingofthesethingstheuseoflanguageisapttooccasionsomeobscurityandconfusion，andcreateinuswrongideas；forlanguagebeingaccommodatedtothecommonnotionsandprejudicesofmen，itisscarcepossibletodeliverthenakedandprecisetruthwithoutgreatcircumlocution，impropriety，and（toanunwaryreader）seemingcontradictions；IdothereforeonceforalldesirewhoevershallthinkitworthhiswhiletounderstandwhatIhavewrittenconcerningvision，thathewouldnotstickinthisorthatphrase，ormannerofexpression，butcandidlycollectmymeaningfromthewholesumandtenorofmydiscourse，andlayingasidethewordsasmuchaspossible，considerthebarenotionsthemselves，andthenjudgewhethertheyareagreeabletotruthandhisownexperience，orno。
121。Wehaveshewnthewaywhereinthemindbymediationofvisibleideasdothperceiveorapprehendthedistance，magnitudeandsituationoftangibleobjects。Wecomenowtoinquiremoreparticularlyconcerningthedifferencebetweentheideasofsightandtouch，whicharecalledbythesamenames，andseewhethertherebeanyideacommontobothsenses。
Fromwhatwehaveatlargesetforthanddemonstratedintheforegoingpartsofthistreatise，itisplainthereisnooneselfsamenumericalextensionperceivedbothbysightandtouch；butthattheparticularfiguresandextensionsperceivedbysight，howevertheymaybecalledbythesamenamesandreputedthesamethingswiththoseperceivedbytouch，areneverthelessdifferent，andhaveanexistencedistinctandseparatefromthem：sothatthequestionisnotnowconcerningthesamenumericalideas，butwhethertherebeanyoneandthesamesortofspeciesofideasequallyperceivabletobothsenses；or，inotherwords，whetherextension，figure，andmotionperceivedbysightarenotspecificallydistinctfromextension，figure，andmotionperceivedbytouch。
122。ButbeforeIcomemoreparticularlytodiscussthismatter，Ifinditpropertoconsiderextensioninabstract：forofthisthereismuchtalk，andIamapttothinkthatwhenmenspeakofextensionasbeinganideacommontotwosenses，itiswithasecretsuppositionthatwecansingleoutextensionfromallothertangibleandvisiblequalities，andformthereofanabstractidea，whichideatheywillhavecommonbothtosightandtouch。Wearethereforetounderstandbyextensioninabstractanideaofextension，forinstance，alineorsurfaceentirelystrippedofallothersensiblequalitiesandcircumstancesthatmightdetermineittoanyparticularexistence；itisneitherblacknorwhite，norred，norhathitanycolouratall，oranytangiblequalitywhatsoeverandconsequentlyitisofnofinitedeterminatemagnitude：forthatwhichboundsordistinguishesoneextensionfromanotherissomequalityorcircumstancewhereintheydisagree。
123。NowIdonotfindthatIcanperceive，imagine，oranywiseframeinmymindsuchanabstractideaasisherespokenof。Alineorsurfacewhichisneitherblack，norwhite，norblue，noryellow，etc。，norlong，norshort，norrough，norsmooth，norsquare，norround，etc。，isperfectlyincomprehensible。ThisIamsureofastomyself：howfarthefacultiesofothermenmayreachtheybestcantell。
124。Itiscommonlysaidthattheobjectofgeometryisabstractextension：
butgeometrycontemplatesfigures：now，figureistheterminationofmagnitude：
butwehaveshewnthatextensioninabstracthathnofinitedeterminatemagnitude。Whenceitclearlyfollowsthatitcanhavenofigure，andconsequentlyisnottheobjectofgeometry。Itisindeedatenetaswellofthemodernasoftheancientphilosophersthatallgeneraltruthsareconcerninguniversalabstractideas；withoutwhich，wearetold，therecouldbenoscience，nodemonstrationofanygeneralpropositioningeometry。Butitwerenohardmatter，didIthinkitnecessarytomypresentpurpose，toshewthatpropositionsanddemonstrationsingeometrymightbeuniversal，thoughtheywhomakethemneverthinkofabstractgeneralideasoftrianglesorcircles。
125。Afterreiteratedendeavourstoapprehendthegeneralideaatriangle，Ihavefounditaltogetherincomprehensible。Andsurelyifanyonewereabletointroducethatideaintomymind，itmustbetheauthoroftheEssayconcerningHumanUnderstanding；hewhohassofardistinguishedhimselffromthegeneralityofwritersbytheclearness—andsignificancyofwhathesays。Letusthereforeseehowthiscelebratedauthordescribesthegeneralorabstractideaofatriangle。’Itmustbe（sayshe）neitherobliquenorrectangular，neitherequilateral，equicrural，norscalenum；
butallandnoneoftheseatonce。Ineffect，itissomewhatimperfectthatcannotexist；anidea，whereinsomepartsofseveraldifferentandinconsistentideasareputtogether’EssayonHum。Understand。B。
iv。C。7。S。9·；Thisistheideawhichhethinksneedfulfortheenlargementofknowledge，whichisthesubjectofmathematicaldemonstration，andwithoutwhichwecouldnevercometoknowanygeneralpropositionconcerningtriangles。Thatauthoracknowledgesitdoth’requiresomepainsandskilltoformthisgeneralideaofatriangle。’ibid。Buthadhecalledtomindwhathesaysinanotherplace，towit，’Thatideasofmixedmodeswhereinanyinconsistentideasareputtogethercannotsomuchasexistinthemind，i。e。beconceived。’vid。B。iii。C。10。S。33。ibid。Isay，hadthisoccurredtohisthoughts，itisnotimprobablehewouldhaveowneditaboveallthepainsandskillhewasmasteroftoformtheabove—mentionedideaofatriangle，whichismadeupofmanifest，staringcontradictions。Thatamanwholaidsogreatastressonclearanddeterminateideasshouldneverthelesstalkatthisrateseemsverysurprising。Butthewonderwilllessenifitbeconsideredthatthesourcewhencethisopinionflowsistheprolificwombwhichhasbroughtforthinnumerableerrorsanddifficultiesinallpartsofphilosophyandinallthesciences：butthismatter，takeninitsfullextent，wereasubjecttoocomprehensivetobeinsistedoninthisplace。Andsomuchforextensioninabstract。
126。Some，perhaps，maythinkpurespace，vacuum，ortrinedimensiontobeequallytheobjectofsightandtouch：butthoughwehaveaverygreatpropensiontothinktheideasofoutnessandspacetobetheimmediateobjectofsight，yet，ifImistakenot，intheforegoingpartsofthisessaythathathbeenclearlydemonstatedtobeameredelusion，arisingfromthequickandsuddensuggestionoffancy，whichsocloselyconnectstheideaofdistancewiththoseofsight，thatweareapttothinkitisitselfaproperandimmediateobjectofthatsensetillreasoncorrectsthemistake。