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Isis,2002,93:585-613

?2002by TheHistoryof ScienceSociety.All rightsreserved.

0021-1753/02/9304-0002$10.00

585

PhotogenicVenus

The"CinematographicT urn"andIts

AlternativesinNineteenth-Century France

ByJimenaCanales*

ABSTRACT

Duringthelate nineteenthcentury, scientistsaroundthe worlddisagreedas tothetypes ofinstrumentsand methodsthatshould beusedfor determiningthemost importantcon- stantofcelestial mechanics:thesolar parallax.Venus' s1874transit acrossthe sunwas seenasthe bestopportunityfor endingdecadesof debate.However, amysterious "black drop"thatappeared betweenVenus andthesun andindividualdif ferencesinobservations ofthephenomenon broughttraditionalmethodsintodisrepute.T ocombatthese difficulties, theastronomerJules Janssendeviseda controversialnewinstrument, the"photographic revolver,"thatphotographedVenus atregularintervals. Anothersolutioncame fromphys- icists,whorivaled theastronomers'dominance inprecisionmeasurements bydeducing thesolarparallax fromphysicalmeasurements ofthespeed oflight.Y etotherastronomers reliedondrawings andwell-trainedobservers. Thenewspace emergingfrom thisdebate wascharacterizedby adeclinein faithin(nonstandardized, nonreproducible)photography andin(pure) geometryandby thegrowingrealization oftheimportance ofalternative elementsneededfor establishingscientifictruths: powerandauthority ,skilland discipline, standardization,mechanicalreproducibility ,andtheatricality .Byexaminingthe"cinemat- ographicturn"in scienceandits alternatives,thisessay bringstolight unexploredmulti- disciplinaryconnectionsthat contributetothe historiesofpsychology ,philosophy ,physics, andfilmstudies. Why,inotherwords, isnote verythinggivenat once,asonthefilm ofthe cinematograph? - HenriBergson D URINGTHESECOND HALFOFTHE NINETEENTHCENTURY scientistsaround theworlddisagreed aboutwhattypes ofinstrumentsand methodsshouldbe usedto *Departmentof theHistoryof Science,HarvardUniversity ,ScienceCenter 235,Cambridge, Massachusetts

02138.

Iwouldlike tothankPeter Galison,DavidKaiser ,Franc¸oiseLaunay,SimonSchaf fer,andtheIsisreferees fortheirgenerous commentsandencouragement.

586PHOTOGENICVENUS

observethe"astronomical eventof thecentury":V enus's1874 transitacrossthe sun. 1 The transitwasexpected toclose acenturyof debatesurroundingthe mostimportantconstant ofcelestialmechanics, thesolarparallax. Areliablefigure forthesolar parallaxwould enableastronomersto determinethedistance fromtheearth tothesun, setthedimensions ofthesolar system,and,using Newton'slaw ,deducethe massesofthe planets. 2 Astronomershadlong knownthatobserving thetransitof Venus,which in1874would onlybevisible farfromthe Europeancontinent,was nottheonly waytoestablish avalue forthesolar parallax.Butall knownalternatives furnishedradicallydif ferentresults.While observationsof theprevioustransit (1769)movedmost astronomerstosettle on8.57 secondsofarc, recentresearch onplanetarymovements aswellas newdeterminationsof thespeed oflight(1862) hadledsome tobelievethat thetruevalue wasaround8.86 secondsofarc. 3 InFrance,the Acade´miedesSciences,theBureau desLongitudes,the 1 Givenitsimportance atthetime, thecurrenthistoriography ofthetransits ofVenus issurprisingly limited.

Secondarysources includePeterHingley andFranc¸oiseLaunay,"Passagesde Ve´nus,1874et1882," inDans

lechamp dese´toiles:Lesphotographes etleciel 1850-2000(Paris:Re´uniondesMuse´esNationaux,2000),

pp.119- 121;MoniqueSicard,"PassagedeVe´nus:Lerevolverphotographiquede JulesJanssen,"E tudesPho- tographiques,1998,4:45-63;A.Chapman,"TheTransits ofVenus," Endeavour,1998,22:148-151;DavidH. DeVorkin,"Venus1882:Public, Parallax,andHNR,"SkyandTelescope, 1982,22:524-526;DeVorkin,Henry NorrisRussell:Dean ofAmericanAstr onomers(Princeton,N.J.:Princeton Univ.Press, 2000),pp.44, 46,49,

60;StevenJ. Dick,W ayneOrchiston,and TomLove, "SimonNewcomb,WilliamHarkness,and theNineteenth-

CenturyAmericanT ransitofV enusExpeditions,"JournalfortheHistoryof Astronomy, 1998,29:221-255;Paul M.Janiczekand L.Houchins,"T ransitsofV enusandthe AmericanExpedition of1874,"SkyTelesc.,1974,

48:366-371;andJaniczek,"Remarksonthe Transitof VenusExpedition of1874,"in SkywithOceanJoined:

ProceedingsoftheSesquicentennial Symposiaofthe U.S.Naval Observatory,Dec. 5and8, ed.Dickand LeRoy E.Dogget(W ashington,D.C.:U.S. NavalObservatory,1983),pp.53 -74. Forapartial accountofphotography

andthetransits duringthisperiod thatdoesnot evenmentionJanssen' sphotographic revolverseeJohn Lankford,

"Photographyandthe Nineteenth-CenturyTransits ofVenus," TechnologyandCulture,1987,28:648-657.Per- hapsthemost widelyreadEnglish-language accountofthe transitswasRichard A.Proctor, TransitsofVenus: APopular AccountofPastand ComingTr ansits(NewYork: Worthington,1875).Forathorough discussionof problemsofevidence inscience seethevarious essaysinArnold I.Davidson,James Chandler,and Harry Harootunian,eds.,QuestionsofEvidence: Proof, Practice, andPersuasionacrosstheDisciplines (Chicago: Univ.ChicagoPress,1991);and PeterGalison,HowExperimentsEnd (Chicago:Univ. ChicagoPress,1987), Ch.4. 2

"Parallax"generally referstothe angularchangeof anobjectwhen itisobserved fromtwodif ferentpositions.

Ifthedistance betweenthetwo observationalpositions isknown,it canbethought ofasthe baseofa triangle that,whencombined withmeasurements ofthedirection oftheobject asseenfrom bothpoints,can beused to

determinethe distancetothe object.Thesolar parallaxcanbe determinedusingHalley' smethod,which consisted

inobservingthe transitof Venusacross thesun.This wasdoneeither throughthemethodofdurationsor the methodofDe l'Isle.In themethodof durationsthetimes ofthetransit asviewedfrom twodifferent stations weredetermined, thelengthsof thechordswere deduced,andfrom thesetheleast distancebetweenthe centers ofthesun andV enuswasfound. However,since themethodofdurationsrequiredthe observationofthe whole transit,the methodofDe l'Islewasproposed. Thismethodrequired theprecisedetermination ofthetime of contactbetweenV enusand thesunattwodifferent stations,whichwere eithertime-coordinatedor whose differenceinlongitudewasaccurately known.Theprecision ofthismethoddependedingreatpartontheaccuracy ofthelongitude determinations. 3 Onthe"Black Dropeffect" seeBradleyE. Schaefer,"The TransitofVenus andtheNotorious BlackDrop Effect,"JournalfortheHistoryof Astronomy, 2001,34:325-336.TheBerlinastronomerFranzEncke (1824)

assignedthevalue of8.57seconds ofarcto thesolarparallax fromhisanalysis ofthe eighteenth-centurytransits,

whichrangedfrom 8.1to9.4 secondsofarc. ObservationsofMars' soppositionsagainst thesunconvinced many astronomersto adoptavalue exceeding8.9seconds ofarc.Y etanothermethod, usinglunar theory,pointed to resultsaround 8.916(PeterAndreas Hansen)or8.850 (EdwardJamesStone) secondsofarc. Usingplanetary

theoryandthe equationofthe moon,UrbainLe Verrier, directorofthe ParisObservatory ,setthe solarparallax

at8.859seconds ofarc.By adoptingthisvalue hewasable toreconcilediscrepancies inthe theoriesofV enus, Earth,andMars. Fordeterminingthe exacttimeof contactssomeastronomers advocatedspectroscopic obser- vations,while othersuseda double-imagemicrometer. Amicrometeris atelescopeaccessory formeasuring smallangles.For descriptionsofthese methodsseeGeor geForbes,TheTr ansitofVenus(NatureSeries)(London:

Macmillan,1874);Edmond Dubois,"Nouvelleme ´thodepourde´terminerlaparallaxedeVe ´nussansattendreles

passagesde1874 ou1882,"ComptesRendusdes Se´ancesdel'Acade´miedesSciences,20Dec.1869, 69:1290;

JIMENACANALES587

ObservatoiredeParis, andtheE

colePolytechniqueall sponsoreddif ferenttypesof evi- denceto determinethe"true" value.To complicatemattersfurther ,proponentsof these competingtechniqueswere oftensplitintellectually aswellas institutionally.Even when agroupof scientistsagreedon acertainmethod, differingobservations madewith it renderedtheresults highlydiscordant.Who wasright?Particularly puzzlingwasa con- troversial"blackdrop" that,accordingto some,mysteriouslyappeared betweenVenus and thesunexactly whenastronomershad totimethe apparentcontact.At stakein these argumentswasnothinglessthan thedeterminationof "thescaleof theuniverse"and the problemofother worlds.Stillmore important,thetransit ofVenus wasconnected to philosophicaldebatesabout thevalueof geometricmethodsin astronomyandthe nature ofspaceand time - all loftyissuestied toearthlyconcernsofgovernance,nationalpres- tige,andmilitary might. Asthecentury progressed,astronomersincreasingly repudiatedthe geometricmethods thathadcharacterized astronomyduringthe previouscentury. Intheeighteenth century theBritishastronomer EdmondHalley(1656 -1742)had claimedthatthe solarparallax couldbedetermined withexactnessby combiningsimpleEuclidean triangulationswith directobservations ofVenus' sapparentcontact withthesun.Butmorethanahundred yearsafterHalley' sdiscovery, astronomerscametodoubtthepossibility oftimingthe contactbetweenthese twocelestialbodies precisely.While someastronomersblamed the nervoussystemsof observersfordiscrepancies inresults,others thoughttheinstruments wereatfault. Stillothersbelieved thattheproblems weredueto increasinglyunskilled andundisciplinedobservers inastronomy. Andsomeclaimed thatproblematicnongeo- metriccontactsarose fromneitherobservational norinstrumentalerrors butweredue to actualastronomicalphenomena thatneededinvestigation. Perhapsmostalarmingly ,some mathematiciansandphilosophers wereledby theriftbetween theostensiblystraightfor - wardgeometricmethods Halleyhadproposed andtheirapparently chaoticresultsto ques- tionthevery foundationsofmathematics. Asgeometriccertainty becameharderto obtain, many"solutions"were devised,includingartificial transitmachinesfor traininganob- server'sresponsesorformeasuringhisdelayed reactionsandnew camerasthatphoto- graphedtheevent atshortintervals. Yetnone ofthesecould eliminateinsidiousdoubts as totheclaims ofscientificevidence toabsolutetruth. Evenbeforethe Franco-Prussianwar(1870 -1871),but intenselyafterward,the prob- lemsfacinggeometrical astronomyforceda newgenerationof astronomerstodirty their handswithphysics, photography,cinematography ,pedagogy, and"mimeticexperimen- tation"thatreproduced astronomicalphenomenaon earth,buton asmallerscale. 4

Astron-

omerslearnedto buttresstheir claimstotruth byincreasingtheir authoritywiththe gov- ernmentandthe laypublic.They advocatedinternationalcooperation, standardization, mechanicalreproducibility ,andeventheatricality - sometimes turningtotechniques sharedbypopular culture.None oftheseef forts,however, provedentirelysuccessful. Althoughaunified andof ficialeffort toobservethe 1874transitofVenuswas organized bytheFrench governmentandby themostimportant institutionofFrench science,the Acade´miedesSciences,divisionsboth withinandwithout officialcircles promptedthe

Le´onFoucault,"De´terminationexpe´rimentaledelavitessede lalumie`re:Descriptiondesappareils,"ibid.,1862,

55:792-796,Herve´Faye,"Note surlesnouvelles tablesdesplane `tesinte´rieures,"ibid.,1862,54:630;andUrbain

LeVerrier ,"Surlesmassesdesplane`tesetlaparallaxedu soleil,"ibid.,22July1872, 75:165-172. 4 Iborrowthis termfromPeter GalisonandAlexi Assmus,"ArtificialClouds, RealParticles,"in TheUsesof Experiment:Studiesin theNatural Sciences,ed.DavidGooding, TrevorPinch, andSimonSchaf fer(Cambridge:

CambridgeUniv. Press,1989),pp.225- 274.

588PHOTOGENICVENUS

emergenceofalternativeinstruments andmethods.Most notably,the astronomersHerve´ FayeandJules Janssen,whoworked atthe BureaudesLongitudes, UrbainLeV errier, directorofthe ObservatoiredeParis, AlfredCornufrom theE colePolytechnique,and the physicistArmandFizeau cametodisagree withtheacademy' sofficial prescriptions.In theend,no consensuswasreached withrespectto Venus,and scientistshadto waitfor theasteroidEros(1932)toquell thecontroversysurroundingthevalueofthesolar parallax, atleasttemporarily . 5

THECINEMATOGRAPHIC TURN

Amongthevarious methodschampionedby astronomerswasa controversialnewinstru- ment,intriguinglynamed the"photographicrevolver ,"thatphotographed Venus's transit acrossthesun atintervalsof approximatelyonesecond. InventedbyJules Janssento photographthe1874 transit,itwas arguablythe mostpromisingdevice forending the discordasto theexacttime oftheplanet' sapparentcontact withthesun. 6

Janssen'sap-

paratuswassoon modifiedandmoved intootherareas ofscienceand culture,most fa- mouslytoE tienneJulesMarey' sphysiologicallaboratory andthentothestudioof the Lumie`rebrothers,whereit wasgraduallytransformed intowhatwould soonbecalled the cinematographiccamera.Although theMareyand Lumie`reinstrumentsdifferedmarkedly fromJanssen's original,theapplicationsofthe "revolver"tothe studyofliving beingsas wellasits inverseusefor synthesizingimages(either throughprojectionor byarranging themona rotatingdisk)were vauntedbyJanssen asproofof itsbedazzlingability to createassentin visualmatters.From themomentJanssen pointedhisrevolver toward Venus(1874)tothetime whenhestarred inoneof thefirstfilms tobe shownpublicly (1895),thedevice passedthrough apainfulgestation intimatelytiedto thedebateon how toeliminatedif feringobservations.Despite somesuccesses,Janssendidnotinitially con- vinceeveryoneof therevolver' smerits.In fact,thestate-sponsored andofficialeffortfor determiningthesolar parallax,which wasorganized undertheCommission fortheT ransit ofV enusoftheAcade´miedesSciences,didnot adoptthedevice asitsmain instrument. Evenadvocatesof photographyweretorn, somearguing onbehalfof sequentialphotog- raphyandthe advantagesofmechanically reproduciblemethodswhile othersremained fixedontime-tested nonreproducibledaguerreotypes. 7 5 Thevaluefor theparallaxcommonly adoptedafterthe Eroscampaignwas 8.790secondsof arc.This number wassoon displacedbythe valuederivedfrom radarobservationsof theplanets,8.794148 secondsofarc. See R.d'E.Atkinson, "TheErosParallax, 1930- 31,"J.Hist.Astron., 1982,13:77-83. 6 InEnglish, therevolverwas sometimescalledthe "Janssenslide"or simplythe"Janssen." OnJanssensee

DavidAubin,"Orchestrating Observatory, Laboratory,and Field:JulesJanssen,theSpectroscope,and Travel,"

Nuncius,forthcoming;Franc¸oiseLaunay,"JulesJanssen' sInandOutCorrespondence,"in 100Year sofObser- vationalAstronomy andAstrophysics:Homage toMiklosK onkolyThege (1842-1916),ed.C.Sterken andJ.B. Hearnshaw(Brussels:Sterken, 2001),pp.159 -168;Launay ,"Jules Janssenetla photographie,"inDansle

champdese´toiles(cit.n.1), pp.22- 31;Aubin,"La me´tamorphosedese´clipsesdesoleil,"Recherche,June1999,

321:78-83;andMarie-ClaudeMahias,"Lesoleilnoir desNilgiri:L 'astronomie,laphotographie et

l'anthropologiephysiqueen IndeduSud," Gradhiva:Revued'Histoire etd'Archivesdel'Anthr opologie,1998,

24:33-56.

7 Forrecentliterature onvisualpractices inastronomy seeJohnLankford, "TheImpactof Photographyon Astronomy,"inAstrophysicsandTwentieth-CenturyAstr onomy,ed.OwenGingerich (GeneralHistoryof As- tronomy)(Cambridge:Cambridge Univ.Press, 1984),pp.16 -39;HollyRothermel,"Images oftheSun: Warren dela Rue,George BiddellAiry, andCelestialPhotography,"BritishJournal fortheHistoryofScience, 1993,

26:137-169;AlexSoojung-KimPang,"Victorian ObservingPractices,Printing Technologies,and Representa-

tionsofthe SolarCorona,1: The1860's and1870's," J.Hist.Astron.,1994,25:249-274;Pang,"Victorian ObservingPractices,Printing Technologies,and Representationsofthe SolarCorona,2:TheAge ofPhotome-

JIMENACANALES 589

Figure1.DaguerreotypefromJ anssen'sre volvershowingVenus's contactwiththesun.FromMonique Sicard,"Passage deVe´nus:Lerevolverphotog raphiquede JulesJanssen,"E tudesPhotogr aphiques,

1998,no. 4,pp.45-63,on p.63.

Thenewinstruments andtechniquesemployed duringthetransit of1874dramatically alteredtheexact sciences.Moreimportant, thesenewmethods combinedwithother factors tochangethe natureofdebates abouttherole ofscientificevidence. TheinfluentialNobel Prizewinner, philosopher,andcriticHenriBer gsondescribedtheage-oldscientificpractice ofusingstatic, sequentialimagesto illustratemovementthrough timeanddubbed itthe "cinematographicmethod."Referring notmerelyto themoderncinematographic camera butto theproclivityof thehumanmind forarrangingtemporal imagesspatially, hecriti- cizeditsrestrictiveness andurged scientiststo"set thecinematographicalmethod aside" andsearchinstead fora"second kindofknowledge." 8

Inadiscussion whereBergson

soughttoemphasize theconstructed andartificialnature ofourknowledge ofphysical phenomena,the mathematicianLouisCouturat raisedthecounterexample ofthetransit. "Aneclipse,or evenbetter ,thetransit ofVenus acrossthesun,"heargued, wasproofthat somephysicalphenomena werehighlyprecise anddelimitedevents. Bergsondisagreed, insistingthatphysical phenomenawerenever naturallydelimited:"It istheastronomer that,"withthe cinematographicmethod," catchestheposition oftheplanet fromthecon- tinuouscurve ittraverses"(see Figure1).It wasnotonly Venus's form - evenwiththe aidofJanssen' srevolver - thatwaselusive,butallforms: "thereisnoform,sinceform chanicalReproduction,"ibid.,1995,26:63-75;Pang,"'StarsShouldHenceforthRegister Themselves':Astro- photographyatthe EarlyLickObservatory ,"Brit.J. Hist.Sci.,1997,30:177-202;SimonSchaffer,"OnAstro- nomicalDrawing,"in PicturingScience, ProducingArt,ed.Caroline A.Jonesand PeterGalison(New York: Routledge,1998),pp. 441-474; Schaffer, "TheLeviathanofParsontown:LiteraryTechnologyand Scientific Representation,"inInscribingScience, ed.Timothy Lenoir(Stanford,Calif.:StanfordUniv. Press,1998), pp.182- 222;andPang,"Technology,Aesthetics,and theDevelopmentof Astrophotographyatthe LickOb- servatory,"ibid.,pp.223- 248. 8 HenriBergson, CreativeEvolution(Mineola,N.Y.: Dover,1998),p.342.

590PHOTOGENICVENUS

isimmobileand realityis movement.Whatis realisthe continualchangeofform:form isonly asnapshotvie woftr ansition." 9 Thissentimentwas prevalentin manyscientificcircles intheyears beforeandafter the transit,when mostscientistsshunned Janssen'scinematographic typeofevidence and exploredalternative scientificorphilosophical methodologies.Furthermore,the viewsof Bergsonandhisdiscipleshad importantrepercussionsfor bothscienceand philosophyof science.Therenowned philosopherWilliam James,forexample, claimedthatBer gsonhad compelledhimto "giveupthe logic,fairly, squarelyandirrevocably ." 10

Supportedinpart

bytheprevalent disbeliefinthe resultsofthe transitobservations,such criticismsbecame apowerfuland long-lastingjustificationof theneedfor asustainedphilosophical inquiry intoscientificmethodology .Inthis essayIwillexaminethe"cinematographic turn"in scienceandits alternatives,showinghow itaffected astronomy,modern physics,and mathematics.

ORGANIZATIONANDHISTORIOGRAPHY

Threeinterlacedhistories runthrough thisessay. Allhavebroad historiographictraditions oftheirown, butthey havenotbeen studiedinrelation toeachother .Thetopic ofthefirst section,"IndividualDif ferences,"hastraditionally beenconsideredpartofthehistory of psychology;theimplications oftheproblem ofdiffering observationsforthe exactsciences havebeenlar gelyignored. 11 Inthissection Ifocuson howthevarious solutionsproposed foreliminatingsuch differences intheparticular caseofthetransitsofV enuswerecon- nectedtocertain idealsofobjectivity .Heretwo dominantstrategiesare evident,one based ondisciplineand trainingandthe otheronthe useofphotography . Thesecond section,"ThePhotographic Revolver,"deals withathird methodforelim- inatingindividualdif ferencesinobservations. Thismethodwasalsophotographic,but it differeddramaticallyfromthedaguerreian photographyanalyzedin theprevioussection. Itwas mostforcefullyadvocated byJanssen,who soughttointroduce mechanicalrepro- ducibility,standardization,andtechnologiesfor synthesizingchronophotographythat wouldgivesequential imagesthe illusionofmovement. Hisstrategyfor obtainingassent invisualmatters wasnot basedondiscipline andtrainingor onthegeometrical opticsof thecameraobscuraandartisanaldaguerreotypes but,rather, onnewtechnologies ofmass mediathatemer gedalongside theincreasedindustrializationofthelate nineteenthcentury. Thethemesof thissectionhave typicallybeenstudied fromtheperspective ofarthistory orfilmstudies; theirrelationto theexactsciences hasnotbeen appreciated. In"TheNew Logic"Iapproach thecontroversymainly fromtheperspective ofmath- ematicsandphysics. Althoughmanyof theeventsdescribed herehavebeen analyzed 9

"C'estl'astronome quicueillecettepositionde l'astresurla continuite´dela courbequ'ilde ´crit."Henri

Bergson,"Leparalle´lismepsycho-physiqueetlame ´taphysiquepositive,"inMe´langes(1901;Paris:Presses

Univ.France,1972),pp.463 -502,on p.502;and Bergson,CreativeEvolution,p.302.(Here andthroughout thisessay, translationsintoEnglisharemine unlessotherwiseindicated.) 10 WilliamJames,APluralistic Universe(London:Macmillan,1909), p.226, citedinPaul Douglass,"Bergson andCinema:Friends orFoes,"in TheNe wBergson,ed.JohnMullarkey (Manchester:ManchesterUniv .Press,

1999),pp.209 -227,on p.219.

11 Someexceptions areSimonSchaf fer,"Astronomers MarkTime: DisciplineandthePersonalEquation," ScienceinConte xt,1988,2:115-145;andJimenaCanales,"TheSingle Eye:Re-evaluatingAncienRe´gime Science,"HistoryofScience ,2001,39:71-94.Forstandardtreatmentswithinpsychology seeEdwinG. Boring, AHistoryof ExperimentalPsyc hology(NewYork: Appleton-Century-Crofts,1929);andBoring,"TheBeginning andGrowthof Measurementin Psychology,"in Quantification:A Historyofthe MeaningofMeasur ementin theNatural andSocialSciences,ed.HarryW oolf(Indianapolis: Bobbs-Merrill,1961),pp.108-118.

JIMENACANALES591

beforeinhistories ofphysics,mathematics, andphilosophy, theirrelationto thepersonal equationhasbeen allbutfor gotten.Infact, theproblemwas intimatelyconnectedto controversiessurroundingthe foundationsofmathematics intwoimportant ways.First, asgeometrical methodsinastronomy wereincreasinglyconsidered impotent,therelation ofmathematicsto theexperimental scienceswasquestioned. Second,thedif ficultiessur- roundingtheelimination ofindividual differencesin observationalresultscalled intodoubt theexistence ofabsoluteand naturalstandardsof measurement.Physiciststhemselves tried tocircumventthe problemsraisedby thesediffering observationsinnovel ways.Inpar - ticular,somephysicistsandastronomers renewedexperimentson thespeedof lightand itsrelationto theetherin ordertofind analternativesolution totheproblem ofdif fering observationsplaguingscience.

INDIVIDUALDIFFERENCES

Whenastronomersduring thelatenineteenth centuryreviewedobservations ofthe1769 transitofV enustheconclusion wasappalling:differentpeoplesaw differently. Scientists, politicians,andeven NapoleonIIIworriedly debatedthenature ofthesedif ferences,asked whethertheywere duetothe fluctuatingconditionsof thephenomenonitself, tothedif- ferentinstrumentsemployed, tothevisual ormentalapparatus oftheobservers, or, insome rarecases,to outrightdishonesty. 12 Quiteapartfrom thelarger politicalandjuridical con- sequencesofdisagreement, theimmediateproblems wereinsurmountable:if thesolar parallaxremainedcloser tothevalue determinedbythe BerlinastronomerFranz Encke in1824,astronomers wouldhaveto posittheexistence ofaunlikely ninthplanet; andif thedifferences inobservationswerecausedbythe Venusianatmosphere, thenthe possi- bilitythatV enuswasa worldliketheearthwouldhave tobeseriously considered. 13 In 12 Theobservationsof theJesuit priestMaximilianHell (1720-1792) wereparticularlysuspect. 13 Fayeexplainedthe loomingcrisis: "Ifwepersist inourfalse evaluationofthe parallax,thehypothesis that thereexistssome otherplanetwhich hasgoneunperceived untilnow. .. willneedto beconsidered.And, since

wecannotsee suchaprobable planet,sciencefinds itselfforcedinto animpasse.. .. Allthediscordances, all

thecontradictionswhich menacethefuture and,tosome degree,thepresent ofastronomy ,willdisappear ifthe

directdeterminationof solarparallax. ..gives us8?,9insteadof 8?,57."Herve´Faye,"Association Franc¸aise

pourl'Avancement desSciences,congre`sdeLille,confe´rencespubliques:Leprochainpassage deVe ´nussurle

soleil,"RevueScientifique,17Oct.1874, 14(16):361-369,onp.367.Thevalueof thesolarparallax wasdirectly connectedtothe valuesofthe massesofthe planetsandto theproblemof Mercury's perihelion,whichwould

enthrallastronomersuntil itwasexplained byEinstein's theoryofgeneral relativity.After fixinga valueforthe

solarparallaxand forthemass ofEarthfrom observationsofEarth, Mars,andV enus,Le Verrierposited a "missingmass"to explainMercury's perihelion.Hebelieved thatthismass mightbefoundinthe formofeither aplanet(commonly referredtoas Vulcan)or smallerintramercurialplanets. Ifdiscovered, theywouldbe a secondtriumphfor LeVerrier afterhismagnificent "discovery"ofNeptune. However,theirexistenceremained highlycontroversial.Building onLe Verrier' swork,Faye claimedthatthe massofEarthdeducedfromcurrent valuesofthe solarparallaxcould beshownto beerroneousby itslong-term effectson theorbitsof Marsand Venus.Healsobasedhis claimonrecent workonthe oppositionsofMars (George BiddellAiry),parallactic

inequalitiesofthe moon(PeterAndreas Hansen),andthe speedoflight (Le´onFoucault).Forhistoriesof the

problemofMercury' sperihelionthat discussLeVerrier's roleseeN. T. Roseveare,"Leverrierto Einstein:A Reviewofthe MercuryProblem,"VistasinAstronomy ,1979,23:165-171;andR.A.Lyttleton, "Historyofthe MassofMercury ,"QuarterlyJournal oftheRoyalAstronomicalSociety ,1980,21:400-413.Ontherelation

betweentheorbit ofMercury, theso-calledplanet Vulcan,and theimplicationsforNewtoniantheory seeWilliam

SheehanandRichard Baum,InSearc hofPlanetVulcan:TheGhostin Newton's ClockworkUniver se(New York:Plenum,1997).The astronomerandpopularizer ofscienceCamille Flammarionbelievedthe resultsofthe transitsconfirmedthe existenceofa Venusianatmosphere thatprovedto himthat "thisplanetis aworldlike ours."Flammarionwas notalone;even JulesJanssenbelieved thathisinvestigations ofwater vaporweredone toprove "thepresenceof thisaqueouselement whichplayssuch aconsiderablerole inthedevelopment oflife onthesurface ofa world."Whilein 1874Janssenclaimed tohaveproved theexistenceof watervaporin the Venusianatmosphere,after1882 heretractedthis claim.SeeCamille Flammarion,"Lepassage deVe´nus:

592PHOTOGENICVENUS

short,scientistsand theirinstitutionsrisked beingonthe dangerousgroundof convention, speculation,andpossibility . Evenbeforethe problemof individualdifferences inobservationleaked tothegeneral public,governmentsacross theworldbecameconcerned.NapoleonIII'spositivisticempire wasthefirst inFrance topreoccupyitself withthesestrange divergences. 14

In1869the

ministerofpublic instruction,Victor Duruy,addressed aletterto theacademychargingquotesdbs_dbs46.pdfusesText_46

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