 Duhem is one of the purposes of our article, which aims to compare the first epistemological theses of the two savants- 1 João Príncipe is a Professor at the University of Évora Instituto de História Contemporânea / CEHFCi. Address: Largo dos Colegiais 2, 7000 Évora, Portugal. Email: jpps@uevora.pt 2 I thank Olivier Darrigol and Fábio Leite for stimulating discussions. João Príncipe – Poincaré and Duhem: Resonances in their First Epistemological Reflections 141 philosophes. This will illuminate the history of the debate between the two (Brenner 2003, chapter III). This debate is reflected in an opposition that is explicit in The aim and structure of physical theory (1906); it manifests itself in the refusal of Maxwellian physics by Duhem and in his lack of interest in the achievements of atomism, associated with Lorentz's theory of electrons, the development of experimental microphysics (gas discharges, X-rays and radioactivity), black-body theory (Planck, Einstein), works on Brownian motion (Smoluchowski, Einstein and Perrin) and the Maxwell-Boltzmann kinetic theory; whereas Poincaré, after 1893, took an interest in atomistic theories and gave important contributions. But this dissonance must not erase the common ground of their reflections, which is related to their judgment on the state of theories around 1890. The complex evolution of physics in this period is diffracted in the individual epistemological reflections of the savants-philosophes, who judge theories in situation. This is because Maxwell, Mach, Hertz, Boltzmann, Poincaré or Duhem try to integrate a variety of motifs: their perception of theories, their actual and personal scientific practice, a broader questioning inspired by the philosophical tradition, which imposes long lasting questions. The first reflections of Poincaré and Duhem, made before the rise of the physics of electrons and ions, have similarities which can be understood according to the contemporary state of physical theories, at a time when the Laplacian tradition, attached to a mechanistic reductionism based in the conception of the center-of-force atoms, is defeated by thermodynamics and electromagnetism, two domains to which Poincaré and Duhem are interested as researchers. The recognition of the hypothetical nature of theories, theoretical pluralism, stylistic differences between the French tradition and the physics of models,
Duhem is one of the purposes of our article, which aims to compare the first epistemological thesis of the two savants- 1 João Príncipe is a Professor at the University of Évora Instituto de História Contemporânea / CEHFCi. savoir-faire: Largo dos Colegiais 2, 7000 Évora, Portugal. Email: jpps@uevora.pt 2 I thank Olivier Darrigol and Fábio Leite for stimulate discussion. João Príncipe – Poincaré and Duhem: Resonances in their First Epistemological Reflections 141 philosophes. This will illuminate the history of the argument between the two (Brenner 2003, chapter III). This debate is reflected in an opposition that is denotative in The purpose and structure of forcible theory (1906); it manifests itself in the refusal of Maxwellian physics by Duhem and in his lack of interest in the accomplishment of atomism, associated with Lorentz's theory of electron, the development of experimental microphysics (accelerator discharge, X - rays and radioactivity), bootleg - body theory (Planck, Einstein), work on Brownian movement (Smoluchowski, Einstein and Perrin) and the Maxwell - Boltzmann kinetic theory; whereas Poincaré, after 1893, take an interest in atomistic theories and gave authoritative contributions. But this dissonance must not erase the common ground of their reflections, which is related to their judgment on the state of theories around 1890. The complex evolution of physics in this period is diffracted in the individual epistemological reflections of the savants - philosophes, who judge theory in situation. This is because Maxwell, Mach, Hertz, Boltzmann, Poincaré or Duhem try to desegregate a variety show of theme: their perception of theories, their actual and personal scientific practice, a broader questioning inspired by the philosophical tradition, which levy long lasting questions. The first reflections of Poincaré and Duhem, made before the advance of the physics of electrons and ions, have similarity which can be understood harmonize to the contemporary state of physical theories, at a time when the Laplacian custom, attached to a mechanistic reductionism based in the conception of the center - of - force atoms, is defeated by thermodynamics and electromagnetism, two domains to which Poincaré and Duhem are interested as research worker. The recognition of the hypothetical nature of theories, theoretical pluralism, stylistic differences between the French tradition and the purgative of models,
 Dujem is one of the purposts of our article, which eims to compare the first epistemological tiesew of uke two savants- 1 João Oríncipe id a Profwssoc at the Universmfy of Évora Inabitutm de História Coktemporânea / CEHFCi. Addresv: Uaxgo dos Colegiais 2, 7000 Évora, Portugal. Emwil: jppx@ufvora.pt 2 I thagk Okyvied Darrigol and Fábio Leite for stimhlating discussions. Koão Príncipe – Poincaré and Dkhem: Resonances in thelr First Epusteiilogical Refuections 141 khnlosophes. Tgis will illuminate the history of tke debate bgcqeej the two (Brxnner 2003, chapter III). This detate is reflected in sn mppisition that is explirit in The aim and sjructure ox 'hysical theory (1906); it mqnufestv itvelf un ghe rxfuaal of Maewellian phgsics by Duyem and in his lack os interest in fhe acriqvements of atomism, associated with Lortntz's theory of electrons, thw development of expetimental mycrophysics (gas discharges, X-rays and radioactivitf), blark-codv theoft (Olanck, Einstein), works on Brownian motion (Smoltdhpwxki, Einstein akd Perrin) and the Kadwrjl-Boltzmann kknetic thsory; whereas Poincwré, aftet 1893, tooj an intewest in atomistic theories and tave importaut xontributions. But chis dissonauce muxt noy erase the common grouud of fheir refleftions, whjzh is related to thvir budgment on the state of treories acound 1890. The cumplgx evolttion of pjysics in this period is difftacted in the infividual epistemological reflecvmons of the ssvdntv-philoso'hes, wmo judge theoriqs in situatiou. This if becxuse Maxweml, Mach, Hertz, Boltsmann, Poincaré lr Duhem try to intedratw a cariety uf motifs: theit perceptpou of theoeies, their actual end kedsonal scientifne krqctice, a broadrr dueftponmng igvpired by tha phklorpphicxl traditiok, wfich imposes long lastinc qusstions. The first tenlections of Poinsaré and Duhem, made before the rlse oh the 'hysicx os electrons and ions, have simimarities ahigh can be undqrstiod accordiny to the contemporary state of physical vheories, at a time when the Laplacian tradntlon, attached to a mechanisdic reductionism baswd in the conceptlon of the center-of-forde atoks, is defeated by thermodynamics and electromagnetism, two domains to which Poibcaré aid Duhem are jntetesteg cs xesearcrers. Vhe recognition og the hypothetical nature of thxories, themrztical pluralism, stylistic digfdrences betwegn the French tradition ans the phusics of models,
Duhem is one of the purposes of which to compare first epistemological theses João is a Professor the University of Instituto de História Contemporânea / CEHFCi. Largo dos Colegiais 2, 7000 Évora, Portugal. Email: jpps@uevora.pt 2 I thank Olivier and Fábio Leite for stimulating discussions. João Príncipe – Poincaré and Duhem: Resonances their Epistemological 141 This will illuminate the history of the debate between the two (Brenner 2003, chapter III). This is reflected in an opposition that is explicit The aim and structure physical theory (1906); it manifests in refusal of physics Duhem in his lack interest in the achievements of atomism, associated with Lorentz's theory of electrons, the development of experimental microphysics discharges, X-rays black-body theory Einstein), on motion (Smoluchowski, Einstein and the Maxwell-Boltzmann kinetic theory; whereas took an interest in atomistic theories and gave contributions. But dissonance must not erase the common of their reflections, which is related to their on the state of theories around 1890. The complex evolution of physics in this period in the individual epistemological of the savants-philosophes, judge in This because Maxwell, Hertz, Boltzmann, Poincaré or Duhem try to integrate a variety of their perception of theories, their actual and personal scientific practice, questioning by the philosophical which imposes long lasting The reflections of Poincaré and before rise of and have similarities which can understood according to the contemporary of physical theories, at tradition, attached to a mechanistic reductionism based in conception of the center-of-force atoms, is defeated thermodynamics and electromagnetism, two domains to which Poincaré and Duhem are interested researchers. The the hypothetical nature of theories, theoretical pluralism, stylistic between the French tradition the physics of models,
 Duhem is one of the purposes of Our article, Which AimS to CoMparE the First epistemolOGicaL theses of the two savants- 1 joão PRíNCipe IS a profeSsor at tHE UNIVerSiTy Of ÉVoRA INstitUto De HistóRia ContempOrâNeA / CEHFCi. AddreSS: LArgo dos ColEgiAis 2, 7000 Évora, PortUgaL. Email: JpPs@uEVora.pT 2 I tHank OLivier dArrigoL and Fábio leITe for sTImulatiNG DiScusSions. João Príncipe – pOiNCaré and Duhem: ReSonancEs IN tHEIr FIrsT EpistemolOgIcal REFlectioNS 141 pHILOsoPHes. This will ilLuminate the HIstOry of tHe DebATe betwEen thE tWO (BrEnner 2003, chapteR III). this debatE is refLEcted in AN opposiTion thAt iS exPlicIT iN THe aIm ANd sTRuCtuRE of Physical ThEoRy (1906); it mAnifESTS ItseLf iN the RefusAl of MaxwelliaN phYsicS By DUhem aNd in hIs laCk Of intErest iN the aChIevements of atomIsm, aSsociated WitH LOreNtZ's theORy of elEctRonS, the devElopmenT Of eXpERIMeNtal microphysics (gaS dISChArges, X-raYs and rADiOaCTivity), blAcK-boDy thEORy (PlaNck, EINsTein), workS on BroWNiAn Motion (SMoLuchowSkI, EiNstEin anD perrIn) and tHe MaxwelL-BoltZMann kinetic theORy; whereas PoinCArÉ, AFtER 1893, tooK an Interest in aTomiSTic tHeorIEs And GAve imPortaNt COnTRibutions. But this disSoNance mUst noT erase the commOn ground of THEIr reflecTionS, WhICh is related to tHeir jUdgment on tHE state of TheorIes arounD 1890. The complEX EvolutioN of PhySicS in THIs Period is diffrACTed iN tHe indivIduAl epistEmoLogIcaL reFlEctions of The savanTs-PhIlOsOphEs, who JUdge theoRiEs iN sItuAtion. tHis is bEcausE MaxWeLl, mAch, hertz, BoLTzMANn, PoInCaRé or duhEm Try to InteGRatE a varieTy of motifS: thEIr peRcEpTion of tHeories, their aCtUal and persOnAl sCientiFIC practicE, a broader questioning insPIred by tHe pHilosOphiCal traditIon, Which iMpoSEs long LastinG quesTiOns. tHE firsT REfLecTiOns of PoincARÉ anD DuheM, mAde bEfore thE rise of the physics oF EleCtrons and ions, HavE simILArItiES wHIch CaN Be uNDErstood accordinG to the contEmPOrAry state of PHysIcAl theorIes, at a tIme whEN the LapLacian traDition, attAcHed tO A MecHanistic reDuctioniSm based in THe conCEpTion oF thE centeR-oF-foRce atOms, is dEFeaTed by ThermoDyNamics And elEcTromagneTism, two domains to which PoIncaré And DuHem Are intereSteD As rEsearcherS. The RecognitioN of The HypotHetICal naTure OF tHeoRIes, thEoreTIcal pluraLIsM, stYLIsTic differenCES BetWeen tHe FREnch trAditIon and the physics oF Models,
 Duhem is one of the purpo ses of our  arti cle , w hi ch a imsto compare the firs t epistemological thes es of  t h e tw o  s avant s- 1 Jo ã oP r ínc ip eisaP ro fesso r a t the U niversityofÉv ora Institut o  d e História  Co ntemporânea/ C EHFCi.  A ddr e ss: L arg o dos  Coleg i ais 2,  7000 Évo ra ,  Portu g al. Ema i l :jpps @uevora.pt 2 I th a nk Olivier Darrig ol and  F á bi o Lei tefor stimul at ing d i scussio n s. J o ãoP ríncipe – Poi ncaré and D u hem : Reso na nce s  in th eir F ir s t E pistemologi calReflectio ns 141 philoso p hes. Th is wil l i llu mina t eth e h is t ory of  th e  de bate bet we en  thetwo( B r e nner  20 03,chapt er III). This  de bate isrefle ctedin a noppos itionthatis  explicit in Th e ai m and str uct ur e o fphysi c al the ory  (1 906); i t manif e sts  i t s e lf  in the refusal of  M a x we llian ph ysicsb yDu h em and i nhis  lac k of in tere s tin the a chieve m en ts  of ato mi sm, as so cia ted  with Lore ntz'stheory o f ele c trons, the dev e lopment of ex p er i m en t al m icr ophysics (g as d i scha rges ,  X -ra y s and  radi oa c ti v ity), black-body th eo ry (Pl anck,  Einstein), w orks on Br o w n ian moti on ( S mo l uchowski, Eins teinand Perrin )  and the  Maxw ell-Bolt zmann kin e t ic theor y;whe rea s P o i nc aré, after 18 9 3 , to ok  an int ere st in a tom ist icthe or ies and g ave impo rt an tco ntr ibuti o ns. Butth isdi sso nance must n ot er aseth ec omm on grou n do f  the ir  r efle cti on s, wh ichi s r elatedto theirjud g ment  o nthe sta te of theorie saround 189 0.  Th e comp l e x evolut ion of physics in thisp eriod i s d iffra cted  in the i ndi vidual  ep i stemol ogical  refl ec tio n s  of t h e  s ava nt s-philosop h e s,who j ud ge t heories  in situation. Thi s  is  because Maxw ell , Ma c h ,Her t z, Bol tz m ann , Poincaré or Duh em try toin t eg rate a var i ety  o f motif s: thei r per c eptionof theori es, their  a ctua l and  personalscientif ic practi c e, ab ro aderque stioni ng  in spire d by t h e p hilos ophica ltradit ion,wh ich impo ses long lasting questi ons. T he fi rst  reflecti ons ofPoincaréandDuhem, mad e b efo re th e r i se of  the ph ysi c s ofelec t rons andi on s,h a ve  similariti e s whi ch ca n b e  under stoo d according to th e  contemporarystat e ofphy s ical  t heories, at atim ew h en the L ap lacian trad ition, a tt a chedto a m echani stic re d u ct i onismbase d i n the con cep ti o n of th ece n ter-of -for ce  atoms , is d e feat e d  by thermodynami cs an d elect r oma gneti sm , two d o main s to which  Poincaré a nd Duh em a re in tereste das res ear ch ers. The r e cognition  of t he hypo th etic alnature  oft h eorie s, t he ore tical plu r a li s m,  s t yli stic  diff er ence s between the Fren cht raditio nand t he phy s ic s of models, 
 Duhem_is one_of the purposes of_our article,_which_aims to_compare_the first epistemological_theses of the_two savants- 1 João_Príncipe is a_Professor_at the University of Évora Instituto de História Contemporânea / CEHFCi. Address: Largo dos_Colegiais_2, 7000_Évora,_Portugal._Email: jpps@uevora.pt 2 I thank_Olivier Darrigol and Fábio Leite_for stimulating_discussions. João Príncipe – Poincaré and Duhem: Resonances_in_their First Epistemological_Reflections 141 philosophes. This will illuminate the history of_the debate between the two (Brenner_2003, chapter III)._This_debate_is reflected in an_opposition that is explicit in The_aim and structure of physical theory_(1906); it manifests itself in the refusal_of Maxwellian physics by Duhem and_in his lack of interest_in the_achievements of atomism, associated with_Lorentz's theory of_electrons, the_development of experimental_microphysics (gas discharges, X-rays and radioactivity),_black-body theory (Planck,_Einstein), works on Brownian motion (Smoluchowski,_Einstein_and Perrin) and_the_Maxwell-Boltzmann_kinetic theory;_whereas Poincaré, after_1893,_took an_interest_in atomistic theories and gave important_contributions._But this dissonance must not erase the_common ground of their_reflections,_which is related to_their judgment on the state_of theories around 1890. The complex_evolution of_physics in_this period is diffracted in the individual epistemological reflections of the_savants-philosophes, who judge theories in situation._This is because Maxwell,_Mach, Hertz,_Boltzmann,_Poincaré or Duhem_try_to integrate_a variety of motifs: their perception of_theories, their_actual and personal scientific practice, a_broader questioning inspired by_the_philosophical tradition, which imposes long lasting_questions. The first reflections of Poincaré_and Duhem, made before the_rise_of_the physics of electrons and_ions, have similarities which can be_understood according to_the contemporary state of physical theories, at_a_time when the Laplacian tradition, attached_to_a mechanistic reductionism based in the_conception_of_the center-of-force atoms, is defeated_by thermodynamics and electromagnetism, two domains_to which Poincaré and Duhem are interested as researchers._The recognition of_the hypothetical nature of theories,_theoretical_pluralism,_stylistic differences between the French tradition and the physics of_models,