Thisabnormalstateofaffairswasmanifestlyprejudicialtohiswork,butithad,nevertheless,thehappyresultofbringinghisstudentsclosertohim,foritallowedthem,attimes,toshareinhispersonalscientificinterests.
Hisreturntoexperimentalresearchismarkedbyaprofoundstudyofthe"directreadingperiodicprecisionbalanceforleastweights."(,,.)Inthisbalance,theuseofsmallweightsissuppressedbytheemploymentofamicroscopebymeansofwhichonereadsamicrometerattachedtotheextremityofoneofthearmsofthebalance.Thereadingismadewhentheoscillationofthebalanceisarrested,whichcanoccurveryrapidly,thankstotheuseofpneumaticdampenersconvenientlyconstructed.Thisbalancemarksaconsiderableadvanceoveroldsystems.Ithasshownitselfparticularlyvaluableinlaboratoriesforchemicalanalysis,wheretherapidityoftheweighingsisfrequentlyatestofprecision.WecansaythattheintroductionoftheCuriebalancesmarksanepochintheconstructionoftheseinstruments.Theworkdoneinthisfieldwasfarfromempirical;itcomprisedastudyofthetheoryofdampedmovementsandtheconstructionofnumerouscurvesestablishedwiththeaidofsomeofhisstudents.
ItwastowardthatPierreCuriebeganalongseriesofinvestigationsonthemagneticpropertiesofbodiesatdiverstemperatures(fromthenormalupto℃).Theseinvestigations,coveringyears,werepresentedasaDoctor'sthesisbeforetheFacultyofSciencesoftheUniversityofParisin.Inithestatedpreciselyinthefollowingfewwordstheobjectandresultsofhiswork:
"Fromthepointofviewoftheirmagneticproperties,bodiesmaybedividedintotwogroups:diamagneticbodies,bodiesonlyfeeblymagnetic,andparamagneticbodies.Atfirstsightthetwogroupsseementirelyseparate.Theprincipalaimofthisresearchhasbeentodiscoverifthereexisttransitionsbetweenthesetwostatesofmatter,andifitispossibletomakeagivenbodypassprogressivelythroughthem.TodeterminethisIhaveexaminedthepropertiesofagreatnumberofbodiesattemperaturesdifferingasmuchaspossible,inmagneticfieldsofvaryingintensities.
"Myexperimentsfailedtoproveanyrelationbetweenthepropertiesofdiamagneticandthoseofparamagneticbodies.Andtheresultssupportthetheorieswhichattributemagnetismanddiamagnetismtocausesofadifferentnature.Onthecontrary,thepropertiesofferro-magneticbodiesandofbodiesfeeblymagneticareintimatelyunited."
Thisexperimentalworkpresentedmanydifficulties,foritnecessitatedthemeasuringofveryminuteforces(oftheorderof/ofamilligrammeweight)withinacontainerwherethetemperaturecouldattain℃.
AsPierreCuriewellunderstood,theresultsheobtainedare,fromatheoreticpointofview,offundamentalimportance.TheCurielaw,accordingtowhichthecoefficientofmagnetizationofabodyfeeblymagnetizedvariesininverseratiototheabsolutetemperature,isaremarkablysimplelaw.ItisquitecomparabletotheGay-Lussaclawrelatingtothevariationofthedensityofaperfectgaswiththetemperature.InhiswellknowntheoryofmagnetismP.Langevin,in,tookintoaccounttheCurielawandarrivedagain,theoretically,atthedifferencebetweentheoriginsofdiamagnetismandparamagnetism.Hiswork,aswellastheimportantinvestigationsofP.Weiss,demonstratedtheaccuracyofPierreCurie'sconclusions,aswellastheimportanceoftheanalogythatheperceivedbetweentheintensityofmagnetizationandthedensityofafluid——theparamagneticstatebeingcomparabletoagaseousstate,andtheferro-magneticstatetothestateofcondensation.
Inconnectionwiththiswork,PierreCuriespentsometimeinthesearchforunknownphenomenawhoseexistencedidnotseem,apriori,impossibletohim.Hesoughtforbodiesstronglydiamagnetic,butfoundnone.Hetriedtodiscover,too,iftherewerebodiesthatactedasconductorsofmagnetism,andifmagnetismcanexistina"freestate,"likeelectricity.Herealsotheresultwasnegative.Heneverpublishedanyoftheseinvestigations,forhehadthehabitofthusengaginginthepursuitofphenomena,oftenwithlittlehopeofsuccess,solelyfortheloveoftheunforeseen,andwithouteverthinkingofpublication.
Becauseofthisentirelydisinterestedpassionforscientificresearchthepresentationofadoctor'sthesiswhichwouldgiveanaccountoftheseearlyinvestigationshadneverappealedtohim.Hewasalreadythirty-fiveyearsoldwhenhedecidedtogathertogether,insuchathesis,theresultsofhisbeautifulworkonmagnetism.
Ihaveaveryvividmemoryofhowhesustainedhisthesisbeforetheexaminers,forhehadinvitedme,becauseofthefriendshipthatalreadyexistedbetweenus,tobepresentontheoccasion.ThejurywascomposedofProfessorsBonty,Lippmann,andHautefeuille.Intheaudienceweresomeofhisfriends,amongthemhisagedfather,extremelyhappyinhisson'ssuccess.Irememberthesimplicityandtheclarityoftheexposition,theesteemindicatedbytheattitudeoftheprofessors,andtheconversationbetweenthemandthecandidatewhichremindedoneofameetingofthePhysicsSociety.Iwasgreatlyimpressed;itseemedtomethatthelittleroomthatdayshelteredtheexaltationofhumanthought.