Thefunctionofthefloatingweightistoautomaticallykeepthestylusincloseengagementwiththerecord，thusinsuringaccuracyofreproduction。Theweightpressesthestylustoitswork，butbecauseofitsmassitcannotrespondtotheextremelyrapidvibrationsofthestylus。Theyarethereforecommunicatedtothediaphragm。
SomeofEdison\'smostremarkableinventionsarerevealedinanumberofinterestingpatentsrelatingtotheduplicationofphonographrecords。Itwouldbeobviouslyimpossible，fromacommercialstandpoint，toobtainamusicalrecordfromahigh-classartistandsellsuchanoriginaltothepublic，asitscostmightbefromonehundredtoseveralthousanddollars。Consequently，itisnecessarytoprovidesomewaybywhichduplicatesmaybemadecheaplyenoughtopermittheirpurchasebythepublicatareasonableprice。
Themakingofaperfectoriginalmusicalorotherrecordisamatterofnosmalldifficulty，asitrequiresspecialtechnicalknowledgeandskillgatheredfrommanyyearsofactualexperience；butintheexactcopying，orduplication，ofsucharecord，withitsmanymillionsofmicroscopicwavesandsub-waves，thedifficultiesareenormouslyincreased。Theduplicatesmustbemicroscopicallyidenticalwiththeoriginal，theymustbefreefromfalsevibrationsorotherdefects，althoughbothoriginalandduplicatesareofsucheasilydefacablematerialaswax；andtheprocessmustbecheapandcommercialnotascientificlaboratorypossibility。
Formakingduplicatesitwasobviouslynecessarytofirstsecureamoldcarryingtherecordinnegativeorreversedform。Fromthiscouldbemolded，orcast，positivecopieswhichwouldbeidenticalwiththeoriginal。Whiletheartofelectroplatingwouldnaturallysuggestitselfasthemeansofmakingsuchamold，anapparentlyinsurmountableobstacleappearedontheverythreshold。Wax，beinganon-
conductor，cannotbeelectroplatedunlessaconductingsurfacebefirstapplied。Thecoatingsordinarilyusedinelectro-