Thegradualpermeationofthefieldbythegreatdoctrineofconservationsimplyrepeatedthehistoryoftheintroductionofeverynovelandrevolutionarythought。Necessarilytheeldergeneration，towhomallformsofenergywereimponderablefluids，mustpassawaybeforethenewconceptioncouldclaimthefield。
Eventhewordenergy，thoughYounghadintroduceditin1807，didnotcomeintogeneralusetillsometimeafterthemiddleofthecentury。Tothegeneralityofphilosophersthewordphysicistwasevenlessinfavoratthistimethevariousformsofenergywerestillsubtilefluids，andneverwasidearelinquishedwithgreaterunwillingnessthanthis。TheexperimentsofYoungandFresnelhadconvincedalargenumberofphilosophersthatlightisavibrationandnotasubstance；
butsogreatanauthorityasBiotclungtotheoldemissionideatotheendofhislife，in1862，andheldafollowing。
Meantime，however，thecompanyofbrilliantyoungmenwhohadjustservedtheirapprenticeshipwhenthedoctrineofconservationcameuponthescenehadgrownintoauthoritativepositions，andwerebattlingactivelyforthenewideas。Confirmatoryevidencethatenergyisamolecularmotionandnotan\"imponderable\"formofmatteraccumulateddaybyday。
TheexperimentsoftwoFrenchmen，HippolyteL。