Edisonhasalwaysbeendeeplyinterestedin“conservation，“andmuchofhisworkhasbeendirectedtowardtheeconomyoffuelinobtainingelectricalenergydirectlyfromtheconsumptionofcoal。Indeed，itwillbenotedthattheexampleofhishandwritingshowninthesevolumesdealswiththeimportanceofobtainingavailableenergydirectfromthecombustiblewithouttheenormouslossintheinterveningstagesthatmakesourbestmodernmethodsofsteamgenerationandutilizationsobarbarouslyextravagantandwasteful。Severalyearsago，experimentinginthisfield，Edisondevisedandoperatedsomeingeniouspyromagneticmotorsandgenerators，based，asthenameimplies，onthedirectapplicationofheattothemachines。ThemotorisfoundedupontheprinciplediscoveredbythefamousDr。WilliamGilbert——courtphysiciantoQueenElizabeth，andtheFatherofmodernelectricity——thatthemagneticpropertiesofirondiminishwithheat。Atalight-redheat，ironbecomesnon-magnetic，sothatastrongmagnetexertsnoinfluenceoverit。Edisonemployedthispeculiarpropertybyconstructingasmallmachineinwhichapivotedbarisalternatelyheatedandcooled。Itisthusattractedtowardanadjacentelectromagnetwhencoldandisuninfluencedwhenhot，andastheresultmotionisproduced。
Thepyromagneticgeneratorisbasedonthesamephenomenon；itsaimbeingofcoursetogenerateelectricalenergydirectlyfromtheheatofthecombustible。
Thearmature，ormovingpartofthemachine，consistsinrealityofeightseparatearmaturesallconstructedofcorrugatedsheetironcoveredwithasbestosandwoundwithwire。Thesearmaturesareheldinplacebytwocircularironplates，throughthecentreofwhichrunsashaft，carryingatitslowerextremityasemicircularshieldoffire-clay，whichcoverstheendsoffourofthearmatures。Theheat，ofwhateverorigin，isappliedfrombelow，andtheshaftbeingrevolved，fourofthearmatureslosetheirmagnetismconstantly，whiletheotherfourgainit，sotospeak。
Asthemovingpartrevolves，therefore，currentsofelectricityaresetupinthewiresofthearmaturesandarecollectedbyacommutator，asinanordinarydynamo，placedontheupperendofthecentralshaft。
AgreatvarietyofelectricalinstrumentsareincludedinEdison\'sinventions，manyoftheseinfundamentalorearlierformsbeingdevisedforhissystemsoflightandpower，asnotedalready。Therearenumerousothers，anditmightbesaidwithtruththatEdisonishardlyeverwithoutsomenewdeviceofthiskindinhand，asheisbynomeanssatisfiedwiththepresentstatusofelectricalmeasurements。Heholdsingeneralthatthemetersofto-day，whetherforheavyorforfeeblecurrents，aretooexpensive，andthatcheaperinstrumentsareanecessityofthetimes。