XIII
EDISON'SELECTRICRAILWAY
ASnarratedinChapterXVIII，thereweretwoelectricrailroadsinstalledbyEdisonatMenloPark——onein1880，originallyathirdofamilelong，butsubsequentlyincreasedtoaboutamileinlength，andtheotherin1882，aboutthreemileslong。Asthe1880roadwasbuiltverysoonafterEdison'snotableimprovementsindynamomachines，andastheartofoperatingthemtothebestadvantagewasthenbeingdeveloped，thisearlyroadwassomewhatcrudeascomparedwiththerailroadof1882；butbothwerepracticableandserviceableforthepurposeofhaulingpassengersandfreight。
Thescopeofthepresentarticlewillbeconfinedtoadescriptionofthetechnicaldetailsofthesetwoinstallations。
Theillustrationoppositepage454oftheprecedingnarrativeshowsthefirstEdisonlocomotiveandtrainof1880atMenloPark。
Forthelocomotiveafour-wheelirontruckwasused，anduponitwasmountedoneofthelong“Z“type110-voltEdisondynamos，withacapacityof75amperes，whichwastobeusedasamotor。Thismachinewaslaidonitsside，itsarmaturebeinghorizontalandlocatedtowardthefrontofthelocomotive。
WenowquotefromanarticlebyMr。E。W。Hammer，publishedintheElectricalWorld，NewYork，June10，1899，andafterwardelaboratedandreprintedinavolumeentitledEdisonia，compiledandpublishedundertheauspicesofacommitteeoftheAssociationofEdisonIlluminatingCompanies，in1904：“Thegearingoriginallyemployedconsistedofafriction-pulleyuponthearmatureshaft，anotherfriction-
pulleyuponthedrivenaxle，andathirdfriction-pulleywhichcouldbebroughtincontactwiththeothertwobyasuitablelever。Eachwheelofthelocomotivewasmadewithmetallicrimandacentreportionmadeofwoodorpapier-
mache。Athree-leggedspiderconnectedthemetalrimofeachfrontwheeltoabrasshub，uponwhichrestedacollectingbrush。Theotherwheelsweresubsequentlysoequipped。
Itwastheintention，therefore，thatthecurrentshouldenterthelocomotivewheelsatoneside，andafterpassingthroughthemetalspiders，collectingbrushesandmotor，wouldpassoutthroughthecorrespondingbrushes，spiders，andwheelstotheotherrail。“
Astotheroad：“Therailswerelightandwerespikedtoordinarysleepers，withagaugeofaboutthreeandone-halffeet。Thesleeperswerelaiduponthenaturalgrade，andtherewascomparativelynoeffortmadetoballasttheroad……Nospecialprecautionsweretakentoinsulatetherailsfromtheearthorfromeachother。“
Theroadstartedaboutfiftyfeetawayfromthegeneratingstation，whichinthiscasewasthemachineshop。Twoofthe“Z“typedynamoswereusedforgeneratingthecurrent，whichwasconveyedtothetworailsoftheroadbyundergroundconductors。
OnThursday，May13，1880，at4o'clockintheafternoon，thishistoriclocomotivemadeitsfirsttrip，packedwithasmanyofthe“boys“ascouldpossiblyfindaplacetohangon。“Everythingworkedtoacharm，until，instartingupatoneendoftheroad，thefrictiongearingwasbroughtintoactiontoosuddenlyanditwaswrecked。Thisaccidentdemonstratedthatsomeothermethodofconnectingthearmaturewiththedrivenaxleshouldbearranged。
“Asthusoriginallyoperated，themotorhaditsfieldcircuitinpermanentconnectionasashuntacrosstherails，andthisfieldcircuitwasprotectedbyasafety-catchmadebyturninguptwobareendsofthewireinitscircuitandwindingapieceoffinecopperwireacrossfromonebareendtotheother。Thearmaturecircuithadaswitchinitwhichpermittedthelocomotivetobereversedbyreversingthedirectionofcurrentflowthroughthearmature。
“Aftersomeconsiderationofthegearingquestion，itwasdecidedtoemploybeltsinsteadofthefriction-pulleys。“
Accordingly，Edisoninstalledonthelocomotiveasystemofbelting，includinganidler-pulleywhichwasusedbymeansofalevertotightenthemaindriving-belt，andthuspowerwasappliedtothedrivenaxle。Thisinvolvedsomeslippingandconsequentburningofbelts；also，ifthebeltwereprematurelytightened，theburning-outofthearmature。Thislattereventhappenedanumberoftimes，“andprovedtobesuchaseriousannoyancethatresistance-boxeswerebroughtoutfromthelaboratoryandplaceduponthelocomotiveinserieswiththearmature。Thissolvedthedifficulty。
Thelocomotivewouldbestartedwiththeseresistance-boxesincircuit，andafterreachingfullspeedtheoperatorcouldplugthevariousboxesoutofcircuit，andinthatwayincreasethespeed。“Tostop，thearmaturecircuitwasopenedbythemainswitchandthebrakeapplied。
Thisarrangementwasgenerallysatisfactory，buttheresistance-boxesscatteredabouttheplatformandfoot-restsbeingintheway，EdisondirectedthatsomeNo。8B。&S。
copperwirebewoundonthelowerlegofthemotorfield-
magnet。“Bydoingthistheresistancewasputwhereitwouldtakeuptheleastroom，andwhereitwouldserveasanadditionalfield-coilwhenstartingthemotor，anditreplacedalltheresistance-boxeswhichhadheretoforebeeninplainsight。Theboxesundertheseatwerestillretainedinservice。Thecoilofcoarsewirewasinserieswiththearmature，justastheresistance-boxeshadbeen，andcouldbepluggedinoroutofcircuitatthewillofthelocomotivedriver。Thegeneralarrangementthussecuredwasoperatedaslongasthisroadwasincommission。“
Onthisshortstretchofroadthereweremanysharpcurvesandsteepgrades，andinconsequenceofthehighspeedattainedashighasforty-twomilesanhourseveralderailmentstookplace，butfortunatelywithoutseriousresults。
Threecarswereinserviceduringtheentiretimeofoperatingthis1880railroad：oneaflat-carforfreight；oneanopencarwithtwobenchesplacedbacktoback；andthethirdabox-car，familiarlyknownasthe“Pullman。“ThislattercarhadaninterestingadjunctinanelectricbrakingsystemcoveredbyEdison'sPatentNo。248，430。“Eachcaraxlehadalargeirondiskmountedonandrevolvingwithitbetweenthepolesofapowerfulhorseshoeelectromagnet。Thepole-
piecesofthemagnetweremovable，andwouldbeattractedtotherevolvingdiskwhenthemagnetwasenergized，graspingthesameandactingtoretardtherevolutionofthecaraxle。“
InterestingarticlesonEdison'sfirstelectricrailroadwerepublishedinthetechnicalandotherpapers，amongwhichmaybementionedtheNewYorkHerald，May15andJuly23，1880；theNewYorkGraphic，July27，1880；andtheScientificAmerican，June6，1880。
Edison'ssecondelectricrailroadof1882wasmorepretentiousasregardslength，construction，andequipment。Itwasaboutthreemileslong，ofnearlystandardgauge，andsubstantiallyconstructed。Curvesweremodified，andgradeseliminatedwherepossiblebytheerectionofnumeroustrestles。Thisroadalsohadsomefeaturesofconventionalrailroads，suchassidings，turn-tables，freightplatform，andcar-house。“Currentwassuppliedtotheroadbyundergroundfeedercablesfromthedynamo-roomofthelaboratory。
Therailswereinsulatedfromthetiesbygivingthemtwocoatsofjapan，bakingthemintheoven，andthenplacingthemonpadsoftar-impregnatedmuslinlaidontheties。
Theendsoftherailswerenotjapanned，butwereelectroplated，togivegoodcontactsurfacesforfish-platesandcopperbonds。“
ThefollowingnotesofMr。FrederickA。Scheffler，whodesignedthepassengerlocomotiveforthe1882road，throwaninterestinglightonitstechnicaldetails：
“InMay，1881，IwasengagedbyMr。M。F。Moore，whowasthefirstGeneralManageroftheEdisonCompanyforIsolatedLighting，asadraftsmantoundertaketheworkofdesigningandbuildingEdison'selectriclocomotiveNo。2。
“PrevioustothattimeIhadbeenemployedintheengineeringdepartmentofGrantLocomotiveWorks，Paterson，NewJersey，andtheRhodeIslandLocomotiveWorks，Providence，RhodeIsland……
“ItwasMr。Edison'sidea，asIunderstooditatthattime，tobuildalocomotivealongthegenerallinesofsteamlocomotivesatleast，inoutwardappearance，andtocombineinthatrespecttheframework，truck，andotherpartsknowntobesatisfactoryinsteamlocomotivesatthesametime。
“Thisnaturallyrequiredtheservicesofadraftsmanaccustomedtosteam-locomotivepractice……Mr。Moorewasamanofgreatrailroadandlocomotiveexperience，andhisknowledgeinthatdirectionwasofgreatassistanceinthedesigningandbuildingofthislocomotive。
“AtthattimeIhadnoknowledgeofelectricity……Onecouldcountso-calledelectricalengineersonhisfingersthen，andhavesomefingersleftover。
“Consequently，theELECTRICALequipmentwasdesignedbyMr。Edisonandhisassistants。Thedataandparts，suchasmotor，rheostat，switches，etc。，weregiventome，andmyworkwastodesignthesupportingframe，axles，countershafts，drivingmechanism，speedcontrol，wheelsandboxes，cab，runningboard，pilotor`cow-catcher'，buffers，andevensupportsfortheheadlight。IbelieveIalsodesignedabellandsupports。FromthisitwillbeseenthatthelocomotivehadalltheessentialparaphernaliatomakeitLOOKlikeasteamlocomotive。
“Theprincipalpartoftheoutfitwastheelectricmotor。
Atthattimemotorswerecuriosities。Therewerenoelectricmotorsevenforstationarypurposes，exceptfreaksbuiltforexperimentaluses。Thismotorwasmadefromtheparts——
suchasfields，armature，commutator，shaftandbearings，etc。，ofanEdison“Z，“or60-lightdynamo。ItwastheonlysizeofdynamothattheEdisonCompanyhadmarketedatthattime……Asamotor，itwaswoundtorunatmaximumspeedtodevelopatorqueequaltoaboutfifteenhorse-powerwith220volts。AtthegeneratingstationatMenloParkfourZdynamosof110voltswereused，connectedtwoinseries，inmultiplearc，givingalinevoltageof220。
“Themotorwaslocatedinthefrontpartofthelocomotive，onitsside，withthearmatureshaftacrosstheframes，orparallelwiththedrivingaxles。
“Onaccountofthehighspeedofthearmatureshaftitwasnotpossibletoconnectwithdriving-axlesdirect，butthiswasanadvantageinoneway，asbyintroducinganintermediatecounter-shaftcorrespondingtothewell-knowntypeofdouble-reductionmotorusedontrolley-carssince1885，afairlygoodarrangementwasobtainedtoregulatethespeedofthelocomotive，exclusiveofresistanceintheelectriccircuit。
“Endlessleatherbeltingwasusedtotransmitthepowerfromthemotortothecounter-shaft，andfromthelattertothedriving-wheels，whichwerethefrontpair。Averticalidler-pulleywasmountedinaframeoverthebeltfrommotortocounter-shaft，terminatinginaverticalscrewandhand-wheelfortighteningthebelttoincreasespeed，orthereversetolowerspeed。Thishand-wheelwaslocatedinthecab，whereitwaseasilyaccessible……
“Theroughoutlinesketchedbelowshowsthelocationofmotorinrelationtocounter-shaft，belting，driving-wheels，idler，etc。：
“Onaccountofbothrailsbeingusedforcircuits，……thedriving-wheelshadtobesplitcircumferentiallyandcompletelyinsulatedfromtheaxles。Thiswasaccomplishedbymeansofheavywoodblockswellshellackedorotherwisetreatedtomakethemwaterandweatherproof，placedradiallyontheinsideofthewheels，andthensubstantiallyboltedtothehubsandrimsofthelatter。
“Theweightofthelocomotivewasdistributedoverthedriving-wheelsintheusuallocomotivepracticebymeansofspringsandequalizers。
“Thecurrentwastakenfromtherimsofthedriving-wheelsbyathree-prongedcollectorofbrass，againstwhichflexiblecopperbrusheswerepressed——asimplemannerofovercominganyinequalitiesoftheroad-bed。
“ThelateMr。CharlesT。HugheswasinchargeofthetrackconstructionatMenloPark……Hisworkwasexcellentthroughout，andtheresultswerehighlysatisfactorysofarastheycouldpossiblybewiththearrangementoriginallyplannedbyMr。Edisonandhisassistants。
“Mr。CharlesL。Clarke，oneoftheearliestelectricalengineersemployedbyMr。Edison，madeanumberoftestsonthis1882railroad。IbelievethattheenginedrivingthefourZgeneratorsatthepower-houseindicatedashighasseventyhorse-poweratthetimethelocomotivewasactuallyinservice。“
Theelectricalfeaturesofthe1882locomotivewereverysimilartothoseoftheearlierone，alreadydescribed。Shuntandseriesfield-windingswereaddedtothemotor，andtheserieswindingscouldbepluggedinandoutofcircuitasdesired。Theserieswindingwassupplementedbyresistance-
boxes，alsocapableofbeingpluggedinoroutofcircuit。
ThesevariouselectricalfeaturesarediagrammaticallyshowninFig。2，whichalsoillustratestheconnectionwiththegeneratingplant。
WequoteagainfromMr。Hammer，whosays：“Thefreight-
locomotivehadsinglereductiongears，asisthemodernpractice，butthepowerwasappliedthroughafriction-clutchThepassenger-locomotivewasveryspeedy，andninetypassengershavebeencarriedatatimebyit；thefreight-
locomotivewasnotsofast，butcouldpullheavytrainsatagoodspeed。Manythousandpeoplewerecarriedonthisroadduring1882。“ThegeneralappearanceofEdison'selectriclocomotiveof1882isshownintheillustrationoppositepage462oftheprecedingnarrative。InthepictureMr。Edisonmaybeseeninthecab，andMr。Insullonthefrontplatformofthepassenger-car。
XIV
TRAINTELEGRAPHY
WHILEtheone-timeartoftelegraphingtoandfrommovingtrainswasessentiallyawirelesssystem，andalliedinsomeofitsprinciplestotheartofmodernwirelesstelegraphythroughspace，thetwosystemscannot，strictlyspeakingberegardedasidentical，asthepracticeoftheformerwasbasedentirelyonthephenomenonofinduction。
Brieflydescribedinoutline，thetraintelegraphsystemconsistedofaninductioncircuitobtainedbylayingstripsofmetalalongthetoporroofofarailway-car，andtheinstallationofaspecialtelegraphlinerunningparallelwiththetrackandstrungonpolesofonlymediumheight。Thetrain，andalsoeachsignallingstation，wasequippedwithregulationtelegraphapparatus，suchasbattery，key，relay，andsounder，togetherwithinduction-coilandcondenser。Inaddition，therewasaspecialtransmittingdeviceintheshapeofamusicalreed，or“buzzer。“Inpractice，thisbuzzerwascontinuouslyoperatedataspeedofaboutfivehundredvibrationspersecondbyanauxiliarybattery。Itsvibrationswerebrokenbymeansofatelegraphkeyintolongandshortperiods，representingMorsecharacters，whichweretransmittedinductivelyfromthetraincircuittothepolelineorviceversa，andreceivedbytheoperatorattheotherendthroughahigh-resistancetelephonereceiverinsertedinthesecondarycircuitoftheinduction-coil。
Theaccompanyingdiagrammaticsketchofasimpleformofthesystem，asinstalledonacar，willprobablyservetomakethismoreclear。
AninsulatedwirerunsfromthemetalliclayersontheroofofthecartoswitchS，whichisshownopeninthesketch。
Whenamessageistobereceivedonthecarfromastationmoreorlessremote，theswitchisthrowntothelefttocon-
nectwithawirerunningtothetelephonereceiver，T。Theotherwirefromthisreceiverisrundowntooneoftheaxlesandtherepermanentlyconnected，thusmakingaground。
Theoperatorputsthereceivertohisearandlistensforthemessage，whichthetelephonerendersaudibleintheMorsecharacters。
Ifamessageistobetransmittedfromthecartoareceivingstation，nearordistant，theswitch，S，isthrowntotheotherside，thusconnectingwithawireleadingtooneendofthesecondaryofinduction-coilC。Theotherendofthesecondaryisconnectedwiththegroundingwire。Theprimaryoftheinduction-coilisconnectedasshown，oneendgoingtokeyKandtheothertothebuzzercircuit。Theothersideofthekeyisconnectedtothetransmittingbattery，whiletheoppositepoleofthisbatteryisconnectedinthebuzzercircuit。Thebuzzer，R，ismaintainedinrapidvibrationbyitsindependentauxiliarybattery，B。
Whenthekeyispresseddownthecircuitisclosed，andcurrentfromthetransmittingbattery，B，passesthroughprimaryofthecoil，C，andinducesacurrentofgreatlyincreasedpotentialinthesecondary。Thecurrentasitpassesintotheprimary，beingbrokenupintoshortimpulsesbythetremendouslyrapidvibrationsofthebuzzer，inducessimilarlyrapidwavesofhighpotentialinthesecondary，andtheseinturnpasstotheroofandthencethroughtheinterveningairbyinductiontothetelegraphwire。Byacontinuedliftinganddepressionofthekeyintheregularmanner，thesewavesarebrokenupintolongandshortperiods，andarethustransmittedtothestation，viathewire，inMorsecharacters，dotsanddashes。
Thereceivingstationsalongthelineoftherailwayweresimilarlyequippedastoapparatus，and，generallyspeakingtheoperationsofsendingandreceivingmessagesweresubstantiallythesameasabovedescribed。
Theequipmentofanoperatoronacarwasquitesimpleconsistingmerelyofasmalllap-board，onwhichweremountedthekey，coil，andbuzzer，leavingroomfortelegraphblanks。Tothisboardwerealsoattachedflexibleconductorshavingspringclips，bymeansofwhichconnectionscouldbemadequicklywithconvenientlyplacedterminalsoftheground，roof，andbatterywires。Thetelephonereceiverwasheldontheheadwithaspring，theflexibleconnectingwirebeingattachedtothelapboard，thusleavingtheoperatorwithbothhandsfree。
Thesystem，asshowninthesketchandelucidatedbythetext，representstheoperationoftraintelegraphyinasimpleform，butcombiningthemainessentialsoftheartasitwassuccessfullyandcommerciallypracticedforanumberofyearsafterEdisonandGillilandenteredthefield。
Theyelaboratedthesysteminvariousways，makingitmorecomplete；butithasnotbeendeemednecessarytoenlargefurtheruponthetechnicalminutiaeoftheartforthepurposeofthiswork。
XV
KINETOGRAPHANDPROJECTINGKINETOSCOPE
ALTHOUGHmanyoftheartsinwhichEdisonhasbeenapioneerhavebeenenrichedbyhisnumerousinventionsandpatents，whichweresubsequenttothoseofafundamentalnature，theso-calledmotion-pictureartisanexception，asthefollowing，togetherwiththreeotheradditionalpatents[30]
compriseallthathehastakenoutonthissubject：
UnitedStatesPatentNo。589，168，issuedAugust31，1897，reissuedintwoparts——namely，No。12，037，underdateofSeptember30，1902，andNo。12，192，underdateofJanuary12，1904。ApplicationfiledAugust24，1891。
[30]Not491，993，issuedFebruary21，1893；No。493，426，issuedMarch14，1893；No。772，647，issuedOctober18，1904。
Thereisnothingsurprisinginthis，however，asthepossibilityofphotographingandreproducingactualscenesofanimatelifearesothoroughlyexemplifiedandrenderedpracticablebytheapparatusandmethodsdisclosedinthepatentsabovecited，thatthesebasicinventionsinthemselvespracticallyconstitutetheart——itsdevelopmentproceedingmainlyalongthelineofmanufacturingdetails。Thatsuchaviewofhisworkiscorrect，thehighestcriterion——
commercialexpediency——bearswitness；forinspiteofthefactthatthecourtshavesomewhatnarrowedthebroadclaimsofEdison'spatentsbyreasonoftheinvestigationsofearlierexperimenters，practicallyalltheimmenseamountofcommercialworkthatisdoneinthemotion-picturefieldto-dayisaccomplishedthroughtheuseofapparatusandmethodslicensedundertheEdisonpatents。
ThephilosophyofthisinventionhavingalreadybeendescribedinChapterXXI，itwillbeunnecessarytorepeatithere。Sufficeittosaybywayofreminderthatitisfoundeduponthephysiologicalphenomenonknownasthepersistenceofvision，throughwhichaseriesofsequentialphotographicpicturesofanimatemotionprojecteduponascreeninrapidsuccessionwillreproducetotheeyealltheappearanceoftheoriginalmovements。
Edison'sworkinthisdirectioncomprisedtheinventionnotonlyofaspecialformofcameraformakingoriginalphotographicexposuresfromasinglepointofviewwithverygreatrapidity，andofamachineadaptedtoeffectthereproductionofsuchpicturesinsomewhatsimilarmannerbutalsooftheconceptionandinventionofacontinuousuniform，andevenlyspacedtape-likefilm，soabsolutelyessentialforboththeaboveobjects。
Themechanismofsuchacamera，asnowused，consistsofmanypartsassembledinsuchcontiguousproximitytoeachotherthatanillustrationfromanactualmachinewouldnothelptoclearnessofexplanationtothegeneralreader。Henceadiagramshowingasectionalviewofasimpleformofsuchacameraispresentedbelow。
Inthisdiagram，Arepresentsanouterlight-tightboxcontainingalens，C，andtheothernecessarymechanismformakingthephotographicexposures，HandHbeingcasesforholdingreelsoffilmbeforeandafterexposure，Fthelong，tape-likefilm，Gasprocketwhoseteethengageinperforationsontheedgesofthefilm，suchsprocketbeingadaptedtoberevolvedwithanintermittentorstep-by-stepmovementbyhandorbymotor，andBarevolvingshutterhavinganopeningandconnectedbygearswithG，andarrangedtoexposethefilmduringtheperiodsofrest。A
fullviewofthisshutterisalsorepresented，withitsopening，D，inthesmallillustrationtotheright。
Inpractice，theoperationwouldbesomewhatasfollows，generallyspeaking：Thelenswouldfirstbefocussedontheanimatescenetobephotographed。Onturningthemainshaftofthecamerathesprocket，G，ismovedintermittently，anditsteeth，catchingintheholesinthesensitizedfilm，drawsitdownward，bringinganewportionofitslengthinfrontofthelens，thefilmthenremainingstationaryforaninstant。Inthemeantime，throughgearingconnectingthemainshaftwiththeshutter，thelatterisrotated，bringingitsopening，D，coincidentwiththelens，andthereforeexposingthefilmwhileitisstationary，afterwhichthefilmagainmovesforward。Solongastheactioniscontinuedthesemovementsarerepeated，resultinginasuccessionofenormouslyrapidexposuresuponthefilmduringitsprogressfromreelHtoitsautomaticrewindingonreelH。Whilethefilmispassingthroughthevariouspartsofthemachineitisguidedandkeptstraightbyvarioussetsofrollersbetweenwhichitruns，asindicatedinthediagram。
Byaningeniousarrangementofthemechanism，thefilmmovesintermittentlysothatitmayhaveamuchlongerperiodofrestthanofmotion。Asinpracticethepicturesaretakenatarateoftwentyormorepersecond，itwillbequiteobviousthateachperiodofrestisinfinitesimallybrief，beinggenerallyone-thirtiethofasecondorless。Stillitissufficienttobringthefilmtoamomentaryconditionofcompleterest，andtoallowforamaximumtimeofexposure，comparativelyspeaking，thusprovidingmeansfortakingclearlydefinedpictures。Thenegativessoobtainedaredevelopedintheregularway，andthepositiveprintssubsequentlymadefromthemareusedforreproduction。
Thereproducingmachine，or，asitiscalledinpractice，theProjectingKinetoscope，isquitesimilarsofarasitsgeneraloperationsinhandlingthefilmareconcerned。Inappearanceitissomewhatdifferent；indeed，itisintwoparts，theonecontainingthelightingarrangementsandcondensinglens，andtheotherembracingthemechanismandobjectivelens。The“taking“cameramusthaveitspartsenclosedinalight-tightbox，becauseoftheundeveloped，sensitizedfilm，buttheprojectingkinetoscope，usingonlyafullydevelopedpositivefilm，may，and，forpurposesofconvenientoperation，mustbeaccessiblyopen。TheillustrationFig。2
willshowtheprojectingapparatusasusedinpractice。
Thephilosophyofreproductionisverysimple，andisillustrateddiagrammaticallyinFig。3，referencelettersbeingthesameasinFig。1。Astotheadditionalreferenceletters，IisacondenserJthesourceoflight，andKareflector。
Thepositivefilmismovedintermittentlybutswiftlythroughoutitslengthbetweentheobjectivelensandabeamoflightcomingthroughthecondenser，beingexposedbytheshutterduringtheperiodsofrest。Thisresultsinapro-
jectionofthephotographsuponascreeninsuchrapidsuccessionastopresentanapparentlycontinuousphotographofthesuccessivepositionsofthemovingobjects，which，therefore，appeartothehumaneyetobeinmotion。
ThefirstclaimofReissuePatentNo。12，192describesthefilm。Itreadsasfollows：
“Anunbrokentransparentortranslucenttape-likephotographicfilmhavingthereonuniform，sharplydefined，equidistantphotographsofsuccessivepositionsofanobjectinmotionasobservedfromasinglepointofviewatrapidlyrecurringintervalsoftime，suchphotographsbeingarrangedinacontinuousstraight-linesequence，unlimitedinnumbersavebythelengthofthefilm，andsufficientinnumbertorepresentthemovementsoftheobjectthroughoutanextendedperiodoftime。“
XVI
EDISON'SORE-MILLINGINVENTIONS
THEwiderangeofEdison'sactivitiesinthisdepartmentoftheartsiswellrepresentedinthediversityofthenumerouspatentsthathavebeenissuedtohimfromtimetotime。Thesepatentsarebetweenfiftyandsixtyinnumber，andincludemagneticoreseparatorsoftendistincttypes；alsobreaking，crushing，andgrindingrolls，conveyors，dust-proofbearings，screens，driers，mixers，brickingapparatusandmachines，ovens，andprocessesofvariouskinds。
Adescriptionofthemanydevicesineachofthesedivisionswouldrequiremorespacethanisavailable；hence，weshallconfineourselvestoafewitemsofpredominatingimportance，alreadyreferredtointhenarrative。commencingwiththefundamentalmagneticoreseparator，whichwascoveredbyUnitedStatesPatentNo。228，329，issuedJune1，1880。
Theillustrationherepresentediscopiedfromthedrawingformingpartofthispatent。Ahopperwithadjustablefeedissupportedseveralfeetaboveabinhavingacentralpartition。Almostmidwaybetweenthehopperandthebinisplacedanelectromagnetwhosepolarextensionissoarrangedastobealittletoonesideofastreamofmaterialfallingfromthehopper。Normally，astreamoffinelydividedorefallingfromthehopperwouldfallintothatportionofthebinlyingtotheleftofthepartition。If，however，themagnetisenergizedfromasourceofcurrent，themagneticparticlesinthefallingstreamareattractedbyandmovetowardthemagnet，whichissoplacedwithrelationtothefallingmaterialthatthemagneticparticlescannotbeattractedentirelytothemagnetbeforegravityhascarriedthempast。Hence，theirtrajectoryisaltered，andtheyfallontheright-handsideofthepartitioninthebin，whilethenon-magneticportionofthestreamcontinuesinastraightlineandfallsontheotherside，thuseffectingacompleteseparation。
ThissimplebuteffectiveprinciplewastheoneemployedbyEdisoninhisgreatconcentratingplantalreadydescribed。
Inpractice，thenumeroushoppers，magnets，andbinsweremanyfeetinlength；andtheywerearrangedinbatteriesofvariedmagneticstrength，inorderthattheintermingledmassofcrushedrockandironoremightbemorethoroughlyseparatedbybeingpassedthroughmagneticfieldsofsuccessivelyincreasingdegreesofattractingpower。Altogethertherewereaboutfourhundredandeightyoftheseimmensemagnetsintheplant，distributedinvariousbuildingsinbatteriesasabovementioned，thecrushedrockcontainingtheironorebeingdeliveredtothembyconveyors，andthegangueandorebeingtakenawayafterseparationbytwootherconveyorsanddeliveredelsewhere。ThemagneticseparatorsatfirstusedbyEdisonatthisplantwereofthesamegeneralityastheonesemployedsomeyearspreviouslyintheseparationofsea-shoresand，butgreatlyenlargedandimproved。Thevariedexperiencesgainedintheconcentrationofvastquantitiesoforelednaturallytoagreaterdevelopment，andseveralnewtypesandarrangementsofmagneticseparatorswereevolvedandelaboratedbyhimfromfirsttolast，duringtheprogressoftheworkattheconcentratingplant。
Themagneticseparationofironfromitsorebeingthefoundationideaoftheinventionsnowunderdiscussion，aconsiderationoftheseparatorhasnaturallytakenprecedenceoverthoseofcollateralbutinseparableinterest。Theore-
bearingrock，however，mustfirstbegroundtopowderbeforeitcanbeseparated；hence，wewillnowbeginattherootofthisoperationandconsiderthe“giantrolls，“whichEdisondevisedforbreakinghugemassesofrock。InhisapplicationforUnitedStatesPatentNo。672，616，issuedApril23，1901，appliedforonJuly16，1897，hesays：“Theobjectofmyinventionistoproduceamethodforthebreakingofrockwhichwillbesimpleandeffective，willnotrequirethehand-sledgingorblastingoftherockdowntopiecesofmoderatesize，andwillinvolvetheconsumptionofasmallamountofpower。“
Whilethisquotationreferstothemethodas“simple，“
thepatentunderconsiderationcoversoneofthemostboldanddaringprojectsthatEdisonhaseverevolved。Heproposedtoeliminatetheslowandexpensivemethodofbreakinglargebouldersmanually，andtosubstitutethereformomentumandkineticenergyappliedthroughthemediumofmassivemachinery，which，inafewseconds，wouldbreakintosmallpiecesarockasbigasanordinaryuprightcottagepiano，andweighingasmuchassixtons。EngineerstowhomEdisoncommunicatedhisideaswereunanimousindeclaringthethinganimpossibility；itwaslikedrivingtwoexpress-trainsintoeachotheratfullspeedtocrackagreatrockplacedbetweenthem；thatnopracticalmachinerycouldbebuilttostandtheterrificimpactandstrains。Edison'sconvictionswerestrong，however，andhepersisted。
Theexperimentswereofheroicsize，physicallyandfinancially，butafterastruggleofseveralyearsandanexpenditureofabout$100，000，herealizedthecorrectnessandpracticabilityofhisplansinthesuccessofthegiantrolls，whichweretheoutcomeofhislabors。
Thegiantrollsconsistofapairofironcylindersofmassivesizeandweight，withremovablewearingplateshavingirregularsurfacesformedbyprojectingknobs。Theserollsaremountedsidebysideinaveryheavyframeleavingagapofaboutfourteeninchesbetweenthem，andaresobeltedupwiththesourceofpowerthattheyruninoppositedirections。ThegiantrollsdescribedbyEdisonintheabove-
namedpatentashavingbeenbuiltandoperatedbyhimhadacombinedweightof167，000pounds，includingallmovingparts，whichofthemselvesweighedaboutseventytons，eachrollbeingsixfeetindiameterandfivefeetlong。Atopviewoftherollsisshowninthesketch，onerollandoneofitsbearingsbeingshowninsection。
InFig。2therollsareillustrateddiagrammatically。Asasketchofthisnature，evenifgivenwithadefinitescale，doesnotalwayscarryanadequateideaofrelativedimensionstoanon-technicalreader，wepresentinFig。3aperspectiveillustrationofthegiantrollsasinstalledintheconcentratingplant。
Inpractice，asmallamountofpowerisappliedtorunthegiantrollsgraduallyuptoasurfacespeedofseveralthousandfeetaminute。Whenthishighspeedisattained，massesofrockweighingseveraltonsinoneormorepiecesaredumpedintoahopperwhichguidesthemintothegapbetweentherapidlyrevolvingrolls。Theeffectistopartiallyarresttheswiftmotionoftherollsinstantaneously，andtherebydevelopandexpendanenormousamountofkineticenergy，whichwithpile-drivereffectcrackstherocksandbreaksthemintopiecessmallenoughtopassthroughthefourteen-
inchgap。Asthepowerisappliedtotherollsthroughslippingfriction-clutches，thespeedofthedriving-pulleysisnotmateriallyreduced；hencetherollsmayagainbequicklyspeededuptotheirhighestvelocitywhileanotherloadofrockisbeinghoistedinpositiontobedumpedintothehopper。Itwillbeobviousfromtheforegoingthatifitwereattemptedtosupplythegreatenergynecessaryforthisoperationbydirectapplicationofsteam-power，anengineofenormoushorse-powerwouldberequired，andeventhenitisdoubtfulifonecouldbeconstructedofsufficientstrengthtowithstandtheterrificstrainsthatwouldensue。
Buttheworkisdonebythegreatmomentumandkineticenergyobtainedbyspeedingupthesetremendousmassesofmetal，andthensuddenlyopposingtheirprogress，theenginebeingrelievedofallstrainthroughthemediumoftheslippingfriction-clutches。Thus，thiscyclopeanoperationmaybecontinuouslyconductedwithanamountofpowerprodigiouslyinferior，inproportion，totheresultsaccomplished。
ThesketchFig。4showingalargeboulderbeingdumpedintothehopper，orroll-pit，willservetoillustratethemethodoffeedingthesegreatmassesofrocktotherolls，andwillalsoenablethereadertoformanideaoftherapidityofthebreakingoperation，whenitisstatedthataboulderofthesizerepresentedwouldbereducedbythegiantrollstopiecesatriflelargerthanaman'sheadinafewseconds。
Afterleavingthegiantrollsthebrokenrockpassedonthroughothercrushing-rollsofsomewhatsimilarconstruc-
tion。ThesealsowereinventedbyEdison，butantedatedthosepreviouslydescribed；beingcoveredbyPatentNo。
567，187，issuedSeptember8，1896。Theserollswereintendedforthereducingof“one-man-size“rockstosmallpieces，whichatthetimeoftheiroriginalinceptionwasaboutthestandardsizeofsimilarmachines。AttheEdisonconcentratingplantthebrokenrock，afterpassingthroughtheserolls，wasfurtherreducedinsizebyotherrolls，andwasthenreadytobecrushedtoafinepowderthroughthemediumofanotherremarkablemachinedevisedbyNOTE——Figs。3and4arereproducedfromsimilarsketchesonpages84and85
ofMcClure'sMagazineforNovember，1897，bypermissionofS。S。McClureCo。
Edisontomeethisever-recurringandwell-definedideasoftheutmosteconomyandefficiency。Thebestfinegrinding-
machinesthatitwasthenpossibletoobtainweresoinefficientastoinvolvealossof82percent。ofthepowerapplied。Thethoughtofsuchanenormouslosswasunbearable，andhedidnotrestuntilhehadinventedandputintouseanentirelynewgrinding-machine，whichwascalledthe“three-high“rolls。ThedevicewascoveredbyapatentissuedtohimonNovember21，1899，No。637，327。Itwasamostnoteworthyinvention，foritbroughtintotheartnotonlyagreaterefficiencyofgrindingthanhadeverbeendreamedofbefore，butalsoatremendouseconomybythesavingofpower；forwhereasthepreviousefficiencyhadbeen18percent。andtheloss82percent。，Edisonreversedthesefigures，andinhisthree-highrollsproducedaworkingefficiencyof84percent。，thusreducingthelossofpowerbyfrictionto16percent。AdiagrammaticsketchofthisremarkablemachineisshowninFig。5，whichshowsafrontelevationwiththecasings，hopper，etc。，removed，andalsoshowsabovetherollstheropeandpulleys，thesupportsforwhicharealsoremovedforthesakeofclearnessintheillustration。
Fortheconvenienceofthereader，inreferringtoFig。5，wewillrepeatthedescriptionofthethree-highrolls，whichisgivenonpages487and488oftheprecedingnarrative。
Inthetwoend-piecesofaheavyironframeweresetthreerolls，orcylinders——oneinthecentre，anotherbelow，andtheotherabove——allthreebeinginaverticalline。Theserollswereaboutthreefeetindiameter，madeofcast-iron，andhadface-platesofchilled-iron。[31]Thelowestrollwassetinafixedbearingatthebottomoftheframe，and，therefore，couldonlyturnaroundonitsaxis。Themiddleandtoprollswerefreetomoveupordownfromandtowardthelowerroll，andtheshaftsofthemiddleandupperrollsweresetinaloosebearingwhichcouldslipupanddownintheironframe。Itwillbeapparent，therefore，thatanymaterialwhichpassedinbetweenthetopandthemiddlerolls，andthemiddleandbottomrolls，couldbegroundasfineasmightbedesired，dependingentirelyupontheamountofpressureappliedtothelooserolls。Inoperationthematerialpassedfirstthroughtheupperandmiddlerolls，andthenbetweenthemiddleandlowestrolls。
[31]Thefacesoftheserollsweresmooth，butasthree-highrollscameintouselaterinEdison'sPortlandcementoperationsthefaceswerecorrugatedsoastofitintoeachother，gear-fashion，toprovideforahighrateoffeed。
Thispressurewasappliedinamostingeniousmanner。
Ontheendsoftheshaftsofthebottomandtoprollstherewerecylindricalsleeves，orbearings，havingsevensheavesinwhichwasrunahalf-inchendlesswirerope。Thisropewaswoundseventimesoverthesheavesasabove，andledupwardandoverasingle-groovesheave，whichwasoperatedbythepistonofanair-cylinder，andinthismannerthepressurewasappliedtotherolls。Itwillbeseen，thereforethatthesystemconsistedinasingleropepassedoversheavesandsoarrangedthatitcouldbevariedinlength，thusprovidingforelasticityinexertingpressureandregulatingitasdesired。Theefficiencyofthissystemwasincomparablygreaterthanthatofanyotherknowncrusherorgrinder，forwhileapressureofonehundredandtwenty-fivethousandpoundscouldbeexertedbytheserolls，frictionwasalmostentirelyeliminated，becausetheupperandlowerrollbearingsturnedwiththerollsandrevolvedinthewirerope，whichconstitutedthebearingproper。
SeveralotherimportantpatentshavebeenissuedtoEdisonforcrushingandgrindingrolls，someofthembeingforelaborationsandimprovementsofthoseabovedescribedbutallcoveringmethodsofgreatereconomyandeffectivenessinrock-grinding。
Edison'sworkonconveyorsduringtheperiodofhisore-
concentratinglaborswasdistinctivelyoriginal，ingeniousandfarinadvanceofthetimes。Hisconceptionoftheconcentratingproblemwasbroadandembracedanentiresystem，ofwhichaprincipalitemwasthecontinuoustransferofenormousquantitiesofmaterialfromplacetoplaceatthelowestpossiblecost。Ashecontemplatedtheconcentrationofsixthousandtonsdaily，theexpenseofmanuallabortomovesuchanimmensequantityofrock，sand，andorewouldbeabsolutelyprohibitive。Hence，itbecamenecessarytoinventasystemofconveyorsthatwouldbecapableoftransferringthismassofmaterialfromoneplacetoanother。Andnotonlymusttheseconveyorsbecapableofcarryingthematerial，buttheymustalsobedevisedsothattheywouldautomaticallyreceiveanddischargetheirrespectiveloadsatappointedplaces。Edison'singenuity，engineeringability，andinventiveskillwereequaltothetask，however，andweredisplayedinasystemandvarietyofconveyorsthatinpracticeseemedtoactwithalmosthumandiscrimination。Whenfullyinstalledthroughouttheplant，theyautomaticallytransferreddailyamassofmaterialequaltoaboutonehundredthousandcubicfeet，frommilltomill，coveringaboutamileinthetransit。Upanddown，windinginandout，turningcorners，deliveringmaterialfromonetoanother，makinganumberofloopsinthedrying-oven，fillingupbinsandpassingontothenextwhentheywerefull，theseconveyorsinautomaticactionseeminglyplayedtheirpartwithhumanintelligence，whichwasinrealitythereflectionoftheintelligenceandingenuitythathadoriginallydevisedthemandsettheminmotion。
SixofEdison'spatentsonconveyorsincludeavarietyofdevicesthathavesincecameintobroadgeneraluseforsimilarwork，andhavebeenthemeansofeffectinggreateconomiesinnumerousindustriesofwidelyvaryingkinds。
Interestingastheyare，however，weshallnotattempttodescribethemindetail，asthespacerequiredwouldbetoogreat。TheyarespecifiedinthelistofpatentsfollowingthisAppendix，andmaybeexaminedindetailbyanyinterestedstudent。
InthesamelistwillalsobefoundalargenumberofEdison'spatentsonapparatusandmethodsofscreening，drying，mixing，andbriquetting，aswellasfordust-proofbearings，andvarioustypesandgroupingsofseparators，allofwhichwerecalledforthbytheexigenciesandmagnitudeofhisgreatundertaking，andwithoutwhichhecouldnotpossiblyhaveattainedthesuccessfulphysicalresultsthatcrownedhislabors。Edison'spersistenceinreducingthecostofhisoperationsisnoteworthyinconnectionwithhisscreeninganddryinginventions，inwhichtheutmostadvantageistakenofthelawofgravitation。Withitsassistance，whichcostnothing，theseoperationswereperformedperfectly。Itwasonlynecessarytodeliverthematerialatthetopofthechambers，andduringitsnaturaldescentitwasscreenedordriedasthecasemightbe。
Alltheseinventionsanddevices，aswellasthosedescribedindetailaboveexceptmagneticseparatorsandmixingandbriquettingmachines，arebeingusedbyhimto-dayinthemanufactureofPortlandcement，asthatindustrypresentsmanyoftheidenticalproblemswhichpresentedthemselvesinrelationtotheconcentrationofironore。
XVII
THELONGCEMENTKILN
INthisremarkableinvention，whichhasbroughtaboutastrikinginnovationinalong-establishedbusiness，weseeanothercharacteristicinstanceofEdison'sincisivereasoningandboldnessofconceptioncarriedintopracticaleffectinfaceofuniversalopinionstothecontrary。
FortheinformationofthoseunacquaintedwiththeprocessofmanufacturingPortlandcement，itmaybestatedthatthematerialconsistspreliminarilyofanintimatemixtureofcementrockandlimestone，groundtoaveryfinepowder。Thispowderistechnicallyknowninthetradeas“chalk，“andisfedintorotarykilnsand“burned“；thatistosay，itissubjectedtoahighdegreeofheatobtainedbythecombustionofpulverizedcoal，whichisinjectedintotheinteriorofthekiln。Thiscombustioneffectsachemicaldecompositionofthechalk，andcausesittoassumeaplasticconsistencyandtocollecttogetherintheformofsmallsphericalballs。whichareknownas“clinker。“Kilnsareusuallyarrangedwithaslightincline，attheupperendofwhichthechalkisfedinandgraduallyworksitswaydowntotheinteriorflameofburningfuelattheotherend。Whenitarrivesatthelowerend，thematerialhasbeen“burned，“
andtheclinkerdropsoutintoareceivingchamberbelow。
Theoperationiscontinuous，aconstantsupplyofchalkpassinginatoneendofthekilnandacontinuousdribbleofclinker-ballsdroppingoutattheother。Aftercooling，theclinkerisgroundintoveryfinepowder，whichisthePortlandcementofcommerce。
Itisself-evidentthatanidealkilnwouldbeonethatproducedthemaximumquantityofthoroughlyclinkeredmaterialwithaminimumamountoffuel，labor，andinvestment。
WhenEdisonwaspreparingtogointothecementbusiness，helookedthegroundoverthoroughly，and，afterconsiderableinvestigationandexperiment，cametotheconclusionthatprevailingconditionsastokilnswerefarfromideal。
Thestandardkilnstheninusewereaboutsixtyfeetinlength，withaninternaldiameterofaboutfivefeet。Inallrotarykilnsforburningcement，thetrueclinkeringoperationtakesplaceonlywithinalimitedportionoftheirtotallength，wheretheheatisgreatest；hencetheinteriorofthekilnmaybeconsideredasbeingdividedlongitudinallyintotwopartsorzones——namely，thecombustion，orclinkering，zone，andthezoneofoncomingrawmaterial。Inthesixty-
footkilnthelengthofthecombustionzonewasabouttenfeet，extendingfromapointsixoreightfeetfromthelower，ordischarge，endtoapointabouteighteenfeetfromthatend。Consequently，beyondthatpointtherewasazoneofonlyaboutfortyfeet，throughwhichtheheatedgasespassedandcameincontactwiththeoncomingmaterial，whichwasinmovementdowntowardtheclinkeringzone。Sincethebulkofoncomingmaterialwassmall，thegaseswerenotcalledupontopartwithmuchoftheirheat，andthereforepassedonupthestackatveryhightemperatures，rangingfrom1500degreesto1800degreesFahr。Obviously，thisheatwasentirelylost。
Anadditionallossofefficiencyarosefromthefactthatthematerialmovedsorapidlytowardthecombustionzonethatithadnotgivenupallitscarbondioxideonreachingthere；andbythegivingoffoflargequantitiesofthatgaswithinthecombustionzone，perfectandeconomicalcombustionofcoalcouldnotbeeffected。
Thecomparativelyshortlengthofthesixty-footkilnnotonlylimitedtheamountofmaterialthatcouldbefedintoit，butthelimitationinlengthofthecombustionzonemilitatedagainstathoroughclinkeringofthematerial，thisoperationbeingoneinwhichtheelementsoftimeandproperheatareprimeconsiderations。Thusthequantityofgoodclinkerobtainablewasunfavorablyaffected。Byreasonoftheseandotherlimitationsandlosses，ithadbeenpossible，inpractice，toobtainonlyabouttwohundredandfiftybarrelsofclinkerperdayoftwenty-fourhours；andthatwithanexpenditureforcoalproportionatelyequaltoabout29to33percent。ofthequantityofclinkerproduced，evenassumingthatalltheclinkerwasofgoodquality。
Edisonrealizedthatthesecretofgreatercommercialefficiencyandimprovementofqualitylayintheabilitytohandlelargerquantitiesofmaterialwithinagiventime，andtoproduceamoreperfectproductwithoutincreasingcostorinvestmentinproportion。Hisreasoningledhimtotheconclusionthatthisresultcouldonlybeobtainedthroughtheuseofakilnofcomparativelygreatlength，andhisinvestigationsandexperimentsenabledhimtodecideuponalengthofonehundredandfiftyfeet，butwithanincreaseindiameterofonlysixinchestoafootoverthatofthesixty-
footkiln。
TheprincipalconsiderationsthatinfluencedEdisoninmakingthisradicalinnovationmaybebrieflystatedasfollows：
First。Theabilitytomaintaininthekilnaloadfromfivetoseventimesgreaterthanordinarilyemployed，therebytendingtoamoreeconomicaloutput。
Second。Thecombustionofavastlyincreasedbulkofpulverizedcoalandagreatlyenlargedcombustionzone，extendingaboutfortyfeetlongitudinallyintothekiln——thusprovidinganareawithinwhichthematerialmightbemaintainedinaclinkeringtemperatureforasufficientlylongperiodtoinsureitsbeingthoroughlyclinkeredfromperipherytocentre。
Third。Byreasonofsuchagreatlyextendedlengthofthezoneofoncomingmaterialandconsequentlymuchgreaterbulk，thegasesandotherproductsofcombustionwouldbecooledsufficientlybetweenthecombustionzoneandthestacksoastoleavethekilnatacomparativelylowtemperature。
Besides，theoncomingmaterialwouldthusbegraduallyraisedintemperatureinsteadofbeingheatedabruptly，asintheshorterkilns。
Fourth。Thematerialhavingthusbeengreatlyraisedintemperaturebeforereachingthecombustionzonewouldhavepartedwithsubstantiallyallitscarbondioxide，andthereforewouldnotintroduceintothecombustionzonesufficientofthatgastodisturbtheperfectcharacterofthecombustion。
Fifth。Onaccountofthegreatweightoftheheavyloadinalongkiln，therewouldresulttheformationofacontinuousplasticcoatingonthatportionoftheinnersurfaceofthekilnwheretemperaturesarehighest。Thiswouldeffectivelyprotectthefire-brickliningfromthedestructiveeffectsoftheheat。
Such，inbrief，weretheessentialprinciplesuponwhichEdisonbasedhisconceptionandinventionofthelongkiln，whichhassincebecomesowellknowninthecementbusiness。
Manyotherconsiderationsofaminorandmechanicalnature，butwhichwereimportantfactorsinhissolutionofthisdifficultproblem，areworthyofstudybythoseintimatelyassociatedwithorinterestedintheart。NottheleastofthemechanicalquestionswassettledbyEdison'sdecisiontomakethistremendouslylongkilninsectionsofcast-iron，withflanges，boltedtogether，andsupportedonrollersrotatedbyelectricmotors。Longitudinalexpansionandthrustwerealsoimportantfactorstobeprovidedfor，aswellasspecialdevicestopreventthepackingofthemassofmaterialasitpassedinandoutofthekiln。Specialprovisionwasalsomadeforinjectingstreamsofpulverizedcoalinsuchmannerastocreatethelargelyextendedzoneofcombustion。Astothedetailsoftheseandmanyotherin-
geniousdevices，wemustreferthecuriousreadertothepatents，asitismerelyintendedinthesepagestoindicateinabriefmannerthemainprinciplesofEdison'snotableinventions。TheprincipalUnitedStatespatentonthelongkilnwasissuedOctober24，1905，No。802，631。
Thathisreasoningsanddeductionswerecorrectinthiscasehavebeenindubitablyprovenbysomeyearsofexperiencewiththelongkilninitsabilitytoproducefromeighthundredtoonethousandbarrelsofgoodclinkereverytwenty-fourhours，withanexpenditureforcoalproportionatelyequaltoaboutonly20percent。ofthequantityofclinkerproduced。
Toillustratethelongcementkilnbydiagramwouldconveybutlittletothelaymind，andwethereforepresentanillustrationFig。1ofactualkilnsinperspective，fromwhichsenseoftheirproportionsmaybegathered。
XVIII
EDISON'SNEWSTORAGEBATTERY
GENERICALLYconsidered，a“battery“isadevicewhichgenerateselectriccurrent。Therearetwodistinctspeciesofbattery，onebeingknownas“primary，“andtheotheras“storage，“althoughthelatterissometimesreferredtoasa“secondarybattery“or“accumulator。“Everytypeofeachofthesetwospeciesisessentiallyalikeinitsgeneralmake-up；thatistosay，everycellofbatteryofanykindcontainsatleasttwoelementsofdifferentnatureimmersedinamoreorlessliquidelectrolyteofchemicalcharacter。
Onclosingthecircuitofaprimarybatteryanelectriccurrentisgeneratedbyreasonofthechemicalactionwhichissetupbetweentheelectrolyteandtheelements。Thisinvolvesagradualconsumptionofoneoftheelementsandacorrespondingexhaustionoftheactivepropertiesoftheelectrolyte。Byreasonofthis，boththeelementandtheelectrolytethathavebeenusedupmustberenewedfromtimetotime，inordertoobtainacontinuedsupplyofelectriccurrent。
Thestoragebatteryalsogenerateselectriccurrentthroughchemicalaction，butwithoutinvolvingtheconstantreprimingwithactivematerialstoreplacethoseconsumedandexhaustedasabovementioned。Theterm“storage，“asappliedtothisspeciesofbattery，is，however，amisnomer，andhasbeenthecauseofmuchmisunderstandingtonontechnicalpersons。Tothelayminda“storage“batterypresentsitselfintheaspectofadeviceinwhichelectricenergyisSTORED，justascompressedairisstoredoraccumulatedinatank。Thisview，however，isnotinaccordancewithfacts。Itisexactlyliketheprimarybatteryinthefundamentalcircumstancethatitsabilityforgeneratingelectriccurrentdependsuponchemicalaction。Instrictterminologyitisa“reversible“battery，aswillbequiteobviousifweglancebrieflyatitsphilosophy。Whenastoragebatteryis“charged，“byhavinganelectriccurrentpassedthroughit，theelectricenergyproducesachemicaleffect，addingoxygentothepositiveplate，andtakingoxygenawayfromthenegativeplate。Thus，thepositiveplatebecomesoxidized，andthenegativeplatereduced。Afterthechargingoperationisconcludedthebatteryisreadyforuse，anduponitscircuitbeingclosedthroughatranslatingdevice，suchasalampormotor，areversion“discharge“takesplace，thepositiveplategivingupitsoxygen，andthenegativeplatebeingoxidized。Thesechemicalactionsresultinthegenerationofanelectriccurrentasinaprimarybattery。
Asamatteroffact，thechemicalactionsandreactionsinastoragebatteryaremuchmorecomplex，buttheabovewillservetoaffordthelayreaderarathersimpleideaofthegeneralresultarrivedatthroughthechemicalactivityreferredto。
Thestoragebattery，asacommercialarticle，wasintroducedintothemarketintheyear1881。Atthattime，andallthroughthesucceedingyears，untilabout1905，therewasonlyonetypethatwasrecognizedascommerciallypracticable——namely，thatknownasthelead-sulphuric-acidcell，consistingofleadplatesimmersedinanelectrolyteofdilutesulphuricacid。IntheyearlastnamedEdisonfirstbroughtouthisnewformofnickel-ironcellwithalkalineelectrolyte，aswehaverelatedintheprecedingnarrative。
Earlyintheeighties，atMenloPark，hehadgivenmuchthoughttotheleadtypeofstoragebattery，andduringthecourseofthreeyearshadmadeaprodigiousnumberofexperimentsinthedirectionofimprovingit，probablyperformingmoreexperimentsinthattimethantheaggregateofthoseofallotherinvestigators。Eveninthoseearlydayshearrivedattheconclusionthatthelead-sulphuric-acidcombinationwasintrinsicallywrong，anddidnotembracetheelementsofapermanentcommercialdevice。Hedidnotatthattime，however，engageinaserioussearchforanotherformofstoragebattery，beingtremendouslyoccupiedwithhislightingsystemandothermatters。
Itmayherebenoted，fortheinformationofthelayreader，thatthelead-acidtypeofstoragebatteryconsistsoftwoormoreleadplatesimmersedindilutesulphuricacidandcontainedinareceptacleofglass，hardrubber，orotherspecialmaterialnotacteduponbyacid。Theplatesarepreparedand“formed“invariousways，andthechemicalactionsaresimilartothoseabovestated，thepositiveplatebeingoxidizedandthenegativereducedduring“charge，“
andreversedduring“discharge。“Thistypeofcell，however，hasmanyseriousdisadvantagesinherenttoitsverynature。Wewillnameafewofthembriefly。Constantdroppingoffineparticlesofactivematerialoftencausesshort-circuitingoftheplates，andalwaysnecessitatesoccasionalwashingoutofcells；deteriorationthrough“sulphation“
ifdischargeiscontinuedtoofarorifrechargingisnotcommencedquicklyenough；destructionofadjacentmetal-
workbythecorrosivefumesgivenoutduringchargeanddischarge；thetendencyofleadplatesto“buckle“undercertainconditions；thelimitationtotheuseofglass，hardrubber，orsimilarcontainersonaccountoftheactionoftheacid；andtheimmenseweightforelectricalcapacity。Thetremendouslycomplexnatureofthechemicalreactionswhichtakeplaceinthelead-acidstoragebatteryalsorendersitaneasypreytomanytroublesomediseases。
Intheyear1900，whenEdisonundertooktoinventastoragebattery，hedeclareditshouldbeanewtypeintowhichneithersulphuricnoranyotheracidshouldenter。
Hesaidthattheintimateandcontinuedcompanionshipofanacidandametalwasunnatural，andincompatiblewiththeideaofdurabilityandsimplicity。Hefurthermorestatedthatleadwasanunmechanicalmetalforabattery，beingheavyandlackingstabilityandelasticity，andthatasmostmetalswereunaffectedbyalkalinesolutions，hewasgoingtoexperimentinthatdirection。Thesoundnessofhisreasoningisamplyjustifiedbytheperfectionofresultsobtainedinthenewtypeofstoragebatterybearinghisname，andnowtobedescribed。
TheessentialtechnicaldetailsofthisbatteryarefullydescribedinanarticlewrittenbyoneofEdison'slaboratorystaff，WalterE。Holland，whoformanyyearshasbeencloselyidentifiedwiththeinventor'sworkonthiscellThearticlewaspublishedintheElectricalWorld，NewYork，April28，1910；andthefollowingextractsthere-
fromwillaffordanintelligentcomprehensionofthisinvention：
“The`A'typeEdisoncellistheoutcomeofnineyearsofcostlyexperimentationandpersistenttoilonthepartofitsinventorandhisassociates……
“TheEdisoninventioninvolvestheuseofanentirelynewvoltaiccombinationinanalkalineelectrolyte，inplaceofthelead-lead-peroxidecombinationandacidelectrolyte，characteristicofallothercommercialstoragebatteries。Experiencehasproventhatthisnotonlysecuresdurabilityandgreateroutputperunit-weightofbattery，butinadditionthereiseliminatedalonglistoftroublesanddiseasesinherentinthelead-acidcombination……
“Theprincipleonwhichtheactionofthisnewbatteryisbasedistheoxidationandreductionofmetalsinanelectrolytewhichdoesnotcombinewith，andwillnotdissolve，eitherthemetalsortheiroxides；andanelectrolyte，furthermore，which，althoughdecomposedbytheactionofthebattery，isimmediatelyre-formedinequalquantity；andthereforeineffectisaCONSTANTelement，notchangingindensityorinconductivity。
“Abatteryembodyingthisbasicprinciplewillhavefeaturesofgreatvaluewherelightnessanddurabilityaredesiderata。
Forinstance，theelectrolyte，beingaconstantfactor，asexplained，isnotrequiredinanyfixedandlargeamount，asisthecasewithsulphuricacidintheleadbattery；
thusthecellmaybedesignedwithminimumdistancingofplatesandwiththegreatesteconomyofspacethatisconsistentwithsafeinsulationandgoodmechanicaldesign。
Again，theactivematerialsoftheelectrodesbeinginsolublein，andabsolutelyunaffectedby，theelectrolyte，arenotliabletoanysortofchemicaldeteriorationbyactionoftheelectrolyte——nomatterhowlongcontinued……
“TheelectrolyteoftheEdisonbatteryisa21percent。
solutionofpotassiumhydratehaving，inaddition，asmallamountoflithiumhydrate。Theactivemetalsoftheelectrodes——whichwilloxidizeandreduceinthiselectrolytewithoutdissolutionorchemicaldeterioration——arenickelandiron。TheseactiveelementsarenotputintheplatesASMETALS；butone，nickel，intheformofahydrate，andtheother，iron，asanoxide。
“ThecontainingcasesofbothkindsofactivematerialFig。1，andtheirsupportinggridsFig。2，aswellasthebolts，washers，andnutsusedinassemblingFig。3，andeventheretainingcananditscoverFig。4，areallmadeofnickel-platedsteel——amaterialinwhichlightness，durabilityandmechanicalstrengtharemosthappilycombined，andamaterialbeyondsuspicionastocorrosioninanalkalineelectrolyte……
“AnessentialpartofEdison'sdiscoveryofactivema-
setialsforanalkalinestoragebatterywasthePREPARATION
ofthesematerials。Metallicpowderofironandnickel，orevenoxidesofthesemetals，preparedintheordinaryway，arenotchemicallyactiveinasufficientdegreetoworkinabattery。Itisonlywhenspeciallypreparedironoxideofexceedingfineness，andnickelhydrateconformingtocertainphysical，aswellaschemical，standardscanbemadethatthealkalinebatteryispracticable。Needlesstosay，theworkingoutoftheconditionsandprocessesofmanufactureofthematerialshasinvolvedgreatingenuityandendlessexperimentation。“
ThearticlethentreatsofEdison'sinvestigationsintomeansforsupportingandmakingelectricalconnectionwiththeactivematerials，showingsomeofthedifficultiesencounteredandthevariousdiscoveriesmadeindevelopingtheperfectedcell，afterwhichthewritercontinueshisdescriptionofthe“A“typecell，asfollows：
“Itwillbeseenatoncethattheconstructionofthetwokindsofplateisradicallydifferent。ThenegativeorironplateFig。5hasthefamiliarflat-pocketconstruction。
Eachnegativecontainstwenty-fourpockets——apocketbeing1/2inchwideby3incheslong，andhavingamaximumthicknessofalittlemorethan1/8inch。ThepositiveornickelplateFig。6isseentoconsistoftworowsofroundrodsorpencils，thirtyinnumber，heldinaverticalpositionbyasteelsupport-frame。Thepencilshaveflatflangesattheendsformedbyclosinginthemetalcase，bywhichtheyaresupportedandelectricalconnectionismade。Theframeisslitattheinnerhorizontaledges，andthenfoldedinsuchawayastomakeindividualclamping-jawsforeachend-
flange。Theclamping-inisdoneatgreatpressure，andtheresultantplatehasgreatrigidityandstrength。
“Theperforatedtubesintowhichthenickelactivematerialisloadedaremadeofnickel-platedsteelofhighquality。
Theyareputtogetherwithadouble-lappedspiralseamtogiveexpansion-resistingqualities，andasanadditionalprecautionsmallmetalringsareslippedontheoutside。Eachtubeis1/4inchindiameterby41/8incheslong，addhaseightofthereinforcingrings。
“Itwillbeseenthatthe`A'positiveplatehasbeengiventhetheoreticallybestdesigntopreventexpansionandovercometroublefromthatcause。Actualtests，longcontinuedunderverysevereconditions，haveshownthattheconstructionisright，andfulfilsthemostsanguineexpectations。“
Mr。Hollandinhisarticlethengoesontoexplainthedevelopmentofthenickelflakesastheconductingfactorinthepositiveelement，butasthishasalreadybeendescribedinChapterXXII，weshallpassontoalaterpoint，wherehesays：
“Anideaoftheconditionsinsidealoadedtubecanbestbehadbymicroscopicexamination。Fig。7showsamagnifiedsectionofaregularlyloadedtubewhichhasbeensawedlengthwise。Theverticalboundingwallsareedgesoftheperforatedmetalcontainingtube；thedarkhorizontallinesarelayersofnickelflake，whilethelight-coloredthickerlayersrepresentthenickelhydrate。Itshouldbenotedthatthelayersofflakenickelextendpracticallyunbrokenacrossthetubeandmakecontactwiththemetalwallatbothsides。Thesemetallayersconductcurrenttoorfromtheactivenickelhydrateinallpartsofthetubeveryefficiently。Thereareaboutthreehundredandfiftylayersofeachkindofmaterialina41/8-inchtube，eachlayerofnickelhydratebeingabout0。01inchthick；soitwillbeseenthatthecurrentdoesnothavetopenetrateveryfarintothenickelhydrate——one-halfalayer'sthicknessbeingthemaximumdistance。Theperforationsofthecontainingtube，throughwhichtheelectrolytereachestheactivematerial，arealsoshowninFig。7。“
Inconclusion，thearticleenumeratesthechiefcharacteristicsoftheEdisonstoragebatterywhichfititpre-
eminentlyfortransportationservice，asfollows：1。Nolossofactivematerial，hencenosedimentshort-circuits。
2。Nojarbreakage。3。Possibilityofquickdisconnectionorreplacementofanycellwithoutemploymentofskilledlabor。4。Impossibilityof“buckling“andharmlessnessofadeadshort-circuit。5。Simplicityofcarerequired。6。
Durabilityofmaterialsandconstruction。7。Impossibilityof“sulphation。“8。Entireabsenceofcorrosivefumes。
9。Commercialadvantagesoflightweight。10。Durationonaccountofitsdependability。11。Itshighpracticalefficiency。
XIX
EDISON'SPOUREDCEMENTHOUSE
THEinventionsthathavebeenthusfardescribedfallintotwoclasses——first，thosethatwerefundamentalinthegreatartsandindustrieswhichhavebeenfoundedandestablisheduponthem，and，second，thosethathaveenteredintoandenlargedotherartsthatwerepreviouslyinexistence。
Oncomingtoconsiderthesubjectnowunderdiscussion，however，wefindourselves，atthiswriting，onthethresholdofanentirelynewandundevelopedartofsuchboundlesspossibilitiesthatitsultimateextentcanonlybeamatterofconjecture。
Edison'sconcretehouse，however，involvestwomainconsiderations，firstofwhichwastheconceptionorcreationoftheIDEA——vastandcomprehensive——ofprovidingimperishableandsanitaryhomesforthewage-earnerbymoldinganentirehouseinonepieceinasingleoperation，sotospeak，andsosimplythatextensivegroupsofsuchdwellingscouldbeconstructedrapidlyandatveryreasonablecost。Withthisideasuggested，onemightsupposethatitwouldbeasimplemattertomakemoldsandpourinaconcretemixture。
Notso，however。Andherethesecondconsiderationpresentsitself。Anordinarycementmixtureiscomposedofcrushedstone，sand，cement，andwater。Ifsuchamixturebepouredintodeepmoldstheheavystoneandsandsettletothebottom。Shouldthemixturebepouredintoahorizontalmold，likethefloorofahouse，thestoneandsandsettle，forminganununiformmass。Itwasatthispointthatinventioncommenced，inordertoproduceaconcretemixturewhichwouldovercomethiscrucialdifficulty。
Edison，withcharacteristicthoroughness，tookupalineofinvestigation，andafteraprolongedseriesofexperimentssucceededininventingamixturethatuponhardeningre-
maineduniformthroughoutitsmass。Inthebeginningofhisexperimentationhehadmadetheconditionsoftestveryseverebytheconstructionofformssimilartothatshowninthesketchbelow。
Thisconsistedofahollowwoodenformofthedimensionsindicated。Themixturewastobepouredintothehopperuntiltheentireformwasfilled，suchmixtureflowingdownandalongthehorizontallegsanduptheverticalmembers。
Itwastobeleftuntilthemixturewashard，andtherequirementofthetestwasthatthereshouldbeabsoluteuniformityofmixtureandmassthroughout。Thiswasfinallyaccomplished，andfurtherinventionthenproceededalongengineeringlineslookingtowardthedevisingofasystemofmoldswithwhichpracticabledwellingsmightbecast。
Edison'sboldnessandbreadthofconceptionarewellillustratedinhisideaofapouredhouse，inwhichhedisplayshisaccustomedtendencytoreverseacceptedmethods。Infact，itisthisveryreversalofusualprocedurethatrendersitdifficultfortheaveragemindtoinstantlygraspthefullsignificanceoftheprinciplesinvolvedandtheresultsattained。