... 710 ALTERNATING-CURRENT WAVE-FORM. [Sept.28thesampleundertest. In fact,evenwhentheutmostprecau-tionsaretakentokeeptheimpedance of thecircuitexteriortothemagnetizingcoilassmallaspossible,thisexternalim-pedancemaybethecontrollingfactor in thecircuit,particularlyforhighvalues of theflux-density,andcorrespondinglowvalues of thepermeability.Asthisexternalimpedanceispracticallyconstantundersuchconditions,thecurrent in themagnetizingcoilmayhaveverynearlyasineform,andconsequentlyproduceamuchdistortedwave of inducedelectromotiveforce in thesample.Theaccompanyingoscillographrecordsgivethepressure-wavesundervariousconditionsinduced in asecondarywinding on asample of iron weighingabout6lb.Thesamplewasbuiltup of punchings in theform of ahollowsquare5 in. outside,3 in. inside,eachsheet0.14 -in. thick.Themagnetizingcoilhad20turns.Thetotalresistance of thecircuitbetweengeneratorandsamplewasabout0.75ohm, of which0.3ohmwas in theinstruments in thecircuitand0.45 in thestep-downtransfomer(one-halfakilowatt,20to1ratio).Themagnetizingcoilit-selfhadpracticallynoresistance.Thesource of pressurewasasmall110-voltmotor-generator,givingasine-waveelectro-motiveforce.Curve1isfor25cyclesandamaximumflux-density of 6,850lines of inductionpersquarecentimeter.Curve2isfor25cyclesandamaximumflux-density of 11,300Curve3isfor25cyclesandamaximumflux-density of 12,800.Asine-wave of pressureattheterminals of themagnetizingcoilwouldhavegivenflux-densities of 7,000,12,000and15,-000linesrespectivelv.Thefollowingtablegivesforanothersampletheflux-densitiescalculated on thebasis of asinewaveelectromotiveforceandthetrueflux-densitiesdeterminedfromtheaveragevalues of theelectromotiveforcewave:BTrueBRatio of TrueBtoCasldc-Calculated on basislatedB. of sinewave.60Cycles.25Cycles.60Cycles.25Cycles.4,0004,0004,0001.001.007,0006,8006,5000.970.9310,0009,4009,1000.940.9112,00011,00010,6000.920.8815,00012,2000.8117,50013,2000.7620,00014,1000.71A.HenryPikler(byletter):ProfessorBedell'spapergivestheimpressionthatthehysteresisloopistheonlycause of thedis-tortion of alternating-current wave-forms.Thisisnotso.TheÆTHERFORCE ... 70()8ALTERAT'I.V(;-CU,RREXI'AWAE-FORMI.[Sept.28HH1ifA4+BHCES_+SYor,substitutingthereluctance:1HitgivesKennelly'sequation:I1HP=_S+=C+DH.TheseequationsobviouslydonotapplytothetotalinductionB,buttoBo=B-H:thedifference,however,becomesnotice-ableonlyatveryhighmagnetomotiveforcesFIG.1.HaroldPender(byletter):The effect of iron in distorting the wave-form of currentandpressureis of particularimportance in determiningtheenergy-loss in smallsamples of iron bythewattmetermethod. In thismethod of measurementthemaxi-mumfluxdensityisusuallycalculatedfromtheeffectivepres-suremeasuredbyavoltmeteracrosstheterminals of themag-netizingwinding on thesample;ortheinducedpressure in asecondarywinding on thesamplemavbemeasured,thismethodeliminatingtheresistance-drop in themagnetizingwinding. In generalthemaximumfluxdensitvisproportionaltotheaveragevalue of theinducedelectromotiveforceoverhalfacycle;only in case of asinewave of inducedelectromotiveforceÆTHERFORCE ... 692 ALTERNATING-CURRENT WAVE-FORM. [Sept.28 DISCUSSION ON "THE EFFECT OF IRON IN DISTORTING ALTER-NATING-CURRENT WAVE-FORM& quot;ATNEWYORK,SEPTEMBER28,1906.CharlesProteus Steinmetz: Thispaperdealswiththewave-shapedistortionproduced in alternating-current cir-cuitsbytheintroduction of iron. Itisatheoreticalpaper,andwhile of scientificinterestappearsatfirst of ratherlittlepracticalvaluetotheelectricalengineer.Thereis,however,to-dayonlyaveryshortstepbetweenpurescientificinvestiga-tionandengineeringpractice;andIhopetoshowyouithatthephenomenadealtwith in thispaper,andsimilarphenomena,are of verygreatpracticalimportance in alternating-current dis-__.LjL__...