,illu/ration3 ,,?omas ,a4 ,,edison ,pione] ,electrical ,inve/igator & ,inv5tor ( ,num]\s ,telegraph1 ,telephone1 ,light+1 & ,o!r ,electrical ,devices4 ,cyclop$ia ( ,telephony & ,telegraphy ,a ,g5]al ,ref]5ce ,"w on ,,telephony1 ,,sub/ations1 ,,p>ty ,,l9e ,,sy/ems1 ,,protection1 ,,manual ,,swit*bo>ds1 ,,automatic ,,sy/ems1 ,,p[] ,,plants1 ,,special ,,s]vice ,,features1 ,,con/ruction1 ,,eng9e]+1 ,,op]ation1 ,,ma9t5ance1 ,,telegraphy1 ,,wireless ,,telegraphy ,,& ,,telephony1 ,,etc4 ,prep>$ by a ,corps ( ,,telephone ,,& ,,telegraph ,,exp]ts1 ,,& ,,electrical ,,eng9e]s ,,( ,,! ,,highe/ ,,pr(essional ,,/&+ ,illu/rat$ ) ov] ,two ,?\s& ,engrav+s ,,f\r ,,volumes ,,*icago ,,am]ican ,,s*ool ,,( ,,correspond5ce #aiai ,,copyright1 #aiaa1 #aiab1 ,,by ,,am]ican ,,s*ool ,,( ,,correspond5ce ,,copyright1 #aiaa1 #aiab ,,by ,,am]ican ,,te*nical ,,society ,ent]$ at ,/ation]s' ,hall1 ,london ,all ,rights ,res]v$ ,au?ors & ,collaborators 99 99 99 99 99 ,,kemp/] ,b4 ,,mill]1 ,m4,e4 ,consult+ ,eng9e] & ,telephone ,exp]t ,( ! ,firm ( ,mc,meen & ,mill]1 ,electrical ,eng9e]s & ,pat5t ,exp]ts1 ,*icago ,am]ican ,in/itute ( ,electrical ,eng9e]s ,we/]n ,society ( ,eng9e]s 99 99 99 99 99 ,,george ,w4 ,,patt]son1 ,s4,b41 ,ph4,d4 ,head1 ,dep>tm5t ( ,electrical ,eng9e]+1 ,univ]sity ( ,mi*igan 99 99 99 99 99 ,,*>les ,,?om ,*ief ( ,quadruplex ,dep>tm5t1 ,we/]n ,union ,ma9 ,(fice1 ,new ,york ,city 99 99 99 99 99 ,,rob]t ,,&rews ,,millikan1 ,ph4,d4 ,associate ,pr(essor ( ,physics1 ,univ]sity ( ,*icago ,memb]1 ,executive ,c\ncil1 ,am]ican ,physical ,society 99 99 99 99 99 ,,samuel ,g4 ,mc,m,e,e,n ,consult+ ,eng9e] & ,telephone ,exp]t ,( ! ,firm ( ,mc,meen & ,mill]1 ,electrical ,eng9e]s & ,pat5t ,exp]ts1 ,*icago ,am]ican ,in/itute ( ,electrical ,eng9e]s ,we/]n ,society ( ,eng9e]s 99 99 99 99 99 ,,lawr5ce ,k4 ,,sag]1 ,s4,b41 ,m4,p4,l4 ,pat5t ,attorney & ,electrical ,exp]t ,=m]ly ,assi/ant ,exam9]1 ,u4,s4 ,pat5t ,(fice 99 99 99 99 99 ,,gl5n ,m4 ,,hobbs1 ,ph4,d4 ,secret>y1 ,am]ican ,s*ool ( ,correspond5ce ,=m]ly ,in/ructor 9 ,physics1 ,univ]sity ( ,*icago ,am]ican ,physical ,society 99 99 99 99 99 ,,*>les ,g4 ,,a%ley ,electrical ,eng9e] & ,exp]t 9 ,wireless ,telegraphy & ,telephony 99 99 99 99 99 ,a4 ,,fr$]ick ,,coll9s ,editor1 ,coll9s ,wireless ,bullet9 ,au?or ( ,wireless ,telegraphy1 ,its ,hi/ory1 ,!ory1 & ,practice 99 99 99 99 99 ,,francis ,b4 ,,crock]1 ,e4,m41 ,ph4,d4 ,head1 ,dep>tm5t ( ,electrical ,eng9e]+1 ,columbia ,univ]sity ,pa/-,presid5t1 ,am]ican ,in/itute ( ,electrical ,eng9e]s 99 99 99 99 99 ,,morton ,,ar5dt1 ,e4,e4 ,in/ructor 9 ,electrical ,eng9e]+1 ,columbia ,univ]sity1 ,new ,york 99 99 99 99 99 ,,edw>d ,b4 ,,waite ,head1 ,in/ruction ,dep>tm5t1 ,am]ican ,s*ool ( ,correspond5ce ,am]ican ,society ( ,me*anical ,eng9e]s ,we/]n ,society ( ,eng9e]s 99 99 99 99 99 ,,david ,p4 ,,moreton1 ,b4,s41 ,e4,e4 ,associate ,pr(essor ( ,electrical ,eng9e]+1 ,arm\r ,in/itute ( ,te*nology ,am]ican ,in/itute ( ,electrical ,eng9e]s 99 99 99 99 99 ,,leigh ,s4 ,,kei?1 ,b4,s4 ,manag+ ,eng9e] ) ,mc,meen & ,mill]1 ,electrical ,eng9e]s & ,pat5t ,exp]ts ,*icago ,associate ,memb]1 ,am]ican ,in/itute ( ,electrical ,eng9e]s 99 99 99 99 99 ,,jessie ,m4 ,,%eph]d1 ,a4,b4 ,associate ,editor1 ,textbook ,dep>tm5t1 ,am]ican ,s*ool ( ,correspond5ce 99 99 99 99 99 ,,erne/ ,l4 ,,wallace1 ,b4,s4 ,assi/ant ,exam9]1 ,unit$ ,/ates ,pat5t ,(fice1 ,wa%+ton1 ,d4 ,c4 99 99 99 99 99 ,,george ,r4 ,,metcalfe1 ,m4,e4 ,editor1 ,am]ican ,in/itute ( ,electrical ,eng9e]s ,=m]ly ,head ( ,publication ,dep>tm5t1 ,we/+h\se ,elec4 ,mfg4 ,co4 99 99 99 99 99 ,j4 ,p4 ,,s*roet] ,graduate1 ,muni* ,te*nical ,s*ool ,in/ructor 9 ,electrical ,eng9e]+1 ,am]ican ,s*ool ( ,correspond5ce 99 99 99 99 99 ,,james ,,dixon1 ,e4,e4 ,am]ican ,in/itute ( ,electrical ,eng9e]s 99 99 99 99 99 ,,h>ris ,c4 ,,tr[1 ,s4,b41 ,manag+ ,editor ,editor-9-,*ief1 ,textbook ,dep>tm5t1 ,am]ican ,s*ool ( ,correspond5ce ,au?orities ,consult$ ,! editors h freely consult$ ! /&>d te*nical lit]ature ( ,am]ica & ,europe 9 ! prep>ation ( ^! volumes4 ,!y desire to express _! indebt$ness p>ticul>ly to ! foll[+ em95t au?orities1 ^: well-kn[n works %\ld be 9 ! libr>y ( e telephone & telegraph eng9e]4 ,grateful ackn[l$gm5t is "h made also = ! invaluable co-op]ation ( ! =emo/ eng9e]+ firms & manufactur]s 9 mak+ ^! volumes ?or\ghly repres5tative ( ! v be/ & late/ practice 9 ! transmission ( intellig5ce1 also = ! valuable draw+s1 data1 sugge/ions1 criticisms1 & o!r c\rtesies4 99 99 99 99 99 ,,ar?ur ,e4 ,,k5nely1 ,d4,sc4 ,pr(essor ( ,electrical ,eng9e]+1 ,h>v>d ,univ]sity4 ,jo9t ,au?or ( ,! ,electric ,telephone1 ,! ,electric ,telegraph1 ,alt]nat+ ,curr5ts1 ,arc ,light+1 ,electric ,heat+1 ,electric ,motors1 ,electric ,railways1 ,inc&esc5t ,light+1 etc4 99 99 99 99 99 ,,h5ry ,,smi? ,,c>h>t1 ,a4,m41 ,,ll4,d4 ,pr(essor ( ,physics & ,director ( ! ,physical ,laboratory1 ,univ]sity ( ,mi*igan4 ,au?or ( ,prim>y ,batt]ies1 ,elem5ts ( ,physics1 ,univ]sity ,physics1 ,electrical ,measurem5ts1 ,high ,s*ool ,physics1 etc4 99 99 99 99 99 ,,francis ,b4 ,,crock]1 ,m4,e41 ,ph4,d4 ,head ( ,dep>tm5t ( ,electrical ,eng9e]+1 ,columbia ,univ]sity1 ,new ,york2 ,pa/-,presid5t1 ,am]ican ,in/itute ( ,electrical ,eng9e]s4 ,au?or ( ,electric ,light+2 ,jo9t ,au?or ( ,managem5t ( ,electrical ,ma*9]y4 99 99 99 99 99 ,,horatio ,a4 ,,fo/] ,consult+ ,eng9e]2 ,memb] ( ,am]ican ,in/itute ( ,electrical ,eng9e]s2 ,memb] ( ,am]ican ,society ( ,me*anical ,eng9e]s4 ,au?or ( ,electrical ,eng9e]'s ,pocket-,book4 99 99 99 99 99 ,,william ,s4 ,,frankl91 ,m4,s41 ,d4,sc4 ,pr(essor ( ,physics1 ,lehigh ,univ]sity4 ,jo9t ,au?or ( ,! ,elem5ts ( ,electrical ,eng9e]+1 ,! ,elem5ts ( ,alt]nat+ ,curr5ts4 99 99 99 99 99 ,,lam> ,,lyndon1 ,b4,e41 ,m4,e4 ,consult+ ,electrical ,eng9e]2 ,associate ,memb] ( ,am]ican ,in/itute ( ,electrical ,eng9e]s2 ,memb]1 ,am]ican ,electro-,*emical ,society4 ,au?or ( ,/orage ,batt]y ,eng9e]+4 99 99 99 99 99 ,,rob]t ,,&rews ,,millikan1 ,ph4,d4 ,pr(essor ( ,physics1 ,univ]sity ( ,*icago4 ,jo9t ,au?or ( ,a ,fir/ ,c\rse 9 ,physics1 ,electricity1 ,s\nd & ,light1 etc4 99 99 99 99 99 ,,kemp/] ,b4 ,,mill]1 ,m4,e4 ,consult+ ,eng9e] & ,telephone ,exp]t2 ( ! ,firm ( ,mc,meen & ,mill]1 ,electrical ,eng9e]s & ,pat5t ,exp]ts1 ,*icago4 ,au?or ( ,am]ican ,telephone ,practice4 99 99 99 99 99 ,,william ,h4 ,,preece ,*ief ( ! ,briti% ,po/al ,telegraph4 ,jo9t ,au?or ( ,telegraphy1 ,a ,manual ( ,telephony1 etc4 99 99 99 99 99 ,,l\is ,,bell1 ,ph4,d4 ,consult+ ,electrical ,eng9e]2 ,lectur] on ,p[] ,transmission1 ,massa*usetts ,in/itute ( ,te*nology4 ,au?or ( ,electric ,p[] ,transmission1 ,p[] ,di/ribution = ,electric ,railways1 ,! ,art ( ,illum9ation1 ,wireless ,telephony1 etc4 99 99 99 99 99 ,,oliv] ,,heaviside1 ,f4,r4,s4 ,au?or ( ,electro-,magnetic ,!ory1 ,electrical ,pap]s1 etc4 99 99 99 99 99 ,,silvanus ,p4 ,,?ompson1 ,d4,sc41 ,b4,a41 ,f4,r4,s41 ,f4,r4,a4,s4 ,pr9cipal & ,pr(essor ( ,physics 9 ! ,city & ,guilds ( ,london ,te*nical ,college4 ,au?or ( ,electricity & ,magnetism1 ,dynamo-,electric ,ma*9]y1 ,polyphase ,electric ,curr5ts & ,alt]nate-,curr5t ,motors1 ,! ,electromagnet1 etc4 99 99 99 99 99 ,,&rew ,,gray1 ,m4,a41 ,f4,r4,s4,e4 ,au?or ( ,absolute ,measurem5ts 9 ,electricity & ,magnetism4 99 99 99 99 99 ,,alb]t ,,cu%+ ,,crehore1 ,a4,b41 ,ph4,d4 ,electrical ,eng9e]2 ,assi/ant ,pr(essor ( ,physics1 ,d>tm\? ,college2 ,=m]ly ,in/ructor 9 ,physics1 ,cornell ,univ]sity4 ,au?or ( ,syn*ron\s & ,o!r ,multiple ,telegraphs2 ,jo9t ,au?or ( ,alt]nat+ ,curr5ts4 99 99 99 99 99 ,j4 ,j4 ,,?omson1 ,d4,sc41 ,,ll4,d41 ,ph4,d41 ,f4,r4,s4 ,fell[ ( ,tr9ity ,college1 ,cambridge ,univ]sity2 ,cav5di% ,pr(essor ( ,exp]im5tal ,physics1 ,cambridge ,univ]sity4 ,au?or ( ,! ,conduction ( ,electricity ?r\gh ,gases1 ,electricity & ,matt]4 99 99 99 99 99 ,,fr$]ick ,,b$ell1 ,ph4,d4 ,pr(essor ( ,appli$ ,electricity1 ,cornell ,univ]sity4 ,au?or ( ,! ,pr9ciples ( ! ,trans=m]2 ,jo9t ,au?or ( ,alt]nat+ ,curr5ts4 99 99 99 99 99 ,,dugald ,c4 ,,jackson1 ,c4,e4 ,head ( ,dep>tm5t ( ,electrical ,eng9e]+1 ,massa*usetts ,in/itute ( ,te*nology2 ,memb]1 ,am]ican ,in/itute ( ,electrical ,eng9e]s1 etc4 ,au?or ( ,a ,textbook on ,electromagnetism & ! ,con/ruction ( ,dynamos2 ,jo9t ,au?or ( ,alt]nat+ ,curr5ts & ,alt]nat+-,curr5t ,ma*9]y4 99 99 99 99 99 ,,mi*ael ,,idvorsky ,,pup91 ,a4,b41 ,sc4,d41 ,ph4,d4 ,pr(essor ( ,electro-,me*anics1 ,columbia ,univ]sity1 ,new ,york4 ,au?or ( ,propagation ( ,long ,electric ,waves1 & ,wave-,transmission ov] ,non-,uni=m ,cables & ,long-,di/ance ,air ,l9es4 99 99 99 99 99 ,,frank ,,baldw9 ,,jewett1 ,a4,b41 ,ph4,d4 ,transmission & ,protection ,eng9e]1 ) ,am]ican ,telephone ,telegraph ,co4 ,au?or ( ,mod]n ,telephone ,cable1 ,effect ( ,pressure on ,insulation ,resi/ance4 99 99 99 99 99 ,,ar?ur ,,crot* ,=m]ly ,lectur] on ,telegraphy & ,telephony at ! ,municipal ,te*nical ,s*ools1 ,norwi*1 ,eng4 ,au?or ( ,telegraphy & ,telephony4 99 99 99 99 99 ,,james ,,ersk9e-,,murray1 ,d4,sc4 ,fell[ ( ! ,royal ,society ( ,ed9burgh2 ,memb] ( ! ,in/itution ( ,electrical ,eng9e]s4 ,au?or ( ,a ,h&book ( ,wireless ,telegraphy4 99 99 99 99 99 ,a4 ,h4 ,mc,m,i,l,l,a,n1 ,a4,b41 ,,ll4,b4 ,au?or ( ,telephone ,law1 ,a ,manual on ! ,organization & ,op]ation ( ,telephone ,companies4 99 99 99 99 99 ,,william ,,e/y1 ,s4,b41 ,m4,a4 ,head ( ,dep>tm5t ( ,electrical ,eng9e]+1 ,lehigh ,univ]sity4 ,jo9t ,au?or ( ,! ,elem5ts ( ,electrical ,eng9e]+4 99 99 99 99 99 ,,george ,w4 ,,wild]1 ,ph4,d4 ,=m]ly ,pr(essor ( ,telephone ,eng9e]+1 ,arm\r ,in/itute ( ,te*nology4 ,au?or ( ,telephone ,pr9ciples & ,practice1 ,simultane\s ,telegraphy & ,telephony1 etc4 99 99 99 99 99 ,,william ,l4 ,,hoop]1 ,ph4,d4 ,head ( ,dep>tm5t ( ,electrical ,eng9e]+1 ,tufts ,college4 ,jo9t ,au?or ( ,electrical ,problems = ,eng9e]+ ,/ud5ts4 99 99 99 99 99 ,,david ,s4 ,,hulfi% ,te*nical ,editor1 ,! ,nickelodeon2 ,telephone & ,motion-,picture ,exp]t2 ,solicitor ( ,pat5ts4 ,au?or ( ,h[ to ,read ,telephone ,circuit ,diagrams4 99 99 99 99 99 ,j4 ,a4 ,,flem+1 ,m4,a41 ,d4,sc4 7,lond471 ,f4,r4,s4 ,pr(essor ( ,electrical ,eng9e]+ 9 ,univ]sity ,college1 ,london2 ,late ,fell[ & ,s*ol> ( ,/4 ,john's ,college1 ,cambridge2 ,fell[ ( ,univ]sity ,college1 ,london4 ,au?or ( ,! ,alt]nate-,curr5t ,trans=m]1 ,radiotelegraphy & ,radiotelephony1 ,pr9ciples ( ,electric ,wave ,telegraphy1 ,cantor ,lectures on ,electrical ,oscillations & ,electric ,waves1 ,h]tzian ,wave ,wireless ,telegraphy1 etc4 99 99 99 99 99 ,f4 ,a4 ,c4 ,,p]r9e1 ,a4,m41 ,d4,sc4 ,consult+ ,eng9e]2 ,=m]ly ,presid5t1 ,/anley ,electric ,manufactur+ ,company2 ,=m]ly ,pr(essor ( ,electrical ,eng9e]+1 ,lel& ,/an=d1 ,jr4 ,univ]sity4 ,au?or ( ,conductors = ,electrical ,di/ribution4 99 99 99 99 99 ,a4 ,,fr$]ick ,,coll9s ,editor1 ,college ,wireless ,bullet94 ,au?or ( ,wireless ,telegraphy1 ,its ,hi/ory1 ,!ory & ,practice1 ,manual ( ,wireless ,telegraphy1 ,design & ,con/ruction ( ,induction ,coils1 etc4 99 99 99 99 99 ,,s*uyl] ,s4 ,,:eel]1 ,d4,sc4 ,presid5t1 ,crock]-,:eel] ,co42 ,pa/-,presid5t1 ,am]ican ,in/itute ( ,electrical ,eng9e]s4 ,jo9t ,au?or ( ,managem5t ( ,electrical ,ma*9]y4 99 99 99 99 99 ,,*>les ,,proteus ,,/e9metz ,consult+ ,eng9e]1 ) ! ,g5]al ,electric ,co42 ,pr(essor ( ,electrical ,eng9e]+1 ,union ,college4 ,au?or ( ,! ,!ory & ,calculation ( ,alt]nat+-,curr5t ,ph5om5a1 ,!oretical ,elem5ts ( ,electrical ,eng9e]+1 etc4 99 99 99 99 99 ,,george ,w4 ,,patt]son1 ,s4,b41 ,ph4,d4 ,head ( ,dep>tm5t ( ,electrical ,eng9e]+1 ,univ]sity ( ,mi*igan4 ,jo9t ,au?or ( ,electrical ,measurem5ts4 99 99 99 99 99 ,,william ,,mav]1 ,jr4 ,ex-,electrician ,baltimore & ,ohio ,telegraph ,company2 ,memb] ( ! ,am]ican ,in/itute ( ,electrical ,eng9e]s4 ,au?or ( ,am]ican ,telegraphy & ,encyclop$ia ( ! ,telegraph1 ,wireless ,telegraphy4 99 99 99 99 99 ,,john ,,price ,,jackson1 ,m4,e4 ,pr(essor ( ,electrical ,eng9e]+1 ,p5nsylvania ,/ate ,college4 ,jo9t ,au?or ( ,alt]nat+ ,curr5ts & ,alt]nat+-,curr5t ,ma*9]y4 99 99 99 99 99 ,,augu/us ,,treadwell1 ,jr41 ,e4,e4 ,associate ,memb]1 ,am]ican ,in/itute ( ,electrical ,eng9e]s4 ,au?or ( ,! ,/orage ,batt]y1 ,a ,practical ,treatise on ,second>y ,batt]ies4 99 99 99 99 99 ,,edw9 ,j4 ,,h\/on1 ,ph4,d4 ,pr(essor ( ,physics1 ,frankl9 ,in/itute1 ,p5nsylvania2 ,jo9t ,inv5tor ( ,?omson-,h\/on ,sy/em ( ,arc ,light+2 ,electrical ,exp]t & ,consult+ ,eng9e]4 ,jo9t ,au?or ( ,! ,electric ,telephone1 ,! ,electric ,telegraph1 ,alt]nat+ ,curr5ts1 ,arc ,light+1 ,electric ,heat+1 ,electric ,motors1 ,electric ,railways1 ,inc&esc5t ,light+1 etc4 99 99 99 99 99 ,,william ,j4 ,,hopk9s ,pr(essor ( ,physics 9 ! ,drexel ,in/itute ( ,art1 ,sci5ce1 & ,indu/ry1 ,philadelphia4 ,au?or ( ,telephone ,l9es & _! ,prop]ties4 ,illu/ration3 ,,grosse ,,po9t ,,ex*ange ,,rack ,detroit ,home ,telephone ,company1 ,detroit1 ,mi*4 ,! ,dean ,electric ,co4 ,illu/ration3 ,,l9e ,,side ,,( ,,l>ge ,,ma9 ,,di/ribut+ ,,frame ,=eword ,! pres5t day developm5t ( ! talk+ wire has annihilat$ bo? "t & space1 & has enabl$ m5 ?\s&s ( miles ap>t to get into almo/ in/ant communication4 ,! us] ( ! telephone & ! telegraph =gets ! trem5d\sness ( ! feat 9 ! simplicity ( its accompli%m5t2 b ! man :o has made ! feat possible kn[s t its v simplicity is due to ! complexity ( ! pr9ciples & appliances involv$2 & he realizes 8 ne$ ( a practical1 work+ und]/&+ ( ea* pr9ciple & its application4 ,! ,cyclop$ia ( ,telephony & ,telegraphy pres5ts a compreh5sive & au?oritative treatm5t ( ! :ole art ( ! electrical transmission ( intellig5ce4 ,! communication eng9e]--if s he may be call$--requires a k bo? ( ! me*anism ( 8 in/rum5ts & ( ! vag>ies ( ! curr5t t makes !m talk4 ,he requires z well a k ( plants & build+s1 ( (fice equipm5t1 ( poles & wires & conduits1 ( (fice sy/em & "t-sav+ me?ods1 = ! transmission ( intellig5ce is a bus9ess z well z an art4 ,& to ea* ( ^! subjects1 & to all o!rs p]t95t1 ! ,cyclop$ia gives prop] space & treatm5t4 ,! sections on ,telephony cov] ! in/allation1 ma9t5ance1 & op]ation ( all /&>d types ( telephone sy/ems2 !y pres5t )\t prejudice ! respective m]its ( manual & automatic ex*anges2 & !y give special att5tion to ! prev5tion & h&l+ ( op]at+ tr\bles4 ,! sections on ,telegraphy cov] bo? comm]cial s]vice & tra9 dispat*+4 ,practical me?ods ( wireless communication--bo? by telephone & by telegraph--are ?or\ghly treat$4 ,! draw+s1 diagrams1 & photographs incorporat$ into ! ,cyclop$ia h be5 prep>$ especially = ?is "w2 & _! in/ructive value is z great z t ( ! text itself4 ,!y h be5 us$ to illu/rate & illum9ate ! text1 & n z a m$ium ar\nd :i* to build ! text4 ,bo? draw+s & diagrams h be5 simplifi$ s f> z is compatible ) _! correctness1 ) ! result t !y tell _! own /ory & always 9 ! same language4 ,! ,cyclop$ia is a compilation ( _m ( ! mo/ valuable ,in/ruction ,pap]s ( ! ,am]ican ,s*ool ( ,correspond5ce1 & ! me?od adopt$ 9 its prep>ation is t :i* ?is ,s*ool has develop$ & employ$ s successfully = _m ye>s4 ,?is me?od is n an exp]im5t1 b has /ood ! sev]e/ ( all te/s--t ( practical use--:i* has demon/rat$ x to be ! be/ yet devis$ = ! education ( ! busy1 practical man4 ,9 conclusion1 grateful ackn[l$gm5t is due to ! /aff ( au?ors & collaborators1 )\t ^: he>ty co-op]ation ?is "w w\ld h be5 impossible4 ,table ( ,cont5ts ,,volume ,,ii ,,manual ,,swit*bo>ds ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen,a ,page,b #aa ,common-,batt]y ,swit*bo>ds--,l9e ,signals--,cord ,circuit--,lamps--,me*anical ,signals--,relays--,jacks--,swit*bo>d ,assembly--,transf] ,swit*bo>d--,transf] ,l9es--,h&l+ ,transf]s--,multiple ,swit*bo>d--,busy ,te/--,influ5ce ( ,traffic--,magneto-,multiple ,swit*bo>d--,multiple ,bo>ds3 ,s]ies1 ,bran*-,t]m9al1 ,mod]n ,magneto1 ,common-,batt]y--,we/]n ,electric ,no4 #a ,relay ,bo>d--,we/]n ,electric ,no4 #aj ,bo>d--,types ( ,multiple ,bo>ds--,app>atus--,trunk+--,we/]n ,electric & ,kellogg ,trunk ,circuits ,,automatic ,,sy/ems ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,page #ace ,automatic vs4 ,manual--,op]ation--,select+ ,swit*--,l9e ,swit*--,trunk+ ,sy/ems--,two- & ,?ree-,wire ,sy/ems--,subscrib]'s ,/ation ,app>atus--,fir/ & ,second ,selector ,op]ation--,connector--,release aft] ,conv]sation--,multi-,(fice ,sy/em--,automatic ,sub-,(fices--,rot>y ,connector--,p>ty ,l9es--,two-,wire ,automatic ,sy/em--,lorim] ,sy/em--,c5tral-,(fice ,app>atus--,op]ation--,automanual ,sy/em--,op]ation--,subscrib]'s ,app>atus--,op]ator's ,equipm5t--,swit*+ ,equipm5t--,di/ribution ( ,calls--,connection--,spe$ ,,p[] ,,plants ,,& ,,build+s ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,page #bbg ,curr5ts ,employ$--,types--,op]ator's ,transmitt] ,supply--,r++-,curr5t ,supply--,auxili>y ,signal+ ,curr5t--,prim>y ,s\rces--,duplicate ,app>atus--,/orage ,batt]ies--,p[] ,swit*bo>ds--,circuits--,c5tral-,(fice ,build+--,arrangem5t ( ,app>atus--,manual ,(fices--,automatic ,(fices ,,special ,,s]vice ,,features ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,page #bga ,private-,bran* ,ex*anges--,swit*bo>ds--,sup]vision--,) ,automatic ,(fices--,batt]y ,supply--,r++ ,curr5t--,int]-,communicat+ ,sy/ems--,magneto ,sy/em--,common-,batt]y ,sy/ems--,types--,long-,di/ance ,swit*+--,op]ator's ,ord]s--,trunk+--,way ,/ations--,traffic--,measur$ ,s]vice--,*>g+--,rates--,toll ,s]vice--,local ,s]vice ,,telegraph ,,& ,,railway ,,"w ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,page #cba ,phantom1 ,simplex1 & ,composite ,circuits--,r++--,railway ,composite--,telephone ,tra9 ,dispat*+--,railroad ,conditions--,transmitt+ ,ord]s--,app>atus--,telephone ,equipm5t--,types ( ,circuits--,te/ ,bo>ds--,block+ ,sets--,dispat*+ on ,electric ,railways ,,review ,,que/ions ,page #cei ,,index ,page #cgc ,footnote ,a3 ,= pr(essional /&+ ( au?ors1 see li/ ( ,au?ors & ,collaborators at front ( volume4 ,footnote ,b3 ,= page numb]s1 see foot ( pages4 ,illu/ration3 ,,portion ,,( ,,t]m9al ,,room ,,( ,,l>ge ,,common-,,batt]y ,,(fice ,prospect ,(fice1 ,new ,york ,telephone ,co4 ,,*apt] ,,xxii ,,! ,,simple ,,common-,,batt]y ,,swit*bo>d ,advantages ( ,common-,batt]y ,op]ation4 ,! advantages ( ! common-batt]y sy/em ( op]ation1 allud$ to 9 ,*apt] ,,xiii1 may be briefly summ>iz$ "h4 ,! ma9 ga9 9 ! common-batt]y sy/em ( supply is ! simplification ( ! subscrib]s' in/rum5ts1 do+ away ) ! local batt]ies & ! magneto g5]ators1 & ! conc5tration ( all ^! _m s\rces ( curr5t into "o s+le s\rce at ! c5tral (fice4 ,a consid]able sav+ is ?us effect$ f ! /&po9t ( ma9t5ance1 s9ce ! simpl] common-batt]y in/rum5t is n s likely to get out ( ord] &1 !re=e1 does n h to be visit$ s (t5 = repairs1 & ! abs5ce ( local batt]ies1 ( c\rse1 makes ! r5ewal ( ! batt]y p>ts by memb]s ( ! ma9t5ance dep>tm5t1 unnecess>y4 ,ano!r decid$ advantage 9 ! common-batt]y sy/em is ! fact t ! c5traliz$ batt]y /&s ready always to s5d curr5t ov] ! l9e :5 ! subscrib] completes ! circuit ( ! l9e at 8 /ation by remov+ 8 receiv] f its hook4 ,! common-batt]y sy/em1 !re=e1 l5ds itself naturally to ! purposes ( automatic signal+1 s9ce x is only necess>y to place at ! c5tral (fice a device 9 ! circuit ( ea* l9e t w be responsive to ! curr5t :i* fl[s f ! c5tral batt]y :5 ! subscrib] removes 8 receiv] f its hook4 ,x is ?us t ! subscrib] is enabl$ automatically to signal ! c5tral (fice :5 he desires a connection2 & z w be %[n1 x is by ! same sort ( means1 associat$ ) ! cord circuits us$ 9 connect+ 8 l9e ) "s o!r l9e1 t ! op]ator is automatically notifi$ :5 a disconnection is desir$1 ! cessation ( curr5t ?r\gh ! subscrib]'s l9e :5 he hangs up 8 receiv] be+ made to actuate c]ta9 responsive devices :i* are associat$ ) ! cord at t "t connect$ ) 8 l9e1 & :i* convey ! prop] disconnect signal to ! op]ator4 ,conc5tration ( s\rces ( en]gy into a s+le l>ge unit1 ! simplification ( ! subscrib]'s /ation equipm5t1 & ! ready adaptability to automatic signal+ f ! subscrib] to ! c5tral (fice are1 !re=e1 ! reasons = ! exi/5ce ( ! common-batt]y sy/em4 ,common ,batt]y vs4 ,magneto4 ,x mu/ n be suppos$1 h[ev]1 t ! common-batt]y sy/em always has advantages ov] ! magneto sy/em1 & t x is sup]ior to ! magneto or local-batt]y sy/em = all purposes4 ,x is ! outw>d attractiv5ess ( ! common-batt]y sy/em & ! argum5ts 9 its favor1 s readily made by ov]-zeal\s salesm51 t has l$1 9 _m cases1 to ! adoption ( ?is sy/em :5 ! magneto sy/em w\ld bett] h s]v$ ! purpose ( utility & economy4 ,to say ! lea/1 ! telephone transmission to be _h f common-batt]y sy/ems is no bett] ?an t to be _h f local-batt]y sy/ems1 & z a rule1 assum+ equality 9 o!r respects1 x is n z good4 ,x is p]haps true1 h[ev]1 t "u av]age conditions common-batt]y transmission is some:at bett]1 because :]eas ! local batt]ies at ! subscrib]s' /ations 9 ! local-batt]y sy/em are n likely to be 9 uni=mly fir/-class condition1 ! batt]y 9 a common-batt]y sy/em w be kept up to its full voltage except "u ! grosse/ neglect4 ,! places 9 :i* ! magneto1 or local-batt]y1 sy/em is to be pref]r$ to ! common-batt]y sy/em1 9 ! op9ion ( ! writ]s1 are to be f\nd 9 ! small rural communities :]e ! l9es h a r great av]age l5g?2 :]e a good _m subscrib]s are likely to be f\nd on "s ( ! l9es2 :]e ! s\rces ( electrical p[] available = *>g+ /orage batt]ies are likely ei!r n to exi/1 or to be ( a v unc]ta9 nature2 & :]e x is n comm]cially feasible to employ a high-grade class ( att5dants1 or1 9 fact1 any att5dant at all o!r ?an ! op]ator at ! c5tral (fice4 ,9 l>ge or m$ium-siz$ ex*anges x is always possible to procure suitable curr5t = *>g+ ! /orage batt]ies requir$ 9 common-batt]y sy/ems1 & x is frequ5tly economical1 on acc\nt ( ! consid]able quantity ( en]gy t is ?us us$1 to e/abli% a g5]at+ plant 9 connection ) ! c5tral (fice = develop+ ! necess>y electrical en]gy4 ,9 v small rural places !re are frequ5tly no available s\rces ( electrical en]gy1 & ! exp5se ( e/abli%+ a p[] plant = ! purpose _c be ju/ifi$4 ,b ev5 if !re is an electric light or railway sy/em 9 ! small t[n1 s t ! problem ( available curr5t supply does n exi/1 ! e/abli%m5t ( a common-batt]y sy/em ) its /orage batt]y & ! necess>y *>g+ ma*9]y requires ! daily att5dance at ! c5tral (fice ( "s "o to wat* & c>e = ?is batt]y1 & ?is1 on acc\nt ( ! small gross rev5ue t may be d]iv$ f a small telephone sy/em1 (t5 involves a s]i\s f9ancial burd54 ,!re is no royal road to a prop] decision 9 ! matt]1 & no %>p l9e ( dem>cation may be drawn betwe5 ! places :]e common-batt]y sy/ems are sup]ior to magneto & vice v]sa4 ,x may be said1 h[ev]1 t 9 ! build+ ( all new telephone plants hav+ ov] ab\t #ejj local subscrib]s1 ! common-batt]y sy/em is und\bt$ly sup]ior to ! magneto4 ,if ! plant is an old "o1 h[ev]1 & is to be re-equipp$1 ! cont9uance ( magneto app>atus might be ju/ifi$ = consid]ably l>g] ex*anges ?an ^? hav+ #ejj subscrib]s4 ,telephone op]at+ companies :o h *ang$ ov] ! equipm5t ( old plants f magneto to common batt]y h sometimes be5 l$ into r s]i\s difficulty1 ow+ to ! fact t _! l9es1 :ile s]v+ tol]ably well = magneto "w1 7 f\nd inadequate to meet ! m exact+ dem&s ( common-batt]y "w4 ,aga9 9 an old plant ! *ange f magneto to common-batt]y equipm5t involves n only ! *ange ( swit*bo>ds1 b also ! *ange ( subscrib]s' in/rum5ts t are o!rwise good1 & ?is consid]ation alone (t51 9 our op9ion1 ju/ifies ! replac+ ( an old magneto bo>d ) a new magneto bo>d1 ev5 if ! ex*ange is ( su* size z to dem& a small multiple bo>d4 ,:]e ! plant to be e/abli%$ is ( su* size z to leave d\bt z to :e!r a magneto or a common-batt]y swit*bo>d %\ld be employ$1 ! que/ions ( availability ( ! prop] k9d ( p[] = *>g+ ! batt]ies1 ! prop] k9d ( help = ma9ta9+ ! batt]ies & ! m elaborate c5tral-(fice equipm5t1 ! dem&s & previ\s education ( ! public to be s]v$1 all are factors :i* mu/ be consid]$ 9 rea*+ ! decision4 ,x is n prop] to say t any?+ l all ex*anges hav+ few] ?an #ejj local l9es1 %\ld be equipp$ ) magneto s]vice4 ,:]e all ! l9es are %ort1 :]e suitable p[] is available1 & :]e a good grade ( att5dants is available--z1 = in/ance1 9 ! case ( private telephone ex*anges t s]ve "s bus9ess e/abli%m5t or o!r in/itution locat$ 9 "o build+ or a gr\p ( build+s--! common-batt]y sy/em is to be recomm5d$ & is l>gely us$1 ev5 ?\gh x may h b a doz5 or s subscrib]s' l9es4 ,x is = su* uses1 & = use 9 ^? regul> public-s]vice ex*ange sy/ems :]e ! conditions are su* z to w>rant ! common-batt]y sy/em1 & yet :]e ! numb] ( l9es & ! traffic are small en\gh to be h&l$ by su* a small gr\p ( op]ators t any "o ( !m may rea* ov] ! entire face ( ! bo>d1 t ! simple non-multiple common-batt]y sy/em f9ds its prop] field ( usefulness4 ,l9e ,signals4 ,! pr9ciples & means by :i* ! subscrib] is enabl$ to call ! c5tral-(fice op]ator 9 a common-batt]y sy/em h be5 ref]r$ to briefly 9 ,*apt] ,,iii4 ,we w review ^! at ?is po9t & also consid] briefly ! way 9 :i* ! l9e signals are associat$ ) ! connective devices 9 ! subscrib]s' l9es4 ,direct-,l9e ,lamp4 ,! simple/ possible way is to put ! l9e signal directly 9 ! circuit ( ! l9e 9 s]ies ) ! c5tral-(fice batt]y1 & s to arrange ! jack ( ! correspond+ l9e t ! circuit ?r\gh ! l9e signal w be op5 :5 ! op]ator ins]ts a plug into t jack4 ,?is arrangem5t is %[n 9 ,fig4 #cjg :]e ! subscrib]'s /ation at ! left is indicat$ 9 ! simple/ ( its =ms4 ,x is well to repeat "h t 9 all common-batt]y manual sy/ems1 ! subscrib]'s /ation equipm5t1 reg>dless ( ! arrangem5t or type ( its talk+ & signal+ app>atus1 mu/ h ^! features3 ,fir/1 t ! l9e %all be normally op5 to direct curr5ts at ! subscrib]'s /ation2 second1 t ! l9e %all be clos$ to direct curr5ts :5 ! subscrib] removes 8 receiv] f its hook 9 mak+ or 9 answ]+ a call2 ?ird1 t ! l9e normally1 al?\gh op5 to direct curr5ts1 %all af=d a prop] pa? = alt]nat+ or v>y+ curr5ts ?r\gh ! signal receiv+ device at ! sub-/ation4 ,! subscrib]'s /ation arrangem5t %[n 9 ,fig4 #cjg1 & ^? imm$iately foll[+1 is ! simple/ arrangem5t t possesses ^! ?ree necess>y features = common-batt]y s]vice4 ,illu/ration3 ,fig4 #cjg4 ,direct-,l9e ,lamp ,consid]+ ! arrangem5t at ! c5tral (fice1 ,fig4 #cjg1 ! two limbs ( ! l9e are p]man5tly connect$ to ! tip & sleeve contacts ( ! jack4 ,^! two ma9 contacts ( ! jack normally engage two anvils s connect$ t ! tip ( ! jack is ord9>ily connect$ ?r\gh its anvil to gr\nd1 :ile ! sleeve ( ! jack is normally connect$ ?r\gh its anvil to a circuit lead+ ?r\gh ! l9e signal--9 ?is case a lamp--& ! common batt]y1 & !nce to gr\nd4 ,! op]ation is obvi\s4 ,normally no curr5t may fl[ f ! common batt]y ?r\gh ! signal because ! l9e is op5 at ! subscrib]'s /ation4 ,! removal ( ! subscrib]'s receiv] f its hook closes ! circuit ( ! l9e & all[s ! curr5t to fl[ ?r\gh ! lamp1 caus+ x to gl[4 ,:5 ! op]ator ins]ts ! plug into ! jack1 9 response to ! call1 ! circuit ?r\gh ! lamp is cut (f at ! jack & ! lamp goes out4 ,?is arrangem5t1 t]m$ ! direct-l9e lamp arrangem5t1 is l>gely us$ 9 small common-batt]y telephone sy/ems :]e ! l9es are v %ort1 su* z ^? f\nd 9 factories or o!r places :]e ! conf9es ( ! ex*ange are ^? ( a build+ or a gr\p ( neighbor+ build+s4 ,_m ( ! s-call$ private-bran* ex*anges1 :i* w be consid]$ m 9 detail 9 a lat] *apt]1 employ ?is direct-l9e lamp arrangem5t4 ,illu/ration3 ,fig4 #cjh4 ,direct-,l9e ,lamp ) ,balla/ ,direct-,l9e ,lamp ) ,balla/4 ,obvi\sly1 h[ev]1 ?is direct-l9e lamp arrangem5t is n a good "o :]e ! l9es v>y widely 9 l5g? & resi/ance4 ,an inc&esc5t lamp1 z is well kn[n1 mu/ n be subject$ to too great a v>iation 9 curr5t4 ,if ! curr5t t is j "r 9 am\nt to br+ x to its int5d$ degree ( illum9ation is increas$ by a comp>atively small am\nt1 ! life ( ! lamp w be greatly %ort5$1 & too great an increase w result 9 ! lamp's burn+ out imm$iately4 ,on ! o!r h&1 a curr5t t is too small w n result 9 ! prop] illum9ation ( ! lamp1 & a curr5t ( "o-half ! prop] normal value w j suffice to br+ ! lamp to a dull r$ gl[4 ,) l9es t are n approximately uni=m 9 l5g? & resi/ance ! %ort] l9es w\ld af=d too great a fl[ ( curr5t to ! lamps & ! long] l9es too little1 & !re is always ! dang] pres5t1 unless means are tak5 to prev5t x1 t if a l9e becomes %ort-circuit$ or gr\nd$ ne> ! c5tral (fice1 ! lamp w be subject$ to practically ! full batt]y pot5tial &1 !re=e1 to su* a curr5t z w burn x out4 ,"o ( ! v +5i\s &1 we believe1 promis+ me?ods t has be5 propos$ to ov]come ?is difficulty is t ( ! iron-wire balla/1 allud$ to 9 ,*apt] ,,iii4 ,?is1 x w be rememb]$1 consi/s ( an iron-wire resi/ance enclos$ 9 a vacuum *amb] & s proportion$ ) respect to ! fl[ ( curr5t t x w be subject$ to a consid]able heat+ effect by ! am\nt ( curr5t t is prop] to illum9ate ! lamp4 ,z has already be5 po9t$ out1 c>bon has a negative temp]ature coeffici5t1 t is1 its resi/ance decreases :5 heat$4 ,iron1 on ! o!r h&1 has a positive temp]ature coeffici5t1 its resi/ance increas+ :5 heat$4 ,:5 su* an iron-wire balla/ is put 9 s]ies ) ! inc&esc5t lamp =m+ ! l9e signal1 z %[n 9 ,fig4 #cjh1 x is se5 t ! resi/ance ( ! c>bon 9 ! lamp filam5t & ( ! iron 9 ! balla/ w act 9 opposite ways :5 ! curr5t increases or decreases4 ,an increase ( curr5t w t5d to heat up ! iron wire ( ! balla/ &1 !re=e1 increase its resi/ance1 & ! balla/ is s proportion$ t x w hold ! curr5t t may fl[ ?r\gh ! lamp )9 ! prop] maximum & m9imum limits1 reg>dless ( ! resi/ance ( ! l9e 9 :i* ! lamp is us$4 ,?is arrangem5t has n gone into wide use up to ! pres5t "t4 ,l9e ,lamp ) ,relay4 ,by f> ! mo/ common me?od ( associat+ ! l9e lamp ) ! l9e is to employ a relay1 ( :i* ! actuat+ coil is 9 ! l9e circuit1 ?is relay s]v+ to control a local circuit conta9+ ! batt]y & ! lamp4 ,?is arrangem5t & ! way 9 :i* ^! p>ts are associat$ ) ! jack are cle>ly indicat$ 9 ,fig4 #cji4 ,"h ! relay may receive any am\nt ( curr5t1 f ! smalle/ :i* w cause x to pull up its armature1 to ! l>ge/ :i* w n injure its w9d+ by ov]heat4 ,relays may be made :i* w attract _! armatures at a c]ta9 m9imum curr5t & :i* w n burn out :5 en]giz$ by curr5ts ab\t t5 times z l>ge1 & x is ?us se5 t a v l>ge range ( curr5t ?r\gh ! relay w9d+ is p]missible1 & t1 !re=e1 a v great latitude z to l9e resi/ance is secur$4 ,on ! o!r h&1 x is obvi\s t ! lamp circuit1 be+ entirely local1 is ( uni=m resi/ance1 ! lamp always be+ subject$1 9 ! arrangem5t %[n1 to practically ! full batt]y pot5tial1 ! lamp be+ select$ to op]ate on t pot5tial4 ,illu/ration3 ,fig4 #cji4 ,l9e ,lamp ) ,relay ,pilot ,signals4 ,9 ! circuits ( ,figs4 #cjg1 #cjh1 & #cji1 b a s+le l9e & its associat$ app>atus is %[n1 & x may n be altoge!r cle> to ! un9itiat$ h[ x is t ! batt]y %[n 9 ^? figures may s]ve1 )\t int]f]5ce ( any function1 a l>g] numb] ( l9es ?an "o4 ,x is to be rememb]$ t ?is batt]y is ! "o :i* s]ves n only to op]ate ! l9e signals1 b also to supply talk+ curr5t to ! subscrib]s & to supply curr5t = ! op]ation ( ! cord-circuit signals aft] ! cord circuits are connect$ ) ! l9es4 ,9 ,fig4 #caj ?is matt] is made cle> ) respect to ! association ( ?is common batt]y ) ! l9es = op]at+ ! l9e signals1 & also ano!r important feature ( common-batt]y "w is br\ght out1 viz1 ! pilot lamp & its association ) a gr\p ( l9e lamps4 ,?ree subscrib]s' l9es only are %[n1 b ?is s]ves cle>ly to illu/rate ! association ( any l>g] numb] ( l9es ) ! common batt]y4 ,ignor+ at fir/ ! pilot relay & ! pilot lamp1 x w be se5 t ea* ( ! tip-spr+ anvils ( ! jacks is connect$ to a common wire #a :i* is gr\nd$4 ,ea* ( ! sleeve-contact anvils is connect$ ?r\gh ! coil ( ! l9e relay to ano!r common wire #b1 :i* connects ) ! live side ( ! common batt]y4 ,obvi\sly1 !re=e1 ?is arrangem5t corresponds ) t ( ,fig4 #cji1 s9ce ! batt]y may furni% curr5t to en]gize any "o ( ! l9e relays ^u ! closure ( ! circuit ( ! correspond+ l9e4 ,ea* ( ! relay armatures 9 ,fig4 #caj is connect$ to gr\nd4 ,"h we wi% to br+ out an important ?+ ab\t telephone circuit diagrams :i* is sometimes confus+ to ! beg9n]1 b :i* really1 :5 und]/ood1 t5ds to prev5t confusion4 ,! %[+ ( a sep>ate gr\nd = ea* ( ! l9e-relay armatures does n mean t lit]ally ea* "o ( ^! armatures is connect$ by a sep>ate wire to e>?1 & x is to be und]/ood t ! ?ree sep>ate gr\nds %[n 9 connection ) ^! relay armatures is meant to indicate j su* a set ( affairs z is %[n 9 connection ) ! tip-spr+ anvils ( ! jacks1 all ( :i* are connect$ to a common wire :i*1 9 turn1 is gr\nd$4 ,obvi\sly1 ! result is ! same1 b 9 ! case ( ?is p>ticul> diagram x is se5 t a great deal ( cross+ ( l9es is prev5t$ by %[+ a sep>ate gr\nd at ea* "o ( ! relay armatures4 ,! same practice is foll[$ 9 connection ) ! common batt]y4 ,sometimes x is v inconv5i5t 9 a complicat$ diagram to run all ( ! wires t are suppos$ to connect ) "o t]m9al ( ! batt]y across ! diagram to repres5t ?is connection4 ,x is p]missible1 !re=e1 & 9 fact desirable1 t sep>ate batt]y symbols be %[n :]ev] by s do+ ! diagram w be simplifi$1 ! und]/&+ be+1 9 ! abs5ce ( o!r in=mation or ( o!r indications1 t ! same batt]y is ref]r$ to1 j z ! same gr\nd is ref]r$ to 9 connection ) ! relay armatures 9 ! figure "u discussion4 ,ea* l9e lamp 9 ,fig4 #caj is %[n connect$ on "o h& to its correspond+ l9e relay contact & on ! o!r h& to a common wire :i* leads ?r\gh ! w9d+ ( ! pilot relay to ! live side ( ! batt]y4 ,x is obvi\s "h t :5ev] any "o ( ! l9e relays attracts its armature ! local circuit conta9+ ! correspond+ lamp & ! common batt]y w be clos$ & ! lamp illum9at$4 ,:5ev] any l9e relay op]ates1 ! curr5t1 :i* is suppli$ to its lamp1 mu/ come ?r\gh ! pilot-relay w9d+1 & if a numb] ( l9e relays are en]giz$1 !n ! curr5t fl[ ( ! correspond+ lamps mu/ fl[ ?r\gh ?is relay w9d+4 ,!re=e1 ?is relay w9d+ mu/ be ( l[ resi/ance1 s t ! drop ?r\gh its w9d+ may n be suffici5t to int]f]e ) ! prop] burn+ ( ! lamps1 ev5 ?\gh a l>ge numb] ( lamps be f$ simultane\sly ?r\gh x4 ,! pilot relay mu/ be s s5sitive t ! curr5t1 ev5 ?r\gh "o lamp1 w cause x to attract its armature4 ,:5 x does attract its armature x causes illum9ation ( ! pilot lamp 9 ! same way t ! l9e relays cause ! illum9ation ( ! l9e lamps4 ,! pilot lamp1 :i* is commonly associat$ ) a gr\p ( l9e lamps t are plac$ on any "o op]ator's position ( ! swit*bo>d1 is locat$ 9 a conspicu\s place 9 ! swit*bo>d cab9et & is provid$ ) a l>g] l5s s z to make a m /rik+ signal4 ,z a result1 :5ev] any l9e lamp on a giv5 position lights1 ! pilot lamp does also & s]ves to attract ! att5tion1 ev5 ( ^? locat$ 9 di/ant portions ( ! room1 to ! fact t a call exi/s on t position ( ! bo>d1 ! l9e lamp itself1 :i* is simultane\sly light$1 po9t+ out ! p>ticul> l9e on :i* ! call exi/s4 ,pilot lamps1 9 effect1 p]=m simil> s]vice to ! night al>m 9 magneto bo>ds1 b1 ( c\rse1 !y are sil5t & d n attract att5tion unless )9 ! range ( vision ( ! op]ator4 ,!y are us$ n only 9 connection ) l9e lamps1 b also 9 connection ) ! cord-circuit lamps or signals1 z w be po9t$ out4 ,illu/ration3 ,fig4 #caa4 ,batt]y ,supply ,?r\gh ,imp$ance ,coils ,illu/ration3 ,fig4 #cab4 ,batt]y ,supply ?r\gh ,repeat+ ,coils ,illu/ration3 ,fig4 #cac4 ,batt]y ,supply ) ,imp$ance ,coils & ,cond5s]s ,cord ,circuit4 ,batt]y ,supply4 ,7 x n = ! necessity ( provid+ = cord-circuit signals 9 common-batt]y swit*bo>ds1 ! common-batt]y cord circuit w\ld be sc>cely m complex ?an t = magneto work+4 ,/ripp$ ( all details1 su* z signals1 r++ & li/5+ keys1 & op]ator's equipm5t1 cord circuits ( ?ree diff]5t types are %[n 9 ,figs4 #caa1 #cab1 & #cac4 ,^! m]ely illu/rate ! way 9 :i* ! batt]y is associat$ ) ! cord circuits & ?r\gh !m ) ! l9e circuits = supply+ curr5t = talk+ purposes to ! subscrib]s4 ,x is ?\ght t ?is matt] w be cle> 9 view ( ! discussion ( ! me?ods by :i* curr5t is suppli$ to ! subscrib]s' transmitt]s 9 common-batt]y sy/ems z discuss$ 9 ,*apt] ,,xiii4 ,:ile ! arrangem5ts 9 ?is respect ( ,figs4 #caa1 #cab1 & #cac illu/rate only ?ree ( ! me?ods1 ^! ?ree are ! ones t h be5 mo/ widely & successfully us$4 ,sup]visory ,signals4 ,! signals t are associat$ ) ! cord circuits are t]m$ sup]visory signals because ( ! fact t by _! means ! op]ator is enabl$ to sup]vise ! condition ( ! l9es dur+ times :5 !y are connect$ = conv]sation4 ,! op]ation ( ^! sup]visory signals may be be/ und]/ood by consid]+ ! complete circuits ( a simple swit*bo>d & mu/ be /udi$ 9 conjunction ) ! circuits ( ! l9es z well z ^? ( ! cords4 ,illu/ration3 ,fig4 #cad4 ,simple ,common-,batt]y ,swit*bo>d ,complete ,circuit4 ,su* complete circuits are %[n 9 ,fig4 #cad4 ,! p>ticul> arrangem5t indicat$ is t employ$ by ! ,kellogg ,company1 & except = m9or details may be consid]$ z typical ( o!r makes also4 ,two subscrib]s' l9es are %[n ext5d+ f ,/ation ,a & ,/ation ,b1 respectively1 to ! c5tral (fice4 ,! l9e wires are %[n t]m9at+ 9 jacks 9 ! same mann] z indicat$ 9 ,figs4 #cjg1 #cjh1 & #cji1 & _! circuits are normally cont9u$ f ^! jacks to ! gr\nd on "o side & to ! l9e relay & batt]y on ! o!r4 ,! jack 9 ?is case has ?ree contacts adapt$ to regi/] ) ?ree correspond+ contacts 9 ea* ( ! plugs4 ,! ?imble ( ! jack 9 ?is case =ms no "p ( ! talk+ circuit & is di/9ct f ! two jack spr+s :i* =m ! l9e t]m9als4 ,x & ! auxili>y contact #a 9 ea* ( ! plugs ) :i* x regi/]s1 are solely = ! purpose ( co-op]at+ 9 ! control ( ! sup]visory signals4 ,! tip & sleeve /r&s ( ! cord are cont9u\s f "o plug to ! o!r except = ! cond5s]s4 ,! two batt]ies indicat$ 9 connection ) ! cord circuit are sep>ate batt]ies1 a *>act]i/ic ( ! ,kellogg sy/em4 ,"o ( ^! batt]ies s]ves to supply curr5t to ! tip & sleeve /r& ( ! cord circuit ?r\gh ! two w9d+s #c & #d1 respectively1 ( ! sup]visory relay connect$ ) ! answ]+ side ( ! cord circuit1 :ile ! o!r batt]y simil>ly supplies curr5t ?r\gh ! w9d+s #e & #f ( ! sup]visory relay associat$ ) ! call+ side ( ! cord circuit4 ,! w9d+s ( ^! relays1 !re=e1 act z imp$ance coils & ! arrangem5t by :i* batt]y curr5t is suppli$ to ! cord circuits &1 !re=e1 to ! l9es ( ! connect$ subscrib]s1 is se5 to be ! comb9$ imp$ance coil & cond5s] arrangem5t discuss$ 9 ,*apt] ,,xiii4 ,z soon z a plug is ins]t$ into ! jack ( a l9e1 ! l9e relay w be remov$ f ! control ( ! l9e1 & s9ce ! two /r&s ( ! cord circuit n[ =m cont9uations ( ! two l9e conductors1 ! sup]visory relay w be sub/itut$ = ! l9e relay & w be "u control ( ! l9e4 ,s9ce all ( ! curr5t :i* passes to ! l9e aft] a plug is ins]t$ mu/ pass ?r\gh ! cord-circuit connection & ?r\gh ! relay w9d+s1 & s9ce curr5t c only fl[ ?r\gh ! l9e :5 ! subscrib]'s receiv] is (f its hook1 x foll[s t ! sup]visory relays w only be en]giz$ aft] ! correspond+ plug has be5 ins]t$ into a jack ( ! l9e & aft] ! subscrib] has remov$ 8 receiv]4 ,unlike ! l9e relays1 ! sup]visory relays op5 _! contacts to break ! local circuits ( ! sup]visory lamps #g & #h :5 ! relay coils are en]giz$1 & to close !m :5 de-en]giz$2 b ! armatures ( ! sup]visory relays d alone control ! circuits ( ! sup]visory lamps4 ,^! circuits are normally held op5 9 ano!r place1 t is1 betwe5 ! plug contacts #a & ! jack ?imbles4 ,x is only1 !re=e1 :5 a plug is ins]t$ into a jack & :5 ! sup]visory relay is de-en]giz$1 t ! sup]visory lamp may be light$4 ,:5 a plug is ins]t$ into a jack & :5 ! correspond+ sup]visory relay is de-en]giz$1 ! circuit may be trac$ f gr\nd at ! cord-circuit batt]ies ?r\gh ! left-h& batt]y1 = in/ance1 ?r\gh lamp #g1 !nce ?r\gh ! contacts ( ! sup]visory relay to ! contact #a ( ! plug1 !nce ?r\gh ! ?imble ( ! jack to gr\nd4 ,:5 a plug is ins]t$ into ! jack1 !re=e1 ! necess>y arrangem5ts are complet$ = ! sup]visory lamp to be "u ! control ( ! subscrib]4 ,"u ?is condition1 :5ev] ! subscrib]'s receiv] is on its hook1 ! circuit ( ! l9e w be brok51 ! sup]visory relay w be de-en]giz$1 & ! sup]visory lamp w be light$4 ,:51 on ! o!r h&1 ! subscrib]'s receiv] is (f its hook1 ! circuit ( ! l9e w be complete1 ! sup]visory relay w be en]giz$1 & ! sup]visory lamp w be ext+ui%$4 ,sali5t ,features ( ,sup]visory ,op]ation4 ,x w facilitate ! /ud5t's und]/&+ ( ! requirem5ts & mode ( op]ation ( common-batt]y sup]visory signals 9 manual sy/ems1 :e!r simple or multiple1 if he w firmly fix ! foll[+ facts 9 8 m9d4 ,9 ord] t ! sup]visory signal may become op]ative at all1 "s act mu/ be p]=m$ by ! op]ator--?is be+ usually ! act ( plugg+ into a jack--& !n1 until ! connection is tak5 d[n1 ! sup]visory signal is "u ! control ( ! subscrib]1 & x is display$ only :5 ! subscrib]'s receiv] is plac$ on its hook4 ,cycle ( ,op]ations4 ,we may n[ trace ?r\gh ! complete cycle ( op]ations ( ! simple common-batt]y swit*bo>d1 ! circuits ( :i* are %[n 9 ,fig4 #cad4 ,assume all app>atus 9 its normal condition1 & !n assume t ! subscrib] at ,/ation ,a removes 8 receiv] f its hook4 ,?is pulls up ! l9e relay & lights ! l9e lamp1 ! pilot relay also pull+ up & light+ ! common pilot lamp :i* is n %[n4 ,9 response to ?is call1 ! op]ator ins]ts ! answ]+ plug & ?r[s h] li/5+ key ,l4,k4 ,! op]ator's talk+ set is ?us bridg$ across ! cord circuit & %e is enabl$ to conv]se ) ! call+ subscrib]4 ,! answ]+ sup]visory lamp #g did n light :5 ! op]ator ins]t$ ! answ]+ plug into ! jack1 because1 al?\gh ! contacts 9 ! lamp circuit 7 clos$ by ! plug contact #a engag+ ! ?imble ( ! jack1 ! lamp circuit 0 held op5 by ! attraction ( ! sup]visory relay armature1 ! subscrib]'s receiv] be+ (f its hook4 ,le>n+ t ! call$-= subscrib] is ! "o at ,/ation ,b1 ! op]ator ins]ts ! call+ plug into ! jack at t /ation & presses ! r++ key ,r4,k41 9 ord] to r+ ! bell4 ,! act ( plugg+ 91 x w be rememb]$1 cuts (f ! l9e-signal+ app>atus f connection ) t l9e4 ,z ! subscrib] at ,/ation ,b 0 n at 8 telephone :5 call$ & 8 receiv] 01 !re=e1 on its hook1 ! ins]tion ( ! call+ plug did n en]gize ! sup]visory relay coils #e & #f1 &1 !re=e1 t relay did n attract its armature4 ,! sup]visory lamp #h 0 ?us light$1 ! circuit be+ f gr\nd ?r\gh ! "r-h& cord-circuit batt]y1 lamp #h1 back contacts ( ! sup]visory relay1 ?ird /r& ( ! cord to contact #a ( ! call+ plug1 & !nce to gr\nd ?r\gh ! ?imble ( ! jack4 ,! light+ ( ?is lamp is cont9u$ until ! p>ty at ,/ation ,b responds by remov+ 8 receiv] f its hook1 :i* completes ! l9e circuit1 en]gizes relay w9d+s #e & #f1 causes t relay to attract its armature1 & ?us break ! circuit ( ! lamp #h4 ,bo? sup]visory lamps rema9 out z long z ! two subscrib]s are conv]s+1 b :5 ei!r "o ( !m hangs up 8 receiv] ! correspond+ sup]visory relay becomes de-en]giz$ & ! correspond+ lamp lights4 ,:5 bo? ( ! lamps become illum9at$1 ! op]ator kn[s t bo? subscrib]s are ?r\gh talk+ & %e takes d[n ! connection4 ,c\ntless v>iations h be5 work$ 9 ! arrangem5t ( ! l9e & cord circuits1 b ! g5]al mode ( op]ation ( ?is p>ticul> circuit *os5 = illu/ration is /&>d & %\ld be ?or\ghly ma/]$4 ,! op]ation ( o!r arrangem5ts w be readily und]/ood f an inspection ( ! circuits1 once ! fundam5tal mode ( op]ation t is common to all ( !m is well 9 m9d4 ,lamps4 ,! inc&esc5t lamps us$ 9 connection ) l9e & sup]visory signals are specially manufactur$1 b diff] 9 no s5se f ! l>g] lamps employ$ = g5]al light+ purposes1 save 9 ! details ( size1 =m1 & me?od ( m\nt+4 ,usually ^! lamps are rat$ at ab\t "o-?ird c&le-p[]1 al?\gh !y h a some:at l>g] c&le-p[] z a rule4 ,!y are manufactur$ to op]ate on v>i\s voltages1 ! mo/ usual op]at+ pressures be+ #ab1 #bd1 & #dh volts4 ,! #bd-volt lamp consumes ab\t "o-t5? ( an amp]e :5 fully illum9at$1 ! lamp ?us consum+ ab\t #b4d watts4 ,! #ab- & #dh-volt lamps consume ab\t ! same am\nt ( en]gy & correspond+ am\nts ( curr5t4 ,illu/ration3 ,fig4 #cae4 ,swit*bo>d ,lamp ,lamp ,m\nt+4 ,! usual =m ( screw-?read$ m\nt+ employ$ 9 lamps = comm]cial light+ 0 at fir/ appli$ to ! m9iature lamps us$ = swit*bo>d "w1 b ?is 0 f\nd unsatisfactory & ^! lamps are n[ practically always provid$ ) two contact /rips1 "o on ea* side ( ! glass bulb1 ^! /rips =m+ respectively ! t]m9als = ! two ends ( ! filam5t )94 ,su* a con/ruction ( a common =m ( lamp is %[n 9 ,fig4 #cae1 :]e ^! t]m9als are indicat$ by ! num]als #a & #b1 #c be+ a dry wood5 block arrang$ betwe5 ! t]m9als at "o end = secur+ great] rigidity betwe5 !m4 ,illu/ration3 ,fig4 #caf4 ,l9e ,lamp ,m\nt+ ,! me?od ( m\nt+ ^! lamps is subject to a good deal ( v>iation 9 detail1 b ! arrangem5t is always su* t ! lamp is slid 9 betwe5 two metallic contacts =m+ t]m9als ( ! circuit 9 :i* ! lamp is to op]ate4 ,su* an arrangem5t ( spr+s & ! co-op]at+ m\nt+ =m+ a sort ( socket = ! reception ( swit*bo>d lamps is ref]r$ to z a lamp jack4 ,^! are sometimes individually m\nt$ & sometimes m\nt$ 9 /rips 9 mu* ! same way t jacks are m\nt$ 9 /rips4 ,a /rip ( lamp jacks z manufactur$ by ! ,kellogg ,company is %[n 9 ,fig4 #caf4 ,! opalesc5t l5s is adapt$ to be fitt$ 9 front ( ! lamp aft] x has be5 ins]t$ into ! jack4 ,fig4 #cag gives an excell5t view ( an individually-m\nt$ lamp jack ) its lamp & l5s1 ?is also be+ ( ,kellogg manufacture4 ,?is figure %[s a section ( ! plug %elf :i* is bor$ to receive a lamp4 ,9 ord] to protect ! lamps & l5ses f breakage1 due to ! /rik+ ( ! plugs aga9/ !m1 a metal %ield is plac$ ov] ! l5s1 z %[n 9 ?is figure1 ?is be+ s cut away z to all[ suffici5t op5+s = ! light to %9e ?r\gh4 ,sometimes in/ead ( employ+ l5ses 9 front ( ! lamps1 a flat piece ( transluc5t mat]ial is us$ to cov] ! op5+s ( ! lamp1 ?is be+ protect$ by suitable p]=at$ /rips ( metal4 ,a /rip ( lamp jacks employ+ ?is feature is %[n 9 ,fig4 #cah1 ?is be+ ( ,dean manufacture4 ,an advantage ( ?is = c]ta9 types ( "w is t ! flat transluc5t plate 9 front ( ! lamp may readily c>ry designat+ m>ks1 su* z ! numb] ( ! l9e or some?+ to indicate ! "* ( ! l9e1 :i* m>ks may be readily *ang$ z requir$4 ,illu/ration3 ,fig4 #cag4 ,sup]visory ,lamp ,m\nt+ ,illu/ration3 ,fig4 #cah4 ,l9e ,lamp ,m\nt+ ,illu/ration3 ,fig4 #cai4 ,individual ,lamp ,jacks ,9 ! types made by "s manufactur]s ! only diff]5ce betwe5 ! pilot lamp & ! l9e lamp is 9 ! size ( ! l5s 9 front ( x1 ! jack & ! lamp itself be+ ! same = ea*1 :ile o!rs use a l>g] lamp = ! pilot4 ,9 ,fig4 #cai are %[n two individual lamp jacks1 ! "o at ! top be+ = sup]visory lamps & ! "o at ! bottom be+ provid$ ) a l>ge l5s = s]v+ z a pilot lamp4 ,illu/ration3 ,,t]m9al ,,room ,,app>atus ,,9 ,,process ,,( ,,in/allation ,in/all$ by ,dean ,electric ,company at ,detroit1 ,mi*4 ,me*anical ,signals4 ,z has be5 /at$ ! s-call$ me*anical signals are sometimes us$ 9 small common-batt]y swit*bo>ds in/ead ( lamps4 ,:]e ?is is done ! coil ( ! signal1 if x is a l9e signal1 is sub/itut$ 9 ! l9e circuit 9 place ( ! relay coil4 ,if ! signals are us$ 9 connection ) cord circuits = sup]visory signals1 _! coils are put 9 ! circuit 9 place ( ! sup]visory relay coils4 7,^! signals are ref]r$ to 9 ,*apt] ,,iii 9 connection ) ,fig4 #bc47 ,!y are s arrang$ t ! attraction ( ! armature lifts a t>get on ! end ( a lev]1 & ?is causes a display ( color or =m4 ,! release ( ! armature all[s ?is t>get to drop back1 ?us oblit]at+ ! display4 ,su* signals1 (t5 call$ visual signals & electromagnet signals1 %\ld be di/+ui%$ f ! drops consid]$ 9 connection ) magneto swit*bo>ds 9 :i* ! attraction ( ! armature causes ! display ( ! signal by ! fall+ ( a drop1 ! signal rema9+ display$ until re/or$ by "s o!r means1 ! re/oration dep5d+ 9 no wise on :5 ! armature is releas$4 ,we/]n ,electric4 ,! me*anical signal ( ! ,we/]n ,electric ,company1 %[n 9 ,fig4 #cbj1 has a t>get simil> to t %[n 9 ,fig4 #bed b )\t a lat*4 ,x is turn$ to %[ a diff]5t color by ! attraction ( ! armature & all[$ to resume its normal position :5 ! armature is releas$4 ,illu/ration3 ,fig4 #cbj4 ,me*anical ,signal ,kellogg4 ,fig4 #cba gives a good idea ( a /rip ( me*anical signals z manufactur$ by ! ,kellogg ,company4 ,?is is kn[n z ! gridiron signal on acc\nt ( ! cross-b> /rip+ ( its t>get4 ,! :ite b>s on ! t>get normally lie j beh9d ! cross-b>s on ! %ield 9 front1 b a slight rais+ ( ! t>get--ab\t "o-eigh? ( an in*--exposes ^! :ite b>s to view1 opposite ! rectangul> op5+s 9 ! front %ield4 ,illu/ration3 ,fig4 #cba4 ,/rip ( ,gridiron ,signals ,mon>*4 ,9 ,fig4 #cbb is %[n ! visual signal manufactur$ by ! ,mon>* ,telephone ,company4 ,illu/ration3 ,fig4 #cbb4 ,me*anical ,signal ,relays4 ,! l9e relays = common-batt]y swit*bo>ds likewise assume a great v>iety ( =ms4 ,! well-kn[n type ( relay employ$ 9 telegraphy w\ld answ] ! purpose well b = ! am\nt ( room t x occupies1 z x is sometimes necess>y to gr\p a l>ge numb] ( relays 9 a v small space4 ,ne>ly all pres5t-day relays are ( ! s+le-coil type1 & 9 ne>ly all cases ! movem5t ( ! armature causes ! movem5t ( "o or m swit*+ spr+s1 :i* are ?us made to engage or dis5gage _! associat$ spr+ or spr+s4 ,"o ( ! mo/ widely us$ =ms ( relays has an ,l-%ap$ armature hung across ! front ( a =w>dly project+ arm ( iron1 on ! knife-edge corn] ( :i* x rocks z mov$ by ! attraction ( ! magnet4 ,! g5]al =m ( ?is relay 0 illu/rat$ 9 ,fig4 #ie4 ,sometimes ?is relay is made up 9 s+le units & frequ5tly a l>ge numb] ( su* s+le units are m\nt$ on a s+le m\nt+ plate4 ,?is matt] w be dealt ) m 9 detail 9 ! discussion ( common-batt]y multiple swit*bo>ds4 ,9 o!r cases ^! relays are built en bloc1 a rectangul> /rip ( s(t iron long en\gh to af=d space = t5 relays side by side be+ bor$ out ) t5 cyl9drical holes to receive ! electromagnets4 ,! iron ( ! block af=ds a return pa? = ! l9es ( =ce4 ,! ,l-%ap$ armatures are hung ov] ! front edge ( ?is block1 s t _! free ends lie opposite ! magnet cores )9 ! block4 ,?is arrangem5t z employ$ by ! ,kellogg ,company is %[n 9 two views 9 ,figs4 #cbc & #cbd4 ,illu/ration3 ,fig4 #cbc4 ,/rip ( ,relays ,illu/ration3 ,fig4 #cbd4 ,/rip ( ,relays ,a bank ( l9e relays especially adapt$ = small common-batt]y swit*bo>ds z made by ! ,dean ,company1 is %[n 9 ,fig4 #cbe4 ,illu/ration3 ,fig4 #cbe4 ,bank ( ,relays ,jacks4 ,! jacks 9 common-batt]y swit*bo>ds are almo/ always m\nt$ 9 gr\ps ( t5 or tw5ty1 ! arrangem5t be+ simil> to t discuss$ 9 connection ) lamp /rips4 ,ord9>ily 9 common-batt]y "w ! jack is provid$ ) two inn] contacts s z to cut (f bo? sides ( ! signal+ circuit :5 ! op]ator plugs 94 ,a /rip ( su* jacks is %[n 9 ,fig4 #cbf4 ,illu/ration3 ,fig4 #cbf4 ,/rip ( ,cut-,(f ,jacks ,r++ & li/5+ keys = simple common-batt]y swit*bo>ds diff] 9 no ess5tial respect f ^? employ$ 9 magneto bo>ds4 ,illu/ration3 ,fig4 #cbg4 ,details ( ,lamp1 ,plug1 & ,key ,m\nt+ ,swit*bo>d ,assembly4 ,! g5]al assembly ( ! p>ts ( a simple common-batt]y swit*bo>d des]ves "s att5tion4 ,! =m ( ! swit*bo>d ne$ n diff] ess5tially f t employ$ 9 magneto "w1 b ord9>ily ! cab9et is some:at small] on acc\nt ( ! small] am\nt ( room requir$ by its lamps & jacks4 ,an excell5t idea ( ! l9e jacks & lamps1 plugs1 keys1 & sup]visory signals may be obta9$ f ,fig4 #cbg1 :i* is a detail view tak5 f a ,kellogg bo>d4 ,9 ! v]tical panel ( ! bo>d above ! plug %elf are arrang$ ! l9e jacks & ! lamps 9 r[s ( tw5ty ea*1 ea* lamp be+ imm$iately b5ea? its correspond+ jack4 ,su* jacks are ord9>ily m\nt$ on #a_/b-;in* c5t]s bo? v]tically & horizontally1 s t a gr\p ( "o hundr$ lamps & l9e jacks w occupy a space only slightly ov] #aj by #e in*es4 ,su* economy ( space is n requir$ 9 ! simple magneto bo>d1 because ! space might easily be made l>g] )\t 9 any way tax+ ! rea* ( ! op]ator4 ,! reason = ?is comp>atively close m\nt+ is a result1 n ( ! requirem5ts ( ! simple non-multiple common-batt]y bo>d itself1 b ( ! fact t ! jack /rips & lamp /rips1 :i* are requir$ 9 v l>ge numb]s 9 multiple bo>ds1 h to be m\nt$ extremely close toge!r1 & z ! same lamp /rips & jack /rips are (t5 available = simple swit*bo>ds1 an economy 9 manufacture is effect$ by adh]5ce to ! same g5]al dim5sions4 ,illu/ration3 ,fig4 #cbh4 ,simple ,common-,batt]y ,swit*bo>d ) ,removable ,relay ,panel ,a re> view ( a common =m ( swit*bo>d cab9et1 kn[n z ! upright type & manufactur$ by ! ,dean ,company1 is %[n 9 ,fig4 #cbh4 ,9 ?is all ! relays are m\nt$ on a h+$ rack1 :i*1 :5 op5$ out z indicat$1 exposes ! wir+ to view = inspection or repairs4 ,access to bo? sides ( ! relays is ?us giv5 to ! repairman :o may d all 8 "w f ! re> ( ! bo>d )\t di/urb+ ! op]ator4 ,fig4 #cbi %[s a ?ree-position cab9et ( ,kellogg manufacture1 ?is be+ ab\t ! limit 9 size ( bo>ds t c\ld prop]ly be call$ simple4 ,obvi\sly1 :]e a swit*bo>d cab9et mu/ be made ( great] l5g? ?an ?is1 i4 e41 ?an is requir$ to accommodate ?ree op]ators1 x becomes too long = ! op]ators to rea* all ov] x )\t undue ef=t or )\t mov+ f _! seats4 ,! s-call$ transf] bo>d & ! multiple bo>d 7to be consid]$ 9 subsequ5t *apt]s71 con/itute me?ods ( relief f su* a condition 9 l>g] ex*anges4 ,illu/ration3 ,fig4 #cbi4 ,?ree-,position ,lamp ,bo>d ,,*apt] ,,xxiii ,,transf] ,,swit*bo>d ,:5 ! traffic orig9at+ 9 a swit*bo>d becomes s great z to require s _m op]ators t ! bo>d mu/ be made s long t any "o ( ! op]ators _c rea* ov] its entire face1 ! simple swit*bo>d does n suffice4 ,ei!r "s =m ( transf] swit*bo>d or ( multiple swit*bo>d mu/ be us$4 ,9 ?is *apt] ! transf] swit*bo>d w be briefly discuss$4 ,! transf] swit*bo>d is s nam$ because its arrangem5t is su* t "s ( ! connections ?r\gh x are h&l$ by means ( two op]ators1 ! op]ator :o answ]s ! call transf]r+ x to ano!r op]ator :o completes ! connection desir$4 ,limitations ( ,simple ,swit*bo>d4 ,conceive a numb] ( simple magneto swit*bo>ds1 or a numb] ( common-batt]y swit*bo>ds1 arrang$ side by side1 _! numb] be+ s great z to =m1 by _! comb9ation1 a bo>d too long = ! ord9>y cords & plugs to rea* betwe5 its extremities4 ,on ea* ( ^! simple swit*bo>ds1 :i* we w say are ea* ( ! "o-position type1 !re t]m9ates a gr\p ( subscrib]s' l9es s great 9 numb]1 consid]+ ! traffic on !m1 t ! ef=ts ( "o op]ator w j ab\t be tax$ to prop]ly att5d to _! calls dur+ ! busie/ h\rs ( ! day4 ,if1 n[1 ^! subscrib]s w\ld be suffici5tly accommodat+ to call = no o!r subscrib]s ?an ^? ^: l9es t]m9ate on ! same swit*bo>d section or on "o ( ! imm$iately adjac5t swit*bo>d sections1 all w\ld be well1 b subscrib]s w n be s re/rict$4 ,!y dem& univ]sal s]vice2 t is1 !y dem& ! privilege ( hav+ _! own l9es connect$ ) ! l9e ( any o!r p]son 9 ! ex*ange4 ,obvi\sly1 9 ! arrangem5t j conceiv$1 any op]ator may answ] any call orig9at+ at h] own bo>d & complete ! connection ) ! desir$ subscrib] if t subscrib]'s jack t]m9ates on h] own section or on "o ( ! adjac5t ones4 ,beyond t %e is p[]less unless o!r means are provid$4 ,transf] ,l9es4 ,9 ! transf] bo>d ^! o!r means consi/ 9 ! provision ( gr\ps ( local trunk l9es or transf] l9es ext5d+ f ea* swit*bo>d position to ea* o!r non-adjac5t swit*bo>d position4 ,:5 an op]ator receives a call = "s l9e on a non-adjac5t position1 hav+ answ]$ ?is call ) h] answ]+ plug1 %e ins]ts ! call+ plug into ! jack ( "o ( ^! transf] l9es t leads to ! prop] o!r section4 ,! op]ator at t section is notifi$ ei!r v]bally or by signal1 & %e completes ! connection betwe5 ! o!r end ( ! transf] l9e & ! l9e ( ! call$ subscrib]2 ! connection betwe5 ! two subscrib]s ?us be+ effect$ ?r\gh ! cords ( ! two op]ators 9 "q l9k$ toge!r by ! transf] l9e4 ,su* a transf] l9e z j describ$1 requir+ ! connection at ea* ( its ends by "o ( ! plugs ( ! op]ator's cord pair1 is t]m$ a jack-end$ trunk or a jack-end$ transf] l9e because ea* ( its ends t]m9ates 9 a jack4 ,illu/ration3 ,fig4 #ccj4 ,jack-,end$ ,transf] ,circuit ,!re is ano!r me?od ( accompli%+ ! same g5]al result by ! employm5t ( ! s-call$ plug-end$ trunk or plug-end$ transf] l9e4 ,9 ?is ! trunk or transf] l9e t]m9ates at "o end1 ! answ]+ end1 9 a jack z be=e1 & ! connection is made ) x by ! answ]+ op]ator by means ( ! call+ plug ( ! pair ) :i* %e answ]$ ! orig9at+ call4 ,! o!r end ( ?is trunk1 in/ead ( t]m9at+ 9 a jack1 ends 9 a plug & ! second op]ator involv$ 9 ! connection1 aft] be+ notifi$1 picks up ?is plug & ins]ts x 9 ! jack ( ! call$ subscrib]1 ?us complet+ ! connection )\t employ+ "o ( h] regul> cord pairs4 ,jack-,end$ ,trunk4 ,9 ,fig4 #ccj are %[n ! circuits ( a commonly employ$ jack-end$ trunk = transf] bo>ds4 ,! talk+ circuit1 z usual1 is %[n 9 heavy l9es & t]m9ates 9 ! tip & sleeve ( ! transf] jacks at ea* end4 ,! auxili>y contacts 9 ^! jacks & ! circuits connect+ !m are absolutely indep5d5t ( ! talk+ circuit & are = ! purpose ( signal+ only1 ! arrangem5t ( ! jacks be+ su* t :5 a plug is ins]t$1 ! spr+ #a w break f spr+ #b & make ) spr+ #c4 ,obvi\sly1 ! ins]tion ( a plug 9 ei!r ( ! jacks w e/abli% su* connections z to light bo? lamps1 s9ce ! engagem5t ( spr+ #a ) spr+ #c 9 ei!r ( ! jacks w connect bo? ( ! lamps 9 multiple across ! batt]y1 ?is connection includ+ always ! contacts #a & #b ( ! o!r jack4 ,f ?is x foll[s t ! ins]tion ( a plug 9 ! o!r end ( ! trunk w1 by break+ contact betwe5 spr+s #a & #b1 put out bo? ! lamps4 ,"o plug ins]t$ w1 !re=e1 light bo? lamps2 two plugs ins]t$ or two plugs )drawn w ext+ui% bo? lamps4 ,illu/ration3 ,fig4 #cca4 ,jack-,end$ ,transf] ,circuit ,if an op]ator locat$ at "o end ( ?is trunk answ]s a call & f9ds t ! call$-= subscrib]'s l9e t]m9ates )9 rea* ( ! op]ator ne> ! o!r end ( ?is trunk1 %e w ins]t a call+ plug1 correspond+ to ! answ]+ plug us$ 9 answ]+ a call1 into ! jack ( ?is trunk & ?us light ! lamp at bo? its ends4 ,! op]ator at ! o!r end ^u see+ ?is transf] lamp illum9at$ ins]ts "o ( h] answ]+ plugs into ! jack1 & by means ( h] li/5+ key asc]ta9s ! numb] ( ! subscrib] desir$1 & imm$iately ins]ts h] call+ plug into ! jack ( ! subscrib] want$ & r+s him 9 ! usual mann]4 ,! act ( ?is second op]ator 9 ins]t+ h] answ]+ plug into ! jack ext+ui%es ! lamp at h] own end & also at ! end :]e ! call orig9at$1 ?us notify+ ! answ]+ op]ator t ! call has be5 att5d$ to4 ,z long z ! lamps rema9 light$1 ! op]ators "k t !re is an unatt5d$ connection on t transf] l9e4 ,su* a transf] l9e is call$ a two-way l9e or a s+le-track l9e1 because traffic ov] x may be 9 ei!r direction4 ,9 ,fig4 #cca is %[n a trunk t op]ates 9 a simil> way except t ! two lamps1 in/ead ( be+ arrang$ 9 multiple1 are arrang$ 9 s]ies4 ,illu/ration3 ,fig4 #ccb4 ,jack- & ,plug-,end$ ,transf] ,circuit ,plug-,end$ ,trunk4 ,9 ,fig4 #ccb is %[n a plug-end$ trunk1 ?is p>ticul> arrangem5t ( circuits be+ employ$ by ! ,mon>* ,company 9 its transf] bo>ds4 ,?is is ess5tially a "o-way trunk1 & traffic ov] x c pass only 9 ! direction ( ! arr[4 ,traffic 9 ! opposite direction betwe5 any two op]ators is h&l$ by ano!r trunk or gr\p ( trunks simil> to ?is b po9t$ 9 ! o!r direction4 ,= ?is reason su* a sy/em is ref]r$ to z a d\ble-track sy/em4 ,! op]ation ( signals is ! same 9 ?is case z 9 ,fig4 #ccj1 except t ! swit*+ device at ! left-h& end ( ! trunk in/ead ( be+ associat$ ) ! jack is associat$ ) ! plug seat1 :i* is a swit* closely associat$ ) ! seat ( a plug s z to be op]at$ :5ev] ! plug is )drawn f or replac$ 9 its seat4 ,! op]ation ( ?is arrangem5t is z foll[s3 ,:5ev] an op]ator at ! "r-h& end ( ?is trunk receives a call = a subscrib] ^: l9e t]m9ates )9 ! rea* ( ! op]ator at ! left-h& end ( ! trunk1 %e ins]ts ! call+ plug ( ! pair us$ 9 answ]+ ! call+ subscrib] into ! jack ( ! trunk1 & ?us lights bo? ( ! trunk lamps4 ,! op]ator at ! o!r end ( ! trunk1 see+ ! trunk lamp light$1 raises ! plug f its seat &1 hav+ le>n$ ! wi%es ( ! call+ subscrib]1 ins]ts ?is plug into ! jack ( ! call$ subscrib] )\t us+ "o ( h] regul> pairs4 ,:5 %e rais$ ! trunk plug f its seat1 %e p]mitt$ ! long spr+ #a ( ! plug seat swit* to rise1 ?us ext+ui%+ bo? lamps & giv+ ! signal to ! orig9at+ op]ator t ! trunk connection has receiv$ att5tion4 ,on tak+ d[n ! connection1 ! )drawal ( ! plug f ! "r h& ( ! trunk lights bo? lamps1 & ! re/or+ ( ! trunk plug to its normal seat aga9 ext+ui%es bo? lamps4 ,plug-,seat ,swit*4 ,! plug-seat swit* is a device t has receiv$ a good deal ( att5tion n only = use ) transf] sy/ems1 b also = use 9 a great v>iety ( ways ) o!r k9ds ( manual swit*+ sy/ems4 ,! plac+ ( a plug 9 its seat or )draw+ x !refrom (f]s a ready means ( accompli%+ "s swit*+ or signal+ op]ation automatically4 ,! plug-seat swit* has1 h[ev]1 9 spite ( its possibilities1 nev] come into wide use1 & s f> z we are aw>e ! ,mon>* ,telephone ,manufactur+ ,company is ! only company ( prom95ce :i* incorporates x 9 its regul> output4 ,! ,mon>* plug-swit* me*anism is %[n 9 ,fig4 #ccc1 & its op]ation is obvi\s4 ,x may be /at$ at ?is po9t t "o ( ! reasons :y ! plug-seat swit* has n be5 m widely adopt$ = use1 is ! difficulty t has be5 exp]i5c$ due to l9t f ! swit*bo>d cords collect+ on or ab\t ! contact po9ts4 ,9 ! con/ruction giv5 9 ! detail$ cut1 upp] "p1 ,fig4 #ccc1 is %[n ! means adopt$ by ! ,mon>* ,company = obviat+ ?is difficulty4 ,! contact po9ts are c>ri$ 9 ! upp] portion ( an inv]t$ cup m\nt$ on ! "u side ( ! swit*bo>d %elf1 & are ?us protect$1 9 l>ge measure1 f ! damag+ influ5ce ( du/ & l9t4 ,illu/ration3 ,fig4 #ccc4 ,plug-,seat ,swit* ,illu/ration3 ,fig4 #ccd4 ,ord]-,wire ,arrangem5t ,me?ods ( ,h&l+ ,transf]s4 ,"o way ( giv+ ! numb] ( ! call$ subscrib] to ! second op]ator 9 a transf] sy/em is to h t op]ator li/5 9 on ! circuit aft] x is cont9u$ to h] position & receive ! numb] ei!r f ! fir/ op]ator or f ! subscrib]4 ,receiv+ x f ! fir/ op]ator has ! disadvantage ( compell+ ! fir/ op]ator to wait on ! circuit until ! second op]ator responds2 receiv+ x f ! subscrib] has ! disadvantage ( sometimes be+ annoy+ to him4 ,?is1 h[ev]1 is to be pref]r$ to ! loss ( "t on ! "p ( ! orig9at+ op]ator t is entail$ by ! fir/ me?od4 ,a bett] way ?an ei!r ( ^! is to provide betwe5 ! v>i\s op]ators work+ 9 a transf] sy/em1 a s-call$ ord]-wire sy/em4 ,an ord] wire1 z ord9>ily arrang$1 is a circuit t]m9at+ at "o end p]man5tly 9 ! head receiv] ( an op]ator1 & t]m9at+ at ! o!r end 9 a pu% button :i*1 :5 depress$1 w connect ! telephone set ( ! op]ator at t end ) ! ord] wire4 ,! op]ator at ! pu%-button end ( ! ord] wire may1 !re=e1 at w1 communicate ) ! o!r op]ator 9 spite ( any?+ t ! o!r op]ator may d4 ,an ord]-wire sy/em suitable = transf] swit*bo>ds consi/s 9 an ord] wire lead+ f ea* op]ator's receiv] to a pu% button at ea* ( ! o!r op]ator's positions1 s t e op]ator has x )9 h] p[] to depress a key or button & e/abli% communication ) a correspond+ op]ator4 ,:51 !re=e1 an op]ator 9 a transf] sy/em answ]s a call t mu/ be complet$ ?r\gh a transf] circuit1 %e e/abli%es connection ) t transf] circuit & !n in=ms ! op]ator at ! o!r end ( t circuit by ord] wire ( ! numb] ( ! trunk & ! numb] ( ! subscrib] ) :i* t trunk is to be connect$4 ,fig4 #ccd %[s a sy/em ( ord]-wire buttons by means ( :i* ea* op]ator may connect h] telephone set ) t ( e o!r op]ator 9 ! room1 ! numb] 9 ?is case be+ conf9$ to ?ree4 ,assum+ t ea* pair ( wires lead+ f ! l[] portion ( ?is figure t]m9ates respectively 9 ! op]ator's talk+ app>atus ( ! ?ree respective op]ators1 !n x is obvi\s t op]ator ,no4 #a1 by depress+ button ,no4 #b1 w connect h] telephone set ) t ( op]ator ,no4 #b2 likewise t any op]ator may communicate ) any o!r op]ator by depress+ ! key be>+ ! correspond+ numb]4 ,limitations ( ,transf] ,sy/em4 ,x may be /at$ t ! transf] sy/em at pres5t has a limit$ place 9 ! art ( telephony4 ,! multiple swit*bo>d has out/ripp$ x 9 ! race = popul> approval & has demon/rat$ its sup]iority 9 practically all l>ge manual ex*ange "w4 ,?is is n because ( lack ( ef=t on ! "p ( telephone eng9e]s to make ! transf] sy/em a success 9 a broad way4 ,a great v>iety ( diff]5t s*emes1 all embody+ ! fundam5tal idea ( hav+ "o op]ator answ] ! call & ano!r op]ator complete x ?r\gh a trunk l9e1 h be5 tri$4 ,9 ,san ,francisco1 ! ,sab9-,hampton sy/em 0 9 fairly successful s]vice & s]v$ _m ?\s&s ( l9es = a numb] ( ye>s4 ,x 01 h[ev]1 aft]w>ds replac$ by mod]n multiple swit*bo>ds4 ,examples ( ,obsolete ,sy/ems4 ,! ,sab9-,hampton sy/em 0 unique 9 _m respects & involv$ ?ree op]ators 9 ea* connection4 ,x 0 "o ( ! v fir/ sy/ems :i* employ$ automatic signal+ ?r\gh\t & did away ) ! subscrib]s' g5]ators4 ,x did n1 h[ev]1 disp5se ) ! subscrib]s' local batt]ies4 ,ano!r l>ge transf] sy/em1 us$ = ye>s 9 an ex*ange s]v+ at a "t z _m z #e1jjj1 0 employ$ at ,gr& ,rapids1 ,mi*igan4 ,?is 0 lat] replac$ by an automatic swit*bo>d4 ,illu/ration3 ,fig4 #cce4 ,?ree-,position ,transf] ,swit*bo>d ,field ( ,usefulness4 ,! real field ( utility = ! transf] sy/em today is to provide = ! gr[? ( simple swit*bo>ds t h ext5d$ beyond _! orig9ally int5d$ limits4 ,by ! add+ ( additional sections to ! simple swit*bo>d & ! e/abli%m5t ( a comp>atively *eap transf] sy/em1 ! simple bo>ds may be made to d cont9u$ s]vice )\t wa/+ ! inve/m5t 9 !m by disc>d+ !m & e/abli%+ a completely new sy/em4 ,h[ev]1 swit*bo>ds are sometimes manufactur$ 9 :i* ! transf] sy/em is includ$ z a "p ( ! orig9al equipm5t4 ,9 ,fig4 #cce is %[n a ?ree-position transf] swit*bo>d1 manufactur$ by ! ,mon>* ,telephone ,company4 ,at fir/ glance ! swit*bo>d appe>s to be exactly l ^? describ$ 9 ,*apt] ,,xxi1 b on close obs]vation1 ! transf] jacks & signals may be se5 9 ! fir/ & ?ird positions1 j bel[ ! l9e jacks & signals4 ,!re is no transf] equipm5t 9 ! second position ( ?is swit*bo>d because ! op]ator at t position is able to rea* ! jacks ( all ! l9es &1 !re=e1 is able to complete all calls orig9at+ on h] position )\t ! use ( any transf] equipm5t4 ,ref]r+ to ,fig4 #cja1 :i* illu/rates a two-position simple swit*bo>d1 x may readily be se5 t if ! dem&s = telephone s]vice 9 ! locality 9 :i* ?is swit*bo>d is in/all$ %\ld increase s z to require ! addition ( m swit*bo>d positions1 ?is swit*bo>d c\ld readily be conv]t$ to a transf] swit*bo>d by plac+ ! necess>y transf] jacks & signals 9 ! vacant space betwe5 ! l9e jacks & cle>+-out drops4 ,illu/ration3 ,,cable ,,turn+ ,,sections1 ,,betwe5 ,a ,,& ,b ,,bo>ds ,cortl&t ,(fice1 ,new ,york ,telephone ,co4 ,,*apt] ,,xxiv ,,pr9ciples ,,( ,,! ,,multiple ,,swit*bo>d ,field ( ,utility4 ,! multiple swit*bo>d1 unlike ! transf] bo>d1 provides means = ea* op]ator to complete1 )\t assi/ance1 a connection ) any subscrib]'s l9e t]m9at+ 9 ! swit*bo>d no matt] h[ great ! numb] ( l9es may be4 ,x is us$ only :]e ! simple swit*bo>d w n suffice2 t is1 :]e ! numb] ( l9es & ! consequ5t traffic is s great z to require s _m op]ators &1 !re=e1 s great a l5g? ( bo>d z to make x impossible = any "o op]ator to rea* all ov] ! face ( ! bo>d )\t mov+ f h] position4 ,! ,multiple ,feature4 ,! fundam5tal feature ( ! multiple swit*bo>d is ! plac+ ( a jack = e l9e s]v$ by ! swit*bo>d )9 ! rea* ( e op]ator4 ,?is idea und]ly+ ! multiple swit*bo>d may be be/ grasp$ by m]ely consid]+ ! me*anical arrangem5t & gr\p+ ( p>ts )\t reg>d to _! details ( op]ation4 ,! idea is sometimes elusive1 b x is really v simple4 ,if ! /ud5t at ! outset w n be fright5$ by ! v l>ge numb] ( p>ts t are sometimes involv$ 9 multiple swit*bo>ds1 & by ! great complexity :i* is app>5t 9 ! wir+ & 9 ! action ( ^! p>ts2 & w rememb] t ?is app>5t complexity results f ! great numb] ( repetitions ( ! same comp>atively simple gr\p ( app>atus & circuits1 mu* w be done t[>d a ma/]y ( ! subject4 ,! multiple swit*bo>d is divid$ into sections1 ea* section be+ ab\t ! wid? & height t w p]mit an ord9>y op]ator to rea* conv5i5tly all ov] its face4 ,! usual wid? ( a section br\ght ab\t by ?is limitation is f five & "o-half to six feet4 ,su* a section af=ds room = ?ree op]ators to sit side by side be=e x4 ,n[ ea* l9e1 in/ead ( hav+ a s+le jack z 9 ! simple swit*bo>d1 is provid$ ) a numb] ( jacks & "o ( ^! is plac$ on ea* ( ! sections1 s t ea* "o ( ! op]ators may h )9 h] rea* a jack = ea* l9e4 ,x is f ! fact t ea* l9e has a multiplicity ( jacks1 t ! t]m multiple swit*bo>d arises4 ,numb] ( ,sections4 ,s9ce !re is a jack = ea* l9e on ea* section ( ! swit*bo>d1 x foll[s t on ea* section !re are z _m jacks z !re are l9es2 t is1 if ! bo>d 7 s]v+ #e1jjj l9es !re w\ld be #e1jjj jacks4 ,let u see n[ :at x is t det]m9es ! numb] ( sections 9 a multiple swit*bo>d4 ,9 ! f9al analysis1 x is ! am\nt ( traffic t arises 9 ! busie/ p]iod ( ! day4 ,assume t 9 a p>ticul> (fice s]v+ #e1jjj l9es1 ! subscrib]s call at su* a v l[ rate t ev5 at ! busie/ "t ( ! day only en\gh calls are made to keep1 say1 ?ree op]ators busy4 ,9 ?is case !re w\ld be no ne$ = ! multiple swit*bo>d1 = a s+le section w\ld suffice4 ,! ?ree op]ators seat$ be=e t section w\ld be able to answ] & complete ! connections = all ( ! calls t arose4 ,b subscrib]s d n call at ?is exce$+ly l[ rate4 ,a great _m m calls w\ld arise on #e1jjj l9es dur+ ! busie/ h\r ?an c\ld be h&l$ by ?ree op]ators &1 !re=e1 a great _m m op]ators w\ld be requir$4 ,space has to be provid$ = ^! op]ators to "w 91 & z ea* section accommodates ?ree op]ators ! total numb] ( sections mu/ be at lea/ equal to ! total numb] ( requir$ op]ators divid$ by ?ree4 ,let u assume1 = in/ance1 t ea* op]ator c h&le #bjj calls dur+ ! busy h\r4 ,assume fur!r t dur+ ! busy h\r ! av]age numb] ( calls made by ea* subscrib] is two4 ,"o hundr$ subscrib]s w\ld1 !re=e1 orig9ate #bjj calls )9 ?is busy h\r & ?is w\ld be j suffici5t to keep "o op]ator busy4 ,s9ce "o op]ator c h&le only ! calls ( "o hundr$ subscrib]s dur+ ! busy h\r1 x foll[s t z _m op]ators mu/ be employ$ z !re are hundr$s ( subscrib]s ^: l9es are s]v$ 9 a swit*bo>d1 & ?is means t 9 an ex*ange ( #e1jjj subscrib]s1 #ej op]ators' positions w\ld be requir$1 or #af-b_/c sections4 ,ea* ( ^! sections w\ld be equipp$ ) ! full #e1jjj jacks1 s t ea* op]ator c\ld h a connection t]m9al = ea* l9e4 ,! ,multiple4 ,^! gr\ps ( #e1jjj jacks1 repeat$ on ea* ( ! sections are t]m$ multiple jacks1 & ! entire equipm5t ( ^! multiple jacks & _! wir+ is ref]r$ to z ! multiple4 ,x w be %[n pres5tly t ! multiple jacks are only us$ = enabl+ ! op]ator to connect ) ! call$ subscrib]4 ,9 o!r words ^! jacks are = ! purpose ( enabl+ ea* op]ator to h )9 h] rea* any l9e t may be call$ = reg>dless ( :at l9e orig9ates ! call4 ,we w n[ consid] :at arrangem5ts are provid$ = enabl+ ! op]ator to receive ! signal indicat+ a call & :at provisions are made = h] to answ] ! call 9 response to su* a signal4 ,l9e ,signals4 ,obvi\sly x is n necess>y to h ! l9e signals repeat$ on ea* section ( ! bo>d z are ! multiple jacks4 ,if a l9e has "o def9ite place on ! swit*bo>d :]e its signal may be receiv$ & its call may be answ]$1 t suffices4 ,ea* l9e1 !re=e1 9 addition to hav+ its multiple jacks di/ribut$ "o on ea* section ( ! swit*bo>d1 has a l9e signal & an individual jack imm$iately associat$ ) x1 locat$ on "o only ( ! sections4 ,?is signal usually is 9 ! =m ( a lamp & is t]m$ ! l9e signal1 & ?is jack is t]m$ ! answ]+ jack s9ce x is by means ( x t ! op]ator always answ]s a call 9 response to ! l9e signal4 ,di/ribution ( ,l9e ,signals4 ,x is evid5t t x w\ld n d to h all ( ^! l9e signals & answ]+ jacks locat$ at "o section ( ! bo>d = !n !y w\ld n be available to all ( ! op]ators4 ,!y are1 !re=e1 di/ribut$ along ! bo>d 9 su* a way t "o gr\p ( !m w be available to "o op]ator1 ano!r gr\p to ano!r op]ator1 & s on2 ! numb] ( answ]+ jacks & signals 9 any "o gr\p be+ s proportion$ ) respect to ! numb] ( calls t come 9 ov] !m dur+ ! busy h\r t x w af=d j ab\t en\gh calls to keep ! op]ator at t position busy4 ,we may summ>ize ^! conditions ) respect to ! jack & l9e-signal equipm5t ( ! multiple swit*bo>d by say+ t ea* l9e has a multiple jack on ea* section ( ! bo>d & 9 addition to ?is has on "o section ( ! bo>d an answ]+ jack & a l9e signal4 ,^! answ]+ jacks & l9e signals are di/ribut$ 9 gr\ps along ! face ( ! bo>d s t ea* op]ator w receive h] prop] quota ( ! orig9at+ calls :i* %e w answ] &1 by virtue ( ! multiple jack1 be able to complete ! connections ) ! desir$ subscrib]s )\t mov+ f h] position4 ,cord ,circuits4 ,ea* op]ator is also provid$ ) a numb] ( pairs ( cords & plugs ) prop] sup]visory or cle>+-out signals & r++ & li/5+ keys1 ! arrangem5t 9 ?is respect be+ simil> to t already describ$ 9 connection ) ! simple swit*bo>d4 ,gu>d+ aga9/ ,d\ble ,connections4 ,f :at has be5 said x is se5 t a call orig9at+ on a giv5 l9e may be answ]$ at "o place only1 b an outgo+ connection ) t l9e may be made at any position4 ,?is fact t a l9e may be connect$ ) :5 call$ = at any "o ( ! sections ( ! swit*bo>d makes necess>y ! provision t two or m connections w n be made ) ! same l9e at ! same "t4 ,= in/ance1 if a call came 9 ov] a l9e ^: signal 0 locat$ on ! fir/ position ( ! swit*bo>d = a connection ) l9e ,no4 #a1jjj1 ! op]ator at ! fir/ position w\ld connect ?is call+ l9e ) ,no4 #a1jjj ?r\gh ! multiple jack on ! fir/ section ( ! swit*bo>d4 ,assume n[ t "s l9e1 ^: signal 0 locat$ on ! #ci? position ( ! swit*bo>d1 %\ld call also = l9e ,no4 #a1jjj :ile t l9e 0 /ill connect$ ) ! fir/ call+ subscrib]4 ,obvi\sly confusion w\ld result if ! op]ator at ! #ci? position1 n kn[+ t l9e ,no4 #a1jjj 0 already busy1 %\ld connect ?is second l9e ) x1 !reby leav+ bo? ( ! call+ subscrib]s connect$ ) l9e ,no4 #a1jjj1 & z a result all ( ^! ?ree subscrib]s connect$ toge!r4 ,! provisions = suitable means = prev5t+ ! mak+ ( a connection ) a l9e t is already swit*$ at "s o!r section ( ! swit*bo>d1 has (f]$ "o ( ! mo/ f]tile fields = inv5tion 9 ! :ole telephone art4 ,! ways t h be5 propos$ = accompli%+ ?is are legion4 ,=tunately common practice has settl$ on "o g5]al plan ( action & t is to s arrange ! circuits t :5ev] a l9e is swit*$ at "o section1 su* an electrical condition w be e/abli%$ on ! =w>d contacts ( all ( its multiple jacks t any op]ator at any o!r section 9 attempt+ to make a connection ) t l9e w be notifi$ ( ! fact t x is already swit*$ by an audible signal1 :i* %e w receive 9 h] head receiv]4 ,on ! o!r h& ! arrangem5t is su* t :5 a l9e is n busy1 i4 e41 x is n swit*$ at any ( ! positions ( ! swit*bo>d1 ! op]ator on attempt+ to make a connection ) su* a l9e w receive no su* gu>d+ signal & w1 !re=e1 proce$ ) ! connection4 ,we may lik5 a l9e 9 a multiple swit*bo>d to a lane hav+ a numb] ( gates giv+ access to x4 ,"o ( ^! gates--! answ]+ jack--is = ! exclusive use ( ! proprietor ( t lane4 ,all ( ! o!r gates to ! lane--! multiple jacks--are = af=d+ means = ! public to ent]4 ,b :5ev] any p]son ent]s "o ( ^! gates1 a signal is automatically put up at all ( ! o!r gates =bidd+ any o!r p]son to ent] ! lane z long z ! fir/ p]son is /ill )94 ,illu/ration3 ,fig4 #ccf4 ,pr9ciple ( ,multiple ,swit*bo>d ,diagram ,%[+ ,multiple ,bo>d ,pr9ciple4 ,= ^? to :om ! =ego+ description ( ! multiple bo>d is n altoge!r cle>1 ! diagram ( ,fig4 #ccf may (f] "s assi/ance4 ,five subscrib]s' l9es are %[n runn+ ?r\gh f\r sections ( a swit*bo>d4 ,ea* ( ^! l9es is provid$ ) a multiple jack on ea* section ( ! bo>d4 ,ea* l9e is also provid$ ) an answ]+ jack & a l9e signal on "o ( ! sections ( ! bo>d4 ,?us ! answ]+ jacks & ! l9e signals ( l9es #a & #b are %[n 9 ,section ,i1 t ( l9e #d is %[n 9 ,section ,,ii1 t ( l9e #c 9 ,section ,,iii1 & t ( l9e #e 9 ,section ,,iv4 ,at ,section ,i1 l9e #a is %[n 9 ! condition ( hav+ made a call & hav+ _h ?is call answ]$ by ! op]ator ins]t+ "o ( h] plugs into its answ]+ jack4 ,9 response to ! in/ructions giv5 by ! subscrib]1 ! op]ator has ins]t$ ! o!r plug ( ?is same pair 9 ! multiple jack ( l9e #b1 ?us connect+ ^! two l9es = conv]sation4 ,at ,section ,,iii1 l9e #c is %[n z hav+ made a call1 & ! op]ator z hav+ answ]$ by ins]t+ "o ( h] plugs into ! answ]+ jack4 ,x happ5s t ! subscrib] on l9e #c reque/s a connection ) l9e #a1 & ! condition at ,section ,,iii is t :]e ! op]ator is ab\t to apply ! tip ( ! call+ plug to ! jack ( l9e #a to asc]ta9 :e!r or n t l9e is busy4 ,z be=e /at$1 :5 ! contact is made betwe5 ! tip ( ! call+ plug & ! =w>d contact ( ! multiple jack1 ! op]ator w receive a click 9 ! e> 7by means t w be m fully discuss$ 9 lat] *apt]s71 ?is click indicat+ to h] t l9e #a is n available = connection because x is already swit*$ at "s o!r section ( ! swit*bo>d4 ,busy ,te/4 ,! busy signal1 by :i* an op]ator 9 attempt+ to make a connection is in=m$ t ! l9e is already busy1 has assum$ a great v>iety ( =ms & has br\ght =? _m inv5tions4 ,x has be5 propos$ by "s t ! ins]tion ( a plug into any "o ( ! jacks ( a l9e w\ld automatically close a little door 9 front ( ea* ( ! o!r jacks ( ! l9e1 !re=e mak+ x impossible = any o!r op]ator to ins]t a plug z long z ! l9e is 9 use4 ,x has be5 propos$ by o!rs to r+ bells or to op]ate buzz]s :5ev] ! attempt 0 made by an op]ator to plug into a l9e t 0 already 9 use4 ,/ill o!rs h propos$ to s arrange ! circuits t ! op]ator w\ld get an electric %ock :5ev] %e attempt$ to plug into a busy l9e4 ,! s*eme t has met ) univ]sal adoption1 h[ev]1 is t ! op]ator %all1 :5 ! tip ( h] call+ plug t\*es ! =w>d contact ( ! jack ( a l9e t is already swit*$1 receive a click 9 h] telephone :i* w =bid h] to ins]t ! plug4 ,! abs5ce ( ?is click1 or sil5ce 9 h] telephone1 in=ms h] t %e may safely make ! connection4 ,pr9ciple4 ,! means by :i* ! op]ator receives or fails to receive ?is click1 accord+ to :e!r ! l9e is busy or idle1 v>y widely1 b s f> z ! writ]s are aw>e !y all h "o fundam5tal feature 9 common4 ,! tip ( ! call+ plug & ! te/ contact ( all ( ! multiple jacks ( an idle l9e mu/ be absolutely at ! same pot5tial be=e ! te/1 s t no curr5t w fl[ ?r\gh ! te/ circuit :5 ! te/ is actually made4 ,! te/ ?imbles ( all ! jacks ( a busy l9e mu/ be at a diff]5t pot5tial f ! tip ( ! te/ plug s t a curr5t w fl[ & a click result :5 ! te/ is made4 ,pot5tial ( ,te/ ,?imbles4 ,x has be5 f\nd an easy matt] to s arrange ! contacts 9 ! jacks ( a multiple swit*bo>d t :5ev] ! l9e is idle ! te/ ?imbles ( t l9e w be a c]ta9 pot5tial1 ! same z t ( all ! unus$ call+ plug tips4 ,x has also be5 easy to s arrange ^! contacts t ! ins]tion ( a plug into any "o ( ! jacks w1 by virtue ( ! contacts e/abli%$1 *ange ! pot5tial ( all ! te/ ?imbles ( t l9e s t !y w be at a diff]5t pot5tial f t ( ! tips ( ! call+ plugs4 ,x has n be5 s easy1 h[ev]1 to provide t ^! conditions %all exi/ "u all conditions ( practice4 ,a great _m busy te/s t look$ well on pap] h be5 f\nd faulty 9 practice4 ,z is always ! case 9 su* in/ances1 ?is has be5 true because ! p :o consid]$ ! s*eme on pap] did n =esee all ( ! conditions t w\ld arise 9 practice4 ,_m busy-te/ sy/ems w op]ate prop]ly :ile ev]y?+ connect$ ) ! swit*bo>d & ! l9es s]v$ by x rema9s 9 prop] ord]4 ,b no su* condition z ?is c be dep5d$ on 9 practice4 ,swit*bo>ds1 no matt] h[ p]fectly made & no matt] ) h[ great c>e !y may be in/all$ & ma9ta9$1 w get out ( ord]4 ,telephone l9es w become gr\nd$ or %ort-circuit$ or cross$ or op5$4 ,su* conditions1 9 a faulty busy-te/ sy/em1 may result 9 a l9e t is really idle pres5t+ a busy te/1 & ?us b>r+ ! subscrib] on t l9e f receiv+ calls f o!r l9es j z completely z if 8 l9e 7 brok54 ,on ! o!r h&1 faulty conditions ei!r 9 ! swit*bo>d or 9 ! l9e may make a l9e t is really busy1 te/ idle1 & ?us result 9 ! confusion ( hav+ two or m subscrib]s connect$ to ! same l9e at ! same "t4 ,busy-,te/ ,faults4 ,to %[ h[ elusive "s ( ! faults ( a busy te/ may be1 :5 consid]$ on pap]1 x has come )9 ! obs]vation ( ! writ]s t a new busy-te/ sy/em 0 ?\ght well en\gh ( by a gr\p ( exp]i5c$ eng9e]s to w>rant its in/allation 9 a gr\p ( v l>ge multiple swit*bo>ds1 ! co/ ( :i* am\nt$ to hundr$s ( ?\s&s ( doll>s1 & yet :5 s in/all$ x develop$ t a s+le %ort-circuit$ cord 9 a position w\ld make ! te/ inop]ative on all ! cords ( t position--obvi\sly an intol]able condition4 ,luckily ! rem$y 0 simple & easily appli$4 ,9 a well-design$ busy-te/ sy/em !re %\ld be complete sil5ce :5 ! te/ is made ( an idle l9e1 & always a well-def9$ click :5 ! te/ is made ( a busy l9e4 ,! te/ on busy l9es %\ld result 9 a uni=m click reg>dless ( l5g? ( l9es or ! condition ( ! app>atus4 ,x does n suffice to h a little click = an idle l9e & a big click = a busy l9e1 z practice has %[n t ?is results 9 frequ5t errors on ! "p ( ! op]ators4 ,good op]at+ requires t ! tip ( ! call+ plug be tapp$ aga9/ ! te/ ?imble sev]al times 9 ord] to make sure ( ! /ate ( ! call$ l9e4 ,9 "s multiple swit*bo>ds ! arrangem5t has be5 su* t ! jacks ( a l9e w\ld te/ busy z soon z ! subscrib] on t l9e remov$ 8 receiv] f its hook to make a call1 z well z :ile any plug 0 9 any jack ( t l9e4 ,! advocates ( ?is add$ feature1 9 connection ) ! busy te/1 h claim$ t ! receiv]1 :5 remov$ f its hook 9 mak+ a call1 %\ld make ! l9e te/ busy & t a l9e %\ld n be connect$ ) :5 ! subscrib]'s receiv] 0 (f its hook any m ?an x %\ld be :5 x 0 already connect$ ) at "s o!r section ( ! swit*bo>d4 ,:ile x is true t a l9e may be prop]ly t]m$ busy :5 ! subscrib] has remov$ 8 receiv] 9 ord] to make a call1 x is n true t !re is any real necessity = gu>d+ aga9/ a connection ) x :ile he is wait+ = ! op]ator to answ]4 ,leav+ ! l9e ungu>d$ = ?is brief p]iod may result 9 ! subscrib]1 :o int5d$ to make ! call1 hav+ to def] 8 call until he has conv]s$ ) ! p>ty :o is try+ to rea* him4 ,?is _c be said to be a detrim5t to ! s]vice1 h[ev]1 s9ce ! second p>ty gets ! connection he desires mu* soon] ?an he o!rwise w\ld1 & ! fir/ p>ty may /ill make 8 fir/ int5d$ call z soon z he has dispos$ ( ! p>ty :o rea*$ him :ile he 0 wait+ = 8 own op]ator to answ]4 ,x may be said1 !re=e1 9 connection ) ?is matt] ( mak+ ! l9e te/ busy z soon z a subscrib] has remov$ 8 receiv] f ! hook1 t x is n consid]$ an ess5tial1 & 9 case ( ^? swit*bo>d sy/ems :i* naturally "w out t way x is n consid]$ a disadvantage4 ,field ( ,ea* ,op]ator4 ,x 0 /at$ e>li] 9 ?is *apt] t z ea* section accommodat$ ?ree op]ators1 ! total numb] ( sections 9 a swit*bo>d w be at lea/ "o-?ird ! total numb] ( requir$ op]ators4 ,?is ?\ght ne$s fur!r developm5t1 = to /op at t /atem5t is to arrive some:at %ort ( ! tru?4 ,9 ord] to d ?is x is necess>y to consid] ! field 9 ! multiple1 rea*$ by ea* op]ator4 ,! section is ( su* size1 or %\ld be1 t an op]ator seat$ 9 ! c5t] position ( x may1 )\t undue ef=t1 rea* all ov] ! multiple4 ,b ! op]ator at ! "r-h& position _c rea* ! extreme left portion ( ! multiple ( t section1 nor c ! op]ator at ! left rea* ! extreme "r4 ,h[ !n may ea* op]ator rea* a jack = e l9e8 ,rememb]+ t ! multiple jacks are arrang$ exactly ! same 9 ea* section1 ea* jack always occupy+ ! same relative position1 x is easy to see t :ile ! op]ator at a "r-h& position ( a section _c rea* ! left-h& ?ird ( ! multiple 9 h] own section1 %e may rea* ! left-h& ?ird ( ! multiple 9 ! section at h] "r1 & ?is1 toge!r ) ! c5t] & "r-h& ?irds ( h] own section1 repres5ts ! entire numb] ( l9es4 ,s x is ) ! left-h& op]ator at any section1 %e rea*es two-?irds ( all ! l9es 9 ! multiple ( h] own section & "o-?ird 9 t ( ! section at h] left4 ,end ,positions4 ,?is makes x necess>y to inquire ab\t ! op]ators at ! end positions ( ! entire bo>d4 ,to provide = ^! ! multiple is ext5d$ "o-?ird ( a section beyond !m1 s z to supply at ! ends ( ! swit*bo>d jacks = ^? l9es :i* ! end op]ators _c rea* on _! own sections4 ,sometimes in/ead ( add+ ^! end sections to ! multiple = ! end op]ators1 ! same result is accompli%$ by us+ only ! full & regul> sections ( ! multiple1 & leav+ ! end positions )\t op]ators' equipm5t1 z well z )\t answ]+ jacks1 l9e signals1 & cords & plugs1 s t 9 reality ! end op]ator is at ! middle position ( ! end section4 ,?is1 9 our op9ion1 is ! bett] practice1 s9ce x leaves ! sections /&>d1 & makes x easi] to ext5d ! swit*bo>d 9 l5g?1 z x gr[s1 by ! m]e addition ( new sections )\t di/urb+ any ( ! old multiple4 ,influ5ce ( ,traffic4 ,we wi% aga9 to emphasize ! fact t x is ! traffic dur+ ! busie/ "t ( day & n ! numb] ( l9es t det]m9e ! size ( a multiple swit*bo>d s f> z its l5g? is conc]n$4 ,! numb] ( l9es det]m9es ! size ( ! multiple 9 any "o section1 b x is ! am\nt ( traffic1 ! numb] ( calls t are made 9 ! busie/ p]iod1 t det]m9es ! numb] ( op]ators requir$1 & ?us ! numb] ( positions4 ,_h ?is n[ v obvi\s fact be5 m fully realiz$ 9 ! pa/1 "s companies w\ld be op]at+ at less exp5se1 & "s manufactur]s w\ld h sold less exp5sive swit*bo>ds4 ,! :ole "q z to ! numb] ( positions boils d[n to h[ _m answ]+ jacks & l9e signals may be plac$ at ea* op]ator's position )\t ov]burd5+ ! op]ator ) incom+ traffic at ! busy "t ( day4 ,obvi\sly1 "s l9es w call m frequ5tly ?an o!rs1 & h5ce ! prop] numb] ( answ]+ jacks at ! diff]5t positions w v>y4 ,obvi\sly1 also1 due to *anges 9 ! p]sonnel ( ! subscrib]s1 ! rates ( call+ ( diff]5t gr\ps ( l9es w *ange f "t to "t1 & ?is may necessitate a regr\p+ ( ! l9e signals & answ]+ jacks on ! positions2 & *anges 9 ! p]sonnel ( ! op]ators or 9 _! skill also dem& su* regr\p+4 ,int]m$iate ,frame4 ,! int]m$iate di/ribut+ frame is provid$ = ?is purpose1 & w be m fully discuss$ 9 subsequ5t *apt]s4 ,suffice x to say "h t ! int]m$iate di/ribut+ frame p]mits ! answ]+ jacks & l9e signals to be %ift$ ab\t among ! op]ators' positions1 s t ea* position w h j en\gh orig9at+ traffic to keep ea* ( ! op]ators economically busy dur+ ! busie/ "t ( ! day4 ,,*apt] ,,xxv ,,! ,,magneto ,,multiple ,,swit*bo>d ,field ( ,utility4 ,! pr9ciples ( ! multiple swit*bo>d set =? 9 ! la/ *apt] 7 all develop$ long be=e ! common-batt]y sy/em came into exi/5ce1 & consequ5tly all ( ! fir/ multiple swit*bo>ds 7 ( ! magneto type4 ,al?\gh once v widely us$1 ! magneto multiple swit*bo>d has almo/ pass$ out ( exi/5ce1 s9ce x has become almo/ univ]sal practice to equip ex*anges l>ge en\gh to employ multiple bo>ds ) common-batt]y sy/ems4 ,nev]!less !re is a field = magneto multiple swit*bo>ds1 & 9 ?is field x has rec5tly be5 com+ into increas+ favor4 ,9 ^? t[ns equipp$ ) magneto sy/ems employ+ simple swit*bo>ds or transf] swit*bo>ds1 & :i* require new swit*bo>ds by virtue ( hav+ outgr[n or worn out _! old ones1 ! magneto multiple swit*bo>d is frequ5tly f\nd to be/ fit ! requirem5ts ( economy & good practice4 ,! reason = ?is is t by its use ! magneto telephones already 9 s]vice may be cont9u$1 no *ange be+ requir$ outside ( ! c5tral (fice4 ,fur!rmore1 ) ! magneto multiple swit*bo>d no provision ne$ be made = a p[] plant1 :i*1 9 t[ns ( small size1 is (t5 an important consid]ation4 ,aga91 _m companies op]ate ov] a consid]able area1 involv+ a collection ( t[ns & hamlets4 ,x may be t all ( ^! t[ns except "o are cle>ly ( a size to dem& magneto equipm5t & t magneto equipm5t is ! /&>d ?r\gh\t ! entire t]ritory ( ! company4 ,if1 h[ev]1 "o ( ! t[ns1 by virtue ( gr[?1 dem&s a multiple swit*bo>d1 ?is condition af=ds an additional argum5t = ! employm5t ( ! magneto multiple swit*bo>d1 s9ce ! same /&>ds ( equipm5t & con/ruction may be ma9ta9$ ?r\gh\t ! entire t]ritory ( ! op]at+ company1 a manife/ advantage4 ,on ! o!r h&1 x may be said t ! magneto multiple swit*bo>d has no prop] place 9 mod]n ex*anges ( consid]able size--say1 hav+ upw>d ( "o ?\s& subscrib]s--at lea/ "u conditions f\nd 9 ! ,unit$ ,/ates4 ,not)/&+ ! obsolesc5ce ( ! magneto multiple swit*bo>d = l>ge ex*anges1 a brief discussion ( "s ( ! e>ly magneto multiple swit*bo>ds1 & p>ticul>ly ( "o ( ! l>ge ones1 is wor? :ile1 9 t a consid]ation ( ! defects ( ^? e>ly ef=ts w give "o a bett] und]/&+ & appreciation ( ! mod]n multiple swit*bo>d1 & p>ticul>ly ( ! mod]n multiple common-batt]y swit*bo>d1 ! mo/ highly organiz$ ( all ! manual swit*+ sy/ems4 ,brief ref]5ce w1 !re=e1 be made to ! s-call$ s]ies multiple swit*bo>d1 & !n to ! bran* t]m9al multiple swit*bo>d1 :i* latt] 0 ! highe/ type ( swit*bo>d developm5t at ! "t ( ! adv5t ( common-batt]y work+4 ,illu/ration3 ,fig4 #ccg4 ,s]ies ,magneto ,multiple ,swit*bo>d ,s]ies-,multiple ,bo>d4 ,9 ,fig4 #ccg are %[n ! circuits ( a s]ies magneto multiple swit*bo>d z develop$ by ! eng9e]s ( ! ,we/]n ,electric ,company dur+ ! eighties4 ,z is usual1 two subscrib]s' l9es & a s+le cord circuit are %[n4 ,"o side ( ea* l9e passes directly f ! subscrib]'s /ation to "o side ( ! drop1 & also bran*es (f to ! sleeve contact ( ea* ( ! jacks4 ,! o!r side ( ! l9e passes fir/ to ! tip spr+ ( ! fir/ jack1 !nce to ! anvil ( t jack & to ! tip spr+ ( ! next jack1 & s on 9 s]ies ?r\gh all ( ! jacks belong+ 9 t l9e to ! o!r t]m9al ( ! drop coil4 ,normally1 !re=e1 ! drop is connect$ across ! l9e ready to be responsive to ! signal s5t f ! subscrib]'s g5]ator4 ,! cord circuit is ( ! two-conductor type1 ! plugs be+ provid$ ) tip & sleeve contacts1 ! tips be+ connect$ by "o ( ! flexible conductors ?r\gh ! prop] r++ & li/5+ key spr+s1 & ! sleeve be+ likewise connect$ ?r\gh ! o!r flexible conductor & ! o!r spr+s ( ! r++ & li/5+ keys4 ,x is obvi\s t :5 any plug is ins]t$ into a jack1 ! circuit ( ! l9e w be cont9u$ to ! cord circuit & at ! same "t ! l9e drop w be cut out ( ! circuit1 because ( ! lift+ ( ! tip spr+ ( ! jack f its anvil4 ,p]man5tly connect$ betwe5 ! sleeve side ( ! cord circuit & gr\nd is a ret>dation coil #a & a batt]y4 ,ano!r ret>dation coil #b is connect$ betwe5 ! gr\nd & a po9t on ! op]ator's telephone circuit betwe5 ! op]ator's head receiv] & ! second>y ( h] induction coil4 ,^! two ret>dation coils h to d ) ! busy te/1 ! action ( :i* is z foll[s3 normally1 or :5 a l9e is n swit*$ at ! c5tral (fice1 ! te/ ?imbles w all be at sub/antially gr\nd pot5tial1 i4 e41 !y are suppos$ to be4 ,! po9t on ! op]ator's receiv] circuit :i* is gr\nd$ ?r\gh ! ret>dation coil #b w also be ( gr\nd pot5tial because ( t connection to gr\nd4 ,9 ord] to te/1 ! op]ator always has to ?r[ h] li/5+ key ,l4,k4 into ! li/5+ position4 ,%e also has to t\* ! tip ( ! call+ plug ,pc to a sleeve or jack ( ! l9e t is be+ te/$4 ,if1 !re=e1 a te/ is made ( an idle or non-busy l9e1 ! t\*+ ( ! tip ( ! call+ plug ) ! te/ ?imble ( t l9e w result 9 no fl[ ( curr5t ?r\gh ! op]ator's receiv]1 because !re w be no diff]5ce ( pot5tial any:]e 9 ! te/ circuit1 :i* te/ circuit may be trac$ f ! te/ ?imble ( ! l9e "u te/ to ! tip ( ! call+ plug1 !nce ?r\gh ! tip /r& ( ! cord to ! li/5+ key1 !nce to ! out] anvil ( ! li/5+ key on t side1 ?r\gh ! op]ator's receiv] to gr\nd ?r\gh ! imp$ance coil #b4 ,if1 h[ev]1 ! l9e _h already be5 swit*$ at "s o!r section by ! ins]tion ( ei!r a call+ or answ]+ plug1 all ( ! te/ ?imbles ( t l9e w\ld h be5 rais$ to a pot5tial above t ( ! gr\nd1 by virtue ( ! batt]y connect$ ) ! sleeve side ( ! cord circuit ?r\gh ! ret>dation coil #a4 ,if ! op]ator _h made a te/ ( su* a l9e1 ! tip ( h] te/+ plug w\ld h f\nd ! ?imble rais$ to ! pot5tial ( ! batt]y &1 !re=e1 a fl[ ( curr5t w\ld occur :i* w\ld give h] ! busy click4 ,! complete te/ circuit ?us =m$ 9 te/+ a busy l9e w\ld be f ! ungr\nd$ pole ( ! batt]y ?r\gh ! imp$ance coil #a associat$ ) ! cord t 0 already 9 connection ) ! l9e1 !nce to ! sleeve /r& ( t cord to ! sleeve ( ! jack at :i* ! l9e 0 already swit*$1 !nce ?r\gh t portion ( ! l9e circuit to :i* all ( ! sleeve contacts 7 connect$1 & !re=e to ! sleeve or te/ ?imble ( ! jack at :i* ! te/ is made1 !nce ?r\gh ! tip ( ! call+ plug employ$ 9 mak+ ! te/ ?r\gh ! tip side ( t cord circuit to ! out] li/5+ key contact ( ! op]ator mak+ ! te/1 & !nce to gr\nd ?r\gh ! op]ator's receiv] & ! imp$ance coil #b4 ,! resultant click w\ld be an indication to ! op]ator t ! l9e 0 already 9 use & t1 !re=e1 %e mu/ n make ! connection4 ,! cond5s] #c is associat$ ) ! op]ator's talk+ set & ) ! extra spr+ 9 ! li/5+ key ,l4,k4 9 su* a mann] t :5 ! li/5+ key is ?r[n1 ! tip /r& ( ! cord circuit is divid$ & ! cond5s] includ$ betwe5 !m4 ,?is is = ! purpose ( prev5t+ any pot5tials1 :i* might exi/ on ! l9e ) :i* ! answ]+ plug ,pa 0 connect$1 f affect+ ! busy-te/ conditions4 ,op]ation4 ,! op]ation ( ! sy/em aside f ! busy-te/ feature is j l t describ$ 9 connection ) ! simple magneto swit*bo>d4 ,assum+ t ! subscrib] at ,/ation ,a makes ! call1 he turns 8 h& g5]ator1 :i* ?r[s ! drop on 8 l9e at ! c5tral (fice4 ,! op]ator1 see+ ! signal1 ins]ts ! answ]+ plug ( "o ( h] idle pairs ( cords into ! answ]+ jack & ?r[s h] li/5+ key ,l4,k4 ,?is enables ! op]ator to talk ) ! call+ subscrib]1 & hav+ f\nd t he desires a connection ) ! l9e ext5d+ to ,/ation ,b1 %e t\*es ! tip ( h] call+ plug to ! multiple jack ( t l9e t is )9 h] rea*1 x be+ rememb]$ t ea* "o ( ! multiple jacks %[n is on a diff]5t section4 ,%e leaves ! li/5+ key 9 ! li/5+ position :5 %e does ?is4 ,if ! l9e is busy1 ! click w notify h] t %e mu/ n make ! connection1 9 :i* case %e in=ms ! call+ subscrib] t ! l9e is busy & reque/s him to call aga94 ,if1 h[ev]1 %e receiv$ no click1 %e w\ld ins]t ! call+ plug into ! jack1 ?us complet+ ! connection betwe5 ! two l9es4 ,%e w\ld !n press ! r++ key associat$ ) ! call+ plug & t mom5t>ily disconnects ! call+ plug f ! answ]+ plug & at ! same "t e/abli%es connection betwe5 ! r++ g5]ator & ! call$ l9e4 ,! release ( ! r++ key aga9 connects ! call+ & answ]+ plugs &1 !re=e1 connects ! two subscrib]s' l9es ready = conv]sation4 ,all t is !n necess>y is t ! call$ subscrib] %all respond & remove 8 receiv] f its hook1 ! call+ subscrib] already hav+ done ?is4 ,:5 ! conv]sation is f9i%$1 bo? ( ! subscrib]s 7if !y rememb] x7 w op]ate _! r++ g5]ators1 :i* w ?r[ ! cle>+-out drop z a signal to ! op]ator = disconnection4 ,if x %\ld become necess>y = ! op]ator to r+ back on ! l9e ( ! call+ subscrib]1 %e may d s by press+ ! r++ key associat$ ) ! call+ plug4 ,frequ5tly ?is multiple swit*bo>d arrangem5t 0 us$ ) gr\nd$ l9es1 9 :i* case ! s+le l9e wire ext5d+ f ! subscrib]'s /ation to ! swit*bo>d 0 connect$ ) ! tip spr+ ( ! fir/ jack1 ! circuit be+ cont9u$ 9 s]ies ?r\gh ! jack to ! drop & !nce to gr\nd ?r\gh a high non-inductive resi/ance4 ,defects4 ,?is s]ies multiple magneto sy/em 0 us$ ) a great _m v>iations1 & x _h a good _m defects4 ,"o ( ^! defects 0 due to ! necess>y ext5d+ ( "o limb ( ! l9e ?r\gh a l>ge numb] ( s]ies contacts 9 ! jacks4 ,?is is n to be desir$ 9 any case1 b x 0 p>ticul>ly objectionable 9 ! e>ly days be=e jacks _h be5 develop$ to _! pres5t high /ate ( p]fection4 ,a p>ticle ( du/ or o!r insulat+ matt]1 lodg+ betwe5 ! tip spr+ & its anvil 9 any "o ( ! jacks1 w\ld leave ! l9e op51 ?us disabl+ ! l9e to incom+ signals1 & also = conv]sation 9 case ! break happ5$ to occur betwe5 ! subscrib] & ! jack t 0 us$ 9 connect+ ) ! l9e4 ,ano!r defect due to ! same cause 0 t ! l9e ?r\gh ! swit*bo>d 0 always unbalanc$ by ! ins]tion ( a plug1 "o limb ( ! l9e always ext5d+ cle> ?r\gh ! swit*bo>d to ! drop & ! o!r1 :5 ! plug 0 ins]t$1 ext5d+ only "p way ?r\gh ! swit*bo>d & be+ cut (f at ! jack :]e ! connection 0 made4 ,! objection w be app>5t :5 x is rememb]$ t ! wires 9 ! l9e circuit connect+ ! multiple jacks are necess>ily v closely bun*$ toge!r &1 !re=e1 !re is v likely to be cross-talk betwe5 two adjac5t l9es unless ! two limbs ( ea* l9e are exactly balanc$ ?r\gh\t _! entire l5g?4 ,aga9 ! busy-te/ conditions ( ?is circuit 7 n ideal4 ,! fact t ! te/ r+s ( ! l9e 7 connect$ p]man5tly ) ! outside l9e circuit subject$ ^! te/ r+s to :atev] pot5tials might exi/ on ! outside l9es1 due to any causes :atev]1 su* z a cross ) "s o!r wire2 ?us ! te/ r+s ( an idle l9e might by "s ext]ior cause be rais$ to su* a pot5tial t ! l9e w\ld te/ busy4 ,x may be laid d[n z a fundam5tal pr9ciple 9 good multiple swit*bo>d practice t ! busy-te/ condition %\ld be made indep5d5t ( any conditions on ! l9e circuit outside ( ! c5tral (fice1 & su* is n ! case 9 ?is circuit j describ$4 ,illu/ration3 ,,cable ,,run ,,f ,,int]m$iate ,,frame ,,to ,,multiple ,cortl&t ,(fice1 ,new ,york ,telephone ,co4 ,bran*-,t]m9al ,multiple ,bo>d4 ,! next important /ep 9 ! developm5t ( ! magneto multiple swit*bo>d 0 t :i* produc$ ! s-call$ bran*-t]m9al bo>d4 ,?is came into wide use 9 ! v>i\s ,bell op]at+ companies be=e ! adv5t ( ! common-batt]y sy/ems4 ,its circuits & ! pr9ciples ( op]ation may be und]/ood 9 connection ) ,fig4 #cch4 ,9 ! bran*-t]m9al sy/em !re are no s]ies contacts 9 ! jacks & no unbalanc+ ( ! l9e due to a cutt+ (f ( a portion ( ! l9e circuit :5 a connection 0 made ) x4 ,fur!rmore1 ! te/ circuits 7 entirely local to ! c5tral (fice & 7 n likely to be affect$ by outside conditions on ! l9e4 ,?is swit*bo>d also add$ ! feature ( ! automatic re/oration ( ! drops1 ?us reliev+ ! op]ator ( ! burd5 ( do+ t manually1 & also p]mitt+ ! drops to be m\nt$ on a portion ( ! swit*bo>d t 0 n available = ! m\nt+ ( jacks1 & ?us p]mitt+ a great] capacity 9 jack equipm5t4 ,illu/ration3 ,fig4 #cch4 ,bran*-,t]m9al ,magneto ,multiple ,swit*bo>d ,ea* jack has five contacts1 & ! answ]+ & multiple jacks are alike1 bo? 9 respect to _! con/ruction & _! connection ) ! l9e4 ,! drops are ! electrically self-re/or+ type %[n 9 ,fig4 #bfc4 ,! l9e circuits ext5d$ p]man5tly f ! subscrib]'s /ation to ! l9e w9d+ ( ! drop & ! two limbs ( ! l9e bran*$ (f to ! tip & sleeve contacts #a & #b respectively ( ea* jack4 ,ano!r pair ( wires ext5d$ ?r\gh ! multiple p>allel to ! l9e wires & ^! bran*$ (f respectively to ! contact spr+s #c & #d ( ea* ( ! jacks4 ,?is pair ( wires =m$ portions ( ! drop-re/or+ circuit1 includ+ ! re/or+ coil #f & ! batt]y #g1 z indicat$4 ,! te/ ?imble #e ( ea* ( ! jacks is connect$ p]man5tly ) ! spr+ #c ( ! correspond+ jack &1 !re=e1 ) ! wire :i* connects ?r\gh ! re/or+ coil #f ( ! correspond+ drop to gr\nd ?r\gh ! batt]y #g4 ,! plugs 7 ea* provid$ ) ?ree contacts4 ,two ( ^! 7 ! usual tip & sleeve contacts connect$ ) ! two /r&s ( ! cord circuit4 ,! ?ird contact #h 0 n connect$ ) any portion ( ! cord circuit1 be+ m]ely an insulat$ contact on ! plug adapt$1 :5 ! plug 0 fully ins]t$1 to connect toge!r ! spr+s #c & #d4 ,! cord circuit itself is readily und]/ood f ! draw+1 hav+ two features1 h[ev]1 :i* m]it att5tion4 ,"o is ! e/abli%+ ( a gr\nd$ batt]y connection to ! c5t] portion ( ! w9d+ ( ! receiv] = ! purposes ( ! busy te/1 & ! o!r is ! provision ( a re/or+ coil & re/or+ circuit = ! cle>+-out drop1 ?is circuit be+ clos$ by an additional contact on ! li/5+ key s z to re/ore ! cle>+-out drop :5ev] ! li/5+ key 0 op]at$4 ,op]ation4 ,an und]/&+ ( ! op]ation ( ?is sy/em is easy4 ,! turn+ ( ! subscrib]'s g5]ator1 :5 ! l9e 0 9 its normal condition1 caus$ ! display ( ! l9e signal4 ,! ins]tion ( ! answ]+ plug1 9 response to ?is call1 did ?ree ?+s3 7#a7 ,x ext5d$ ! l9e circuit to ! tip & sleeve /r& ( ! cord circuit4 7#b7 ,x en]giz$ ! re/or+ coil #f ( ! drop by e/abli%+ ! circuit f ! contact spr+ #c ?r\gh ! plug contact #h to ! o!r contact spr+ #d1 ?us complet+ ! circuit betwe5 ! two normally op5 auxili>y wires4 7#c7 ,! connect+ ( ! spr+s #c & #d e/abli%$ a connection f gr\nd to ! te/ ?imbles ( all ! jacks on a l9e1 ! spr+ #d be+ always gr\nd$ & ! spr+ #c be+ always connect$ to ! te/ ?imble #e4 ,x is to be not$ t on idle l9es ! te/ r+s are always at ! same pot5tial z ! ungr\nd$ pole ( ! batt]y #g1 be+ connect$ !reto ?r\gh ! w9d+ #f ( ! re/or+ coil4 ,on all busy l9es1 h[ev]1 ! te/ r+s are dead gr\nd$ ?r\gh ! contact #h ( ! plug t is connect$ ) ! l9e4 ,! tip ( ! te/+ plug at ! "t ( mak+ a te/ w also be at ! same pot5tial z t ( ! ungr\nd$ pole ( ! batt]y #g1 s9ce ?is pole ( ! batt]y #g is always connect$ to ! c5t] portion ( ! op]ator's receiv] w9d+1 & :5 ! li/5+ key is ?r[n ! tip ( ! call+ plug is connect$ !re) & is at ! same pot5tial4 ,:51 !re=e1 ! op]ator t\*es ! tip ( ! call+ plug to ! te/ ?imble ( an idle l9e1 %e w get no click1 s9ce ! tip ( ! plug & ! te/ ?imble w be at ! same pot5tial4 ,if1 h[ev]1 ! l9e has already be5 swit*$ at ano!r section ( ! bo>d1 !re w be a diff]5ce ( pot5tial1 because ! te/ ?imble w be gr\nd$1 & ! circuit1 ?r\gh :i* ! curr5t :i* causes ! click fl[s1 may be trac$ f ! ungr\nd$ pole ( ! batt]y #g to ! c5t] portion ( ! op]ator's receiv]1 !nce ?r\gh "o-half ( ! w9d+ to ! tip ( ! call+ plug1 !nce to ! te/ ?imble ( ! jack "u te/1 !nce to ! spr+ #c ( ! jack on ano!r section at :i* ! connection exi/s1 ?r\gh ! contact #h on ! plug ( t jack to ! spr+ #d1 & !nce to gr\nd & back to ! o!r t]m9al ( ! batt]y #g4 ,magnet ,w9d+s4 ,coils ( ! l9e & cle>+-out drops by :i* ^! drops are ?r[n1 are w\nd to su* high resi/ance & imp$ance z to make x prop] to leave !m p]man5tly bridg$ across ! talk+ circuit4 ,! necessity = cutt+ !m out is1 !re=e1 done away )1 ) a consequ5t avoidance1 9 ! case ( ! l9e drops1 ( ! provision ( s]ies contacts 9 ! jacks4 ,arrangem5t ( ,app>atus4 ,9 bo>ds ( ?is type ! l9e & cle>+-out drops 7 m\nt$ 9 ! extreme upp] portion ( ! swit*bo>d face s z to be )9 ! range ( vision ( ! op]ator1 b yet out ( h] rea*4 ,!re=e1 ! :ole face ( ! bo>d t 0 )9 ! limit ( ! op]ator's rea* 0 available = ! answ]+ & multiple jacks4 ,a front view ( a little ov] "o ( ! sections ( ! swit*bo>d1 involv+ ?ree complete op]ator's positions1 is %[n 9 ,fig4 #cci1 :i* is a portion ( ! swit*bo>d in/all$ by ! ,we/]n ,electric ,company 9 "o ( ! l>ge ex*anges 9 ,p>is1 ,france4 7,?is has rec5tly be5 replac$ by a common-batt]y multiple bo>d47 ,9 ?is ! l9e drops may be se5 at ! extreme top ( ! face ( ! swit*bo>d1 & imm$iately b5ea? ^! ! cle>+-out drops4 ,b5ea? ^! are ! multiple jacks arrang$ 9 banks ( "o hundr$1 ea* hundr$ consi/+ ( five /rips ( tw5ty4 ,at ! extreme l[] portion ( ! jack space are %[n ! answ]+ jacks & b5ea? ^! on ! horizontal %elf1 ! plugs & keys4 ,^! jacks 7 m\nt$ on #a_/b-;in* c5t]s1 bo? v]tically & horizontally & ea* section _h 9 multiple #ij banks ( #ajj ea*1 mak+ #i1jjj 9 all4 ,subsequ5t practice has %[n t ?is involves too l>ge a rea* = ! op]ators & t1 !re=e1 #i1jjj is too l>ge a numb] ( jacks to place on "o section if ! jacks are n spac$ clos] ?an on #a_/b-;in* c5t]s4 ,) ! jack involv+ z _m p>ts z t requir$ by ?is bran* t]m9al sy/em1 x 0 h>dly feasible to make !m small] ?an ?is )\t sacrific+ _! durability1 & "o ( ! important features ( ! common-batt]y multiple sy/em :i* has supplant$ ?is bran*-t]m9al magneto sy/em is t ! jacks are ( su* a simple nature z to l5d !mselves to m\nt+ on #c_/h-;in* c5t]s1 & 9 "s cases on #c_/aj-;in* c5t]s4 ,illu/ration3 ,fig4 #cci4 ,face ( ,magneto ,multiple ,swit*bo>d ,mod]n ,magneto ,multiple ,bo>d4 ,com+ n[ to a consid]ation ( mod]n magneto multiple swit*bo>ds1 & be>+ 9 m9d t su* bo>ds are to be f\nd 9 mod]n practice only 9 comp>atively small in/allations & !n only "u r peculi> conditions1 z already set =?1 we w consid] ! swit*bo>d ( ! ,mon>* ,telephone ,manufactur+ ,company z typical ( good practice 9 ?is respect4 ,illu/ration3 ,fig4 #cdj4 ,mon>* ,magneto ,multiple ,swit*bo>d ,circuits ,l9e ,circuit4 ,! l9e & cord circuits ( ! ,mon>* sy/em are %[n 9 ,fig4 #cdj4 ,x w be se5 t ea* jack has 9 all five contacts1 numb]$ f #a to #e respectively1 ( :i* #a & #d are ! spr+s :i* regi/] ) ! tip & r+ contacts ( ! plug & ?r\gh :i* ! talk+ circuit is cont9u$1 :ile #b & #c are s]ies contacts = cutt+ (f ! l9e drop :5 a plug is ins]t$1 & #e is ! te/ contact or ?imble adapt$ to regi/] ) ! sleeve contact on ! plug :5 ! plug is fully ins]t$4 ,! l9e circuit ?r\gh ! drop may be trac$ normally f "o side ( ! l9e ?r\gh ! drop coil1 !nce ?r\gh all ( ! pairs ( spr+s #b & #c 9 ! jacks ( t l9e1 & !nce to spr+ #a ( ! la/ jack1 ?is spr+ always be+ /rapp$ to ! spr+ #b 9 ! la/ jack1 & !nce to ! o!r side ( ! l9e4 ,all ! r+ spr+s #a are p]man5tly tapp$ on to "o side ( ! l9e1 & all ( ! tip spr+s #d are p]man5tly tapp$ to ! o!r side ( ! l9e4 ,?is sy/em may1 !re=e1 prop]ly be call$ a bran*-t]m9al sy/em4 ,x is se5 t z soon z a plug is ins]t$ into any ( ! jacks1 ! circuit ?r\gh ! drop w be brok5 by ! op5+ ( ! spr+s #b & #c 9 t jack4 ,! drop %[n imm$iately above ! answ]+ jack is s associat$ me*anically ) t jack z to be me*anically self-re/or$ :5 ! answ]+ plug is ins]t$ into ! answ]+ jack 9 response to a call4 ,! arrangem5t 9 ?is respect is ! same z t %[n 9 ,fig4 #bei1 illu/rat+ ! ,mon>* comb9$ drop & jack4 ,cord ,circuit4 ,! cord circuit ne$s little explanation4 ,! tip & r+ /r&s are ! ones :i* c>ry ! talk+ curr5t & across ^! is bridg$ ! d\ble-w\nd cle>+-out drop1 a cond5s] be+ includ$ 9 s]ies 9 ! tip /r& betwe5 ! two drop w9d+s 9 ! mann] already expla9$ 9 connection ) ,fig4 #bhd4 ,! ?ird or sleeve /r& ( ! cord is cont9u\s f plug to plug1 & betwe5 x & ! gr\nd !re is p]man5tly connect$ a ret>dation coil4 ,te/4 ,! te/ is dep5d5t on ! pres5ce or abs5ce ( a pa? to gr\nd f ! te/ ?imbles ?r\gh "s ret>dation coil associat$ ) a cord circuit4 ,obvi\sly1 9 ! case ( an idle l9e !re w be no pa? to gr\nd f ! te/ ?imbles1 s9ce normally !y are m]ely connect$ to ea* o!r & are insulat$ f ev]y?+ else4 ,:51 h[ev]1 a plug is ins]t$ into a multiple or answ]+ jack1 ! te/ ?imbles ( t l9e are connect$ to gr\nd ?r\gh ! ret>dation coil associat$ ) ! ?ird /r& ( ! plug us$ 9 mak+ ! connection4 ,:5 ! op]ator applies ! tip ( ! call+ plug to a te/ contact ( a multiple jack !re w be no pa? to gr\nd af=d$ if ! l9e is idle1 :ile if x is busy ! pot5tial ( ! tip ( ! te/ plug w cause a curr5t to fl[ to gr\nd ?r\gh ! imp$ance coil associat$ ) ! plug us$ 9 mak+ ! connection4 ,?is w be made cle>] by trac+ ! te/ circuit4 ,) ! li/5+ key ?r[n ?is may be trac$ f ! live side ( ! batt]y ?r\gh ! ret>dation coil #f1 :i* is common to an op]ator's position1 !nce ?r\gh ! tip side ( ! li/5+ key to ! tip conductor ( ! call+ cord1 & !nce to ! tip ( ! call+ plug & ! ?imble ( ! jack "u te/4 ,if ! l9e is idle !re w be no pa? to gr\nd f ?is po9t & no click w result1 b if ! l9e is busy1 curr5t w fl[ f ! tip ( ! te/ plug to ! ?imble ( ! jack te/$1 !nce by ! te/ wire 9 ! multiple to ! ?imble ( ! jack at :i* a connection already exi/s1 & !nce to gr\nd ?r\gh ! ?ird /r& ( ! cord us$ 9 mak+ t connection & ! imp$ance coil associat$ !re)4 ,! curr5t :i* fl[s 9 ?is te/ circuit *anges mom5t>ily ! pot5tial ( ! tip side ( ! op]ator's telephone circuit1 ?us unbalanc+ h] talk+ circuit & caus+ a click4 ,illu/ration3 ,fig4 #cda4 ,magneto ,multiple ,swit*bo>d ,if ?is te/ sy/em 7 us$ 9 a v l>ge bo>d :]e ! multiple w\ld ext5d ?r\gh a great _m sections1 !re w\ld be "s liability ( a false te/ due to ! /atic capacity ( ! te/ contacts & ! te/ wire runn+ ?r\gh ! multiple4 ,= small bo>ds1 h[ev]1 :]e ! multiple is %ort1 ?is sy/em has prov5 reliable4 ,a multiple magneto swit*bo>d employ+ ! =m ( circuits j describ$ is %[n 9 ,fig4 #cda4 ,?is swit*bo>d consi/s ( ?ree sections ( two positions ea*4 ,! comb9$ answ]+ jacks & drops may be se5 at ! l[] "p ( ! face ( ! swit*bo>d & occupy+ some:at ov] "o-half ( ! jack & drop space4 ,! multiple jacks are above ! answ]+ jacks & drops & x may be not$ t ! same arrangem5t & numb] ( ^! jacks is repeat$ 9 ea* section4 ,?is swit*bo>d may be ext5d$ by add+ m sections & increas+ ! multiple 9 ^? already in/all$ to s]ve #a1fjj l9es4 ,assembly4 ,9 connection ) ! assembly ( ^! magneto multiple swit*bo>ds1 z in/all$ by ! ,mon>* ,company1 ,fig4 #cdb %[s ! details ( ! cord rack at ! back ( ! bo>d4 ,x %[s h[ ! ends ( ! swit*bo>d cords opposite to ! ends t are fa/5$ to ! plugs are connect$ p]man5tly to t]m9als on ! cord rack1 at :i* po9t ! flexible conductors are br\ght out to t]m9al clips or b9d+ po/s1 to :i* ! wires lead+ f ! o!r portions ( ! cord circuit are l$4 ,9 ord] to relieve ! conductors 9 ! cords f /ra91 ! out] braid+ ( ! cord at ! rack end is usually ext5d$ to =m :at is call$ a /ra9 cord1 & ?is atta*$ to an eyelet "u ! cord rack1 s t ! weight ( ! cord & ! cord weights w be borne by ! braid+ r ?an by ! conductors4 ,?is leaves ! insulat$ conductors ext5d+ f ! ends ( ! cords free to hang loose )\t /ra9 & be connect$ to ! t]m9als z %[n4 ,?is me?od ( connect+ cords1 ) v>iations 9 =m & detail1 is practically univ]sal 9 all types ( swit*bo>ds4 ,illu/ration3 ,fig4 #cdb4 ,cord-,rack ,connectors ,a detail ( ! assembly ( ! drops & jacks 9 su* a swit*bo>d is %[n 9 ,fig4 #cdc4 ,! s+le pair ( cle>+-out drops is m\nt$ 9 ! l[] "p ( ! v]tical face ( ! swit*bo>d j above ! space occupi$ by ! plug %elf4 ,v]tical /ile /rips ext5d above ! cle>+-out drop space = support+ ! drops & jacks4 ,a s+le r[ ( #aj answ]+ jacks & ! correspond+ l9e drops are %[n 9 place4 ,above ^! !re w\ld be plac$1 9 ! completely assembl$ bo>d1 ! o!r answ]+ jacks & l9e signals t 7 to occupy ?is panel1 & above ^! ! /rips ( multiple jacks4 ,! re>w>dly project+ p9s f ! /ile /rips are = ! support ( ! multiple jack /rips1 ^! p9s support+ ! /rips horizontally by suitable multiple clips at ! ends ( ! jack /rips2 ! jack /rips be+ fa/5$ f ! re> by means ( nuts engag+ ! screw ?reads on ^! p9s4 ,?is me?od ( support+ drops & jacks is "o t is equally adaptable = use 9 o!r =ms ( bo>ds1 su* z ! simple magneto swit*bo>d4 ,illu/ration3 ,fig4 #cdc4 ,drop & ,jack ,m\nt+ ,illu/ration3 ,fig4 #cdd4 ,keybo>d ,wir+ ,9 ,fig4 #cdd is %[n a detail photograph ( ! key %elf wir+ 9 "o ( ^! ,mon>* magneto swit*bo>ds4 ,9 ?is ! "u side ( ! keys is %[n1 ! key %elf be+ rais$ on its h+e = t purpose4 ,! cable1 conta9+ all ( ! insulat$ wires lead+ to ^! keys1 ent]s ! space "u ! key %elf at ! extreme left & f ! re>4 ,x !n passes to ! "r ( ?is space :]e a knee is =m$1 aft] :i* ! cable is securely /rapp$ to ! "u side ( ! key %elf4 ,by ?is con/ruction suffici5t flexibility is provid$ = 9 ! cable to p]mit ! rais+ & l[]+ ( ! key %elf1 ! long rea* ( ! cable betwe5 ! knee & ! po9t ( entry at ! left s]v+ z a torsion memb]1 s t ! rais+ ( ! %elf w give ! cable a slight twi/ r ?an b5d x at a %>p angle4 ,,*apt] ,,xxvi ,,! ,,common-,,batt]y ,,multiple ,,swit*bo>d ,we/]n ,electric ,no4 #a ,relay ,bo>d4 ,! common-batt]y multiple swit*bo>d diff]s f ! simple or non-multiple common-batt]y swit*bo>d ma9ly 9 ! provision ( multiple jacks & 9 ! add$ features :i* are involv$ 9 ! provision = a busy te/4 ,! pr9ciples ( signal+ & ( supply+ curr5t to ! subscrib]s = talk+ are ! same z 9 ! non-multiple common-batt]y bo>d4 ,= purposes ( illu/rat+ ! practical work+s ( ! common-batt]y multiple swit*bo>d1 we w take ! /&>d =m ( ! ,we/]n ,electric ,company1 *oos+ ?is only because x is ! /&>d ) ne>ly all ! ,bell op]at+ companies ?r\gh\t ! ,unit$ ,/ates4 ,illu/ration3 ,fig4 #cde4 ,l9e ,circuit ,we/]n ,electric ,no4 #a4 ,bo>d ,l9e ,circuit4 ,we w fir/ consid] ! l9e circuit 9 simplifi$ =m1 z %[n 9 ,fig4 #cde4 ,at ! left 9 ?is figure ! common-batt]y circuit is %[n at ! subscrib]'s /ation1 & at ! "r ! c5tral-(fice app>atus is indicat$ s f> z equipm5t ( a s+le l9e is conc]n$4 ,9 ?is simplifi$ diagram no attempt has be5 made to %[ ! relative positions ( ! v>i\s p>ts1 ^! hav+ be5 gr\p$ 9 ?is figure 9 su* a way z to give z cle> & simple an idea z possible ( ! circuit arrangem5ts4 ,x is se5 at a glance t ?is is a bran* t]m9al bo>d1 ! ?ree contacts ( ea* jack be+ connect$ by sep>ate taps or legs to ?ree wires runn+ ?r\gh\t ! l5g? ( ! bo>d1 ^! ?ree wires be+ individual to ! jacks ( "o l9e4 ,on ?is acc\nt ?is l9e circuit is commonly ref]r$ to z a ?ree-wire circuit4 ,by ! same consid]ations x w be se5 t ! swit*bo>d l9e circuit ( ! bran*-t]m9al multiple magneto sy/em1 %[n 9 ,fig4 #cch1 w\ld be call$ a f\r-wire circuit4 ,x w be %[n lat] t o!r multiple swit*bo>ds 9 wide use h a /ill fur!r r$uction 9 ! numb] ( wires runn+ ?r\gh ! jacks1 or ?r\gh ! multiple z x is call$1 su* be+ ref]r$ to z two-wire swit*bo>ds4 ,! two limbs ( ! l9e :i* ext5d f ! subscrib]'s circuit1 beside be+ connect$ by taps to ! tip & sleeve contacts ( ! jack respectively1 connect ) ! two back contacts ( a cut-(f relay1 & :5 ?is relay is 9 its normal or un5]giz$ condition1 ^! two limbs ( ! l9e are cont9u$ ?r\gh ! w9d+s ( ! l9e relay & !nce "o to ! ungr\nd$ or negative side ( ! common-batt]y & ! o!r to ! gr\nd$ side4 ,! subscrib]'s /ation circuit be+ normally op51 no curr5t fl[s ?r\gh ! l9e1 b :5 ! subscrib] removes 8 receiv] = ! purpose ( mak+ a call ! l9e circuit is complet$ & curr5t fl[s ?r\gh ! coil ( ! l9e relay1 ?us en]giz+ t relay & caus+ x to complete ! circuit ( ! l9e lamp4 ,! cut-(f relay plays no "p 9 ! op]ation ( ! subscrib]'s call+1 b m]ely leaves ! circuit ( ! l9e connect$ ?r\gh to ! call+ relay & batt]y4 ,! coil ( ! cut-(f relay is connect$ to gr\nd on "o side & on ! o!r side to ! ?ird wire runn+ ?r\gh ! swit*bo>d multiple & :i* is tapp$ (f to ea* ( ! te/ r+s on ! jacks4 ,z w be %[n lat]1 :5 ! op]ator plugs into ! jack ( a l9e1 su* a connection is e/abli%$ t ! te/ r+ ( t jack w be connect$ to ! live or negative pole ( ! common batt]y1 :i* w cause curr5t to fl[ ?r\gh ! coil ( ! cut-(f relay1 :i* w !n op]ate to cut (f bo? ( ! limbs ( ! l9e f _! normal connection ) gr\nd & ! batt]y & ! l9e relay4 ,h5ce ! "n cut-(f relay4 ,! use ( ! cut-(f relay to sev] ! call+ app>atus f ! l9e at all times :5 ! l9e is swit*$ s]ves to make possible a v mu* simpl] jack ?an w\ld o!rwise be requir$1 z w be obvi\s to anyone :o tries to design a common-batt]y multiple sy/em )\t a cut-(f relay4 ,! additional complication introduc$ by ! cut-(f relay is m ?an (fset by ! sav+ 9 complexity ( ! jacks4 ,x is desirable1 on acc\nt ( ! great numb] ( jacks necess>ily employ$ 9 a multiple swit*bo>d1 t ! jacks be ( ! simple/ possible con/ruction1 ?us r$uc+ to a m9imum _! fir/ co/ & mak+ !m mu* less likely to get out ( ord]4 ,cord ,circuit4 ,! cord circuit ( ! ,we/]n ,electric /&>d multiple common-batt]y swit*bo>d is %[n 9 ,fig4 #cdf4 ,?is cord circuit involves ! use ( ?ree /r&s 9 ! flexible cords ( bo? ! call+ & ! answ]+ plugs4 ,two ( ^! are ! ord9>y tip & r+ conductors ov] :i* spee* is transmitt$ to ! connect$ subscrib]'s wire4 ,! ?ird1 ! sleeve /r&1 c>ries ! sup]visory lamps & has associat$ ) x o!r app>atus = ! control ( ^! lamps & ( ! te/ circuit4 ,illu/ration3 ,fig4 #cdf4 ,cord ,circuit ,we/]n ,electric ,no4 #a ,bo>d ,! sy/em ( batt]y fe$ is ! well-kn[n split repeat+-coil arrangem5t already discuss$4 ,! tip /r& runs /raight ?r\gh to ! repeat+ coil1 :ile ! r+ /r& conta9s1 9 ea* case1 ! w9d+ ( ! sup]visory relay correspond+ to ei!r ! call+ or ! answ]+ plug4 ,9 ord] t ! pres5ce 9 ! talk+ circuit ( a magnet w9d+ possess+ consid]able imp$ance may n int]f]e ) ! talk+ effici5cy1 ea* ( ^! sup]visory relay w9d+s is %unt$ by a non-inductive resi/ance4 ,9 practice ! sup]visory relay w9d+s h ea* a resi/ance ( ab\t #bj ohms & ! %unt ar\nd !m ea* a resi/ance ( ab\t #ca ohms4 ,9 ! ?ird /r& ( ea* cord is plac$ a #ab-volt sup]visory lamp1 & 9 s]ies ) x a resi/ance ( ab\t #hj ohms4 ,ea* sup]visory relay is adapt$1 :5 en]giz$1 to close a #dj-ohm %unt ab\t its sup]visory lamp4 ,! arrangem5t & proportion ( ^! resi/ances is su* t :5 a plug is ins]t$ into ! jack ( a l9e ! lamp w receive curr5t f a circuit trac$ f ! negative pole ( ! batt]y 9 ! c5t] ( ! cord circuit ?r\gh ! lamp & ! #hj-ohm s]ies resi/ance1 ?r\gh ! ?ird /r& ( ! cord to ! te/ ?imble ( ! jack1 & !nce to ! positive or gr\nd$ pole ( ! batt]y ?r\gh ! ?ird conductor 9 ! multiple & ! w9d+ ( ! cut-(f relay4 ,?is curr5t always fl[s z long z ! plug is ins]t$1 & x is j suffici5t to illum9ate ! lamp :5 ! sup]visory relay armature is n attract$4 ,:51 h[ev]1 ! sup]visory relay armature is attract$1 ! %unt+ ( ! lamp by ! #dj-ohm resi/ance cuts d[n ! curr5t to su* a degree z to prev5t ! illum9ation ( ! lamp1 al?\gh "s curr5t /ill fl[s ?r\gh x4 ,! usual r++ & li/5+ key is associat$ ) ! call+ plug1 & 9 "s cases a r+-back key is associat$ ) ! answ]+ plug1 b ?is is n /&>d practice4 ,op]ation4 ,! op]ation ( ?is cord circuit 9 conjunction ) ! l9e circuit ( ,fig4 #cde may be/ be und]/ood by ref]5ce to ,fig4 #cdg4 ,?is figure employs a little diff]5t arrangem5t ( ! l9e circuit 9 ord] m cle>ly to indicate h[ ! two l9es may be connect$ by a cord2 a /udy ( ! two l9e circuits1 h[ev]1 w %[ t !y are id5tical 9 actual connections4 ,x is to be rememb]$ t all ( ! batt]y symbols %[n 9 ?is figure repres5t 9 reality ! same batt]y1 sep>ate symbols be+ %[n = great] simplicity 9 circuit connections4 ,we w assume ! subscrib] at ,/ation ,a calls = ! subscrib] at ,/ation ,b4 ,! op]ation ( ! l9e relay & ! consequ5t light+ ( ! l9e lamp1 & also ! op]ation ( ! pilot relay w be obvi\s f :at has be5 /at$4 ,! response ( ! op]ator by ins]t+ ! answ]+ plug into ! answ]+ jack1 & ! ?r[+ ( h] li/5+ key s z to bridge h] talk+ circuit across ! cord 9 ord] to place h]self 9 communication ) ! subscrib]1 is also obvi\s4 ,! ins]tion ( ! answ]+ plug into ! answ]+ jack complet$ ! circuit ?r\gh ! ?ird /r& ( ! cord & ! w9d+ ( ! cut-(f relay ( ! call+ l9e1 & ?is accompli%es ?ree desirable results4 ,! circuit s complet$ may be trac$ f ! negative or ungr\nd$ side ( ! batt]y to ! c5t] portion ( ! cord circuit1 !nce ?r\gh ! sup]visory lamp #a1 resi/ance #b1 to ! ?ird conductor on ! plug1 te/ ?imble on ! jack1 !nce ?r\gh ! w9d+ ( ! cut-(f relay to gr\nd1 :i* =ms ! o!r t]m9al ( ! batt]y4 ,! results accompli%$ by ! clos+ ( ?is circuit are3 fir/1 ! en]giz+ ( ! cut-(f relay to cut (f ! signal+ portion ( ! l9e2 second1 ! fl[+ ( curr5t ?r\gh ! lamp t is almo/ suffici5t to illum9ate x1 b n q s because ( ! closure ( ! %unt ab\t x1 = ! reason t w be describ$2 ?ird1 ! rais+ ( ! pot5tial ( all ! contact ?imbles on ! jacks f z]o to a pot5tial diff]5t f t ( ! gr\nd & equal 9 am\nt to ! fall ( pot5tial ?r\gh ! w9d+ ( ! cut-(f relay4 ,a condition is ?us e/abli%$ at ! te/ r+s su* t "s o!r op]ator at "s o!r section 9 te/+ ! l9e w f9d x busy & w n connect ) x4 ,illu/ration3 ,fig4 #cdg4 ,we/]n ,electric ,no4 #a ,bo>d ,! reason :y ! lamp #a1 connect$ ) ! answ]+ plug1 0 n light$ 0 t ! sup]visory relay #c1 associat$ ) ! answ]+ plug1 became en]giz$ :5 ! op]ator plugg$ 91 due to ! fl[ ( curr5t f ! batt]y ?r\gh ! call+ subscrib]'s talk+ app>atus1 ?is fl[ ( curr5t be+ p]mitt$ by ! removal ( ! call+ subscrib]'s receiv] f its hook4 ,! en]giz+ ( ?is relay magnet by caus+ ! attraction ( its armature1 clos$ ! %unt ab\t ! lamp #a1 :i* %unt conta9s ! #dj-ohm resi/ance #d1 & ?us prev5ts ! lamp f receiv+ en\gh curr5t to illum9ate x4 ,obvi\sly1 z soon z ! call+ subscrib] replaces 8 receiv] on its hook1 ! sup]visory relay #c w be de-en]giz$1 ! %unt ar\nd ! lamp w be brok51 & ! lamp w be illum9at$ to indicate to ! op]ator ! fact t ! subscrib] ) ^: l9e h] call+ plug is connect$ has replac$ 8 receiv] on its hook4 ,te/+--,call$ ,l9e ,idle4 ,hav+ n[ %[n h[ ! op]ator connects ) ! call+ subscrib]'s l9e & h[ t l9e automatically becomes gu>d$ z soon z x is connect$ )1 s t no o!r op]ator w connect ) x1 we w discuss h[ ! op]ator te/s ! call$ l9e & subsequ5tly connects ) t l9e1 if x is f\nd prop] to d s4 ,if1 on mak+ ! te/ ) "o ( ! multiple jacks ( ! l9e lead+ to ,/ation ,b1 t l9e is idle & free to be connect$ )1 its te/ r+s w all be at z]o pot5tial because ( ! fact t !y are connect$ ) gr\nd ?r\gh ! cut-(f relay w9d+ ) no s\rce ( curr5t connect$ ) !m4 ,! tip ( ! call+ plug w also be at z]o pot5tial 9 mak+ ?is te/1 because x is connect$ to gr\nd ?r\gh ! tip side ( ! call+-plug circuit & "o w9d+ ( ! cord-circuit repeat+ coil4 ,z a result no fl[ ( curr5t w occur1 ! op]ator w receive no click1 & %e w "k t %e is free to connect ) ! l9e4 ,z soon z %e does s1 by ins]t+ ! plug1 ! ?ird /r& ( ! cord w be connect$ ) ! te/ ?imble ( ! call+ l9e & ! result+ fl[ ( curr5t w br+ ab\t ?ree results1 two ( :i* are ! same1 & "o ( :i* is slightly diff]5t f ^? describ$ z result+ f ! ins]tion ( ! answ]+ plug into ! jack ( ! call+ l9e4 ,fir/1 ! cut-(f relay w be op]at$ & cut (f ! l9e signal+ app>atus f ! call$ l9e2 second1 a fl[ ( curr5t w result ?r\gh ! call+ sup]visory lamp #e1 :i* 9 ?is case w be suffici5t to illum9ate t lamp = ! reason t ! call$ subscrib] has n yet respond$1 ! call+ sup]visory relay #f has1 !re=e1 n yet be5 en]giz$1 & ! lamp has n1 !re=e1 be5 %unt$ by its associat$ resi/ance #g2 ?ird1 ! te/ ?imbles ( ! call$ l9e w be rais$ to a pot5tial above t ( ! e>?1 & ?us ! l9e w be gu>d$ aga9/ connection at ano!r section ( ! swit*bo>d4 ,z soon z ! call$ subscrib] responds to ! r++ curr5t s5t out by ! op]ator1 curr5t w fl[ ov] ! cord circuit & ov] 8 l9e ?r\gh 8 transmitt]4 ,?is w cause ! call+ sup]visory relay to be en]giz$ & ! call+ lamp to be ext+ui%$4 ,bo? lamps #a & #e rema9 ext+ui%$ z long z ! connect$ subscrib]s are 9 conv]sation1 b z soon z ei!r "o ( !m hangs up 8 receiv] ! correspond+ lamp w be light$1 due to ! de-en]gization ( ! sup]visory relay & ! break+ ( ! %unt ar\nd ! lamp4 ,! light+ ( bo? lamps associat$ ) a cord circuit is a signal to ! op]ator = disconnection4 ,illu/ration3 ,,t]m9al ,,room ,,9 ,,m$ium-,,siz$ ,,manual ,,(fice ,relay ,rack at ,"r4 ,?is ,employs ! ,kellogg ,p>allel ,arrangem5t ( ,frames4 ,te/+--,call$ ,l9e ,busy4 ,if we n[ assume t ! call$ l9e 0 already busy1 by virtue ( be+ connect$ ) at ano!r section1 ! te/ r+s ( t l9e w\ld accord+ly all be rais$ to a pot5tial above t ( ! e>?4 ,z a result1 :5 ! op]ator appli$ ! tip ( h] call+ plug to a te/ ?imble on t l9e1 curr5t w\ld fl[ f ?is te/ ?imble ?r\gh ! tip ( ! call+ plug & tip /r& ( ! cord & ?r\gh "o w9d+ ( ! cord-circuit repeat+ coil to gr\nd4 ,?is w\ld cause a slight rais+ ( pot5tial ( ! entire tip side ( ! cord circuit & a consequ5t mom5t>y fl[ ( curr5t ?r\gh ! second>y ( ! op]ator's circuit bridg$ across ! cord circuit at t "t4 ,op]ator's ,circuit ,details4 ,! details ( ! op]ator's talk+ circuit %[n 9 ,fig4 #cdg des]ve "s att5tion4 ,! batt]y supply to ! op]ator's transmitt] is ?r\gh an imp$ance coil #i4 ,! cond5s] #ab is bridg$ ar\nd ! transmitt] & ! two prim>y w9d+s #aj & #aa1 :i* w9d+s are 9 p>allel s z to af=d a local circuit = ! passage ( fluctuat+ curr5ts set up by ! transmitt]4 ,! two prim>y w9d+s #aj & #aa are on sep>ate induction coils1 ! second>y w9d+s #ac & #ad be+1 !re=e1 on sep>ate cores4 ,! w9d+ #ae1 9 circuit ) ! second>y w9d+ #ad & ! receiv]1 is a non-inductive w9d+ & is suppos$ to h a resi/ance ab\t equal to ! effective resi/ance to fluctuat+ curr5ts ( a subscrib]'s l9e ( av]age l5g?4 ,ow+ to ! respective directions ( ! prim>y & second>y w9d+s #aj & #aa1 #ac & #ad1 ! result is t ! outgo+ curr5ts set up by ! op]ator's transmitt] are l>gely neutraliz$ 9 ! op]ator's receiv]4 ,incom+ curr5ts f ei!r ( ! connect$ subscrib]s1 h[ev]1 pass1 9 ! ma91 ?r\gh ! second>y coil #ac & ! op]ator's receiv]1 r ?an ?r\gh ! %unt pa? =m$ by ! second>y #ad1 & ! non-inductive resi/ance #ae4 ,?is is kn[n z an anti-side tone arrangem5t1 & its object is to prev5t ! op]ator f receiv+ h] own voice transmission s l\dly z to make h] e> ins5sitive to ! feebl] voice curr5ts com+ 9 f ! subscrib]s4 ,ord]-,wire ,circuits4 ,! two keys #af & #ag1 %[n 9 connection ) ! op]ator's talk+ circuit 9 ,fig4 #cdg1 play no "p 9 ! regul> op]ation ( connect+ two local l9es1 z describ$ above4 ,!y are ord]-wire keys1 & ! circuits ) :i* !y connect lead to ! telephone sets ( o!r op]ators at di/ant c5tral (fices1 & by press+ ei!r "o ( ^! keys ! op]ator is enabl$ to place h]self 9 communication ov] ^! s-call$ ord]-wire circuits ) su* o!r op]ators4 ,! function & mode ( op]ation ( ^! ord]-wire circuits w be describ$ 9 ! next *apt]1 :]e9 int]-(fice connections w be discuss$4 ,wir+ ( ,l9e ,circuit4 ,! l9e circuits %[n 9 ,figs4 #cde & #cdg are1 z /at$1 simplifi$ to facilitate und]/&+1 al?\gh ! connections %[n are ^? :i* actually exi/4 ,! m complete wir+ ( a s+le l9e circuit is %[n 9 ,fig4 #cdh4 ,! l9e wires are %[n ent]+ at ! left4 ,!y pass imm$iately1 ^u ent]+ ! c5tral (fice1 ?r\gh ! ma9 di/ribut+ frame1 ! functions & con/ruction ( :i* w be consid]$ 9 detail 9 a subsequ5t *apt]4 ,! dott$ portions ( ! circuit %[n 9 connection ) ?is ma9 di/ribut+ frame indicate ! pa? f ! t]m9als on "o side ( ! frame to ^? on ! o!r ?r\gh s-call$ jump] wires4 ,! two limbs ( ! l9e !n pass to t]m9als #a & #b on "o side ( ! s-call$ int]m$iate di/ribut+ frame4 ,"h ! circuit ( ea* limb ( ! l9e divides1 pass+1 on ! "o h&1 to ! tip & sleeve spr+s ( all ! multiple jacks belong+ to t l9e2 &1 on ! o!r h&1 ?r\gh ! jump] wires indicat$ by dott$ l9es on ! int]m$iate di/ribut+ frame1 & !nce to ! tip & r+ contacts ( ! answ]+ jack4 ,a consid]ation ( ?is connection w %[ t ! actual electrical connections s f> z already describ$ are exactly ^? ( ,figs4 #cde & #cdg1 al?\gh ^? figures omitt$ ! ma9 & int]m$iate di/ribut+ frames4 ,only two limbs ( ! l9e are involv$ 9 ! ma9 frame4 ,9 ! int]m$iate frame ! te/ wire runn+ ?r\gh ! multiple is also involv$4 ,?is te/ wire1 x w be se51 leads f ! te/ ?imbles ( all ! multiple jacks to ! t]m9al #c on ! int]m$iate frame1 !nce ?r\gh ! jump] wire to ! t]m9al #f ( ?is frame1 & to ! te/ ?imble ( ! answ]+ jack4 ,"h aga9 ! electrical connections are exactly ^? repres5t$ 9 ,figs4 #cde & #cdg1 al?\gh ^? figures d n %[ ! int]m$iate frame4 ,! two t]m9als #d & #e ( ! int]m$iate frame1 besides be+ connect$ to ! tip & sleeve spr+s ( ! answ]+ jack1 are connect$ to ! contacts ( ! cut-(f relay1 & !nce ?r\gh ! coils ( ! l9e relay to gr\nd on "o side & to batt]y on ! o!r4 ,?us ! l9e relay & batt]y are normally includ$ 9 ! circuit ( ! l9e4 ,! contact #f on ! int]m$iate di/ribut+ frame1 besides be+ connect$ to ! te/ ?imble ( all ! jacks1 is connect$ ?r\gh ! coil ( ! cut-(f relay to gr\nd1 ?us e/abli%+ a pa? by :i* curr5t is suppli$ to ! cut-(f relay :5 connection is made to ! l9e at any jack4 ,!re is ano!r contact #g on ! int]m$iate di/ribut+ frame :i* m]ely =ms a t]m9al = jo9+ "o side ( ! l9e lamp to ! back contact ( ! l9e relay4 ,functions ( ,di/ribut+ ,frames4 ,s9ce ! l9e circuit ?us f> describ$ 9 connection ) ,fig4 #cdh is exactly ! same z t ( ,fig4 #cde 9 its electrical connections1 x becomes obvi\s t ! ma9 & int]m$iate di/ribut+ frames play no "p 9 ! op]ation ( ! circuit any m ?an a b9d+ po/ ( a telephone plays a "p 9 its op]ation4 ,^! frames c>ry t]m9als = facilitat+ ! connection ( ! v>i\s wires 9 ! l9e circuit &1 z w be %[n lat]1 = facilitat+ c]ta9 *anges 9 ! l9e connection4 ,illu/ration3 ,fig4 #cdh4 ,l9e ,circuit ,no4 #a ,bo>d ,rememb]+ t ! dott$ l9es 9 ,fig4 #cdh indicate jump] wires ( ! ma9 & int]m$iate di/ribut+ frames1 & t ^! are 9 ! nature ( tempor>y or readily *angeable connections1 & t ! full l9es1 :e!r heavy or light1 are p]man5t connections n readily *angeable1 x w be se5 t ! wires lead+ ?r\gh ! multiple jacks ( a c]ta9 l9e are p]man5tly associat$ ) ea* o!r1 & ) c]ta9 t]m9als on ! ma9 di/ribut+ frame & c]ta9 o!r t]m9als on ! int]m$iate di/ribut+ frame4 ,x w also be se5 t ! l9e lamp & ! answ]+ jack1 toge!r ) ! cut-(f relay & l9e relay1 are p]man5tly associat$ ) ea* o!r & ) ano!r gr\p ( t]m9als #d1 #e1 #f1 & #g on ! int]m$iate di/ribut+ frame4 ,x w also be app>5t t by *ang+ ! jump] wires on ! ma9 frame1 any outside l9e may be connect$ ) any diff]5t set ( l9e swit*bo>d equipm5t1 & also t by mak+ *anges 9 ! jump] wires on ! int]m$iate frame1 any giv5 answ]+ jack & l9e lamp ) its associat$ l9e cut-(f relay may be associat$ ) any set ( multiple jacks4 ,pilot ,signals4 ,9 a portion ( ! circuit lead+ f ! batt]y t is common to a gr\p ( l9e lamps is ! w9d+ ( ! pilot relay1 :i* is common to ?is gr\p ( l9e lamps4 ,?is controls1 z already describ$1 ! circuit ( ! pilot lamp common to ! same gr\p ( l9e lamps4 ,9 addition1 a night-bell circuit is sometimes provid$1 ?is usually be+ 9 ! =m ( an ord9>y pol>iz$ r+]1 ! circuit ( :i* is controll$ by a night-bell relay common to ! entire (fice4 ,normally1 ?is relay is %unt$ out ( ! circuit ( ! common portion ( ! lead to ! pilot relay contacts by ! key #h1 b :5 ! key #h is op5$ all curr5t t is f$ to ! pilot lamps passes ?r\gh ! night-bell relay1 & ?us1 :5ev] any pilot lamp is light$1 ! night-bell relay w attract its armature & ?us close ! circuit ( ! call+ g5]ator ?r\gh ! night bell4 ,a /udy ( ?is figure w make cle> to ! /ud5t h[ ! portions ( ! circuit t are individual to ! l9e are associat$ ) su* ?+s z ! batt]y1 t are common to ! entire (fice1 & su* z ! pilot relay & lamp1 t are common to a gr\p ( l9es t]m9at+ 9 "o position4 ,modifi$ ,relay ,w9d+s4 ,9 "s cases1 ! l9e relay in/ead ( be+ d\ble w\nd1 z %[n1 is made ) a s+le w9d+1 ?is w9d+ be+ normally includ$ betwe5 ! r+ side ( ! cut-(f relay & ! batt]y1 ! tip side ( ! cut-(f relay be+ run direct to gr\nd4 ,! pres5t practice ( ! ,we/]n ,electric ,company is t[>ds ! d\ble-w\nd relay1 h[ev]1 & t is consid]$ /&>d 9 all ( _! l>ge ,no4 #a multiple bo>ds1 except :]e ! cu/om]1 ow+ to special reasons1 dem&s a s+le w\nd relay on ! r+ side ( ! l9e4 ,! prime reason = ! two-w9d+ l9e relay is ! less5$ click 9 ! call+-subscrib]'s receiv] :i* occurs :5 ! op]ator answ]s4 ,all l9e relays prior to #aijb 7 s+le-w\nd1 b aft] t !y 7 made d\ble & us$ "s turns ( resi/ance wire to limit ! normal call+ curr5t4 ,relay ,m\nt+4 ,9 ! /&>d ,no4 #a relay bo>d ( ! ,we/]n ,electric ,company &1 9 fact1 9 ne>ly all common-batt]y multiple bo>ds t are manufactur$ by o!r companies1 ! l9e & cut-(f relays are m\nt$ on sep>ate racks outside ! swit*bo>d room & adjac5t to ! ma9 & int]m$iate di/ribut+ frames1 ! wir+ be+ ext5d$ f ! relays to ! jacks & lamps on ! swit*bo>d prop] by means ( suitable cables4 ,! ,we/]n ,electric ,company has rec5tly in/itut$ a dep>ture f ?is practice 9 ! case ( "s ( _! small] ,no4 #a swit*bo>d in/allations4 ,:]e x is ?\ght t ! ultimate capacity requir$ by ! bo>d w n be above #c1jjj l9es1 ! relay rack is disp5s$ ) & all ( ! l9e & cut-(f relays1 z well z ! sup]visory relays1 are m\nt$ 9 ! re> ( ! swit*bo>d frame4 ,= ?is purpose ! l9e & cut-(f relays are specially made ) ! view to secur+ ! utmo/ compactness4 ,9 /ill o!r cases1 9 swit*bo>ds ( relatively small ultimate capacity1 !y use ?is small l9e & cut-(f relay m\nt$ on a sep>ate relay rack1 9 :i* case ! bo>d is ! /&>d ,no4 #a bo>d except = ! type ( relays4 ,9 all ( ^! modifications ( ! ,no4 #a bo>d adapt$ = ! use ( ! small] & *eap] relays1 ! l9e relay has b a s+le w9d+1 ! small size ( ! relay w9d+ n l5d+ itself readily to d\ble w9d+ ) ! add$ necess>y coil t]m9als4 ,capacity ,range4 ,! ,no4 #a ,we/]n ,electric bo>d is made 9 /&>d sizes up to an ultimate capacity ( #i1fjj l9es4 ,= all capacities above #d1ijj l9es1 a #c_/h-;in* jack1 v]tical & horizontal face dim5sions1 is employ$4 ,= ?is capacity ! small] types ( cut-(f & l9e relays are n employ$4 ,up to ultimate capacities ( #d1ijj l9es1 #a_/b-;in* jacks are employ$1 & ei!r ! small or ! l>ge relays m\nt$ on a sep>ate rack are available4 ,up to #c1jjj l9es ultimate capacity1 ! #a_/b-;in* jack is employ$1 & ei!r ! small or ! l>ge cut-(f & l9e relays are available1 b 9 case ! small type is us$ ! pur*as] has ! option ( m\nt+ !m on a sep>ate relay rack1 z 9 ord9>y practice1 or m\nt+ !m 9 ! swit*bo>d cab9et & disp5s+ ) ! relay rack4 ,we/]n ,electric ,no4 #aj ,bo>d4 ,! ,no4 #a common-batt]y multiple swit*bo>d1 reg>dless ( its size & type ( arrangem5t ( l9e & cut-(f relays1 involves two relays = ea* l9e1 ! l9e relay en]giz$ by ! tak+ ( ! receiv] (f its hook1 & ! cut-(f relay en]giz$ by ! act ( ! op]ator on plugg+ 9 & s]v+ to remove ! l9e relay f ! circuit :5ev] & z long z a plug is ins]t$ into any jack ( ! l9e4 ,?is seems to involve a consid]able exp5se 9 relays1 b ?is1 z has be5 /at$1 is w>rant$ by ! great] simplicity 9 jacks :i* ! use ( ! cut-(f relay makes possible4 ,9 addition to ?is exp5se ( inve/m5t 9 ! l9e & cut-(f relays1 ! am\nt ( curr5t requir$ to hold up ! cut-(f relays dur+ conv]sations foots up to a consid]able item ( exp5se1 p>ticul>ly z ! sy/em ( sup]visory signals is "o 9 :i* ! sup]visory lamp takes curr5t n only :ile burn+1 b its circuit takes ev5 m curr5t :5 ! lamp is ext+ui%$ dur+ ! "t ( a connection4 ,= all ( ^! reasons1 & "s o!r m9or ones1 x 0 deem$ exp$i5t by ! eng9e]s ( ! ,we/]n ,electric ,company to design a common-batt]y multiple swit*bo>d = small & m$ium-siz$ ex*anges 9 :i* c]ta9 sacrifices might be made to ! end ( accompli%+ c]ta9 sav+s4 ,! result has be5 a type ( swit*bo>d1 designat$ ! ,no4 #aj1 :i* may be f\nd 9 a numb] ( ,bell ex*anges1 x be+ consid]$ p>ticul>ly adaptable to in/allations ( f #ejj to #c1jjj l9es4 ,al?\gh ?is bo>d has be5 subject to a good deal ( adv]se criticism1 & al?\gh x seems probable t ev5 = ! *eap] bo>ds ! ,no4 #a type ) "s ( ! modifications j describ$ w ev5tually sup]s$e ?is ,no4 #aj bo>d1 yet ! pres5t ext5t ( use ( ! ,no4 #aj bo>d & ! in/ructive features :i* its type displays w>rant its discussion "h4 ,circuits4 ,! circuits ( ?is swit*bo>d are %[n 9 ,fig4 #cdi1 ?is indicat+ two-l9e circuits & a connect+ cord circuit1 toge!r ) ! auxili>y app>atus employ$ 9 connection ) ! op]ator's telephone circuit1 ! pilot & night al>m circuits4 ,! mo/ noticeable feature is t cut-(f jacks are employ$1 ! circuit ( ! l9e normally ext5d+ ?r\gh ! sets ( jack spr+s 9 ! multiple1 & answ]+ jacks to ! l9e relay & batt]y on "o side ( ! l9e1 & to gr\nd on ! o!r side4 ,obvi\sly1 ! additional complexity ( ! jack saves ! use ( a cut-(f relay & ! relay equipm5t ( ea* l9e consi/s1 !re=e1 ( b a s+le l9e relay1 :i* controls ! lamp 9 an obvi\s mann]4 ,illu/ration3 ,fig4 #cdi4 ,we/]n ,electric ,no4 #aj ,bo>d ,! cord circuit is ( ! ?ree-conductor type1 ! two talk+ /r&s ext5d+ to ! usual split repeat+-coil arrangem5t1 & batt]y curr5t = talk+ purposes be+ f$ ?r\gh ^! w9d+s z 9 ! /&>d ,no4 #a bo>d4 ,! sup]visory relay is includ$ 9 ! r+ /r& ( ! cord circuit & is %unt$ by a non-inductive resi/ance1 s t its imp$ance w n int]f]e ) ! talk+ curr5ts4 ,! armature ( ! sup]visory relay closes ! lamp contact on its back /roke1 s t ! lamp is always held ext+ui%$ :5 ! relay is en]giz$4 ,! sup]visory lamp is includ$ 9 a connection betwe5 ! back contact ( ! sup]visory relay & gr\nd1 ?is connection includ+ ! c5tral-(fice batt]y4 ,z a result1 ! illum9ation ( ! sup]visory lamp is impossible until a plug has be5 ins]t$ into a jack1 9 :i* case1 assum+ ! sup]visory relay to be de-en]giz$1 ! lamp circuit is complet$ ?r\gh ! wire connect+ all ( ! te/ ?imbles & ! resi/ance p]man5tly bridg$ to gr\nd f t wire4 ,te/4 ,= purposes ( ! te/ x is evid5t t ! te/ r+s ( an idle l9e are always at gr\nd pot5tial1 due to _! connection to gr\nd ?r\gh ! resi/ance coil4 ,x is also evid5t t ! tip ( an unus$ call+ plug w always be at gr\nd pot5tial &1 !re=e1 t ! te/+ ( an idle l9e w result 9 no click 9 ! op]ator's receiv]4 ,:5 a l9e is swit*$1 h[ev]1 ! pot5tial ( all ! te/ r+s w be rais$ due to _! be+ connect$ ) ! live pole ( ! batt]y ?r\gh ! ?ird /r& ( ! cord4 ,:5 ! op]ator 9 te/+ t\*es ! te/ contact ( ! jack ( a busy l9e1 a curr5t w1 !re=e1 fl[ f ?is te/ contact to ! tip /r& ( ! cord & !nce to gr\nd ?r\gh "o ( ! repeat+ coil w9d+s4 ,! pot5tial ( ! tip side ( ! cord w1 !re=e1 be mom5t>ily alt]$1 & ?is w result 9 a click 9 ! op]ator's receiv] bridg$ across ! cord circuit at ! "t4 ,! details ( ! op]ator's cord circuit & ( ! pilot lamp & night al>m circuits w be cle> f ! diagram4 ,op]ation4 ,a brief summ>y ( ! op]ation ( ?is sy/em is z foll[s3 ,! subscrib] removes 8 receiv] f its hook1 ?us draw+ up ! armature ( ! l9e relay & light+ 8 l9e lamp4 ,! op]ator answ]s4 ,! l9e lamp is ext+ui%$ by ! fall+ back ( ! l9e-relay armature1 due to ! break+ ( ! relay circuit at ! jack contacts4 ,! subscrib] !n receives curr5t = 8 transmitt] ?r\gh ! cord-circuit batt]y connections4 ,! sup]visory relay connect$ ) ! answ]+ cord is n light$1 because1 al?\gh ! lamp-circuit connection is complet$ at ! jack1 ! sup]visory relay is op]at$ to hold ! lamp circuit op54 ,conv]sation ensues betwe5 ! op]ator & ! subscrib]1 aft] :i* ! op]ator te/s ! l9e call$ = ) ! tip ( ! call+ plug ( ! pair us$ 9 answ]+4 ,if ! call$ l9e is n busy1 no click w ensue1 because bo? ! te/$ r+ & ! call+ plug are at ! same pot5tial4 ,f9d+ no click1 ! op]ator w ins]t ! plug & r+ by means ( ! r++ key4 ,:5 ! op]ator plugs 91 ! sup]visory lamp1 associat$ ) ! call+ plug1 becomes light$ because ! circuit is complet$ at ! jack & ! sup]visory relay rema9s de-en]giz$1 s9ce ! l9e circuit is op5 at ! subscrib]'s /ation4 ,:5 ! call$ subscrib] responds1 ! call+ sup]visory lamp goes out because ( ! en]gization ( ! sup]visory relay4 ,bo? lamps rema9 out dur+ ! conv]sation1 b :5 ei!r subscrib] hangs up1 ! correspond+ sup]visory lamp w be light$ because ( ! fall+ back ( ! sup]visory relay armature4 ,if ! call$ l9e is busy1 a click w be he>d1 = ! reason describ$1 & ! op]ator w s in=m ! call+ subscrib]4 ,x goes )\t say+1 t 9 any multiple-swit*bo>d sy/em a plug may be f\nd 9 ! actual multiple jack t is rea*$ =1 9 :i* case1 al?\gh no te/ w be made1 ! busy condition w be report$ back to ! call+ subscrib]4 ,economy4 ,x has be5 ! belief ( ! ,we/]n ,electric eng9e]s t a real economy is accompli%$ 9 ?is type ( bo>d by ! sav+ 9 relay equipm5t4 ,x is1 ( c\rse1 app>5t at a glance t ) a swit*bo>d long en\gh & ( sections en\gh1 ! co/ ( extra jack spr+s & _! plat9um contacts mu/ become great en\gh to (fset ! sav+ accompli%$ by omitt+ ! cut-(f relay4 ,?is makes x app>5t t if !re is any economy 9 ?is type ( multiple swit*bo>d1 x mu/ be f\nd 9 ! v small bo>ds :]e !re are b few jacks p] l9e & :]e ! extra co/ ( ! cut-(f jack is n en\gh to (fset ! extra co/ ( an add$ relay4 ,x is ! gr[+ belief1 h[ev]1 among eng9e]s1 t ! multiple swit*bo>d mu/ be v small inde$ 9 ord] t ! add$ complexity ( ! cut-(f jacks & wir+ may be able to save any?+ ov] ! two-relay type ( l9e2 & x is believ$ t :]e economy is necess>y 9 small bo>ds1 x may be be/ effect$ by employ+ *eap] & m compact =ms ( relays & m\nt+ !m1 if necess>y1 directly 9 ! swit*bo>d cab9et4 ,,note4 ,^! two /&>d types ( common-batt]y multiple swit*bo>ds ( ! ,we/]n ,electric ,company repres5t ! developm5t ?r\gh long ye>s ( c>eful "w on ! "p ( ! ,we/]n ,electric & ,bell eng9e]s1 cr$it be+ p>ticul>ly due to ,scribn]1 ,mc,berty1 & ,mc,quarrie ( ! ,we/]n ,electric ,company1 & ,hayes ( ! ,am]ican ,telephone & ,telegraph ,company4 ,kellogg ,two-,wire ,multiple ,bo>d4 ,! simplicity 9 ! jacks p]mitt$ by ! use ( ! cut-(f relay 9 ! ,we/]n ,electric common-batt]y multiple swit*bo>d = l>g] ex*anges 0 c>ri$ a /ep fur!r by ,dunb> & ,mill] 9 ! developm5t ( ! s-call$ two-wire common-batt]y multiple swit*bo>d1 :i* = _m ye>s has be5 ! /&>d ( ! ,kellogg ,swit*bo>d & ,supply ,company4 ,! p>ticul> condition :i* l$ to ! developm5t ( ! two-wire sy/em 0 ! dem& at t "t on ! ,kellogg ,company = c]ta9 v l>ge multiple swit*bo>ds1 involv+ z _m z #ah1jjj l9es 9 ! multiple4 ,obvi\sly1 ?is necessitat$ a small jack1 & obvi\sly a jack hav+ only two contacts1 a tip spr+ & a sleeve1 c\ld be made m easily & ) great] durability ( ?is v small size ?an a jack requir+ ?ree or m contacts4 ,o!r reasons t 7 consid]$ 71 ( c\rse1 *eapness 9 co/ ( con/ruction & extreme simplicity1 :i*1 o!r ?+s be+ equal1 l5ds itself to l[ co/ ( ma9t5ance4 ,l9e ,circuit4 ,l ! /&>d ,we/]n ,electric bo>d = l>ge (fices1 ! ,kellogg two-wire bo>d employs two relays = ea* l9e1 ! l9e relay "u ! control ( ! subscrib] & 9 turn controll+ ! lamp1 & a cut-(f relay "u ! control ( ! op]ator & 9 turn controll+ ! connection ( ! l9e relay ) ! l9e4 ,! l9e circuit z orig9ally develop$ & z widely us$ by ! ,kellogg ,company is %[n 9 ,fig4 #cej4 ,! extreme simplicity ( ! jacks is app>5t1 z is also ! fact t b two wires lead ?r\gh ! multiple4 ,ano!r di/+ui%+ feature is1 t all ( ! multiple & answ]+ jacks are normally cut (f f ! l9e at ! cut-(f relay1 b :5 ! cut-(f relay op]ates x s]ves1 9 addition to cutt+ (f ! l9e relay1 to atta* ! two limbs ( ! l9e to ! two wires lead+ ?r\gh ! multiple & answ]+ jacks4 ,! control ( ! l9e relay by ! subscrib]'s swit* hook is cle> f ! figure4 ,! control ( ! cut-(f relay is secur$ by atta*+ "o t]m9al ( ! cut-(f relay w9d+ p]man5tly to t wire lead+ ?r\gh ! multiple :i* connects ) ! sleeve contacts ( ! jack1 ! o!r t]m9al ( ! cut-(f relay be+ gr\nd$4 ,! way 9 :i* ?is relay is op]at$ w be und]/ood :5 x is /at$ t ! sleeve contacts ( bo? ! answ]+ & call+ plugs always c>ry full batt]y pot5tial &1 !re=e1 :5ev] any plug is ins]t$ into any jack1 curr5t fl[s f ! sleeve ( ! jack ?r\gh ! sleeve contact ( ! jack to gr\nd1 ?r\gh ! w9d+ ( ! cut-(f relay1 :i* relay becomes en]giz$ & p]=ms ! functions j /at$4 ,x is se5 t ! wire runn+ ?r\gh ! multiple to :i* ! sleeve jack contacts are atta*$1 is ?us made to s]ve ! d\ble purpose ( answ]+ z "o side ( ! talk+ circuit1 & also ( p]=m+ ! functions c>ri$ out by ! sep>ate or ?ird wire 9 ! ?ree-wire sy/em4 ,x w be %[n also t1 9 addition1 ?is wire is made to l5d itself to ! purposes ( ! busy te/ )\t any ( ^! functions int]f]+ ) ea* o!r 9 any way4 ,illu/ration3 ,fig4 #cej4 ,two-,wire ,l9e ,circuit ,cord ,circuit4 ,! cord circuit 9 some:at simplifi$ =m is %[n 9 ,fig4 #cea4 ,"h aga9 !re are b two conductors to ! plugs & two /r&s to ! cords4 ,?is great] simplicity is 9 "s measure (fset by ! fact t f\r relays are requir$1 two = ea* plug4 ,?is s-call$ f\r-relay cord circuit may be mo/ readily und]/ood by consid]+ half ( x at a "t1 s9ce ! two relays associat$ ) ! answ]+ plug act 9 exactly ! same way z ^? connect$ ) ! call+ plug4 ,illu/ration3 ,fig4 #cea4 ,two-,wire ,cord ,circuit ,associat$ ) ea* plug ( a pair are two relays #a & #b1 9 ! case ( ! answ]+ cord1 & #c & #d 9 ! case ( ! call+ cord4 ,! coils ( ! relays #a & #b are connect$ 9 s]ies & bridg$ across ! answ]+ cord1 a batt]y be+ includ$ betwe5 ! coils 9 ?is circuit4 ,! coils ( ! relays #c & #d are simil>ly connect$ across ! call+ cord4 ,a peculi> feature ( ! ,kellogg sy/em is t two batt]ies are us$ 9 connection ) ! cord circuit1 "o ( !m be+ common to all answ]+ cords & ! o!r to all call+ cords4 ,! op]ation ( ! sy/em w\ld1 h[ev]1 be exactly ! same if a s+le batt]y 7 sub/itut$ = ! two4 ,sup]visory ,signals4 ,consid]+ ! relays associat$ ) ! answ]+ cord1 x is obvi\s t ^! two relays #a & #b toge!r control ! circuit ( ! sup]visory lamp #e1 ! circuit ( ?is lamp be+ clos$ only :5 ! relay #a is de-en]giz$ & ! relay #b is en]giz$4 ,we w f9d 9 discuss+ ! op]ation ( ^! t ! relay #b is :olly "u ! control ( ! op]ator1 & t ! relay #a1 aft] its plug has be5 connect$ ) a l9e1 is :olly "u ! control ( ! subscrib] on t l9e4 ,x is ?r\gh ! w9d+s ( ^! two relays t curr5t is f$ to ! l9e ( ! subscrib] connect$ ) ! correspond+ cord4 ,:5 a plug--! answ]+ plug1 = in/ance--is ins]t$ into a jack1 curr5t at once fl[s f ! positive pole ( ! left-h& batt]y ?r\gh ! w9d+ ( ! relay #b to ! sleeve ( ! plug1 !nce to ! sleeve ( ! jack & ?r\gh ! cut-(f relay to gr\nd4 ,?is at once en]gizes ! sup]visory relay #b & ! cut-(f relay associat$ ) ! l9e4 ,! cut-(f relay acts1 z /at$1 to cont9ue ! tip & sleeve wires associat$ ) ! jacks to ! l9e lead+ to ! subscrib]1 & also to cut (f ! l9e relay4 ,! sup]visory relay #b acts at ! same "t to attract its armature & ?us complete its "p 9 clos+ ! circuit ( ! sup]visory lamp4 ,:e!r or n ! lamp w be light$ at ?is "t dep5ds on :e!r ! relay #a is en]giz$ or n1 & ?is1 x w be se51 dep5ds on :e!r ! subscrib]'s receiv] is (f or on its hook4 ,if (f its hook1 curr5t w fl[ ?r\gh ! metallic circuit ( ! l9e = en]giz+ ! subscrib]'s transmitt]1 & z :atev] curr5t goes to ! subscrib]'s l9e mu/ fl[ ?r\gh ! relay #a1 t relay w be en]giz$ & prev5t ! light+ ( ! sup]visory lamp #e4 ,if1 on ! o!r h&1 ! subscrib]'s receiv] is on its hook1 no curr5t w fl[ ?r\gh ! l9e1 ! sup]visory relay w n be en]giz$1 & ! lamp #e w be light$4 ,9 a nut%ell1 ! sleeve sup]visory relay normally prev5ts ! light+ ( ! correspond+ sup]visory lamp1 b z soon z ! op]ator ins]ts a plug into ! jack ( ! l9e1 ! relay #b e/abli%es su* a condition z to make possible ! light+ ( ! sup]visory lamp1 & ! light+ ( ?is lamp is !n controll$ entirely by ! relay #a1 :i* is1 9 turn1 controll$ by ! position ( ! subscrib]'s swit* hook4 ,batt]y ,fe$4 ,a #b-micr(>ad cond5s] is includ$ 9 ea* /r& ( ! cord1 & batt]y is f$ ?r\gh ! relay w9d+s to ! call+ & call$ subscrib]s on opposite sides ( ^! cond5s]s1 9 accordance ) ! comb9$ imp$ance coil & cond5s] me?od describ$ 9 ,*apt] ,,xiii4 ,"h ! relay w9d+s d d\ble duty1 s]v+ z magnets = op]at+ ! relays & z ret>dation coils 9 ! sy/em ( batt]y supply4 ,complete ,cord & ,l9e ,circuits4 ,! complete cord & l9e circuits ( ! ,kellogg two-wire sy/em are %[n 9 ,fig4 #ceb4 ,9 ! m rec5t in/allations ( ! ,kellogg ,company ! cord & l9e circuits h be5 slightly *ang$ f ^? %[n 9 ,figs4 #cej & #cea1 & ^! *anges h be5 incorporat$ 9 ,fig4 #ceb4 ,! pr9ciples ( op]ation describ$ 9 connection ) ! simplifi$ figures rema91 h[ev]1 exactly ! same4 ,"o ( ! *anges is1 t ! tip side ( ! l9es is p]man5tly connect$ to ! tips ( ! jacks in/ead ( be+ normally cut (f by ! cut-(f relay1 z 0 done 9 ! sy/em z orig9ally develop$4 ,ano!r *ange is1 t ! l9e relay is associat$ ) ! tip side ( ! l9e1 r ?an ) ! sleeve side1 z 0 =m]ly done4 ,! cord circuit %[n 9 ,fig4 #ceb %[s exactly ! same arrangem5t ( sup]visory relays & exactly ! same me?od ( batt]y fe$ z 9 ! simplifi$ cord circuit ( ,fig4 #cea1 b 9 addition to ?is ! detail$ connections ( ! op]ator's talk+ set & ( h] ord]-wire keys are indicat$1 & also ! r++ equipm5t is indicat$ z be+ adapt$ = f\r-p>ty h>monic "w4 ,illu/ration3 ,fig4 #ceb4 ,kellogg ,two-,wire ,bo>d ,9 connection ) ?is r++ key x may be /at$ t ! spr+s #g1 #h1 #i1 & #aj are individually op]at$ by ! pressure ( "o ( ! r++ key buttons1 :ile ! spr+ #ag1 connect$ ) ! sleeve side ( ! call+ plug1 is always op]at$ simultane\sly ) ! op]ation ( any "o ( ! o!r spr+s4 ,z a result ! prop] r++ circuit is e/abli%$1 x be+ und]/ood t ! upp] contacts ( ! spr+s #g1 #h1 #i1 & #aj lead to ! t]m9als ( _! respective r++ g5]ators1 ! o!r t]m9als ( :i* are gr\nd$4 ,! circuit is1 !re=e1 f ! g5]ator1 ?r\gh ! r++ key1 out ?r\gh ! tip side ( ! l9e1 back ov] ! sleeve side ( ! l9e1 & to gr\nd ?r\gh ! spr+ #ag1 resi/ance #aa1 & ! batt]y1 :i* is "o ( ! cord-circuit batt]ies4 ,! object ( ?is coil #aa & ! batt]y connection ?r\gh x to ! r++-key spr+ is to prev5t ! fall+ back ( ! cut-(f relay :5 ! r++ key is op]at$4 ,?is w be cle> :5 x is rememb]$ t ! cut-(f relay is en]giz$ by batt]y curr5t f$ ov] ! sleeve /r& ( ! cord1 & obvi\sly1 s9ce x is necess>y :5 ! r++ key is op]at$ to cut (f ! supply wire back ( ! key1 ?is w\ld de-en]gize ! cut-(f relay :5 ! r++ key 0 depress$1 & ! fall+ back ( ! cut-(f relay contacts w\ld make x impossible to r+ because ! sleeve side ( ! l9e w\ld be cut (f4 ,! batt]y supply ?r\gh ! resi/ance #aa is1 !re=e1 sub/itut$ on ! sleeve /r& ( ! cord = ! batt]y supply ?r\gh ! normal connection4 ,busy ,te/4 ,! busy te/ dep5ds on all ( ! te/ r+s be+ at z]o pot5tial on an idle l9e & at a high] pot5tial on a busy l9e4 ,obvi\sly1 :5 ! l9e is n swit*$1 ! te/ r+s are at z]o pot5tial on acc\nt ( a gr\nd ?r\gh ! cut-(f relay4 ,:51 h[ev]1 a plug is ins]t$ 9 ei!r ! answ]+ or multiple jacks1 ! te/ r+s w all be rais$ 9 pot5tial due to be+ connect$ ) ! live side ( ! batt]y ?r\gh ! sleeve /r& ( ! cord4 ,conditions on ! l9e ext]nal to ! c5tral (fice _c make an idle l9e te/ busy because1 ow+ to ! pres5ce ( ! cut-(f relay1 ! sleeve contacts ( all ! jacks are disconnect$ f ! l9e :5 x is idle4 ,! te/ circuit f ! tip ( ! call+ plug to gr\nd at ! op]ator's set passes ?r\gh ! tip /r& ( ! cord1 !nce ?r\gh a pair ( normally clos$ extra contacts on ! sup]visory relay #d1 !nce 9 s]ies ?r\gh all ! r++ key spr+s #aj1 #i1 #h1 & #g1 !nce ?r\gh an extra pair ( spr+s #ab & #ac on ! li/5+ key--clos$ only :5 ! li/5+ key is op]at$--& !nce to gr\nd ?r\gh a ret>dation coil #ad4 ,no batt]y or o!r s\rce ( pot5tial exi/s 9 ?is circuit betwe5 gr\nd & ! tip ( ! call+ plug &1 !re=e1 ! tip is normally at gr\nd pot5tial4 ,! sleeve r+ ( ! jack be+ at gr\nd pot5tial if ! l9e is idle1 no curr5t w fl[ & no click w be produc$ 9 te/+ su* a l9e4 ,if1 h[ev]1 ! l9e is busy1 ! te/ r+ w be at a high] pot5tial &1 !re=e1 curr5t w fl[ f ! tip ( ! call+ plug to gr\nd ov] ! pa? j trac$1 & ?is w cause a rise 9 pot5tial at ! t]m9al ( ! cond5s] #ae & a mom5t>y fl[ ( curr5t ?r\gh ! t]ti>y w9d+ #af ( ! op]ator's induction coil2 h5ce ! click4 ,illu/ration3 ,,swit* ,,room ,,( ,,citiz5s' ,,telephone ,,company1 ,,gr& ,,rapids1 ,,mi*4 ,"o ( ! ,e>lie/ ,l>ge ,automatic ,(fices4 ,obvi\sly ! te/+ circuit f ! tip ( ! call+ plug to gr\nd at ! op]ator's set is only useful dur+ ! "t :5 ! call+ plug is n 9 a jack1 & z ! tip /r& ( ! call+ plug has to d d\ble duty 9 te/+ & 9 s]v+ z a "p ( ! talk+ circuit1 ! arrangem5t is made t ! te/+ circuit w be automatically brok5 & ! talk+ circuit ?r\gh ! tip /r& automatically complet$ :5 ! plug is ins]t$ into a jack 9 e/abli%+ a connection4 ,?is is accompli%$ by means ( ! extra contact on ! relay #d1 :i* relay1 x w be rememb]$1 is held en]giz$ :5 its correspond+ plug is ins]t$ 9 a jack4 ,dur+ ! "t :5 ! plug is n ins]t$1 ?is relay is n en]giz$ & ! te/ circuit is complet$ ?r\gh ! back contact ( its "r-h& armature4 ,:5 connection is made at ! jack1 ?is relay becomes en]giz$ & ! tip /r& ( ! cord circuit is made complete by ! "r-h& lev] be+ pull$ aga9/ ! front contact ( ?is relay4 ,! keys %[n to ! "r ( ! op]ator's set are ord]-wire keys4 ,summ>y ( ,op]ation4 ,we may give a brief summ>y ( ! op]ation ( ?is sy/em z %[n 9 ,fig4 #ceb4 ,! left-h& /ation calls & ! l9e relay pulls up1 light+ ! lamp4 ,! op]ator ins]ts an answ]+ plug 9 ! answ]+ jack1 ?us en]giz+ ! cut-(f relay :i* op]ates to cut (f ! l9e relay & to complete ! connection betwe5 ! jacks & ! ext]nal l9e4 ,! act ( plugg+ 9 by ! op]ator also raises ! pot5tial ( all ! te/ r+s s z to gu>d ! l9e aga9/ intrusion by o!r call]s4 ,! sup]visory lamp #e rema9s unlight$ because1 al?\gh ! relay #b is op]at$1 ! relay #a is also op]at$1 due to ! call+ subscrib]'s receiv] be+ (f its hook4 ,! op]ator ?r[s h] li/5+ key1 communicates ) ! subscrib]1 &1 le>n+ t ! "r-h& /ation is want$1 proce$s to te/ t l9e4 ,if ! l9e is idle1 %e w get no click1 because ! tip ( h] call+ plug & ! te/$ r+ w be at ! same gr\nd pot5tial4 ,%e !n plugs 9 & presses ! prop] r++-key button to s5d out ! prop] frequ5cy to r+ ! p>ticul> subscrib] on ! l9e--if !re be m ?an "o--! curr5t f ! batt]y ?r\gh ! coil #aa & spr+ #ag s]v+ dur+ ?is op]ation to hold up ! cut-(f relay4 ,z soon z ! op]ator plugs 9 ) ! call+ plug1 ! sup]visory lamp #f lights1 assum+ t ! call$ subscrib] _h n already remov$ 8 receiv] f its hook1 due to ! fact t ! relay #d is en]giz$ & ! relay #c is n4 ,z soon z ! call$ subscrib] responds1 ! relay #c becomes en]giz$ & ! sup]visory lamp goes out4 ,if ! l9e call$ = _h be5 busy by virtue ( be+ plugg$ at ano!r section1 ! tip ( ! op]ator's plug 9 te/+ w\ld h f\nd ! te/ r+ rais$ to a pot5tial above ! gr\nd1 &1 z a consequ5ce1 curr5t w\ld h fl[$ f ! tip ( ?is plug ?r\gh ! back contact ( ! "r-h& lev] ( relay #d1 !nce ?r\gh ! r++ key spr+s & ! auxili>y li/5+-key spr+s to gr\nd ?r\gh ! ret>dation coil #ad4 ,?is w\ld h produc$ a click by caus+ a mom5t>y fl[ ( curr5t ?r\gh ! t]ti>y w9d+ #af ( ! op]ator's set4 ,wir+ ( ,l9e ,circuit4 ,! m complete wir+ diagram ( a s+le subscrib]'s l9e1 ,fig4 #cec1 %[s ! plac+ 9 ! circuits ( ! t]m9als & jump] wires ( ! ma9 di/ribut+ frame & ( ! int]m$iate di/ribut+ frame1 & also %[s h[ ! pilot lamps & night-al>m circuits are associat$ ) a gr\p ( l9es4 ,! ma9 di/ribut+ frame occupies ! same relative position 9 ?is l9e circuit z 9 ! ,we/]n ,electric1 be+ locat$ 9 ! ma9 l9e circuit outside ( all ! swit*bo>d app>atus4 ,! int]m$iate di/ribut+ frame occupies a diff]5t relative position f t 9 ! ,we/]n ,electric l9e4 ,x w be recall$ by ref]5ce to ,fig4 #cdh t ! l9e lamp & ! answ]+ jack 7 p]man5tly associat$ ) ! l9e & cut-(f relays1 su* mutations ( arrangem5t z 7 possible at ! int]m$iate di/ribut+ frame s]v+ only to v>y ! connection betwe5 ! multiple ( a l9e & "o ( ! v>i\s gr\ps ( app>atus consi/+ ( an answ]+ jack & l9e lamp & associat$ relays4 ,9 ! ,kellogg arrangem5t1 ,fig4 #cec1 ! l9e & cut-(f relays1 in/ead ( be+ p]man5tly associat$ ) ! answ]+ jack & l9e lamp1 are p]man5tly associat$ ) ! multiple jacks1 no *anges1 ( :i* ! int]m$iate or ma9 frames are capable1 be+ able to alt] ! relation betwe5 a gr\p ( multiple jacks & its associat$ l9e & cut-(f relays4 ,9 ?is ,kellogg arrangem5t ! int]m$iate di/ribut+ frame may only alt] ! connection ( an answ]+ jack & l9e lamp ) ! multiple & its p]man5tly associat$ relays4 ,! pilot & night al>m arrangem5ts ( ,fig4 #cec %\ld be obvi\s f ! description already giv5 ( o!r simil> sy/ems4 ,illu/ration3 ,fig4 #cec4 ,kellogg ,two-,wire ,l9e ,circuit ,dean ,multiple ,bo>d4 ,9 ,fig4 #ced are %[n ! circuits ( ! multiple swit*bo>d ( ! ,dean ,electric ,company4 ,! subscrib]'s /ation equipm5t %[n at ,/ation ,a & ,/ation ,b w be recogniz$ z ! ,:eat/one-bridge circuit ( ! ,dean ,company4 ,l9e ,circuit4 ,! l9e circuit is easily und]/ood 9 view ( :at has be5 said conc]n+ ! ,we/]n ,electric l9e circuit1 ! l9e relay #a be+ s+le w\nd & betwe5 ! live side ( ! batt]y & ! r+ side ( ! l9e4 ,! cut-(f relay #b is op]at$ :5ev] a plug is ins]t$ 9 a jack & s]ves to sev] ! connection ( ! l9e ) ! normal l9e signal+ app>atus4 ,cord ,circuit4 ,! cord circuit is ( ! f\r-relay type1 b employs ?ree conductors in/ead ( two1 z 9 ! two-wire sy/em4 ,! relay #c1 be+ 9 s]ies betwe5 ! batt]y & ! sleeve contact on ! plug1 is en]giz$ :5ev] a plug is ins]t$ 9 ! jack1 its w9d+ be+ plac$ 9 s]ies ) ! cut-(f relay ( ! l9e ) :i* ! plug is connect$4 ,?is completes ! circuit ?r\gh ! associat$ sup]visory lamp unless ! relay #d is en]giz$1 ! local lamp circuit be+ controll$ by ! back contact ( relay #d & ! front contact ( relay #c4 ,x is ?r\gh ! two w9d+s ( ! relay #d t curr5t is f$ to ! subscrib]'s /ation1 &1 !re=e1 ! armature ( ?is relay is responsive to ! movem5ts ( ! subscrib]'s hook4 ,z ! relay #c holds ! sup]visory lamp circuit clos$ z long z a plug is ins]t$ 9 a jack ( ! l9e1 x foll[s t dur+ a connection ! relay #d w h entire control ( ! sup]visory lamp4 ,li/5+ ,key4 ,! li/5+ key1 z usual1 s]ves to connect ! op]ator's set across ! talk+ /r&s ( ! cord circuit1 & ! action ( ?is 9 connection ) ! op]ator's set ne$s no fur!r explanation4 ,r++ ,keys4 ,! r++-key arrangem5t illu/rat$ is adapt$ = use ) h>monic r++1 ! s+le spr+s #e1 #f1 #g1 & #h ea* be+ controll$ by a sep>ate button & s]v+ to select ! p>ticul> frequ5cy t is to be s5t to l9e4 ,! two spr+s #i & #aj always act to op5 ! cord circuit back ( ! r++ keys1 :5ev] any "o ( ! selective buttons is depress$1 9 ord] to prev5t int]f]5ce by r++ curr5t ) ! o!r op]ations ( ! circuit4 ,two views ( ^! r++ keys are %[n 9 ,figs4 #cee & #cef4 ,fig4 #cef is an end view ( ! entire set4 ,9 ,fig4 #cee ! li/5+ key is %[n at ! extreme "r & ! f\r selective buttons at ! left4 ,:5 a button is releas$ x rises f> en\gh to cause ! dis5gagem5t ( ! contacts1 b rema9s p>tially depress$ to s]ve z an indication t x 0 la/ us$4 ,! gr\p ( spr+s at ! extreme left ( ,fig4 #cee are ! ones repres5t$ at #i & #aj 9 ,fig4 #ced & by ! anvils ) :i* ^? spr+s co-op]ate4 ,illu/ration3 ,fig4 #ced4 ,dean ,multiple ,bo>d ,circuits ,te/4 ,! te/ 9 ?is ,dean sy/em is simple1 &1 l ! ,we/]n ,electric & ,kellogg sy/ems1 x dep5ds on ! rais+ ( ! pot5tial ( ! te/ ?imbles ( all ! l9e jacks ( a l9e :5 a connection is made ) t l9e by a plug at any position4 ,:5 an op]ator makes a te/ by apply+ ! tip ( ! call+ plug to ! te/ ?imble ( a busy l9e1 curr5t passes f ! te/ ?imble ?r\gh ! tip /r& ( ! cord to gr\nd ?r\gh ! left-h& w9d+ ( ! call+ sup]visory relay #d4 ,! drop ( pot5tial ?r\gh ?is w9d+ causes ! tip /r& ( ! cord to be rais$ to a high] pot5tial ?an x 0 be=e1 & z a result ! upp] plate ( ! cond5s] #aa is ?us alt]$ 9 pot5tial & ?is *ange 9 pot5tial across ! cond5s] results 9 a click 9 ! op]ator's e>4 ,illu/ration3 ,fig4 #cee4 ,dean ,p>ty ,l9e ,r++ ,key ,illu/ration3 ,fig4 #cef4 ,dean ,p>ty ,l9e ,r++ ,key ,/romb]g-,c>lson ,multiple ,bo>d4 ,l9e ,circuit4 ,9 ,fig4 #ceg is %[n ! multiple common-batt]y swit*bo>d circuits employ$ by ! ,/romb]g-,c>lson ,telephone ,manufactur+ ,company4 ,! subscrib]'s l9e circuits %[n 9 ?is draw+ are ( ! ?ree-wire type &1 ) ! exception ( ! subscrib]'s /ation1 are ! same z already describ$ = ! ,we/]n ,electric ,company's sy/em4 ,cord ,circuit4 ,! cord circuit employ$ is ( ! two-conductor type1 ! plugs be+ s con/ruct$ z to connect ! r+ & ?imble contacts ( ! jack :5 ins]t$4 ,?is cord circuit is some:at simil> to t employ$ by ! ,kellogg ,swit*bo>d & ,supply ,company1 %[n 9 ,fig4 #ceb1 except t only "o batt]y is employ$1 & t c]ta9 functions ( ?is circuit are p]=m$ me*anically by ! int]-action ( ! armatures ( ! relays4 ,sup]visory ,signals4 ,:5 ! answ]+ plug is ins]t$ 9 a jack1 9 response to a call1 ! curr5t pass+ to ! subscrib]'s /ation & also ?r\gh ! cut-(f relay mu/ fl[ ?r\gh ! relay #a1 ?us en]giz+ x4 ,z ! call+ subscrib]'s receiv] is at ?is "t remov$ f ! hook swit*1 ! pa? = curr5t w be complet$ ?r\gh ! tip ( ! jack1 !nce ?r\gh ! tip ( ! plug1 ?r\gh relay #b to gr\nd1 caus+ relay #b to be op]at$ & to break ! circuit ( ! answ]+ sup]visory lamp4 ,! two relays #a & #b are s associat$ me*anically t ! armature ( #a controls ! armature ( #b 9 su* a mann] z to normally hold ! circuit ( ! answ]+ sup]visory lamp op54 ,b1 h[ev]1 :5 ! plug is ins]t$ 9 a jack1 relay #a is op]at$ & all[s ! op]ation ( relay #b to be controll$ by ! hook swit* at ! subscrib]'s /ation4 ,! sup]visory relay #c associat$ ) ! call+ cord is op]at$ :5 ! call+ plug is plac$ 9 a jack1 & ?is relay normally holds ! armature ( relay #d 9 an op]at$ position 9 a simil> mann] z ! armature ( relay #a controll$ t ( relay #b4 ,sup]visory relay #d is "u ! control ( ! hook swit* at ! call$ subscrib]'s /ation4 ,te/4 ,9 ?is circuit1 z 9 sev]al previ\sly describ$1 :5 a plug is ins]t$ 9 a jack ( a l9e1 ! ?imble contacts ( ! jacks associat$ ) t l9e are rais$ to a high] pot5tial ?an t :i* !y normally h4 ,! op]ator 9 te/+ a busy l9e1 ( c\rse hav+ previ\sly mov$ ! li/5+ key to ! li/5+ position1 closes a pa? f ! te/ ?imble ( ! jack1 ?r\gh ! tip ( ! call+ plug1 ?r\gh ! contacts ( ! relay #d1 ! inside spr+s ( ! li/5+ key1 !nce ?r\gh a w9d+ ( ! induction coil associat$ ) h] set to gr\nd4 ,! circuit ?us e/abli%$ all[s curr5t to fl[ f ! te/ ?imble ( ! jack ?r\gh ! w9d+ ( h] induction coil to gr\nd1 caus+ a click 9 h] telephone receiv]4 ,! arrangem5t ( ! r++ circuit does n diff] mat]ially f t already describ$ = o!r sy/ems &1 !re=e1 ne$s no fur!r explanation4 ,illu/ration3 ,fig4 #ceg4 ,/romb]g-,c>lson ,multiple ,bo>d ,circuits ,multiple ,swit*bo>d ,app>atus4 ,com+ n[ to a discussion ( ! details ( app>atus employ$ 9 multiple swit*bo>ds1 x may be /at$ t mu* ( ! app>atus us$ 9 ! simpl] types is capable ( do+ duty 9 multiple swit*bo>ds1 al?\gh1 ( c\rse1 modification 9 detail is (t5 necess>y to make ! app>atus fit ! p>ticul> dem&s ( ! sy/em 9 :i* x is to be us$4 ,jacks4 ,probably ! mo/ important piece ( app>atus 9 ! multiple swit*bo>d is ! jack1 its importance be+ increas$ by ! fact t su* v l>ge numb]s ( !m are sometimes necess>y4 ,swit*bo>ds hav+ hundr$s ( ?\s&s ( jacks are n uncommon4 ,! multiple jacks are ne>ly always m\nt$ 9 /rips ( tw5ty & ! answ]+ jacks usually 9 /rips ( t51 ! l5g? ( ! jack /rip be+ ! same 9 ea* case 9 ! same bo>d &1 !re=e1 giv+ twice z wide a spac+ 9 ! answ]+ z 9 ! multiple jacks4 ,! di/ance betwe5 c5t]s 9 ! multiple jacks v>ies f a qu>t] ( an in*--:i* is p]haps ! extreme m9imum--to half an in*1 beyond :i* l>g] limit !re seems to be no ne$ ( go+ 9 any case4 ,x is cu/om>y t ! jack /rip %all be made ( ! same total ?ickness z ! di/ance betwe5 ! c5t]s ( two ( its jacks1 & f ?is x foll[s t ! /rips :5 pil$ "o ^u ! o!r give ! same v]tical di/ance betwe5 jack c5t]s z ! horizontal di/ance4 ,9 ,fig4 #ceh is %[n a /rip ( multiple & a /rip ( answ]+ jacks ( ,we/]n ,electric make1 ?is be+ ! type employ$ 9 ! ,no4 #a /&>d swit*bo>ds = l>ge ex*anges4 ,9 ,fig4 #cei are %[n ! multiple & answ]+ jacks employ$ 9 ! ,no4 #aj ,we/]n ,electric swit*bo>d4 ,! multiple jacks 9 ! ,no4 #a swit*bo>d are m\nt$ on #c_/h-;in* c5t]s1 ! jacks hav+ ?ree bran* t]m9al contacts4 ,! multiple jacks ( ! ,no4 #aj swit*bo>d indicat$ 9 ,fig4 #cei are m\nt$ on #a_/b-;in* c5t]s1 ea* jack hav+ five contacts z indicat$ by ! requirem5t ( ! circuits 9 ,fig4 #cdi4 ,9 ,fig4 #cfj are %[n ! answ]+ & multiple jacks ( ! ,kellogg ,swit*bo>d & ,supply ,company's two-wire sy/em4 ,! extreme simplicity ( ^! is p>ticul>ly well %[n 9 ! cut ( ! answ]+ jack1 & ^! figures also %[ cle>ly ! cu/om>y me?od ( numb]+ jacks4 ,9 v l>ge multiple bo>ds x has be5 ! practice ( ! ,kellogg ,company to space ! multiple jacks on #c_/aj-;in* c5t]s1 & 9 _! small] multiple "w1 !y employ ! #a_/b-;in* spac+4 ,) ! #c_/aj-;in* spac+ t company has be5 able to build bo>ds hav+ a capacity ( #ah1jjj l9es1 t _m jacks be+ plac$ )9 ! rea* ( ea* op]ator4 ,9 all mod]n multiple swit*bo>ds ! te/ ?imble or sleeve contacts are drawn up f %eet brass or ,g]man silv] into tubul> =m & ins]t$ 9 prop]ly spac$ bor+s 9 /rips ( h>d rubb] =m+ ! faces ( ! jacks4 ,^! /rips sometimes are re9=c$ by brass /rips on _! "u sides4 ,! spr+s =m+ ! o!r t]m9als ( ! jack are m\nt$ 9 mill$ slots 9 ano!r /rip ( h>d rubb] m\nt$ 9 ! re> ( & p>allel to ! front /rip & rigidly atta*$ !reto by a suitable metal framework4 ,9 ?is way desir$ rigidity & high insulation betwe5 ! v>i\s p>ts is secur$4 ,illu/ration3 ,fig4 #ceh4 ,answ]+ & ,multiple ,jacks = ,no4 #a ,bo>d ,lamp ,jacks4 ,! lamp jacks employ$ 9 multiple "w ne$ no fur!r description 9 view ( :at has be5 said 9 connection ) lamp jacks = simple common-batt]y bo>ds4 ,! lamp jack spac+ is always ! same z ! answ]+ jack spac+1 s t ! lamps w come 9 ! same v]tical alignm5t z _! correspond+ answ]+ jacks :5 ! lamp /rips & answ]+ jack /rips are m\nt$ 9 alt]nate lay]s4 ,illu/ration3 ,fig4 #cei4 ,answ]+ & ,multiple ,jacks = ,no4 #aj ,bo>d ,illu/ration3 ,fig4 #cfj4 ,answ]+ & ,multiple ,jacks = ,kellogg ,two-,wire ,bo>d ,relays4 ,next 9 ord] ( importance 9 ! matt] ( individual p>ts = multiple swit*bo>ds is ! relay4 ,! necessity = reliability ( action 9 ^! is app>5t1 & ?is means t !y mu/ n only be well con/ruct$1 b t !y mu/ be protect$ f du/ & moi/ure & mu/ h contact po9ts ( su* a nature z n to corrode ev5 9 ! pres5ce ( consid]able sp>k+ & ( ! mo/ adv]se atmosph]ic conditions4 ,economy ( space is also a factor & has l$ to ! almo/ univ]sal adoption ( ! s+le-magnet type ( relay = l9e & cut-(f z well z sup]visory purposes4 ,illu/ration3 ,fig4 #cfa4 ,type ( ,l9e ,relay ,illu/ration3 ,fig4 #cfb4 ,type ( ,cut-,(f ,relay ,! ,we/]n ,electric ,company employs diff]5t types ( relays = l9e1 cut-(f1 & sup]visory purposes4 ,?is is contr>y to ! practice ( mo/ ( ! o!r companies :o make ! same g5]al type ( relay s]ve = all ( ^! purposes4 ,a good idea ( ! type ( ,we/]n ,electric l9e relay1 z employ$ 9 its ,no4 #a bo>d1 may be _h f ,fig4 #cfa4 ,z is se5 ?is is ( ! tilt+ armature type1 ! armature rock+ back & =? on a knife-edge contact at its base1 ! "p on :i* x re/s be+ ( iron & ( su* =m z to practically complete1 ) ! armature & core1 ! magnetic circuit4 ,! cut-(f relay1 ,fig4 #cfb1 is ( an entirely diff]5t type4 ,! armature 9 ?is is loosely susp5d$ by means ( a flexible spr+ und]nea? two ,l-%ap$ pol> ext5sions1 "o ext5d+ up f ! re> end ( ! core & ! o!r f ! front end4 ,:5 en]giz$ ?is armature is pull$ away f ! core by ^! ,l-%ap$ pieces & imp>ts its motion ?r\gh a h>d-rubb] p9 to ! upp] pair ( spr+s s z to effect ! necess>y *anges 9 ! circuit4 ,illu/ration3 ,fig4 #cfc4 ,we/]n ,electric ,comb9$ ,l9e & ,cut-(f ,relay ,illu/ration3 ,fig4 #cfd4 ,we/]n ,electric ,sup]visory ,relay ,illu/ration3 ,fig4 #cfe4 ,l9e ,relay ,no4 #aj ,bo>d ,mu* economy 9 space & 9 wir+ is secur$ 9 ! type ( swit*bo>ds employ+ cut-(f z well z l9e relays by m\nt+ ! two relays toge!r & 9 mak+ ( !m1 9 fact1 a unit>y piece ( app>atus4 ,s9ce ! l9e relay is always associat$ ) ! cut-(f relay ( ! same l9e & ) no o!r1 x is obvi\s t ?is unit>y arrangem5t effects a great sav+ 9 wir+ & also secures a great advantage 9 ! matt] ( conv5i5ce ( inspection4 ,su* a comb9$ cut-(f & l9e relay1 employ$ 9 ! ,we/]n ,electric ,no4 #a relay bo>d1 is %[n 9 ,fig4 #cfc4 ,^! are m\nt$ 9 banks ( t5 pairs1 a common du/ cap ( %eet iron cov]+ ! entire gr\p4 ,! ,we/]n ,electric sup]visory relay1 ,fig4 #cfd1 is ( ! tilt+ armature type & is copp] clad4 ,! du/ cap 9 ?is case fits on ) a bayonet jo9t z cle>ly indicat$4 ,9 ,fig4 #cfe is %[n ! l9e relay employ$ 9 ! ,we/]n ,electric ,no4 #aj bo>d4 ,illu/ration3 ,fig4 #cff4 ,kellogg ,l9e & ,cut-(f ,relays ,illu/ration3 ,fig4 #cfg4 ,/rip ( ,kellogg ,l9e & ,cut-,(f ,relays ,! ,kellogg ,company employs ! type ( relay ( :i* ! magnetic circuit 0 illu/rat$ 9 ,fig4 #ie4 ,9 its multiple bo>ds x commonly m\nts ! l9e & cut-(f relays toge!r1 z %[n 9 ,fig4 #cff4 ,a s+le1 s(t iron %ell is us$ to cov] bo? ( ^!1 ?us s]v+ z a du/ %ield & also z a magnetic %ield to prev5t cross-talk betwe5 adjac5t relays--an important feature1 s9ce x w be rememb]$ ! cut-(f relays are left p]man5tly connect$ ) ! talk+ circuit4 ,fig4 #cfg1 :i* %[s a /rip ( tw5ty su* pairs ( relays1 f five ( :i* ! cov]s h be5 remov$1 is an excell5t detail view ( ! g5]al practice 9 ?is respect2 obvi\sly1 a v l>ge numb] ( su* relays may be m\nt$ 9 a comp>atively small space4 ,! m\nt+ /rip %[n 9 ?is cut is ( heavy roll$ iron & is provid$ ) op5+s ?r\gh :i* ! connection t]m9als--%[n m cle>ly 9 ,fig4 #cff--project4 ,on ! back ( ?is m\nt+ /rip all ! wir+ is done & mu* ( ?is wir+--t connect+ adjac5t t]m9als on ! back ( ! relay /rip--is made by means ( ?9 copp] wires )\t insulation1 ! wires be+ s %ort z to support !mselves )\t dang] ( cross+ ) o!r wires4 ,:5 ^! wires are adjac5t to gr\nd or batt]y wires !y may be protect$ by sleev+1 s z to prev5t crosses4 ,illu/ration3 ,fig4 #cfh4 ,mon>* ,relay ,an int]e/+ feature 9 relay con/ruction is f\nd 9 ! relay ( ! ,mon>* ,telephone ,manufactur+ ,company %[n 9 ,figs4 #cfh & #cfi4 ,! assembl$ relay & its m\nt+ /rip & cap are %[n 9 ,fig4 #cfh4 ,?is relay is s con/ruct$ t by ! lift+ ( a s+le lat* n only ! armature b ! coil may be bodily remov$1 z %[n 9 ,fig4 #cfi1 9 :i* ! lat* is %[n 9 its rais$ position4 ,z se51 ! armature has an ,l-%ap$ projection :i* s]ves to op]ate ! contact spr+s ly+ on ! iron plate above ! coil4 ,! simplicity ( ?is device is attractive1 & x is ( conv5i5ce n only f ! /&po9t ( easy repairs b also f ! /&po9t ( factory assembly1 s9ce by manufactur+ /&>d coils ) diff]5t *>act]s ( w9d+s & /&>d gr\ps ( spr+s1 x is possible to produce )\t special manufacture almo/ any comb9ation ( relay4 ,illu/ration3 ,fig4 #cfi4 ,mon>* ,relay ,assembly4 ,! arrangem5t ( ! key & jack equipm5t 9 complete multiple swit*bo>d sections is cle>ly %[n 9 ,fig4 #cgj1 :i* %[s a s+le ?ree-position section ( "o ( ! small multiple swit*bo>ds ( ! ,kellogg ,swit*bo>d & ,supply ,company4 ,! arrangem5t ( keys & plugs on ! key %elf is sub/antially ! same z 9 simple common-batt]y bo>ds4 ,z 9 ! simple swit*bo>ds ! sup]visory lamps are usually m\nt$ on ! h+$ key %elf imm$iately 9 ! re> ( ! li/5+ & r++ keys & ) su* spac+ z to lie imm$iately 9 front ( ! plugs to :i* !y correspond4 ,! reason = m\nt+ ! sup]visory lamps on ! key %elf is to make !m easy ( access 9 case ( ! necessity ( lamp r5ewals or repairs on ! wir+4 ,! space at ! bottom ( ! v]tical panels1 conta9+ ! jacks1 is left blank1 z ?is space is ob/ruct$ by ! /&+ plugs 9 front ( x4 ,above ! plugs1 h[ev]1 are se5 ! alt]nate /rips ( l9e lamps & answ]+ jacks1 ! lamps 9 ea* case be+ directly bel[ ! correspond+ answ]+ jacks4 ,above ! l9e lamps & answ]+ jacks 9 ! two positions at ! "r !re are blank /rips into :i* additional l9e lamps & jacks may be plac$ 9 case ! future ne$s ( ! sy/em dem& x4 ,! space above ^! is ! multiple jack space1 & x is evid5t f ! small numb] ( multiple jacks 9 ?is little swit*bo>d t ! pres5t equipm5t ( ! bo>d is small4 ,x is also evid5t f ! am\nt ( blank space left = future in/allations ( multiple jacks t a consid]able gr[? is expect$4 ,?us1 :ile !re are b f\r banks ( #ajj multiple jacks1 or #djj 9 all1 !re is room 9 ! multiple = #cjj banks ( #ajj multiple jacks1 or #c1jjj 9 all4 ,! me?od ( gr\p+ ! jacks 9 banks ( #ajj & ( provid+ = _! future gr[? is cle>ly indicat$ 9 ?is figure4 ,! next section at ! "r ( ! "o %[n w\ld conta9 a duplicate set ( multiple jacks & also an additional equipm5t ( answ]+ jacks & lamps4 ,illu/ration3 ,a ,,multiple ,,manual ,,swit*+ ,,bo>d ,,= ,,toll ,,connections ,,9 ,,an ,,automatic ,,sy/em ,multiple ,jacks are ,provid$ = ,ea* ,l9e ?r\gh ,:i* ,toll ,connections are ,h&l$ ,directly4 ,illu/ration3 ,fig4 #cgj4 ,small ,multiple ,bo>d ,section ,= ord9>y local s]vice no op]ator w\ld sit at ! left-h& position ( ! section %[n1 t be+ ! end position1 s9ce ! op]ator !re w\ld n be able easily to rea* ! extreme "r-h& portion ( ! ?ird position & w\ld h no?+ to rea* at h] left4 ,?is end position 9 ?is p>ticul> bo>d illu/rat$ is provid$ ) toll-l9e equipm5t1 a practice n uncommon 9 small multiple bo>ds4 ,to prev5t confusion let u assume t ! multiple jack space conta9s its full equipm5t ( #c1jjj jacks on ea* section4 ,! op]ator 9 ! c5t] position ( ! section %[n c\ld easily rea* any "o ( ! jacks on t section4 ,! op]ator at ! ?ird position c\ld rea* any jack on ! second & ?ird position ( h] section1 b c\ld n well rea* multiple jacks 9 ! fir/ position4 ,%e w\ld1 h[ev]1 h a duplicate ( ! multiple jacks 9 ?is fir/ position 9 ! section at h] "r1 i4 e41 9 ! f\r? position1 & x makes no diff]5ce on :at portion ( ! swit*bo>d %e plugs into ! multiple s long z %e plugs into a jack ( ! "r l9e4 ,,*apt] ,,xxvii ,,trunk+ ,,9 ,,multi-,,(fice ,,sy/ems ,x has be5 /at$ t a s+le ex*ange may involve a numb] ( (fices1 9 :i* case x is t]m$ a multi-(fice ex*ange4 ,9 a multi-(fice ex*ange1 swit*bo>ds are necess>y at ea* (fice 9 :i* ! subscrib]s' l9es ( ! correspond+ (fice di/rict t]m9ate4 ,means = int]communication betwe5 ! subscrib]s 9 "o (fice & ^? 9 any o!r (fice are af=d$ by int]-(fice trunks ext5d$ betwe5 ea* (fice & ea* ( ! o!r (fices4 ,if ! "* ( ! community is su* t ea* ( ! (fices has s few l9es z to make ! simple swit*bo>d suffice = its local connections1 !n ! trunk+ betwe5 ! (fices may be c>ri$ out 9 exactly ! same way z expla9$ betwe5 ! v>i\s simple swit*bo>ds 9 a transf] sy/em1 ! only diff]5ce be+ t ! trunks are long en\gh to rea* f "o (fice to ano!r in/ead ( be+ %ort & entirely local to a s+le (fice4 ,su* a condition ( affairs w\ld only be f\nd 9 cases :]e sev]al small communities 7 gr\p$ closely en\gh toge!r to make !m op]ate z a s+le ex*ange di/rict1 & t is r unusual4 ,! subject ( int]-(fice trunk+ s f> z manual swit*bo>ds are conc]n$ is1 !re=e1 conf9$ ma9ly to trunk+ betwe5 a numb] ( (fices ea* equipp$ ) a manual multiple swit*bo>d4 ,necessity = ,multi-,(fice ,ex*anges4 ,be=e tak+ up ! details ( ! me?ods & circuits employ$ 9 trunk+ 9 multi-(fice sy/ems1 x may be well to discuss briefly :y ! multi-(fice ex*ange is a necessity1 & :y x w\ld n be j z well to s]ve all ( ! subscrib]s 9 a l>ge city f a s+le huge swit*bo>d 9 :i* all ( ! subscrib]s' l9es w\ld t]m9ate4 ,x _c be d5i$1 :5 o!r ?+s are equal1 t x is bett] to h only "o op]ator involv$ 9 any connection :i* means less labor & less liability ( error4 ,! reasons1 h[ev]1 :y ?is is n feasible 9 really l>ge ex*anges are sev]al4 ,! ma9 "o is t ( ! l>g] inve/m5t requir$4 ,consid]+ ! inve/m5t fir/ f ! /&po9t ( ! subscrib]'s l9e1 x is q cle> t ! av]age l5g? ( subscrib]'s l9e w be v mu* great] 9 a giv5 community if all ( ! l9es are run to a s+le (fice1 ?an w be ! case if ! ex*ange di/rict is divid$ into small] (fice di/ricts & ! l9es run m]ely f ! subscrib]s to ! ne>e/ (fice4 ,!re is a direct & v l>ge ga9 9 ?is respect1 9 ! multi-(fice sy/em ov] ! s+le (fice sy/em 9 l>ge cities1 b ?is is n a net ga91 s9ce !re is an (fsett+ inve/m5t necess>y 9 ! trunk l9es betwe5 ! (fices1 :i* ( c\rse are sep>ate f ! subscrib]s' l9es4 ,approa*+ ! matt] f ! /&po9t ( swit*bo>d con/ruction & op]ation1 ano!r /rong reason becomes app>5t = ! employm5t ( m ?an "o (fice 9 l>ge ex*ange di/ricts4 ,bo? ! difficulties ( op]ation & ! exp5se ( con/ruction & ma9t5ance increase v rapidly :5 swit*bo>ds gr[ beyond a c]ta9 r well-def9$ limit4 ,obvi\sly1 ! limitation ( ! multiple swit*bo>d z to size involves ! numb] ( multiple jacks t x is feasible to place on a section4 ,multiple swit*bo>ds h be5 con/ruct$ 9 ?is c\ntry 9 :i* ! sections _h a capacity ( #ah1jjj jacks4 ,s*emes h be5 propos$ & put into effect ) v>y+ success1 = d\bl+ & quadrupl+ ! capacity ( multiple swit*bo>ds1 "o ( ^! be+ ! s-call$ divid$ multiple bo>d devis$ by ! late ,milo ,g4 ,kellogg1 & once us$ 9 ,clevel&1 ,ohio1 & ,/4 ,l\is1 ,miss\ri4 ,ea* ( ^! bo>ds _h an ultimate capacity ( #bd1jjj l9es1 & ea* has be5 replac$ by a /raight multiple bo>d ( small] capacity4 ,9 g5]al1 ! pres5t practice 9 ,am]ica does n sanction ! build+ ( multiple bo>ds ( m ?an ab\t #aj1jjj l9es capacity1 & z an example ( ?is x may be cit$ t ! l>ge/ /&>d section manufactur$ = ! ,bell companies has an ultimate capacity ( #i1fjj l9es4 ,european eng9e]s h %[n a t5d5cy t[>ds ! opposite practice1 & an example ( ! extreme 9 ?is case is ! multiple swit*bo>d manufactur$ by ! ,ericsson ,company1 & in/all$ 9 ,/ockholm1 9 :i* ! jacks h be5 r$uc$ to su* small dim5sions z to p]mit an ultimate capacity ( #fj1jjj l9es4 ,! reasons gov]n+ ! decision ( ,am]ican eng9e]s 9 e/abli%+ ! practice ( employ+ no multiple swit*bo>ds ( great] capacity ?an ab\t #aj1jjj l9es1 briefly outl9$1 are z foll[s3 ,! build+ ( swit*bo>ds ) l>g] capacity1 :ile p]fectly possible1 makes necess>y ei!r a v small jack or "s add$ complexity1 su* z t ( ! divid$ multiple swit*bo>d1 ei!r ( :i* is consid]$ objectionable4 ,extremely small jacks & l>ge multiples introduce difficulties z to ! durability ( ! jacks & ! plugs1 & also !y t5d to sl[ d[n ! "w ( op]ators & to introduce errors4 ,!y also introduce ! necessity ( a small] gauge ( wire ?r\gh ! multiple ?an x has be5 f\nd desirable to employ4 ,consid]$ f ! /&po9t ( exp5se1 x is evid5t t z a multiple swit*bo>d increases 9 numb] ( l9es1 its size increases 9 two dim5sions1 i4 e41 9 l5g? ( bo>d & height ( section1 & ?is elem5t ( exp5se1 !re=e1 is a function ( ! squ>e ( ! numb] ( l9es4 ,! matt] ( insurance1 bo? ) respect to ! risk z to prop]ty loss & ! risk z to breakd[n ( ! s]vice1 also po9ts di/9ctly 9 ! direction ( a plurality ( (fices r ?an "o4 ,bo? f ! /&po9t ( risk aga9/ fire & o!r haz>ds1 :i* might damage ! physical prop]ty1 & ( risk aga9/ int]ruption to s]vice due to a breakd[n ( ! swit*bo>d itself1 or a failure ( its s\rces ( curr5t1 or an accid5t to ! cable approa*es1 ! s+le (fice practice is l putt+ all "o's eggs 9 "o basket4 ,ano!r factor t has contribut$ to ! adoption ( small] swit*bo>d capacities is ! fact t 9 ! v l>ge cities ev5 a #dj1jjj l9e multiple swit*bo>d w\ld /ill n remove ! necessity ( multi-(fice ex*anges ) ! consequ5t c]ta9ty t a l>ge proportion ( ! calls w\ld h to be trunk$ anyway4 ,und\bt$ly1 "o ( ! reasons = ! diff]5ce betwe5 ,am]ican & ,european practice is ! bett] results t ,am]ican op]at+ companies h be5 able to secure 9 ! h&l+ ( calls at ! incom+ end ( trunks4 ,?is is due1 no d\bt1 9 "p to ! diff]5ces 9 social & economic conditions "u :i* ex*anges are op]at$ 9 ?is c\ntry & abroad1 & also 9 "p to ! *>act]i/ics ( ! ,engli% tongue :5 comp>$ to "s ( ! o!r tongues 9 ! matt] ( ease ) :i* numb]s may be spok54 ,9 ,am]ica x has be5 f\nd possible to s p]fect ! op]ation ( trunk+ "u prop] op]at+ conditions & ) good equipm5t z to relieve multi-(fice practice ( _m ( ! disadvantages :i* h be5 urg$ aga9/ x4 ,classification4 ,broadly speak+ !re are two g5]al me?ods t may be employ$ 9 trunk+ betwe5 ex*anges4 ,! fir/ & simple/ ( ^! me?ods is to employ s-call$ two-way trunks4 ,^!1 z _! "n indicates1 may be us$ = complet+ connections betwe5 (fices 9 ei!r direction1 t is1 :e!r ! call orig9ates at "o end or ! o!r4 ,! o!r way is by ! use ( "o-way trunks1 :]e9 ea* trunk c>ries traffic 9 "o direction only4 ,:]e su* is ! case1 "o end ( ! trunk is always us$ = connect+ ) ! call+ subscrib]'s l9e & is t]m$ ! outgo+ end1 & ! o!r end is always us$ 9 complet+ ! connection ) ! call$ subscrib]'s l9e1 & is ref]r$ to z ! incom+ end4 ,traffic 9 ! o!r direction is h&l$ by ano!r set ( trunks diff]+ f ! fir/ set only 9 t _! outgo+ & incom+ ends are rev]s$4 ,z has already be5 po9t$ out1 a sy/em ( trunks employ+ two-way trunks is call$ a s+le-track sy/em1 & a sy/em involv+ two sets ( "o-way trunks is call$ a d\ble-track sy/em4 ,x is to be not$ t ! t]ms outgo+ & incom+1 z appli$ to ! ends ( trunks & also z appli$ to traffic1 always ref] to ! direction 9 :i* ! trunk h&les traffic or ! direction 9 :i* ! traffic is fl[+ ) respect to ! p>ticul> (fice "u consid]ation at ! "t4 ,?us an incom+ trunk at "o (fice is an outgo+ trunk at ! o!r4 ,two-,way ,trunks4 ,two-way trunks are ne>ly always employ$ :]e ! traffic is v small & !y are ne>ly always op]at$ by hav+ ! ,a-op]ator plug directly into ! jack at h] end ( ! trunk & display+ a signal at ! o!r end by r++ ov] ! trunk z %e w\ld ov] an ord9>y subscrib]'s l9e4 ,! op]ator at ! di/ant ex*ange answ]s z %e w\ld on an ord9>y l9e1 by plugg+ into ! jack ( t trunk1 & receives h] ord]s ov] ! trunk ei!r f ! orig9at+ op]ator or f ! subscrib]1 & !n completes ! connection ) ! call$ subscrib]4 ,su* trunks are (t5 ref]r$ to z r+-d[n trunks1 & _! equipm5t consi/s 9 a drop & jack at ea* end4 ,9 case !re is a multiple bo>d at ei!r or bo? ( ! (fices1 !n ! equipm5t at ea* end ( ! trunk w\ld consi/ ( a drop & answ]+ jack1 toge!r ) ! full quota ( multiple jacks4 ,x is readily se5 t ?is mode ( op]ation is sl[1 z ! "w t ea* op]ator has to d is ! same z t 9 connect+ two local subscrib]s1 plus ! "t t x takes = ! op]ators to communicate ) ea* o!r ov] ! trunk4 ,"o-,way ,trunks4 ,:]e "o-way trunks are employ$ 9 ! d\ble-track sy/em1 ! trunks1 assum+ t !y connect multiple bo>ds1 are provid$ ) multiple jacks only at _! outgo+ ends1 s t any op]ator may rea* !m = an outgo+ connection1 & at _! incom+ ends !y t]m9ate ea* 9 a s+le plug & 9 suitable signals & r++ keys1 ! purpose ( :i* w be expla9$ lat]4 ,ov] su* trunks !re is no v]bal communication betwe5 ! op]ators1 ! in/ructions pass+ betwe5 ! op]ators ov] sep>ate ord]-wire circuits4 ,?is is done 9 ord] t ! trunk may be available z mu* z possible = actual conv]sation betwe5 ! subscrib]s4 ,x may be /at$ at ?is po9t t ! duration ( ! p]iod f ! "t :5 a trunk is appropriat$ by ! op]ators = ! mak+ ( a c]ta9 connection until ! "t :5 ! trunk is f9ally releas$ & made available = ano!r connection is call$ ! hold+ "t1 & ?is hold+ "t includes n only ! p]iod :ile ! subscrib]s are 9 actual conv]sation ov] x1 b also ! p]iods :ile ! op]ators are mak+ ! connection & aft]w>ds :ile !y are tak+ x d[n4 ,x may be said1 !re=e1 t ! purpose ( employ+ sep>ate ord] wires = communication betwe5 ! op]ators is to make ! hold+ "t on ! trunks z small z possible &1 !re=e1 = ! purpose ( enabl+ a giv5 trunk to take "p 9 z _m connections 9 a giv5 "t z possible4 ,9 outl9e ! op]ation ( a "o-way trunk betwe5 common-batt]y1 manual1 multiple swit*bo>ds is1 ) modifications t w be po9t$ out aft]w>ds1 z foll[s3 ,:5 a subscrib]'s l9e signal is display$ at "o (fice1 ! op]ator 9 att5dance at t position answ]s & f9d+ t ! call is = a subscrib] 9 ano!r (fice1 %e presses an ord]-wire key & !reby connects h] telephone set directly ) t ( a ,b-op]ator at ! prop] o!r (fice4 ,unless %e f9ds t o!r op]ators are talk+ ov] ! ord] wire1 %e m]ely /ates ! numb] ( ! call$ subscrib]1 & ! ,b-op]ator ^: telephone set is p]man5tly connect$ ) t ord] wire m]ely repeats ! numb] ( ! call$ subscrib] & foll[s ?is by designat+ ! numb] ( ! trunk :i* ! ,a-op]ator is to employ 9 mak+ ! connection4 ,! ,a-op]ator1 !reupon1 imm$iately & )\t te/+1 ins]ts ! call+ plug ( ! pair us$ 9 answ]+ ! call into ! trunk jack designat$ by ! ,b-op]ator2 ! ,b-op]ator simultane\sly te/s ! multiple jack ( ! call$ subscrib] &1 if %e f9ds x n busy1 ins]ts ! plug ( ! designat$ trunk into ! multiple jack ( ! call$ subscrib] & r+s 8 bell by press+ ! r++ key associat$ ) ! trunk cord us$4 ,! "w on ! "p ( ! ,a-op]ator 9 connect+ ) ! outgo+ end ( ! trunk & on ! "p ( ! ,b-op]ator 9 connect+ ! incom+ end ( ! trunk ) ! l9e goes on simultane\sly1 & x makes no diff]5ce :i* ( ^! op]ators completes ! connection fir/4 ,x is ! common practice ( ! ,bell op]at+ companies 9 ?is c\ntry to employ :at is call$ automatic or ma*9e r++ 9 connection ) ! ,b-op]ator's "w4 ,:5 ! ,b-op]ator presses ! r++ key associat$ ) ! incom+ trunk cord1 %e pays no fur!r att5tion to x1 & %e has no sup]visory lamp to in=m h] z to :e!r or n ! subscrib] has answ]$4 ,! r++ key is held d[n1 aft] its depression by ! op]ator1 ei!r by an electromagnet or by a magnet-controll$ lat*1 & ! r++ ( ! subscrib]'s bell cont9ues at p]iodic int]vals z controll$ by ! r++ commutator associat$ ) ! r++ ma*9e4 ,:5 ! subscrib] answ]s1 h[ev]1 ! closure ( 8 l9e circuit results 9 su* an op]ation ( ! magnet associat$ ) ! r++ key z to release ! r++ key & ?us to automatically discont9ue ! r++ curr5t4 ,:5 a connection is e/abli%$ betwe5 two subscrib]s ?r\gh su* a trunk ! sup]vision ( ! connection falls entirely ^u ! ,a-op]ator :o e/abli%$ x4 ,?is means t ! call+ sup]visory lamp at ! ,a-op]ator's position is controll$ ov] ! trunk f ! /ation ( ! call$ subscrib]1 ! answ]+ sup]visory lamp be+1 ( c\rse1 "u ! control ( ! call+ subscrib] z 9 ! case ( a local connection4 ,x is1 !re=e1 ! ,a-op]ator :o always initiates ! tak+ d[n ( a trunk connection1 & :51 9 response to ! light+ ( ! two lamps1 %e )draws h] call+ plug f ! trunk jack1 ! sup]visory lamp associat$ ) ! incom+ end ( ! trunk at ! o!r (fice is light$1 & ! ,b-op]ator obeys x by pull+ d[n ! plug4 ,if1 ^u te/+ ! multiple jack ( ! call$ subscrib]'s l9e1 ! ,b-op]ator f9ds ! l9e to be busy1 %e at once ins]ts ! trunk plug into a s-call$ busy-back jack1 :i* is m]ely a jack ^: t]m9als are p]man5tly connect$ to a circuit t is int]mitt5tly op5$ & clos$1 & :i* also has impress$ ^u x an alt]nat+ curr5t ( su* a nature z to produce ! famili> buzz-buzz 9 a telephone receiv]4 ,! op5+ & clos+ ( ?is circuit causes ! call+ sup]visory lamp ( ! ,a-op]ator to fla% at p]iodic int]vals j z if ! call$ subscrib] _h rais$ & l[]$ 8 receiv]1 b m regul>ly4 ,?is is ! indication to ! ,a-op]ator t ! l9e call$ = is busy4 ,! buzz+ s\nd is repeat$ back ?r\gh ! cord circuit ( ! ,a-op]ator to ! call+ subscrib] & is a notification to him t ! l9e is busy4 ,sometimes1 z is practic$ 9 ,new ,york ,city1 = in/ance1 ! buzz+ feature is omitt$1 & ! only indication t ! call+ subscrib] receives t ! call$-= l9e is busy is be+ told s by ! ,a-op]ator4 ,?is may be consid]$ a special feature & x is employ$ 9 ,new ,york because !re ! cu/om exi/s ( tell+ a call+ subscrib]1 :5 ! l9e he has call$ = has be5 f\nd busy1 t ! p>ty w be secur$ = him & t he1 ! call+ subscrib]1 w be call$1 if he desires4 ,a modification ( ?is busy-back feature t has be5 employ$ 9 ,bo/on1 & p]haps 9 o!r places1 is to associate ) ! busy-back jack at ! ,b-op]ator's position a phonograph :i*1 l a p>rot1 keeps repeat+ ,l9e busy--please call aga94 ,:]e ?is is done ! call+ subscrib]1 if he und]/&s :at ! phonograph says1 is suppos$ to hang up 8 receiv]1 at :i* "t ! ,a-op]ator takes d[n ! connection & ! ,b-op]ator foll[s 9 response to ! notification ( h] sup]visory lamp4 ,! phonograph busy-back s*eme1 :ile +5i\s1 has n be5 a success & has g5]ally be5 ab&on$4 ,z a rule ! indep5d5t op]at+ companies 9 ?is c\ntry h n employ$ automatic r++1 & 9 ?is case ! ,b-op]ators h be5 requir$ to op]ate _! r++ keys & to wat* = ! response ( ! call$ subscrib]4 ,9 ord] to arrange = ?is1 ano!r sup]visory lamp1 t]m$ ! r++ lamp1 is associat$ ) ea* incom+ trunk plug1 ! go+ out ( ?is lamp be+ a notification to ! ,b-op]ator to discont9ue r++4 ,we/]n ,electric ,trunk ,circuits4 ,! pr9ciples involv$ 9 int]-(fice trunk+ ) automatic r++1 are well illu/rat$ 9 ! trunk circuit employ$ by ! ,we/]n ,electric ,company 9 connection ) its ,no4 #a relay bo>ds4 ,! dott$ divid+ l9e ?r\gh ! c5t] ( ,fig4 #cga repres5ts ! sep>at+ space betwe5 two (fices4 ,! call+ subscrib]'s l9e 9 ! fir/ (fice is %[n at ! extreme left & ! call$ subscrib]'s l9e 9 ! second (fice is %[n at ! extreme "r4 ,bo? ( ^! l9es are /&>d multiple swit*bo>d l9es ( ! =m already discuss$4 ,! equipm5t illu/rat$ 9 ! fir/ (fice is t ( an ,a-bo>d1 ! cord circuit %[n be+ t ( ! regul> ,a-op]ator4 ,! outgo+ trunk jacks connect+ ) ! trunk lead+ to ! o!r (fice are1 x w be und]/ood1 multipl$ ?r\gh ! ,a-sections ( ! bo>d & conta9 no relay equipm5t1 b ! te/ r+s are connect$ to gr\nd ?r\gh a resi/ance coil #a1 :i* takes ! place ( ! cut-(f relay w9d+ ( a regul> l9e s f> z te/ conditions & sup]visory relay op]ation are conc]n$4 ,! equipm5t illu/rat$ 9 ! second (fice is t ( a ,b-bo>d1 x be+ und]/ood t ! call$ subscrib]'s l9e is multipl$ ?r\gh bo? ! ,a- & ,b-bo>ds at t (fice4 ,! "p ( ! equipm5t t is at ?is po9t unfamili> to ! read] is1 !re=e1 ! cord circuit at ! ,b-op]ator's bo>d4 ,?is includes1 broadly speak+1 ! means3 7#a7 = furni%+ batt]y curr5t to ! call$ subscrib]2 7#b7 = accompli%+ ! r++ ( ! call$ subscrib] & = automatically /opp+ ! r++ :5 he %all respond2 7#c7 = p]=m+ ! ord9>y swit*+ functions 9 connection ) ! relays ( ! call$ subscrib]'s l9e 9 j ! same way t an ,a-op]ator's cord c>ries out ^! functions2 & 7#d7 = caus+ ! op]ation ( ! call+ sup]visory relay ( ! ,a-op]ator's cord circuit 9 j ! same mann]1 "u control ( ! connect$ call$ subscrib]1 z if t subscrib]'s l9e _h be5 connect$ directly to ! ,a-op]ator's cord circuit4 ,illu/ration3 ,fig4 #cga4 ,int]-,(fice ,connection--,we/]n ,electric ,sy/em ,! op]ation ( ^! devices 9 ! ,b-op]ator's cord circuit may be be/ und]/ood by foll[+ ! e/abli%m5t ( ! connection4 ,assum+ t ! call+ subscrib] 9 ! fir/ (fice desires a connection ) ! subscrib]'s l9e %[n 9 ! second (fice1 & t ! ,a-op]ator at ! fir/ (fice has answ]$ ! call1 %e w !n communicate by ord] wire ) ! ,b-op]ator at ! second (fice1 /at+ ! numb] ( ! call$ subscrib] & receiv+ f t op]ator 9 return ! numb] ( ! trunk to be employ$4 ,! two op]ators w !n proce$ simultane\sly to e/abli% ! connection1 ! ,a-op]ator ins]t+ ! call+ plug into ! outgo+ trunk jack1 & ! ,b-op]ator ins]t+ ! trunk plug into ! multiple jack ( ! call$ subscrib]'s l9e aft] te/+4 ,we w assume at fir/ t ! call$ subscrib]'s l9e is f\nd idle & t bo? ( ! op]ators complete _! respective portions ( ! "w at ! same "t & we w consid] fir/ ! condition ( ! call+ sup]visory relay at ! ,a-op]ator's position4 ,! circuit ( ! call+ sup]visory lamp w h be5 clos$ ?r\gh ! resi/ance coil #a connect$ ) ! outgo+ trunk jacks & ! lamp w be light$ because1 z w be %[n1 x is n yet %unt$ out by ! op]ation ( its associat$ sup]visory relay4 ,trac+ ! circuit ( ! call+ sup]visory relay ( ! ,a-op]ator's circuit1 x w be f\nd to pass f ! live side ( ! batt]y to ! r+ side ( ! trunk circuit ?r\gh "o w9d+ ( ! repeat+ coil ( ! ,b-op]ator's cord2 beyond ?is ! circuit is op51 s9ce no pa? exi/s ?r\gh ! cond5s] #b bridg$ across ! trunk circuit or ?r\gh ! normally op5 contacts ( ! relay #c connect$ 9 ! talk+ circuit ( ! trunk4 ,! association ( ?is relay #c ) ! repeat+ coil & ! batt]y ( ! trunk is se5 to be j ! same z t ( a sup]visory relay 9 ! ,a-op]ator's cord1 & x is cle>1 !re=e1 t ?is relay #c w n be en]giz$ until ! call$ subscrib] has respond$4 ,:5 x is en]giz$ x w complete ! pa? to gr\nd ?r\gh ! ,a-op]ator's call+ sup]visory relay & op]ate to %unt out ! ,a-op]ator's call+ sup]visory lamp 9 j ! same mann] z if ! ,a-op]ator's call+ plug _h be5 connect$ directly ) ! l9e ( ! call+ subscrib]4 ,9 o!r words1 ! call$ subscrib] 9 ! second (fice controls ! relay #c1 :i*1 9 turn1 controls ! call+ sup]visory relay ( ! ,a-op]ator1 :i*1 9 turn1 %unts out its lamp4 ,! connection be+ complet$ betwe5 ! two subscrib]s1 ! ,b-op]ator depresses "o or ! o!r ( ! r++ keys #e or #f1 accord+ to :i* p>ty on ! l9e is call$1 assum+ t x is a two-p>ty l9e4 ,x w be notic$ t ! spr+s ( ^! r++ keys are n s]ially arrang$ 9 ! talk+ circuit1 b ! cutt+ (f ( ! trunk circuit back ( ! r++ keys is accompli%$ by ! set ( spr+s %[n j at ! left ( ! r++ keys1 :i* set ( spr+s #g is op]at$ :5ev] ei!r "o ( ! r++ keys is depress$4 ,an auxili>y pair ( contacts1 %[n j bel[ ! gr\p ( spr+s #g1 is also op]at$ me*anically :5ev] ei!r "o ( ! r++ keys is depress$1 & ?is s]ves to close "o ( two normally op5 po9ts 9 ! circuit ( ! r++-key hold+ magnet #h4 ,?is hold+ magnet #h is s arrang$ ) respect to ! contacts ( ! r++ key t :5ev] any "o ( !m is depress$ by ! op]ator1 x w be held depress$ z long z ! magnet is en]giz$ j ! same z if ! op]ator kept h] f+] on ! key4 ,! o!r normally op5 po9t 9 ! circuit ( ! hold+ magnet #h is at ! l[] pair ( contacts ( ! te/ & hold+ relay #i4 ,?is relay is op]at$ :5ev] ! trunk plug is ins]t$ 9 ! jack ( a call$ l9e1 reg>dless ( ! position ( ! subscrib]'s equipm5t on t l9e4 ,! circuit may be trac$ f ! live side ( ! batt]y ?r\gh ! trunk disconnect lamp #d1 coil #i1 sleeve /r& ( cord1 & to gr\nd ?r\gh ! cut-(f relay ( ! l9e4 ,! ins]tion ( ! trunk plug into ! jack ?us leaves ! completion ( ! hold+-magnet circuit dep5d5t only ^u ! auxili>y contact on ! r++ key1 &1 !re=e1 z soon z ! op]ator presses ei!r "o ( ^! keys1 ! clut* magnet is en]giz$ & ! key is held d[n1 s t r++ curr5t cont9ues to fl[ at regul> int]vals to ! call$ subscrib]'s /ation4 ,! r++ curr5t issues f ! g5]ator #aj1 b ! supply circuit f x is p]iodically int]rupt$ by ! commutator #aa ge>$ to ! r++-ma*9e %aft4 ,?is p]iodically int]rupt$ r++ curr5t passes to ! r++-key contacts ?r\gh ! coil ( ! r++ cut-(f relay #ab1 & !nce to ! subscrib]'s l9e4 ,! r++ curr5t is1 h[ev]1 insuffici5t to cause ! op]ation ( ?is relay #ab z long z ! high resi/ance & imp$ance ( ! subscrib]'s bell & cond5s] are 9 ! circuit4 ,x is1 h[ev]1 suffici5tly s5sitive to be op]at$ by ?is r++ curr5t :5 ! subscrib] responds & ?us sub/itutes ! comp>atively l[ resi/ance & imp$ance pa? ( 8 talk+ app>atus = ! previ\s pa? ?r\gh 8 bell4 ,! pull+ up ( ! r++ cut-(f relay #ab breaks a ?ird normally clos$ contact 9 ! circuit ( ! hold+ coil #h1 de-en]giz+ t coil & releas+ ! r++ key1 ?us cutt+ (f r++ curr5t4 ,!re is a ?ird bru% on ! commutator #aa connect$ ) ! live side ( ! c5tral batt]y1 & ?is is m]ely = ! purpose ( assur+ ! en]giz+ ( ! r++ cut-(f relay #ab1 %\ld ! subscrib] respond dur+ ! int]val :ile ! commutator #aa held ! r++ curr5t cut (f4 ,! relay #ab may ?us be en]giz$ ei!r f ! batt]y1 if ! subscrib] responds dur+ a p]iod ( sil5ce ( 8 r+]1 or f ! g5]ator #aj1 if ! subscrib] responds dur+ a p]iod :ile 8 bell is s\nd+2 9 ei!r case ! r++ curr5t w be promptly cut (f by ! release ( ! r++ key4 ,! trunk op]ator's disconnect lamp is %[n at #d1 & x is to be rememb]$ t ?is lamp is light$ only :5 ! ,a-op]ator takes d[n ! connection at h] end1 & also t ?is lamp is entirely out ( ! control ( ! subscrib]s1 ! conditions :i* det]m9e its illum9ation be+ dep5d5t on ! positions ( ! op]ators' plugs at ! two ends ( ! trunk4 ,) bo? plugs up1 ! lamp #d w receive curr5t1 b w be %unt$ to prev5t its illum9ation4 ,! pa? ov] :i* x receives ?is curr5t may be trac$ f batt]y ?r\gh ! lamp #d1 !nce ?r\gh ! coil ( ! relay #i & ! cut-(f relay ( ! call$ subscrib]'s l9e4 ,?is curr5t w\ld be suffici5t to illum9ate ! lamp1 b ! lamp is %unt$ by a circuit :i* may be trac$ f ! live side ( batt]y ?r\gh ! contact ( ! relay #ac1 clos$ at ! "t1 & ?r\gh ! coil ( ! trunk cut-(f relay coil #ad4 ,! resi/ance ( ?is coil is s proportion$ to ! o!r p>ts ( ! circuit z to prev5t ! illum9ation ( ! lamp j exactly z 9 ! case ( ! %unt+ resi/ances ( ! lamps 9 ! ,a-op]ator's cord4 ,x w be se51 !re=e1 t ! supply ( curr5t to ! trunk disconnect lamp is dep5d5t on ! trunk plug be+ ins]t$ into ! jack ( ! subscrib]'s l9e & t ! %unt+ out ( ?is lamp is dep5d5t on ! en]gization ( ! relay #ac4 ,?is relay #ac is en]giz$ z long z ! ,a-op]ator's plug is ins]t$ into ! outgo+ trunk jack1 ! pa? ( ! en]giz+ circuit be+ trac$ f ! live side ( ! batt]y at ! second (fice ?r\gh ! "r-h& w9d+ ( ?is relay1 !nce ov] ! tip side ( ! trunk to gr\nd at ! fir/ (fice4 ,f ?is x foll[s t z long z bo? plugs are up1 ! disconnect lamp w receive curr5t b w be %unt$ out1 & z soon z ! ,a-op]ator pulls d[n ! connection1 ! relay #ac w be de-en]giz$ & w ?us remove ! %unt f ab\t ! lamp1 all[+ its illum9ation4 ,! left-h& w9d+ ( ! relay #ac p]=ms no op]at+ function1 b is m]ely to ma9ta9 ! balance ( ! talk+ circuit1 x be+ bridg$ dur+ ! connection f ! r+ side ( ! trunk to gr\nd 9 ord] to balance ! bridge connection ( ! "r-h& coil f ! live side ( batt]y to ! tip side ( ! trunk circuit4 ,! relay #ad1 already ref]r$ to z =m+ a %unt = ! trunk disconnect lamp1 has = its function ! keep+ ( ! talk+ circuit ?r\gh ! trunk op5 until su* "t z ! relay #ac op]ates1 ?is be+ purely an insurance aga9/ unnecess>y r++ ( a subscrib] 9 case ! ,a-op]ator %\ld by mi/ake plug into ! wrong trunk4 ,x is n1 !re=e1 until ! ,a-op]ator has plugg$ into ! trunk & ! relay #ac has be5 op]at$ to cause ! en]gization ( ! relay #ad t ! r++ ( ! call$ subscrib] c occur1 reg>dless ( :at ! ,b-op]ator may h done4 ,! relay #i has an additional function to t ( help+ to control ! circuit ( ! r++-key hold+ magnet4 ,?is is ! hold+ ( ! te/ circuit complete until ! op]ator has te/$ & made a connection & !n automatically op5+ x4 ,! te/ circuit ( ! ,b-op]ator's trunk may be trac$1 at ! "t ( te/+1 f ! ?imble ( ! multiple jack "u te/1 ?r\gh ! tip ( ! cord1 !nce ?r\gh ! upp]mo/ pair ( contacts ( ! relay #i to gr\nd ?r\gh a w9d+ ( ! ,b-op]ator's induction coil4 ,aft] ! te/ has be5 made & ! plug ins]t$1 ! relay #i1 :i* is op]at$ by ! ins]tion ( ! plug1 acts to op5 ?is te/ circuit & at ! same "t complete ! tip side ( ! cord circuit4 ,9 ! upp] portion ( ,fig4 #cga ! ord]-wire connections1 by :i* ! ,a-op]ator & ! ,b-op]ator communicate1 are indicat$4 ,x mu/ be rememb]$ 9 connection ) ^! t ! ,a-op]ator only has control ( ?is connection1 ! ,b-op]ator be+ compell$ necess>ily to he> :atev] ! ,a-op]ators h to say :5 ! ,a-op]ators come 9 on ! circuit4 ,illu/ration3 ,fig4 #cgb4 ,incom+ ,trunk ,circuit ,! incom+ trunk circuit employ$ by ! ,we/]n ,electric ,company = f\r-p>ty l9e r++ is %[n 9 ,fig4 #cgb1 x be+ necess>ily some:at modifi$ f t %[n 9 ,fig4 #cga1 :i* is adapt$ = two-p>ty l9e r++ only4 ,9 addition to ! provision ( ! f\r-p>ty l9e r++ keys1 by :i* positive or negative pulsat+ curr5t is receiv$ ov] ei!r limb ( ! l9e1 & to ! provision ( ! regul> alt]nat+ curr5t r++ key = r++ on s+le p>ty l9es1 x is necess>y 9 ! r++ cut-(f relay to provide = keep+ ! alt]nat+ & ! pulsat+ r++ curr5ts entirely sep>ate4 ,= ?is reason1 ! r++ cut-(f relay #ab is provid$ ) two w9d+s1 t at ! "r be+ 9 ! pa? ( ! alt]nat+ r++ curr5ts t are suppli$ to ! alt]nat+ curr5t key1 & t at ! left be+ 9 ! gr\nd return pa? = all ( ! pulsat+ r++ curr5ts suppli$ to ! pulsat+ keys4 ,) ?is explanation x is believ$ t ?is circuit w be und]/ood f :at has be5 said 9 connection ) ,fig4 #cga4 ,! op]ation ( ! hold+ coil #h is ! same 9 ea* case1 ! hold+ magnet 9 ,fig4 #cgb s]v+ to hold depress$ any "o ( ! five r++ keys t may h be5 us$ 9 call+ ! subscrib]4 ,illu/ration3 ,,automatic ,,equipm5t1 ,,ma9 ,,(fice1 ,,b]keley1 ,,cali=nia ,a ,feature ( ,int]e/ ,"h is ,t ! ,cem5t ,floor is ,treat$ ) a ,fill] & ,pa9t$1 ) ,no ,o!r ,cov]+4 ,illu/ration3 ,fig4 #cgc4 ,we/]n ,electric ,trunk ,r++ ,key ,! /&>d f\r-p>ty l9e1 trunk r++ key ( ! ,we/]n ,electric ,company is %[n 9 ,fig4 #cgc4 ,9 ?is ! v>i\s keys op]ate n by pressure b r by be+ pull$ by ! f+] ( ! op]ator 9 su* a way z to subject ! key %aft to a twi/+ movem5t4 ,! hold+ magnet lies on ! side opposite to t %[n 9 ! figure & ext5ds along ! full l5g? ( ! set ( keys1 ea* key %aft be+ provid$ ) an armature :i* is held by ?is magnet until ! magnet is de-en]giz$ by ! action ( ! r++ cut-(f relay4 ,illu/ration3 ,fig4 #cgd4 ,trunk ,relay ,illu/ration3 ,fig4 #cge4 ,trunk ,relay ,! /&>d trunk relays employ$ by ! ,we/]n ,electric ,company 9 connection ) ! circuits j describ$ are %[n 9 ,figs4 #cgd & #cge4 ,9 ea* case ! du/-cap or %ield is also %[n4 ,! relay ( ,fig4 #cgd is simil> to ! regul> cut-(f relay & is ! "o us$ = relays #i & #ad ( ,figs4 #cga & #cgb4 ,! relay ( ,fig4 #cge is some:at simil> to ! subscrib]'s l9e relay 9 t x has a tilt+ armature1 & is ! "o us$ at #ac 9 ,figs4 #cga & #cgb4 ,! trunk relay #c 9 ,figs4 #cga & #cgb is ! same z ! ,a-op]ator's sup]visory relays already discuss$4 ,x has be5 /at$ t "u c]ta9 circum/ances ,b-op]ator's trunk circuits devoid ( r++ keys1 & consequ5tly ( all keys1 may be employ$4 ,?is1 s f> z ! practice ( ! ,bell companies is conc]n$1 is true only 9 (fices :]e !re are no p>ty l9es1 or :]e1 z 9 _m ( ! ,*icago (fices1 ! p>ty l9es are work$ on ! jack p] /ation basis4 ,9 jack p] /ation work+1 ! selection ( ! /ation on a p>ty l9e is det]m9$ by ! jack on :i* ! plug is put1 r ?an by a r++ key1 & h5ce ! keyless trunk may be employ$4 ,illu/ration3 ,fig4 #cgf4 ,keyless ,trunk ,a keyless trunk z us$ 9 ,new ,york is %[n 9 ,fig4 #cgf4 ,?is has no manually op]at$ keys :atev]1 & ! relay #ag1 :5 x is op]at$1 e/abli%es connection betwe5 ! r++ g5]ator & ! conductors ( ! trunk plug4 ,! relays #c1 #ac1 & #ab op]ate 9 a mann] id5tical ) ^? be>+ correspond+ numb]s 9 ,fig4 #cga4 ,z soon z ! trunk op]ator plugs into ! multiple jack ( ! call$ subscrib]1 ! relay #af w op]ate = ! same reason t ! relay #i op]at$ 9 connection ) ,fig4 #cga4 ,! trunk disconnect lamp w receive curr5t1 b if ! op]ator has already e/abli%$ connection ) ! o!r end ( ! trunk1 ?is lamp w n be light$ because %unt$ by ! relay #ag1 due to ! pull+ up ( ! armature ( ! relay #ac4 ,! relay #ae plays no "p 9 ! op]ation s f> describ$1 because ( ! fact t its w9d+ is %ort-circuit$ by its own contacts & ^? ( relay #ab1 :5 ! latt] is n en]giz$4 ,z a result ( ! op]ation ( ! relay #ag1 r++ curr5t is s5t to l9e1 ! supply circuit includ+ ! coil ( ! relay #ab4 ,z soon z ! subscrib] responds to ?is r++ curr5t1 ! armature ( ! relay #ab is pull$ up1 ?us break+ ! %unt ab\t ! relay #ae1 :i*1 !re=e1 />ts to op]ate 9 s]ies ) ! relay #ag1 b z its armatures assume _! attract$ position1 ! relay #ag is cut out ( ! circuit1 ! coil ( ! relay #ae be+ sub/itut$ = t ( ! relay #ag 9 ! %unt pa? ar\nd ! lamp #d4 ,! relay #ag falls back & cuts (f ! r++ curr5t4 ,! relay #ae n[ occupies ! place ) respect to ! %unt ar\nd ! lamp #d t ! relay #ag =m]ly did1 ! cont9uity ( ?is %unt be+ det]m9$ by ! en]gization ( ! relay #ac4 ,:5 ! ,a-op]ator at ! di/ant ex*ange )draws ! call+ plug f ! trunk jack1 ?is relay #ac becomes de-en]giz$1 break+ ! %unt ab\t ! lamp #d & p]mitt+ ! display ( t lamp z a signal to ! op]ator to take d[n ! connection4 ,x may be ask$ :y ! fall+ back ( relay #ae w n aga9 en]gize relay #ag & ?us cause a false r+ on ! call$ subscrib]4 ,?is w n occur because bo? ! relays #ae & #ag dep5d = _! en]gization on ! closure ( ! contacts ( ! relay #ac1 & :5 ?is falls back ! relay #ag _c aga9 be en]giz$ ev5 ?\gh ! relay #ae assumes its normal position4 ,kellogg ,trunk ,circuits4 ,! provision = prop] work+ ( trunk circuits 9 connection ) ! two-wire multiple swit*bo>ds is n an altoge!r easy matt]1 ow+ p>ticul>ly to ! small] numb] ( wires available 9 ! plug circuits4 ,x has be5 work$ out 9 a highly +5i\s way1 h[ev]1 by ! ,kellogg ,company1 & a diagram ( _! incom+ trunk circuit1 toge!r ) ! associat$ circuits involv$ 9 an int]-(fice connection1 is %[n 9 ,fig4 #cgg4 ,illu/ration3 ,fig4 #cgg4 ,int]-,(fice ,connection--,kellogg ,sy/em ,?is figure illu/rates a connection f a regul> two-wire multiple subscrib]'s l9e 9 "o (fice1 ?r\gh an ,a-op]ator's cord circuit !re1 to ! outgo+ trunk jacks at t (fice1 !nce ?r\gh ! incom+ trunk circuit at ! o!r (fice to ! regul> two-wire multiple subscrib]'s l9e at t second (fice4 ,! portion ( ?is diagram to be p>ticul>ly consid]$ is t ( ! ,b-op]ator's cord circuit4 ,! trunk circuit t]m9ates 9 ! multipl$ outgo+ trunk jacks at ! fir/ (fice1 ! trunk ext5d+ betwe5 (fices consi/+1 ( c\rse1 ( b two wires4 ,we w fir/ consid] ! control ( ! call+ sup]visory lamp 9 ! ,a-op]ator's cord circuit1 x be+ rememb]$ t ?is control mu/ be f ! call$ subscrib]'s /ation4 ,x w be notic$ t ! left-h& armature ( ! relay #a s]ves normally to bridge ! w9d+ ( relay #b across ! cord circuit ar\nd ! cond5s] #c4 ,:51 h[ev]1 ! relay #a pulls up1 ! coil ( relay #d is sub/itut$ 9 ?is bridge connection across ! trunk4 ,! relay #b has a v high resi/ance w9d+--ab\t #ae1jjj ohms--& ?is resi/ance is s great t ! tip sup]visory relay ( ! ,a-op]ator's cord w n pull up ?r\gh x4 ,z a result1 :5 ?is relay is bridg$ across ! trunk circuit1 ! tip relay on ! call+ side ( ! ,a-op]ator's cord circuit is de-en]giz$1 j z if ! trunk circuit 7 op51 & ?is results 9 ! light+ ( ! ,a-op]ator's call+ sup]visory lamp4 ,! w9d+ ( ! relay #d1 h[ev]1 is ( l[ resi/ance--ab\t #ej ohms--& :5 ?is is sub/itut$ = ! high-resi/ance w9d+ ( ! relay #b1 ! tip relay on ! call+ side ( ! ,a-op]ator's cord is en]giz$1 result+ 9 ! ext+ui%+ ( ! call+ sup]visory lamp4 ,! illum9ation ( ! ,a-op]ator's call+ sup]visory lamp dep5ds1 !re=e1 on :e!r ! high-resi/ance relay #b1 or ! l[-resi/ance relay #d1 is bridg$ across ! trunk1 & ?is dep5ds on :e!r ! relay #a is en]giz$ or n4 ,! relay #a1 be+ bridg$ f ! tip side ( ! trunk circuit to gr\nd & s]v+ z ! means ( supply ( batt]y curr5t to ! call$ subscrib]1 is op]at$ :5ev] ! call$ subscrib]'s receiv] is remov$ f its hook4 ,!re=e1 ! call$ subscrib]'s hook controls ! op]ation ( ?is relay #a1 :i*1 9 turn1 controls ! conditions :i* cause ! illum9ation or d>kness ( ! call+ sup]visory lamp at ! di/ant (fice4 ,assum+ t ! ,a-op]ator has receiv$ & answ]$ a call1 & has communicat$ ) ! ,b-op]ator1 tell+ h] ! numb] ( ! call$ subscrib]1 & has receiv$1 9 turn1 ! numb] ( ! trunk to be us$1 & t bo? op]ators h put up ! connection1 !n x w be cle> f :at has be5 said t ! call+ sup]visory lamp ( ! ,a-op]ator w be light$ until ! call$ subscrib] removes 8 receiv] f its hook1 because ! tip relay 9 ! ,a-op]ator's cord circuit w n pull up ?r\gh ! #ae1jjj-ohm resi/ance w9d+ ( ! relay #b4 ,z soon z ! subscrib] responds1 h[ev]1 ! relay #a w be op]at$ by ! curr5t :i* supplies 8 transmitt]4 ,?is w sub/itute ! l[-resi/ance w9d+ ( ! relay #d = ! high-resi/ance w9d+ ( ! relay #b1 & ?is w p]mit ! en]giz+ ( ! tip sup]visory relay ( ! ,a-op]ator & put out ! call+ sup]visory lamp at h] position4 ,z 9 ! ,we/]n ,electric circuit1 !re=e1 ! control ( ! ,a-op]ator's call+ sup]visory lamp is f ! call$ subscrib]'s /ation & is relay$ back ov] ! trunk to ! orig9at+ (fice4 ,9 ?is circuit1 manual in/ead ( automatic r++ is employ$1 !re=e1 unlike ! ,we/]n ,electric circuit1 means mu/ be provid$ = notify+ ! ,b-op]ator :5 ! call+ subscrib] has answ]$4 ,?is is done by plac+ at ! ,b-op]ator's position a r++ lamp associat$ ) ea* trunk cord1 :i* is illum9at$ :5 ! ,b-op]ator places ! plug ( ! incom+ trunk into ! multiple jack ( ! subscrib]'s l9e1 & rema9s illum9at$ until ! subscrib] has answ]$4 ,?is is accompli%$ 9 ! foll[+ mann]3 :5 ! op]ator plugs into ! jack ( ! l9e call$1 relay #e is en]giz$ b is imm$iately de-en]giz$ by ! disconnect+ ( ! circuit ( ?is relay f ! sleeve conductor ( ! cord :5 ! r++ key is depress$1 ! selection ( ! r++ key be+ det]m9$ by ! p>ticul> p>ty on ! l9e desir$4 ,^! r++ keys h associat$ ) !m a set ( spr+s #i1 :i* spr+s are op]at$ :5 any "o ( ! r++ keys is depress$4 ,?us1 ) a r++ key depress$ & ! relay #e de-en]giz$1 ! r++ lamp w be illum9at$ by means ( a circuit z foll[s3 f ! live side ( ! batt]y1 ?r\gh ! r++ lamp #ab1 ?r\gh ! back contact & armature ( ! relay #f1 ?r\gh ! armature & contact ( relay #d1 !n ?r\gh ! armature & front contact ( relay #b--:i* at ?is "t is ! relay bridg$ across ! trunk &1 !re=e1 en]giz$--& !nce ?r\gh ! back contact & armature ( relay #e to gr\nd4 ,:5 ! subscrib] removes 8 receiv] f ! hook1 ! relay #a w become en]giz$ z previ\sly describ$1 & w1 !re=e1 op]ate relay #f to break ! circuit ( ! r++ lamp4 ,! circuit ?us e/abli%$ by ! op]ation ( relay #a is z foll[s3 f ! live side ( batt]y1 ?r\gh ! w9d+ ( relay #f1 ?r\gh ! armature & contact ( relay #a1 ?r\gh ! armature & contact ( relay #d1 ?r\gh ! armature & front contact ( relay #b1 !nce ?r\gh ! armature & back contact ( relay #e to gr\nd4 ,z soon z ! ,b-op]ator notes t ! r++ lamp has gone out1 %e kn[s t no fur!r r++ is requir$ on t l9e1 ?us all[+ ! op]ation ( relay #e & accompli%+ ! lock+ out ( ! r++ lamp dur+ ! rema9d] ( t connection4 ,! relay #f1 aft] hav+ once pull$ up1 rema9s lock$ up ?r\gh ! re> contact ( ! left-h& armature ( relay #e & gr\nd1 until ! plug is remov$ f ! jack4 ,at ! end ( ! conv]sation1 :5 ! ,a-op]ator has disconnect$ h] cord circuit on ! illum9ation ( ! sup]visory signals1 bo? relays #b & #d w be 9 an unop]at$ condition & w provide a circuit = illum9at+ ! disconnect lamp associat$ ) ! ,b-op]ator's cord4 ,?is circuit may be trac$ z foll[s3 f batt]y ?r\gh ! disconnect lamp1 ?r\gh ! armatures & contacts ( relays #b & #d1 !nce ?r\gh ! front contact & armature ( relay #e to gr\nd1 ?us illum9at+ ! disconnect lamp4 ,! r++ lamp w n be re-illum9at$ at ?is "t1 due to ! fact t x has be5 previ\sly lock$ out by relay #f4 ,! op]ator !n removes ! plug f ! jack ( ! l9e call$1 & ! app>atus 9 ! trunk circuit is re/or$ to normal condition4 ,9 ! circuit %[n only keys are provid$ = r++ two p>ties4 ,?is circuit1 h[ev]1 is n conf9$ to ! use ( two-p>ty l9es1 b may be ext5d$ to f\r p>ties by simply duplicat+ ! r++ keys & by connect+ !m ) ! prop] curr5t = selectively r++ ! o!r /ations4 ,! me?od ( det]m9+ z to :e!r ! call$ l9e is free or busy is simil> to t previ\sly describ$ = ! ,a-op]ator's cord circuit :5 mak+ a local connection1 & diff]s only 9 ! fact t 9 ! case ( ! trunk cord ! te/ circuit is controll$ ?r\gh ! contacts ( a relay1 :]eas 9 ! case ( ! ,a-op]ator's cord1 ! te/ circuit 0 controll$ ?r\gh ! contacts ( ! li/5+ key4 ,! function ( ! resi/ance #aj & ! batt]y connect$ !reto is ! same z has be5 previ\sly describ$4 ,! g5]al make-up ( trunk+ swit*bo>d sections is n greatly diff]5t f t ( ! ord9>y swit*bo>d sections :]e no trunk+ is involv$4 ,9 small ex*anges :]e r+-d[n trunks are employ$1 ! trunk l9e equipm5t is m]ely add$ to ! regul> jack & drop equipm5t ( ! swit*bo>d4 ,9 common-batt]y multiple swit*bo>ds ! ,a-bo>ds diff] 9 no respect f ! /&>d s+le (fice multiple bo>ds1 except t imm$iately above ! answ]+ jacks & bel[ ! multiple !re are arrang$ 9 suitable numb]s ! jacks ( ! outgo+ trunks4 ,:]e ! (fices are comp>atively small1 ! incom+ trunk portions ( ! ,b-bo>ds are usually m]ely a cont9uance ( ! ,a-bo>ds1 ! subscrib]'s multiple be+ cont9u\s ) & diff]+ 9 no respect f t on ! ,a-sections4 ,in/ead ( ! usual pairs ( ,a-op]ators' plugs1 cords1 & sup]visory equipm5t1 !re are on ! key & plug %elves ( ^! ,b-sections ! incom+ trunk plugs & _! associat$ equipm5t4 ,9 l>ge (fices x is cu/om>y to make ! ,b-bo>d entirely sep>ate f ! ,a-bo>d1 al?\gh ! g5]al *>act]i/ics ( con/ruction rema9 ! same4 ,! reason = sep>ate ,a- & ,b-swit*bo>ds 9 l>ge ex*anges is to provide = indep5d5t gr[? ( ea* )\t ! gr[? ( ei!r int]f]+ ) ! o!r4 ,a portion ( an incom+ trunk1 or ,b-bo>d1 is %[n 9 ,fig4 #cgh4 ,! multiple is z usual1 &1 ( c\rse1 !re are no outgo+ trunk jacks nor regul> cord pairs4 ,in/ead ! key & plug %elves are provid$ ) ! incom+-trunk plug equipm5ts1 ?irty ( ^! be+ ab\t ! usual quota assign$ to ea* op]ator's position4 ,9 multi-(fice ex*anges1 employ+ _m c5tral (fices1 su*1 = in/ance1 z ^? 9 ,new ,york or ,*icago1 x is frequ5tly f\nd t ne>ly all ( ! calls t orig9ate 9 "o (fice are = subscrib]s ^: l9es t]m9ate 9 "s o!r (fice4 ,9 o!r words1 ! numb] ( calls t h to be trunk$ to o!r (fices is greatly 9 excess ( ! numb] ( calls t may be h&l$ ?r\gh ! multiple ( ! ,a-bo>d 9 :i* !y orig9ate4 ,x is n infrequ5t to h ! p]c5tage ( trunk$ calls run z high z #ge p] c5t ( ! total numb] ( calls orig9at+ 9 any "o (fice1 & 9 "s ( ! (fices 9 ! l>g] cities ?is p]c5tage runs high] ?an #ij p] c5t4 ,illu/ration3 ,fig4 #cgh4 ,section ( ,trunk ,swit*bo>d ,illu/ration3 ,fig4 #cgi4 ,section ( ,p>tial ,multiple ,swit*bo>d ,?is fact has br\ght up = consid]ation ! problem z to :e!r1 :5 ! nature ( ! traffic is su* t only a v small portion ( ! calls c be h&l$ 9 ! (fice :]e !y orig9ate1 x is wor? :ile to employ ! multiple t]m9als = ! subscrib]s' l9es on ! ,a-bo>ds4 ,9 o!r words1 if s great a proportion z #ij p] c5t ( ! calls h to be trunk$ any way1 is x wor? :ile to provide ! great exp5se ( a full multiple on all ! sections ( ! ,a-bo>d 9 ord] to make x possible to h&le ! rema9+ #aj p] c5t ( ! calls directly by ! ,a-op]ators8 ,z a result ( ?is consid]ation x has be5 g5]ally conc$$ t :]e su* a v great p]c5tage ( trunk+ 0 necess>y1 ! full multiple ( ! subscrib]s' l9es on ea* section 0 n w>rant$1 & :at is kn[n z ! p>tial multiple bo>d has come into exi/5ce 9 l>ge manual ex*anges4 ,9 ^! ! regul> subscrib]s' multiple is entirely omitt$ f ! ,a-bo>d1 all subscrib]s' calls be+ h&l$ ?r\gh outgo+ trunk jacks connect$ by trunks to ,b-bo>ds 9 ! same z well z o!r (fices4 ,9 ^! p>tial multiple ,a-bo>ds1 ! answ]+ jacks are multipl$ a few times1 usually twice1 s t calls on ea* l9e may be answ]$ f m ?an "o position4 ,?is multipl+ ( answ]+ jacks does n 9 any way take ! place ( ! regul> multipl+ 9 full multiple bo>ds1 s9ce 9 no case are ! calls complet$ ?r\gh ! multiple jacks4 ,x is done m]ely = ! purpose ( contribut+ to team "w betwe5 ! op]ators4 ,a portion ( su* a p>tial multiple ,a-bo>d is %[n 9 ,fig4 #cgi4 ,?is view %[s slightly m ?an "o section1 & ! regul> answ]+ jacks & lamps may be se5 at ! bottom ( ! jack space j above ! plugs4 ,above ^! are plac$ ! outgo+ trunk jacks1 ^? t are 9 use be+ indicat$ ) :ite designation /rips4 ,above ! outgo+ trunk jacks are plac$ ! multiples ( ! answ]+ jacks1 ^! n be+ provid$ ) lamps4 ,! p>tial multiple ,a-section ( ,fig4 #cgi is a portion ( ! swit*bo>d equipm5t ( ! same (fice to :i* ! trunk+ section %[n 9 ,fig4 #cgh belongs4 ,t ?is is a l>ge multiple bo>d may be ga!r$ f ! numb] ( multiple jacks 9 ! trunk+ section1 #h1djj be+ in/all$ ) room = #aj1ejj4 ,t ! bo>d is a portion ( an equipm5t belong+ to an ex*ange ( enorm\s proportions may be ga!r$ f ! numb] ( outgo+ trunk jacks %[n 9 ! ,a-bo>d1 & 9 ! great numb] ( ord]-wire keys %[n betwe5 ea* ( ! sets ( regul> cord-circuit keys4 ,! swit*bo>ds illu/rat$ 9 ^! two figures are ^? ( "o ( ! l>ge (fices ( ! ,new ,york ,telephone ,company on ,manhattan ,isl&1 & ! photographs 7 tak5 especially = ?is "w by ! ,we/]n ,electric ,company4 ,cable ,color ,code4 ,a great "p ( ! wir+ ( swit*bo>ds requires to be done ) insulat$ wires gr\p$ into cables4 ,9 ! wir+ ( manual swit*bo>ds z describ$ 9 ! sev5 prec$+ *apt]s1 & ( automatic & automanual sy/ems & ( private bran*-ex*ange & int]communicat+ sy/ems describ$ 9 succe$+ *apt]s1 cables =m$ z foll[s are widely us$3 ,t9n$ s(t copp] wires1 usually ( ,no4 #bb or ,no4 #bd ,b4 ,s4 gauge1 are insulat$1 fir/ ) two cov]+s ( silk1 !n ) "o cov]+ ( cotton4 ,! out] 7cotton7 insulation ( ea* wire is made ( :ite or ( dy$ ?reads4 ,if dy$1 ! color ei!r is solid r$1 black1 blue1 orange1 gre51 br[n1 or slate1 or x is /rip$1 by comb9+ "o ( ^? colors ) :ite or a rema9+ color4 ,! object ( color+ ! wires is to enable !m to be id5tifi$ by sight in/ead ( by electrical te/+4 ,wires s insulat$ are twi/$ into pairs1 *oos+ ! colors ( ! l9e & mate accord+ to a pr$et]m9$ plan4 ,an assortm5t ( ^! pairs !n is laid up spirally to =m ! cable core1 ov] :i* are plac$ c]ta9 wrapp+s & an out] braid4 ,a widely us$ =m ( swit*bo>d cable has pap] & lead foil wrapp+s ov] ! core1 & ! out] cotton braid f9ally is treat$ ) a fire-resi/+ pa9t4 ,,/&>d ,,color ,,code ,,= ,,cables ---------------------------------------- ------------------------ ,,mate ,,l9e ,,wire ---------------------------------------- ----- ,:ite ,r$ ,black ,r$-,:ite ,black-,:ite ---------------------------------------- -------------------- ,blue #a #ba #da #fa #ha ,orange #b #bb #db #fb #hb ,gre5 #c #bc #dc #fc #hc ,br[n #d #bd #dd #fd #hd ,slate #e #be #de #fe #he ,blue-,:ite #f #bf #df #ff #hf ,blue-,orange #g #bg #dg #fg #hg ,blue-,gre5 #h #bh #dh #fh #hh ,blue-,br[n #i #bi #di #fi #hi ,blue-,slate #aj #cj #ej #gj #ij ,orange-,:ite #aa #ca #ea #ga #ia ,orange-,gre5 #ab #cb #eb #gb #ib ,orange-,br[n #ac #cc #ec #gc #ic ,orange-,slate #ad #cd #ed #gd #id ,gre5-,:ite #ae #ce #ee #ge #ie ,gre5-,br[n #af #cf #ef #gf #if ,gre5-,slate #ag #cg #eg #gg #ig ,br[n-,:ite #ah #ch #eh #gh #ih ,br[n-,slate #ai #ci #ei #gi #ii ,slate-,:ite #bj #dj #fj #hj #ajj ---------------------------------------- -------------------- ,! num]als repres5t ! pair numb]s 9 ! cable4 ,! wires ( sp>e pairs usually are designat$ by solid r$ ) :ite mate = fir/ sp>e pair1 & solid black ) :ite mate = second sp>e pair4 ,individual sp>e wires usually are color$ r$-:ite = fir/ individual sp>e1 & black-:ite = second individual sp>e4 ,,*apt] ,,xxviii ,,fundam5tal ,,consid]ations ,,( ,,automatic ,,sy/ems ,def9ition4 ,! t]m automatic1 z appli$ to telephone sy/ems1 has come to ref] to ^? sy/ems 9 :i* ma*9es at ! c5tral (fice1 "u ! guidance ( ! subscrib]s1 d ! "w t is done by op]ators 9 manual sy/ems4 ,9 all automatic telephone sy/ems1 ! "w ( connect+ & disconnect+ ! l9es1 ( r++ ! call$ subscrib]1 ev5 ?\gh he mu/ be select$ f among ^? on a p>ty l9e1 ( refus+ to connect ) a l9e t is already 9 use1 & in=m+ ! call+ subscrib] t su* l9e is busy1 ( mak+ connections to trunk l9es & ?r\gh !m to l9es 9 o!r (fices & do+ ! same sort ( ?+s !re1 ( c\nt+ & record+ ! successful calls made by a subscrib]1 reject+ ! unsuccessful1 & ne>ly all ! ?\s& & "o o!r acts necess>y 9 telephone s]vice1 are p]=m$ )\t ! pres5ce ( any guid+ intellig5ce at ! c5tral (fice4 ,! fundam5tal object ( ! automatic sy/em is to d away ) ! c5tral-(fice op]ator4 ,9 ord] t ea* subscrib] may control ! mak+ ( 8 own connections !re is add$ to 8 /ation equipm5t a call transmitt+ device by ! manipulation ( :i* he causes ! c5tral-(fice me*anisms to e/abli% ! connections he desires4 ,we ?9k t ! automatic sy/em is "o ( ! mo/ a/oni%+ developm5ts ( human +5uity4 ,! work]s 9 ?is developm5t are wor?y ( p>ticul> notice4 ,f occupy+ a position 9 popul> reg>d 9 common ) long-hair$ m5 & %ort-hair$ wom5 !y h rec5tly appe>$ z sane1 reasonable m5 ) ! c\rage ( _! convictions &1 bett] yet1 ) ! ability to make _! convictions come true4 ,! sc(f]s h rema9$ to pray4 ,argum5ts ,aga9/ ,automatic ,idea4 ,naturally !re has be5 a bitt] fight aga9/ ! automatic4 ,^? :o h oppos$ x h cont5d$3 ,fir/3 t x is too complicat$ &1 !re=e1 c\ld be nei!r reliable or economical4 ,second3 t x is too exp5sive1 & t ! necess>y fir/ co/ c\ld n be ju/ifi$4 ,?ird3 t x is too inflexible & c\ld n adapt itself to special k9ds ( s]vice4 ,f\r?3 t x is all wrong f ! subscrib]s' po9t ( view z ! public w n tol]ate do+ its own op]at+4 ,complexity4 ,?is fir/ objection z to complexity1 & consequ5t alleg$ unreliability & lack ( economy %\ld be c>efully analyz$4 ,x too (t5 happ5s t a new inv5tion is ca/ into out] d>kness by ^? ^: op9ions c>ry weight by su* words z x _c "w2 x is too complicat$4 ,=tunately = ! _w1 ! pati5ce & =titude :i* m5 mu/ possess be=e !y c produce m]itori\s1 ?\gh intricate inv5tions1 are usually suffici5t to prev5t _! be+ cru%$ by any su* (fh& condemnation1 & ! te/ ( "t & s]vice is all[$ to become ! real crit]ion4 ,x w\ld be difficult to f9d an art t has gone =w>d z rapidly z telephony4 ,)9 its %ort life ( a little ov] ?irty ye>s x has gr[n f ! phase ( trifl+ ) a m]e toy to an affair ( mom5t\s importance to civilization4 ,!re has be5 a t5d5cy1 p>ticul>ly m>k$ dur+ rec5t ye>s1 t[>d great] complexity2 & probably e complicat$ new sy/em or piece ( app>atus has be5 r\ndly condemn$1 by ^? v]s$ 9 ! art z x 01 z be+ unable to survive on acc\nt ( its complication4 ,to illu/rate3 ,a prom95t telephone man1 9 argu+ aga9/ ! nickel-9-!-slot me?od ( *>g+ = telephone s]vice once said1 p>tly 9 je/1 ,! ,"l nev] int5d$ telephone s]vice to be giv5 9 t way4 ,?is1 :ile a little (f ! po9t1 is ak9 to ! sweep+ aside ( new telephone sy/ems on ! sole gr\nd t !y are complicat$4 ,^! are n real reasons1 b r conv5i5t ways ( dispos+ ( vex+ problems ) a m9imum am\nt ( labor4 ,important que/ions ly+ at ! v root ( ! developm5t ( a great indu/ry may n be put aside p]man5tly 9 ?is (fh& way4 ,! ,"l has nev]1 s f> z we "k1 indicat$ j :at 8 int5tions 7 9 ! matt] ( nickel s]vice2 & no "o has ev] %[n yet j :at degree ( complexity w prev5t a telephone sy/em f work+4 ,x is safe to say t1 if o!r ?+s are equal1 ! simpl] a ma*9e is1 ! bett]2 b simplicity1 ?\gh desirable1 is n all-important4 ,complexity is w>rant$ if x c %[ en\gh advantages4 ,if "o takes a n>r[ view ( ! developm5t ( ?+s me*anical & electrical1 he w say t ! tr5d is t[>d simplicity4 ,! me*anic 9 design+ a ma*9e to p]=m c]ta9 functions tries to make x z simple z possible4 ,he designs & re-designs1 mak+ "o "p d ! "w ( two & contriv+ s*emes = r$uc+ ! complexity ( action & =m ( ea* rema9+ "p4 ,8 :ole tr5d is away f complication1 & ?is is z x %\ld be4 ,o!r ?+s be+ equal1 ! simpl] ! bett]4 ,a broad view1 h[ev]1 w %[ t ! arts are becom+ m & m complicat$4 ,take ! implem5ts ( ! art ( writ+3 ,! typewrit] is va/ly m complicat$ ?an ! p51 :e!r ( /eel or quill1 yet mo/ ( ! writ+ ( today is done on ! typewrit]1 & is done bett] & m economically4 ,! art ( pr9t+ af=ds ev5 m /rik+ examples4 ,9 telephony1 :ile e ef=t has be5 made to simplify ! compon5t p>ts ( ! sy/em1 ! sy/em itself has ev] develop$ f ! simple t[>d ! complex4 ,! adoption ( ! multiple swit*bo>d1 ( automatic r++1 ( selective r++ on p>ty l9es1 ( measur$-s]vice appliances1 & ( automatic sy/ems h all con/itut$ /eps 9 ?is direction4 ,! adoption ( m complicat$ devices & sy/ems 9 telephony has ne>ly always foll[$ a dem& = ! p]=mance by ! ma*9]y ( ! sy/em ( additional or diff]5t functions4 ,z 9 animal & plant life1 s 9 me*anics--! high] ! organism functionally ! m complex x becomes physically4 ,great] intricacy 9 app>atus & 9 me?ods is w>rant$ :5 x is f\nd desirable to make ! ma*9e p]=m add$ functions4 ,once ! functions are det]m9$ ^u1 !n ! :ole tr5d ( ! developm5t ( ! ma*9e = c>ry+ !m out %\ld be t[>d simplicity4 ,:5 ! ma*9e has rea*$ its highe/ /age ( developm5t "s "o proposes t x be requir$ to d some?+ t has hi!rto be5 done manually1 or by a sep>ate ma*9e1 or n at all4 ,) ?is add$ function a va/ add$ complication may come1 aft] :i*1 if x develops t ! new function may ) economy be p]=m$ by ! ma*9e1 ! process ( simplification aga9 beg9s1 ! :ole design f9ally tak+ on an indef9able elegance :i* appe>s only :5 ea* "p is s made z to be be/ adapt$ 9 composition1 =m1 & /r5g? to ! "w x is to p]=m4 ,a*ievem5ts 9 ! pa/ tea* u t a ma*9e may be made to d almo/ any?+ automatically if only ! "t1 pati5ce1 skill1 & money be br\ght to be>4 ,?is is also true ( a telephone sy/em4 ,! primal "q to decide is1 :at functions ! sy/em is to p]=m )9 itself1 automatically1 & :at is to be done manually or ) manual aid4 ,sometimes great complications are br\ght into ! sy/em 9 an attempt to d some?+ :i* may v easily & *eaply be done by h&4 ,cases might be po9t$ out 9 :i* =tunes & life-works h be5 wa/$ 9 p]fect+ ma*9es = :i* !re 0 no real economic ne$4 ,x is ne$less to cite cases :]e ! rev]se is true4 ,! matt] ( wisely *oos+ ! functions ( ! sy/em is ( fundam5tal importance4 ,9 *oos+ ^! ! "q ( complication is only "o ( _m factors to be consid]$4 ,"o ( ! /ronge/ argum5ts aga9/ intricacy 9 telephone app>atus is its great] initial co/1 its great] co/ ( ma9t5ance1 & its liability to get out ( ord]4 ,great] complexity ( app>atus usually means great] fir/ co/1 b x does n necess>ily mean great] co/ ( up-keep or less5$ reliability4 ,a doll> wat* is m simple ?an an exp5sive "o4 ,! "o1 h[ev]1 does its "w passably & is ?r[n away 9 a ye> or s2 ! o!r does its "w m>vel\sly well & may la/ g5]ations1 be+ h&$ d[n f fa!r to son4 ,m]ely r$uc+ ! numb] ( p>ts 9 a ma*9e does n necess>ily mean great] reliability4 ,frequ5tly ! attempt to make "o "p d sev]al div]se ?+s results 9 su* a sacrifice 9 ! simplicity ( action ( t "p z to cause undue /ra91 or we>1 or unreliable action4 ,bett] results may be atta9$ by add+ p>ts1 s t ea* may h a comp>atively simple ?+ to d4 ,illu/ration3 ,,we/]n ,,electric ,,company ,,typical ,,*>g+ ,,outfit ,,at ,,dawson1 ,,georgia ,! /age ( developm5t ( an art is a factor 9 det]m9+ ! degree ( complexity t may be all[$ 9 ! ma*9]y ( t art4 ,a l9otype ma*9e1 if con/ruct$ by miracle sev]al hundr$ ye>s ago1 w\ld h be5 ( no value to ! pr9t]'s art !n4 ,! skill 0 n available to op]ate & ma9ta9 x1 nor 0 ! ne$ ( ! public suffici5tly develop$ to make x ( use4 ,simil>ly ! automatic telephone ex*ange w\ld h be5 ( little value ?irty ye>s ago4 ,! k ( telephone m5 0 n suffici5tly develop$ to ma9ta9 x1 telephone us]s 7 n suffici5tly num]\s to w>rant x1 & ! public 0 n suffici5tly tra9$ to use x4 ,indu/ries1 l human be+s1 mu/ le>n to creep be=e !y c walk4 ,ano!r factor :i* mu/ be consid]$ 9 det]m9+ ! all[able degree ( complexity 9 a telephone sy/em is ! "* ( ! labor available to c>e = & manage x4 ,usually ! conditions :i* make = unskill$ labor also l5d !mselves to ! use ( comp>atively simple sy/ems4 ,?us1 9 a small village remote f l>ge cities ! complexity inh]5t 9 a common-batt]y multiple swit*bo>d w\ld be objectionable4 ,! village w\ld probably n af=d a man adequately skill$ to c>e = x1 & ! size ( ! ex*ange w\ld n w>rant ! exp5se ( keep+ su* a man4 ,=tunately no su* swit*bo>d is ne$$4 ,a f> simpl] device1 ! pla9 magneto swit*bo>d--s simple t ! girl :o manipulates x may also (t5 c>e = its tr\bles--is admirably adapt$ to ! purpose4 ,s x is ) ! automatic telephone sy/em2 ev5 its mo/ en?usia/ic advocate w\ld be fooli% inde$ to cont5d t = all places & purposes x 0 sup]ior to ! manual4 ,^! rem>ks are f> f be+ int5d$ z a plea = complex telephone app>atus & sy/ems2 e device1 e ma*9e1 & e sy/em %\ld be ( ! simple/ possible nature consi/5t ) ! functions x has to p]=m4 ,!y are r a prote/ aga9/ ! broadca/ condemnation ( complex app>atus & sy/ems j because !y are complicat$1 & )\t reg>d to o!r factors4 ,su* condemnation is detrim5tal to ! progress ( telephony4 ,:]e w\ld ! pr9t+ art be today if ! l9otype1 ! cyl9d] press1 & o!r mod]n pr9t+ ma*9]y ( m>vel\s intricacy _h be5 put aside on acc\nt ( ! fact t !y 7 m complicat$ ?an ! pr9t+ ma*9]y ( our =efa!rs8 ,t ! automatic telephone sy/em is complex1 exce$+ly complex1 _c be d5i$1 b exp]i5ce has amply prov5 t its complexity does n prev5t x f giv+ reliable s]vice1 nor f be+ ma9ta9$ at a reasonable co/4 ,exp5se4 ,! second argum5t aga9/ ! automatic--t x is too exp5sive--is "o t mu/ be analyz$ be=e x means any?+4 ,x is true t = small & m$ium-siz$ ex*anges ! total fir/ co/ ( ! c5tral (fice & subscrib]s' /ation equipm5t1 is great] ?an t = manual ex*anges ( correspond+ sizes4 ,! prices at :i* v>i\s sizes ( automatic ex*ange equipm5ts may be pur*as$ v>y1 h[ev]1 almo/ 9 direct proportion to ! numb] ( l9es1 :]eas 9 manual equipm5t ! price p] l9e increases v rapidly z ! numb] ( l9es increases4 ,f ?is x foll[s t = v l>ge ex*anges ! co/ ( automatic app>atus becomes z l[1 & may be ev5 l[] ?an = manual4 ,r\ghly speak+ ! co/ ( telephones & c5tral-(fice equipm5t = small ex*anges is ab\t twice z great = automatic z = manual1 & = v l>ge ex*anges1 ( ab\t #aj1jjj l9es1 ! co/ ( ! two = swit*bo>ds & telephones is ab\t equal4 ,= all except ! l>ge/ ex*anges1 !re=e1 ! great] fir/ co/ ( automatic app>atus mu/ be put d[n z "o ( ! factors to be weigh$ 9 mak+ ! *oice betwe5 automatic & manual1 ?is factor be+ less & less objectionable z ! size ( ! equipm5t increases & f9ally disappe>+ altoge!r = v l>ge equipm5ts4 ,great] fir/ co/ is1 ( c\rse1 w>rant$ if ! fix$ *>ges on ! great] inve/m5t are m ?an (fset by ! economy result+4 ,! automatic screw ma*9e1 = in/ance1 co/s _m times m ?an ! h& screw ma*9e1 b x has l>gely displac$ ! h& ma*9e nev]!less4 ,flexibility4 ,! ?ird argum5t aga9/ ! automatic telephone sy/em--its flexibility--is "o t only "t & exp]i5ce has be5 able to answ]4 ,en\gh "t has elaps$ & en\gh exp]i5ce has be5 ga9$1 h[ev]1 to disprove ! validity ( ?is argum5t4 ,9 fact1 ! great flexibility ( ! automatic sy/em has be5 "o ( its surpris+ developm5ts4 ,no soon] has ! /atem5t be5 made t ! automatic sy/em c\ld n d a c]ta9 ?+ ?an =?) x has done x4 ,x 0 once q cle> t ! automatic sy/em 0 n practicable = p>ty-l9e selective r++2 yet today _m automatic sy/ems are work+ successfully ) ?is feature2 ! selection betwe5 ! p>ties on a l9e be+ accompli%$ ) j z great c]ta9ty z 9 manual sy/ems4 ,aga9 x has seem$ q obvi\s t ! automatic sy/em c\ld n hope to cope ) ! rev]t+ call problem1 i4 e41 enabl+ a subscrib] on a p>ty l9e to call back to rea* ano!r subscrib] on ! same l9e2 yet today ! automatic sy/em may d ?is 9 a way t is p]haps ev5 m satisfactory ?an ! way 9 :i* x is done 9 multiple manual swit*bo>ds4 ,x is true t ! automatic sy/em has n done away ) ! toll op]ator & x probably nev] w be advantage\s to require x to d s = ! simple reason t ! "w ( ! toll op]ator 9 record+ ! connections & 9 br++ toge!r ! subscrib]s is a matt] t requires n only accuracy b judgm5t1 & ! latt]1 ( c\rse1 no ma*9e c supply4 ,x is probable also t ! private bran*-ex*ange op]ator w survive 9 automatic sy/ems4 ,?is is n because ! automatic sy/em _c readily p]=m ! swit*+ duties1 b ! private bran*-ex*ange op]ator has o!r duties ?an ! m]e build+ up & tak+ d[n ( connections4 ,%e is1 z x 71 a door-keep] gu>d+ ! telephone door ( a bus9ess e/abli%m5t2 l ! toll op]ator %e mu/ be possess$ ( judgm5t & ( c\rtesy 9 l>ge degree1 nei!r ( :i* c be suppli$ by ma*9]y4 ,9 respect to toll s]vice & private bran*-ex*ange s]vice :]e1 z j /at$1 op]ators are requir$ on acc\nt ( ! nature ( ! s]vice1 ! automatic sy/em has aga9 %[n its adaptability & flexibility4 ,x has %[n its capability ( work+ 9 h>mony ) manual swit*bo>ds1 ( :atev] nature1 & !re is a gr[+ t5d5cy to apply automatic devices & automatic pr9ciples ( op]ation to manual swit*bo>ds1 :e!r toll or private bran* or o!r k9ds1 ev5 ?\gh ! s]vices ( an op]ator are requir$1 ! idea be+ to d by ma*9]y t portion ( ! "w :i* a ma*9e is able to d bett] or m economically ?an a human be+4 ,attitude ( ,public4 ,! attitude ( ! public t[>d ! automatic is "o t is /ill op5 to discussion2 at lea/ !re is /ill mu* discussion on x4 ,a few ye>s ago x did seem reasonable to suppose t ! g5]al telephone us] w\ld pref] to get 8 connection by m]ely ask+ = x r ?an to make x himself by spell+ x out on ! dial ( 8 telephone in/rum5t4 ,we h /udi$ ?is po9t c>efully 9 a good _m diff]5t communities & x is our op9ion t ! public f9ds no fault ) be+ requir$ to make its own connections4 ,to our m9ds x is prov5 beyond "q t ei!r ! me?od employ$ 9 ! automatic or t 9 ! manual sy/em is satisfactory to ! public z long z good s]vice results1 & x is beyond "q t ! public may get ?is ) ei!r4 ,subscrib]'s ,/ation ,equipm5t4 ,! add$ complexity ( ! me*anism at ! subscrib]'s /ation is 9 our op9ion ! mo/ valid objection t c be urg$ aga9/ ! automatic sy/em z x exi/s today4 ,?is objection has1 h[ev]1 be5 mu* r$uc$ by ! great] simplicity & great] excell5ce ( mat]ial & workman%ip t is employ$ 9 ! controll+ devices 9 mod]n automatic sy/ems4 ,h[ev]1 ! automatic sy/em mu/ always suff] 9 comp>ison ) ! manual 9 respect ( simplicity ( ! subscrib]'s equipm5t4 ,! simple/ conceivable ?+ to meet all ( ! requirem5ts ( telephone s]vice at a subscrib]'s /ation is ! mod]n common-batt]y manual telephone4 ,! automatic telephone diff]s f ?is only 9 ! addition ( ! me*anism = enabl+ ! subscrib] to control ! c5tral-(fice app>atus 9 ! mak+ ( calls4 ,f ! /&po9t ( ma9t5ance1 simplicity at ! subscrib]'s /ation is1 ( c\rse1 to be /riv5 = s9ce ! prop] c>e ( complex devices scatt]$ all ov] a community is a mu* m s]i\s matt] ?an :]e ! devices are c5t]$ at "o po9t1 z 9 ! c5tral (fice4 ,nev]!less1 z po9t$ out1 complexity is n fatal1 & x is possible1 z has be5 prov51 to s design & con/ruct ! requir$ app>atus 9 connection ) ! subscrib]s' telephones z to make !m subject to an am\nt ( tr\ble t is n s]i\s4 ,comp>ative ,co/s4 ,a comp>ison ( ! total co/s ( own+1 op]at+1 & ma9ta9+ manual & automatic sy/ems usually results 9 favor ( ! automatic1 except 9 small ex*anges4 ,?is seems to be ! cons5sus ( op9ion among ^? :o h /udi$ ! matt] deeply4 ,al?\gh ! automatic usually requires a l>g] inve/m5t1 & consequ5tly a l>g] annual *>ge = int]e/ & depreciation1 assum+ ! same rates = ea* case1 & al?\gh ! automatic requires a some:at high] degree ( skill to ma9ta9 x & to keep x work+ prop]ly ?an ! manual1 ! elim9ation ( op]ators or ! r$uction 9 _! numb] & ! consequ5t sav+ ( sal>ies & contributory exp5ses toge!r ) o!r items ( sav+ t w be m5tion$ s]ves to ?r[ ! balance 9 favor ( ! automatic4 ,! ease ) :i* ! automatic sy/em l5ds itself to int]-(fice trunk+ makes feasible a great] subdivision ( ex*ange di/ricts into (fice di/ricts & p>ticul>ly makes x economical1 :]e su* w\ld n be w>rant$ 9 manual work+4 ,all ?is t5ds t[>d a r$uction 9 av]age l5g? ( subscrib]s' l9es & x seems probable t ?is possibility w be work$ ^u 9 ! future1 m ?an x has be5 9 ! pa/1 to effect a consid]able sav+ 9 ! co/ ( ! wire plant1 :i* is ! "p ( a telephone plant t %[s lea/ & co/s mo/4 ,automatic vs4 ,manual4 ,tak+ x all 9 all ! "q ( automatic v]sus manual may n & c n be dispos$ ( by a consid]ation ( any s+le "o ( ! alleg$ features ( sup]iority or inf]iority ( ei!r4 ,ea* mu/ be look$ at z a practical way ( giv+ telephone s]vice1 & a decision c be rea*$ only by a c>eful weigh+ ( all ! factors :i* contribute to economy1 reliability1 & g5]al desirability f ! /&po9t ( ! public4 ,public s5tim5t mu/ nei!r be ov]look$ nor tak5 lightly1 s9ce1 9 ! f9al analysis1 x is ! public t mu/ be satisfi$4 ,me?ods ( ,op]ation4 ,9 all ( ! automatic telephone sy/ems t h a*iev$ any success :atev]1 ! selection ( ! desir$ subscrib]'s l9e by ! call+ subscrib] is accompli%$ by means ( /ep-by-/ep me*anism at ! c5tral (fice1 controll$ by impulses s5t or caus$ to be s5t by ! acts ( ! subscrib]4 ,/r[g] ,sy/em4 ,9 ! s-call$ ,/r[g] sy/em1 manufactur$ by ! ,automatic ,electric ,company ( ,*icago1 ! subscrib]1 9 call+1 manipulates a dial by :i* ! c5tral-(fice swit*+ me*anism is made to build up ! connection he wants4 ,! dial is mov$ z _m times z !re are digits 9 ! call$ subscrib]'s numb] & ea* movem5t s5ds a s]ies ( impulses to ! c5tral (fice correspond+ 9 numb] respectively to ! digits 9 ! call$ subscrib]'s numb]4 ,dur+ ea* pause1 except ! la/ "o1 betwe5 ^! s]ies ( impulses1 ! c5tral-(fice me*anism op]ates to %ift ! control ( ! call+ subscrib]'s l9e f "o set ( swit*+ app>atus at ! c5tral (fice to ano!r4 ,9 case a f\r-digit numb] is be+ select$ fir/1 ! movem5t ( ! dial by ! call+ subscrib] w correspond to ! ?\s&s digit ( ! numb] be+ call$1 & ! result+ movem5t ( ! c5tral-(fice app>atus w cont9ue ! call+ subscrib]'s l9e ?r\gh a trunk to a piece ( app>atus capable ( fur!r ext5d+ 8 l9e t[>d ! l9e t]m9als ( ! ?\s& subscrib]s ^: numb]s beg9 ) ! digit *os54 ,! next movem5t ( ! dial correspond+ to ! hundr$s digit ( ! call$ numb] w op]ate ?is piece ( app>atus to aga9 ext5d ! call+ subscrib]'s l9e ?r\gh ano!r trunk to app>atus repres5t+ ! p>ticul> hundr$ 9 :i* ! call$ subscrib]'s numb] is4 ,! ?ird movem5t ( ! dial correspond+ to ! t5s digit w pick out ! gr\p ( t5 conta9+ ! call$ subscrib]'s l9e1 & ! f\r? movem5t correspond+ to ! units digit w pick out & connect ) ! p>ticul> l9e call$4 ,lorim] ,sy/em4 ,9 ! ,lorim] automatic sy/em inv5t$ by ! ,lorim] ,bro!rs1 & n[ be+ manufactur$ by ! ,canadian ,ma*9e ,telephone ,company ( ,toronto1 ,canada1 ! subscrib] sets up ! numb] he desires complete by mov+ f\r lev]s on 8 telephone s t ! desir$ numb] appe>s visibly be=e him4 ,he !n turns a h&le & ! c5tral-(fice app>atus1 "u ! control ( ! electrical conditions ?us set up by ! subscrib]1 e/abli%es ! connection4 ,9 ?is sy/em1 unlike ! ,/r[g] sy/em1 ! controll+ impulses are n caus$ by ! movem5t ( ! subscrib]'s app>atus 9 return+ to its normal position aft] be+ set by ! subscrib]4 ,in/ead1 ! conditions e/abli%$ at ! subscrib]'s /ation by ! subscrib] 9 sett+ up ! desir$ numb]1 m]ely det]m9e ! po9t 9 ! s]ies ( impulses correspond+ to ea* digit at :i* ! /epp+ impulses local to ! c5tral (fice %all cease1 & 9 ?is way ! prop] numb] ( impulses 9 ! s]ies correspond+ to ea* digit is det]m9$4 ,magnet- vs4 ,p[]-,driv5 ,swit*es4 ,^! two sy/ems diff] radically 9 ano!r respect4 ,9 ! ,/r[g] sy/em x is ! electrical impulses initiat$ at ! subscrib]'s app>atus t actually cause ! movem5t ( ! swit*+ p>ts at ! c5tral (fice1 ^! impulses en]giz+ electromagnets :i* move ! c5tral-(fice swit*+ devices a /ep at a "t ! desir$ numb] ( /eps4 ,9 ! ,lorim] sy/em ! swit*es are all p[]-driv5 & ! impulses "u ! control ( ! subscrib]'s in/rum5t m]ely s]ve to control ! application ( ?is p[] to ! v>i\s swit*+ me*anisms4 ,^! details w be m fully dealt ) 9 subsequ5t *apt]s4 ,multiple vs4 ,trunk+4 ,x has be5 %[n 9 ! prec$+ portion ( ?is "w t ! t5d5cy 9 manual swit*bo>d practice has be5 away f trunk+ betwe5 ! v>i\s sections or positions ( a bo>d1 & t[>d ! multiple idea ( op]at+1 :]e9 ea* op]ator is able to complete ! connection ) any l9e 9 ! same (fice )\t resort+ to trunks or to ! aid ( o!r op]ators4 ,/rangely en\gh ! rev]se has be5 true 9 ! developm5t ( ! automatic sy/em4 ,z long z ! inv5tors tri$ to foll[ ! mo/ successful practice 9 manual work+1 failure result$4 ,! automatic sy/ems ( today are ess5tially trunk+ sy/ems & :ile !y all involve multiple connections 9 great] or less degree1 all ( !m dep5d fundam5tally ^u ! ext5d+ ( ! call+ l9e by sep>ate l5g?s until x f9ally rea*es & connects ) ! call$ l9e4 ,gr\p+ ( ,subscrib]s4 ,9 ?is connection we wi% to po9t out "h two v ess5tial features )\t :i*1 s f> z we are aw>e1 no automatic telephone sy/em has be5 able to op]ate successfully4 ,! fir/ ( ^! is ! division ( ! total numb] ( l9es 9 any (fice ( ! ex*ange into comp>atively small gr\ps & ! employm5t ( correspond+ly small swit* units = ea* gr\p4 ,_m ( ! e>ly automatic sy/ems t 7 propos$ involv$ ! idea ( hav+ ea* swit* capable 9 itself ( mak+ connection ) any l9e 9 ! entire (fice4 ,z long z ! numb] ( l9es 0 small--"o hundr$ or !reab\ts--?is might be all "r1 b :]e ! l9es numb] 9 ! ?\s&s1 x is readily se5 t ! swit*es w\ld be ( prohibitive size & co/4 ,trunk+ betwe5 ,gr\ps4 ,?is feature made necess>y ! employm5t ( trunk connections betwe5 gr\ps4 ,by means ( ^! ! l9es are ext5d$ a /ep at a "t1 fir/ ent]+ a l>ge gr\p ( gr\ps1 conta9+ ! desir$ subscrib]2 !n ent]+ ! small] gr\p conta9+ t subscrib]2 & la/ly ent]+ into connection ) ! l9e itself4 ,! c>ry+ out ( ?is idea 0 greatly complicat$ by ! necessity ( provid+ = _m simultane\s connections ?r\gh ! swit*bo>d4 ,x 0 comp>atively easy to accompli% ! ext5sion ( "o l9e ?r\gh a s]ies ( l9ks or trunks to ano!r l9e1 b x 0 n s easy to d ?is & /ill leave x possible = any o!r l9e to pick out & connect ) any o!r idle l9e )\t int]f]5ce ) ! fir/ connection4 ,a numb] ( p>allel pa?s mu/ be provid$ = ea* possible connection4 ,gr\ps ( trunks are1 !re=e1 provid$ in/ead ( s+le trunks betwe5 common po9ts to be connect$4 ,! subscrib] :o op]ates 8 in/rum5t 9 mak+ a call kn[s no?+ ( ?is & x is1 ( c\rse1 impossible = him to give any ?\ght to ! matt] z to :i* "o ( ! possible pa?s he %all *oose4 ,x 0 by a realization ( ^! facts t ! failures ( ! pa/ 7 turn$ into ! successes ( ! pres5t4 ,! subscrib] by sett+ 8 signal transmitt] 0 made to gov]n ! action ( ! c5tral-(fice app>atus 9 ! selection ( ! prop] gr\p ( trunks4 ,! gr\p be+ select$1 ! c5tral-(fice app>atus 0 made to act at once automatically to pick out & connect ) ! fir/ idle trunk ( su* gr\p4 ,?us1 we may say t ! subscrib] by ! act p]=m$ on 8 signal transmitt]1 volunt>ily *ooses ! gr\p ( trunks1 & imm$iately !reaft] ! c5tral-(fice app>atus )\t ! volition ( ! subscrib] picks out ! fir/ idle "o ( ?is gr\p ( trunks s *os54 ,?is fundam5tal idea1 s f> z we are aw>e1 und]lies all ( ! successful automatic telephone-ex*ange sy/ems4 ,x provides = ! possibility ( _m simultane\s connections ?r\gh ! swit*bo>d1 & x provides aga9/ ! simultane\s appropriation ( ! same pa? by two or m call+ subscrib]s & ?us assures aga9/ int]f]5ce 9 ! *oice ( ! pa?s4 ,outl9e ( ,action4 ,9 ord] to illu/rate ?is po9t we may briefly outl9e ! action ( ! ,/r[g] automatic sy/em 9 ! mak+ ( a connection4 ,assume t ! call+ subscrib] desires a connection ) a subscrib] ^: l9e be>s ! numb] #i1efg4 ,! subscrib] 9 mak+ ! call w1 by ! fir/ movem5t ( 8 dial1 transmit n9e impulses ov] 8 l9e4 ,?is w cause ! selective app>atus at ! c5tral (fice1 t is at ! "t associat$ ) ! call+ subscrib]'s l9e1 to move its select+ f+]s opposite a gr\p ( t]m9als repres5t+ ! ends ( a gr\p ( trunk l9es lead+ to app>atus employ$ 9 connect+ ) ! n9? ?\s& ( ! subscrib]s' l9es4 ,:ile ! call+ subscrib] is gett+ ready to transmit ! next digit1 ! automatic app>atus1 )\t 8 volition1 />ts to pick out ! fir/ idle "o ( ! gr\p ( trunks s *os54 ,hav+ f\nd ?is x connects ) x & ! call+ subscrib]'s l9e is ?us ext5d$ to ano!r selective app>atus capable ( p]=m+ ! same sort ( function 9 *oos+ ! prop] hundr$s gr\p4 ,9 ! next movem5t ( 8 dial ! call+ subscrib] w s5d five impulses4 ,?is w cause ! la/ *os5 selective swit* to move its selective f+]s opposite a gr\p ( t]m9als repres5t+ ! ends ( a gr\p ( trunks ea* lead+ to a swit* t is capable ( mak+ connection ) any "o ( ! l9es 9 ! fif? hundr$ ( ! n9? ?\s&4 ,aga9 dur+ ! pause by ! subscrib]1 ! swit* t *ose ?is gr\p ( trunks w />t automatically to pick out & connect ) ! fir/ idle "o ( !m1 & w ?us ext5d ! l9e to a selective swit* t is capable ( rea*+ ! desir$ l9e1 s9ce x has access to all ( ! l9es 9 ! *os5 hundr$4 ,! ?ird movem5t ( ! dial s5ds six impulses & ?is causes ?is la/ *os5 swit* to move opposite ! six? gr\p ( t5 t]m9als1 s t !re has n[ be5 *os5 ! n9e hundr$ & fifty-six? gr\p ( t5 l9es4 ,! f9al movem5t ( ! dial s5ds sev5 impulses & ! la/ m5tion$ swit* connects ) ! sev5? l9e t]m9al 9 ! gr\p ( t5 previ\sly *os5 & ! connection is complete1 assum+ t ! call$ l9e 0 n already engag$4 ,if x _h be5 f\nd busy1 ! f9al swit* w\ld h be5 prev5t$ f connect+ ) x by ! electrical condition ( c]ta9 ( its contacts & ! busy signal w\ld h be5 transmitt$ back to ! call+ subscrib]4 ,fundam5tal ,idea4 ,?is idea ( subdivid+ ! subscrib]s' l9es 9 an automatic ex*ange1 ( provid+ diff]5t gr\ps ( trunks s arrang$ z to af=d by comb9ation a numb] ( possible p>allel pa?s betwe5 any two l9es1 ( hav+ ! call+ subscrib] select1 by ! manipulation ( 8 in/rum5t1 ! prop] gr\p ( trunks any "o ( :i* might be us$ to e/abli% ! connection he desires1 & ( hav+ ! c5tral-(fice app>atus act automatically to *oose & connect ) an idle "o 9 ?is *os5 gr\p1 %\ld be firmly grasp$4 ,x appe>s1 z we h said1 9 e successful automatic sy/em capable ( s]v+ m ?an "o small gr\p ( l9es1 & until x 0 evolv$ automatic telephony 0 n a success4 ,te/+4 ,z ea* trunk is *os5 & connect$ )1 conditions are e/abli%$1 by means n unlike ! busy te/ 9 multiple manual swit*bo>ds1 :i* w gu>d t trunk & its associat$ app>atus aga9/ appropriation by any o!r l9e or app>atus z long z x is held 9 use4 ,likewise1 z soon z any subscrib]'s l9e is put into use1 ei!r by virtue ( a call be+ orig9at$ on x1 or by virtue ( its be+ connect$ ) z a call$ l9e1 conditions are automatically e/abli%$ :i* gu>d x aga9/ be+ connect$ ) any o!r l9e z long z x is busy4 ,^! gu>d+ conditions ( bo? trunks & l9es1 z 9 ! manual bo>d1 are e/abli%$ by mak+ c]ta9 contacts1 associat$ ) ! trunks or l9es1 assume a c]ta9 electrical condition :5 busy t is diff]5t f _! electrical condition :5 idle2 b unlike ! manual swit*bo>d ?is diff]5t electrical condition does n act to cause a click 9 any "o's e>1 b r to en]gize or de-en]gize c]ta9 electromagnets :i* w e/abli% or fail to e/abli% ! connection accord+ to :e!r x is prop] or improp] to d s4 ,local & ,int]-,(fice ,trunks4 ,! gr\ps ( trunks t are us$ 9 build+ up connections betwe5 subscrib]s' l9es may be local to ! c5tral (fice1 or !y may ext5d betwe5 diff]5t (fices4 ,! action ( ! two k9ds ( trunks1 local or int]-(fice1 is broadly ! same4 ,,*apt] ,,xxix ,,! ,,automatic ,,electric ,,company',s ,,sy/em ,almo/ :]ev] automatic telephony is to be f\nd--& its use is ext5sive & rapidly gr[+--! s-call$ ,/r[g] sy/em is employ$4 ,x is s nam$ because x is ! outgr[? ( ! "w ( ,almon ,b4 ,/r[g]1 an e>ly inv5tor 9 ! automatic telephone art4 ,t ! sy/em %\ld be> ! "n ( ,/r[g]1 h[ev]1 gives too great prom95ce to 8 "w & too little to t ( ! eng9e]s ( ! ,automatic ,electric ,company "u ! lead]%ip ( ,alex&] ,e4 ,kei?4 ,pr9ciples ( ,select+ ,swit*4 ,! und]ly+ features ( ?is automatic sy/em h already be5 ref]r$ to 9 ! ab/ract4 ,a bett] grasp ( its pr9ciples may1 h[ev]1 be _h by consid]+ a concrete example ( its mo/ important piece ( app>atus--! select+ swit*4 ,! b>e skeleton ( su* a swit*1 suffici5t only to illu/rate ! sali5t po9t 9 its mode ( op]ation1 is %[n 9 ,fig4 #chj4 ,! ess5tial elem5ts ( ?is are a v]tical %aft capable ( bo? longitud9al & rot>y motion2 a pawl & rat*et me*anism actuat$ by a magnet = mov+ ! %aft v]tically a /ep at a "t2 ano!r pawl & rat*et me*anism actuat$ by ano!r magnet = rotat+ ! %aft a /ep at a "t2 an arm c>ry+ wip] contacts on its out] end1 m\nt$ on & mov+ ) ! %aft2 & a bank ( contacts arrang$ on ! inn] surface ( a section ( a cyl9d] adapt$ to be engag$ by ! wip] contacts on ?is movable arm4 ,^! v>i\s elem5ts are indicat$ 9 ! m]e/ outl9e & ) mu* di/ortion 9 ,fig4 #chj1 :i* is int5d$ to illu/rate ! pr9ciples ( op]ation r ?an ! details z !y actually are 9 ! sy/em4 ,9 ! upp] left-h& corn] ( ?is figure1 ! magnet %[n w1 if en]giz$ by impulses ( curr5t1 attract & release its armature &1 9 do+ s1 cause ! pawl controll$ by ?is magnet to move ! v]tical %aft ( ! swit* up a /ep at a "t1 z _m /eps z !re are impulses ( curr5t4 ,! v]tical movem5t ( ?is %aft w c>ry ! wip] arm1 atta*$ to ! l[] end ( ! %aft1 up ! same numb] ( /eps &1 9 do+ s1 w br+ ! contacts ( ?is wip] arm opposite1 b n engag+1 ! correspond+ r[ ( /ation>y contacts 9 ! semi-cyl9drical bank4 ,likewise1 ?r\gh ! rat*et cyl9d] on ! int]m$iate portion ( ! %aft1 ! magnet %[n at ! "r-h& portion ( ?is figure w1 :5 en]giz$ by a succession ( electrical impulses1 rotate ! %aft a /ep at a "t1 z _m /eps z !re are impulses4 ,?is w ?us cause ! contacts ( ! wip] arm to move ov] ! successive contacts 9 ! r[ opposite to :i* ! wip] _h be5 c>ri$ 9 its v]tical movem5t4 ,illu/ration3 ,fig4 #chj4 ,pr9ciples ( ,automatic ,swit* ,at ! l[] left-h& corn] ( ?is figure1 !re is %[n a pair ( keys ei!r "o ( :i*1 :5 op]at$1 w complete ! circuit ( ! magnet to :i* x is connect$1 ?is circuit includ+ a common batt]y4 ,9 a c]ta9 r\gh way ?is pair ( key swit*es 9 ! l[] left-h& corn] ( ! draw+ may be tak5 z repres5t+ ! call-transmitt+ app>atus at ! subscrib]'s /ation1 & ! two wires ext5d+ !refrom may be tak5 z repres5t+ ! l9e wires connect+ t subscrib]'s /ation to ! c5tral (fice2 b ! /ud5t mu/ avoid int]pret+ !m z actual repres5tations ( ! subscrib]'s /ation call+ app>atus or ! subscrib]'s l9e s9ce _! c\nt]p>ts are n to be f\nd 9 ! sy/em z x really exi/s4 ,"h aga9 accuracy has be5 sacrific$ = ease 9 sett+ =? a feature ( op]ation4 ,/ill ref]r+ to ,fig4 #chj1 x w be se5 t ! bank contacts consi/ ( t5 r[s1 ea* hav+ t5 pairs ( contacts4 ,assume aga91 = ! sake ( simplicity1 t ! ex*ange "u consid]ation has "o hundr$ subscrib]s & t ea* pair ( bank contacts repres5ts ! t]m9als ( "o subscrib]'s l9e4 ,assume fur!r t ! key swit*es 9 ! l[] left-h& corn] ( ! figure are be+ manipulat$ by a subscrib] at t /ation & t he wi%es to obta9 a connection ) l9e ,no4 #fg4 ,by press+ & releas+ ! left-h& key six times1 he w cause six sep>ate impulses ( curr5t to fl[ ?r\gh ! upp] left-h& magnet & ?is w cause ! swit* %aft to move up six /eps & br+ ! wip] arm opposite ! six? r[ ( bank contacts4 ,if he n[ presses & releases 8 "r-h& key sev5 times1 he w1 ?r\gh ! action ( ! "r-h& magnet1 rotate ! %aft sev5 /eps1 ?us br++ ! wip]s into contact ) ! sev5? contact ( ! six? r[ & ?us into contact ) ! desir$ l9e4 ,z ! wip] contacts on ! swit* arm =m ! t]m9als ( ! call+ subscrib]'s l9e1 x w be app>5t t ! call+ subscrib] is n[ connect$ ?r\gh 8 swit* ) ! l9e ( subscrib] ,no4 #fg4 ,z /at$1 ea* ( ! pairs ( bank contacts are connect$ ) ! l9e ( a subscrib]2 ! l9e1 ,fig4 #chj1 is %[n s connect$ to ! =ty-fir/ pair ( contacts1 t is to ! fir/ contact 9 ! f\r? r[4 ,! select+ swit* %[n 9 ,fig4 #chj w\ld be = ! sole use ( ! subscrib] on ! l9e ,no4 #da4 ,ea* ( ! o!r subscrib]s w\ld h a simil> swit* = 8 own exclusive use4 ,s9ce any ( ! swit*es mu/ be capable ( rea*+ l9e ,no4 #fg1 = in/ance1 :5 mov$ up six r[s & ar\nd sev51 x foll[s t ! sixty-sev5? pair ( contacts 9 ea* bank ( ! entire "o hundr$ swit*es mu/ also be connect$ toge!r & to l9e ,no4 #fg4 ,! same is1 ( c\rse1 true ( all ! contacts correspond+ to any o!r numb]4 ,multiple connections are ?us involv$ betwe5 ! correspond+ contacts ( ! banks1 9 mu* ! same way z 9 ! correspond+ jacks 9 ! multiple ( a manual swit*bo>d4 ,z a result ( ?is multiple connection ( ! bank contacts1 any subscrib] may move ! wip] arm ( 8 select+ swit* into connection ) ! l9e ( any o!r subscrib]4 ,! ,up-&-,ar\nd ,movem5t4 ,! elem5tal idea to be grasp$ by ! discussion s f>1 is ! s-call$ up-&-ar\nd me?od ( action ( ! select+ swit*es employ$ 9 ?is sy/em4 ,?is prelim9>y discussion may be c>ri$ a /ep fur!r by say+ t ! arrangem5t is su* t :5 a subscrib] presses bo? 8 keys & gr\nds bo? ( ! limbs ( 8 l9e1 su* a condition is br\ght ab\t z w cause all hold+ pawls to be )drawn f ! %aft1 & ?us all[ x to return to its normal position ) respect to bo? its v]tical & rot>y movem5ts4 ,no attempt has be5 made 9 ,fig4 #chj to %[ h[ ?is is accompli%$4 ,function ( ,l9e ,swit*4 ,su* a sy/em z has be5 briefly outl9$ 9 ! =ego+ w\ld require a sep>ate select+ swit* = ea* subscrib]'s l9e & w\ld be limit$ to use 9 ex*anges hav+ n m ?an "o hundr$ l9es4 ,9 ! mod]n sy/em ( ! ,automatic ,electric ,company1 ! requirem5t t ea* subscrib] %all h a selective swit*1 individual to 8 own l9e1 has be5 elim9at$ by introduc+ :at is call$ an individual l9e swit* by means ( :i* any "o ( a gr\p ( subscrib]s' l9es1 mak+ a call1 automatically appropriates "o ( a small] gr\p ( select+ swit*es & makes x its own only :ile ! connection exi/s4 ,subdivision ( ,subscrib]s' ,l9es4 ,! limitation z to ! size ( ! ex*ange has be5 ov]come1 )\t increas+ ! numb] ( bank contacts 9 any select+ swit*1 by divid+ ! subscrib]s' l9es into gr\ps ( "o hundr$ & caus+ select+ swit*es automatically to ext5d ! call+ subscrib]'s l9e fir/ into a gr\p ( gr\ps correspond+1 = in/ance1 to ! ?\s& conta9+ ! call$ subscrib]'s l9e1 & !n into ! p>ticul> gr\p conta9+ ! l9e1 & la/ly1 to connect ) ! individual l9e 9 t gr\p4 ,und]ly+ ,feature ( ,trunk+ ,sy/em4 ,x w be rememb]$ t 9 ! *apt] on fundam5tal pr9ciples ( automatic sy/ems1 x 0 /at$ t ! subscrib]1 by means ( ! signal transmitt] at 8 /ation1 0 made to gov]n ! action ( ! c5tral-(fice app>atus 9 ! selection ( a prop] gr\p ( trunks2 & ! gr\p be+ select$1 ! c5tral-(fice app>atus 0 made to act automatically to pick out & connect ) ! fir/ idle trunk ( su* gr\p4 ,?is selection by ! subscrib] ( a gr\p foll[$ by ! automatic selection f among t gr\p =ms ! basis ( ! trunk+ sy/em4 ,x is impossible1 by means ( any simple diagram1 to %[ a complete s*eme ( trunk+ employ$1 b ,fig4 #cha w give a fundam5tal conception ( x4 ,?is figure %[s h[ a s+le call+ l9e1 indicat$ at ! bottom1 may f9d access into any p>ticul> l9e 9 an (fice hav+ a capacity = t5 ?\s&4 ,names ( ,select+ ,swit*es4 ,select+ swit*es ( ! up-&-ar\nd type are ! means by :i* ! call+ l9e selects & connects ) ! trunk l9es requir$ 9 build+ up ! connection1 & f9ally selects & connects ) ! l9e ( ! call$ subscrib]4 ,:]e su* a swit* is employ$ = ! purpose ( select+ a trunk1 x is call$ a selector swit*4 ,x is a fir/ selector :5 x s]ves to pick out a major gr\p ( l9es1 i4 e41 a gr\p conta9+ a p>ticul> ?\s& l9es or1 9 a multi-(fice sy/em1 a gr\p repres5t$ by a complete c5tral (fice4 ,x is a second selector :5 x s]ves to make ! next subdivision ( gr\ps2 a ?ird selector if fur!r subdivision ( gr\ps is necess>y2 & f9ally x is a connector :5 x is employ$ to pick out & connect ) ! p>ticul> l9e 9 ! f9al gr\p ( "o hundr$ l9es to :i* ! connection has be5 br\ght by ! selectors4 ,9 a s+le (fice ( #aj1jjj-l9e capacity1 !re=e1 we w\ld h fir/ & second selectors & connectors1 ! fir/ selectors pick+ out ! ?\s&s1 ! second selectors ! hundr$s1 & ! connectors ! individual l9e4 ,9 a multi-(fice sy/em we may h fir/1 second1 & ?ird selectors & connectors1 ! fir/ selector pick+ out ! (fice1 ! second selector ! ?\s&s 9 t (fice1 ! ?ird selector ! hundr$s1 & ! connector ! individual l9es4 ,! ,l9e ,swit*4 ,9 addition to ! selectors & connectors !re are l9e swit*es1 :i* are comp>atively simple1 "o individual to ea* l9e4 ,ea* ( ^! has ! function1 purely automatic1 ( always connect+ a l9e1 z soon z a call is orig9at$ on x1 to "s "o ( a small] gr\p ( fir/ selectors available to t l9e4 ,?is idea may be bett] grasp$ :5 x is und]/ood t1 9 ! e>li] sy/ems ( ! ,automatic ,electric ,company1 !re 0 a fir/ selector p]man5tly associat$ ) ea* l9e4 ,by ! addition ( ! comp>atively simple l9e swit*1 a sav+ ( ab\t n9ety p] c5t ( ! fir/ selectors 0 effect$1 s9ce ! numb] ( fir/ selectors 0 !reby r$uc$ f a numb] equal to ! numb] ( l9es 9 a gr\p to a numb] equal to ! numb] ( simultane\s connections result+ f calls orig9at+ 9 t gr\p4 ,9 o!r words1 by ! l9e swit*1 ! numb] ( fir/ selectors is det]m9$ by ! traffic r ?an by ! numb] ( l9es4 ,s*eme ( ,trunk+4 ,) ?is und]/&+ z to ! names & broad] functions ( ! ?+s involv$1 ,fig4 #cha may n[ be und]/ood4 ,! l9e swit* ( ! s+le l9e1 z indicat$ "h1 has only ! p[] ( selection among ?ree trunks1 b x is to be und]/ood t 9 actual practice1 x w\ld h access to a great] numb]1 usually t54 ,s1 also1 ?r\gh\t ?is diagram we h %[n ! app>atus & trunks arrang$ 9 gr\ps ( ?ree in/ead ( 9 gr\ps ( t51 only ! fir/ ?ree ?\s&s gr\ps be+ indicat$ & ! fir/ ?ree hundr$s gr\ps 9 ea* ?\s&4 ,aga9 only ?ree levels in/ead ( t5 are indicat$ = ea* select+ swit*1 x be+ und]/ood t 9 ! diagram ! v>i\s levels are repres5t$ by conc5tric arcs ( circles1 & ! trunk contacts by dots on ^! arcs4 ,l9e-,swit* ,action4 ,:5 ! subscrib]1 ^: l9e is %[n at ! bottom ( ! figure1 beg9s to make a call1 ! l9e swit* acts to connect 8 l9e ) "o ( ! fir/ selector trunks available to x4 ,?is selection is entirely prelim9>y &1 except to />t x1 is 9 no way "u ! control ( ! call+ subscrib]4 ,! call+ l9e n[ has "u its control a fir/ selector :i*1 = ! "t be+1 becomes individual to x4 ,let x be assum$ t ! l9e swit* f\nd ! fir/ ( ! fir/ selector trunks already appropriat$ by "s o!r swit*1 b t ! second "o ( ^! trunks 0 f\nd idle4 ,?is trunk be+ appropriat$ by ! l9e swit* places ! c5t] "o ( ! fir/ selectors %[n "u ! control ( ! subscrib]'s l9e4 ,?is fir/ selector !n acts 9 response to ! fir/ set ( selective impulses s5t out by 8 signal transmitt]4 ,illu/ration3 ,,dean ,,h>monic ,,conv]t] ,dry ,cell ,type = ,magneto ,ex*ange4 ,! ,dean ,electric ,co4 ,illu/ration3 ,fig4 #cha4 ,s*eme ( ,trunk+ ,fir/ ,selector ,action4 ,we w assume t ! call+ subscrib] desires to connect ) ,no4 #cbac4 ,! fir/ movem5t ( ! subscrib]'s signal transmitt] w s5d1 !re=e1 ?ree impulses ov] ! l9e4 ,^! impulses w act on ! v]tical magnet ( ! fir/ selector swit* to move x up ?ree /eps4 ,on ?is level ( ! contact bank ( ?is swit* all ( ! contacts w repres5t second selector trunks lead+ to ! ?ird ?\s& gr\p4 ,! o!r ends ( ^! trunks w t]m9ate 9 ! wip]s & also 9 ! controll+ magnets ( second selectors s]v+ ?is ?\s&4 ,?is function on ! "p ( ! fir/ selector controll$ by ! act ( ! subscrib] w h ?us select$ a gr\p ( trunks lead+ to ! ?ird ?\s&1 b ! subscrib] has no?+ to d ) :i* "o ( ! trunks ( ?is gr\p w actually be us$4 ,imm$iately foll[+ ! v]tical movem5t ( ! fir/ selector swit* ! rot>y movem5t ( ?is swit* w />t & w cont9ue until ! wip]s ( t swit* h f\nd contacts ( an idle trunk lead+ to a second selector4 ,assum+ t ! fir/ trunk 0 ! "o f\nd idle1 ! fir/ selector wip]s w\ld pause on ! fir/ pair ( contacts 9 ! ?ird level ( its bank1 & ! trunk *os5 may be se5 lead+ f t contact (f to ! gr\p ( second selectors belong+ to ! ?ird ?\s&4 ,= cle>ness1 ! *os5 trunks 9 ?is assum$ connection are %[n heavi] ?an ! o!rs4 ,second ,selector ,action4 ,! next movem5t ( ! dial by ! subscrib] 9 e/abli%+ 8 desir$ connection w s5d two impulses1 x be+ desir$ to *oose ! second hundr$ 9 ! ?ird ?\s&4 ,! fir/ selector w h become inop]ative be=e ?is second s]ies ( impulses is s5t &1 !re=e1 only ! second selector w respond4 ,its v]tical magnet act+ "u ! influ5ce ( ^! two impulses w /ep up its wip] contacts opposite ! second r[ ( bank contacts1 & ! subscrib] w ?us h *os5 ! gr\p ( trunks lead+ to ! second hundr$ 9 ! ?ird ?\s&4 ,"h1 aga91 ! automatic op]ation ( pick+ out ! fir/ idle "o ( ?is *os5 gr\p ( trunks w take place )\t ! volition ( ! subscrib]1 & x w be assum$ t ! fir/ two trunks on ?is level ( ! second selector 7 f\nd already engag$ & t ! ?ird 0 !re=e *os54 ,! connection cont9ues1 z indicat$ by heavy l9es 9 ,fig4 #cha1 to ! ?ird "o ( ! connectors 9 ! second hundr$ ( ! ?ird ?\s&4 ,any "o ( ^! connectors w\ld h accompli%$ ! purpose b ?is is assum$ to be ! fir/ "o f\nd idle by ! second selector4 ,connector ,action4 ,! ?ird movem5t ( ! subscrib]'s dial w s5d b "o impulse1 ?is correspond+ to ! fir/ gr\p ( t5 9 ! second hundr$ 9 ! ?ird ?\s&4 ,?is impulse w move ! connector %aft up to ! fir/ level ( bank contacts2 & f n[ on ! action ( ! connector diff]s radically f t ( ! selectors4 ,! connector is n se>*+ = an idle trunk 9 ! gr\p b = a p>ticul> l9e &1 !re=e1 hav+ *os5 ! gr\p ( t5 l9es 9 ! desir$ hundr$1 ! connector swit* waits = fur!r guidance f ! subscrib]4 ,?is comes 9 ! =m ( ! f9al set ( impulses s5t by ! subscrib]'s signal transmitt] :i*1 9 ?is case1 w be ?ree 9 numb]1 correspond+ to ! f9al digit 9 ! numb] ( ! call$ subscrib]4 ,?is s]ies ( impulses w control ! rot>y movem5t ( ! connector wip]s :i* w move along ! fir/ level & /op on ! ?ird "o4 ,! process is se5 to be "o ( successive selection1 fir/ ( a l>ge gr\p1 !n ( a small]1 aga9 ( a small]1 & f9ally ( an individual4 ,if ! l9e is f\nd n busy1 ! connection betwe5 ! two subscrib]s is complete & ! call$ subscrib]'s bell w be rung4 ,if x is f\nd busy1 h[ev]1 ! connector w refuse to connect & w drop back to its normal position1 s5d+ a busy signal back to ! call+ subscrib]4 ,! details ( r++ & ! busy-back op]ation may only be und]/ood by a discussion ( draw+s1 subsequ5tly to be ref]r$ to4 ,two-,wire & ,?ree-,wire ,sy/ems4 ,9 mo/ ( ! sy/ems ( ! ,automatic ,electric ,company 9 use today ! impulses by :i* ! subscrib] controls ! c5tral-(fice app>atus fl[ ov] "o side ( ! l9e or ! o!r & return by gr\nd4 ,! metallic circuit is us$ = talk+ & = r++ ! call$ subscrib]'s bell1 :ile gr\nd return circuits1 on "o side ( ! l9e or ! o!r1 are us$ = s5d+ all ! swit* controll+ impulses4 ,rec5tly ?is company has p]fect$ a sy/em :]e9 no gr\nd is requir$ at ! subscrib]'s /ation & no gr\nd return pa? is us$ = any purpose betwe5 ! subscrib] & ! c5tral (fice4 ,?is lat] sy/em is kn[n z ! two-wire sy/em1 & 9 contra-di/9ction to x1 ! e>li] & mo/ us$ sy/em has be5 ref]r$ to z ! ?ree-wire4 ,x is n meant by ?is t ! l9e circuits actually h ?ree wires b t ea* l9e employs ?ree conductors1 ! two wires ( ! l9e & ! e>?4 ,! ?ree-wire sy/em w be ref]r$ to & describ$ 9 detail1 & f x ! pr9ciples ( ! two-wire sy/em w be readily und]/ood4 ,illu/ration3 ,fig4 #chb4 ,automatic ,wall ,set ,illu/ration3 ,fig4 #chc4 ,automatic ,desk ,/& ,subscrib]'s ,/ation ,app>atus4 ,! detail$ op]ation ( ! ?ree-wire sy/em may be be/ und]/ood by consid]+ ! subscrib]'s /ation app>atus fir/4 ,! g5]al appe>ance ( ! wall set is %[n 9 ,fig4 #chb1 & ( ! desk set 9 ,fig4 #chc4 ,^! in/rum5ts embody ! usual talk+ & call-receiv+ app>atus ( a common-batt]y telephone & 9 addition to ?is1 ! signal transmitt]1 :i* is ! ?+ especially to be consid]$ n[4 ,! diagrammatic illu/ration ( ! signal transmitt] & ( ! relation t its p>ts be> to ! o!r elem5ts ( ! telephone set is %[n 9 ,fig4 #chd4 ,x has already be5 /at$ t ! subscrib] manipulates ! signal transmitt] by rotat+ ! dial on ! face ( ! in/rum5t4 ,a cle>] idea ( ?is dial & ( ! f+] /op = x may be obta9$ f ,figs4 #chb & #chc4 ,illu/ration3 ,fig4 #chd4 ,circuits ( ,telephone ,set ,op]ation4 ,to make a call = a giv5 numb] ! subscrib] removes 8 receiv] f its hook1 !n places 8 =ef+] 9 ! hole opposite ! numb] correspond+ to ! fir/ digit ( ! desir$ numb]4 ,by means ( ! grip ?us secur$1 he rotates ! dial until its movem5t is /opp$ by ! impact ( ! f+] aga9/ ! /op4 ,! dial is !n releas$ & 9 its return movem5t x s5ds ! numb] ( impulses correspond+ to ! fir/ digit 9 ! call$ numb]4 ,a simil> movem5t is made = ea* digit4 ,9 ,fig4 #chd is giv5 a phantom view ( ! dial1 9 ord] to %[ m cle>ly ! relation ( ! me*anical p>ts & contacts controll$ by x4 ,= a correct idea ( its me*anical action x mu/ be und]/ood t ! %aft #a1 ! lev] #b1 & ! int]rupt] segm5t #c are all rigidly fa/5$ to ! dial & move ) x4 ,a coil$ spr+ always t5ds to move ! dial & ^! associat$ p>ts back to _! normal positions :5 releas$ by ! subscrib]1 & a c5trifugal gov]nor1 n %[n1 limits ! spe$ ( ! return movem5t4 ,! subscrib]'s hook swit* is me*anically int]lock$ ) ! dial s z to prev5t ! dial be+ mov$ f its normal position until ! hook is 9 its rais$ position4 ,?is int]lock+ function involves also ! pivot$ dog #d4 ,normally ! l[] end ( ?is dog lies 9 ! pa? ( ! p9 #e c>ri$ on ! lev] #b1 & ?us ! %aft1 dial1 & segm5t are prev5t$ f any consid]able movem5t :5 ! receiv] is on ! hook4 ,h[ev]1 :5 ! receiv] is remov$ f its hook1 ! upw>dly project+ arm f ! hook engages a projection on ! dog #d & moves ! dog out ( ! pa? ( ! p9 #e4 ,?us ! dial is free to be rotat$ by ! subscrib]4 ,! p9 #f is m\nt$ 9 a /ation>y position & s]ves to limit ! backw>d movem5t ( ! dial by ! lev] #b /rik+ aga9/ x4 ,gr\nd ,spr+s3--,five gr\ps ( contact spr+s mu/ be consid]$1 "s ( :i* are controll$ :olly by ! position ( ! swit* hook1 o!rs jo9tly by ! position ( ! swit* hook & ! dial1 o!rs by ! movem5t ( ! dial itself1 & /ill o!rs by ! pressure ( ! subscrib]'s f+] on a button4 ,! fir/ ( ^! gr\ps consi/s ( ! spr+s #g & #h1 ! function ( :i* is to control ! cont9uity ( ! gr\nd connection at ! subscrib]'s /ation4 ,! arrangem5t ( ^! two spr+s is su* t ! gr\nd connection w be brok5 until ! subscrib]'s receiv] is remov$ f its hook4 ,z soon z ! receiv] is rais$1 ^! spr+s come toge!r 9 an obvi\s mann]1 ! dog #d be+ lift$ out ( ! way by ! action ( ! hook4 ,! l$ge on ! l[] portion ( ! spr+ #g s]ves z a re/ = ! insulat$ arm ( ! dog #d to prev5t ?is dog1 :i* is spr+ actuat$1 f return+ & lock+ ! dial until aft] ! receiv] has be5 hung up4 ,bell & ,transmitt] ,spr+s3--,! second gr\p is t embrac+ ! spr+s #i1 #aj1 #aa1 & #ab4 ,! spr+s #aj & #aa are controll$ by ! l[] projection f ! swit* hook1 ! spr+ #aa engag+ ! spr+ #ab only :5 ! hook is d[n4 ,! spr+ #aj engages ! spr+ #i only :5 ! hook lev] is up & n !n unless ! dial is 9 its normal position4 ,:ile ! hook is rais$1 !re=e1 ! spr+s #i & #aj break contact :5ev] ! dial is mov$ & make contact aga9 :5 x returns to its normal position4 ,! spr+s #aa & #ab control ! circuit ?r\gh ! subscrib]'s bell :ile ! spr+s #i & #aj control ! cont9uity ( ! circuit f "o side ( ! l9e to ! o!r s z to isolate ! limbs f ea* o!r :ile ! signal transmitt] is s5d+ its impulses to ! c5tral (fice4 ,impulse ,spr+s3--,! ?ird gr\p embraces spr+s #ac1 #ad1 & #ae & ^! are ! ones by :i* ! c5tral-(fice swit*es are controll$ 9 build+ up a connection4 ,some?+ ( ! prevail+ nom5clature :i* has gr[n up ab\t ! automatic sy/em may be introduc$ at ?is po9t4 ,! movem5ts ( ! select+ swit*es at ! c5tral (fice are ref]r$ to z v]tical & rot>y = obvi\s reasons4 ,on acc\nt ( ?is ! magnet :i* causes ! v]tical movem5t is ref]r$ to z ! v]tical magnet & t :i* accompli%es ! rot>y movem5t z ! rot>y magnet4 ,x happ5s t 9 all cases ! select+ impulses s5t by ! subscrib]'s /ation1 correspond+ respectively to ! numb] ( digits 9 ! call$ subscrib]'s numb]1 are s5t ov] "o side ( ! l9e & 9 ne>ly all cases ^! select+ impulses actuate ! v]tical movem5ts ( ! select+ swit*es4 ,= ?is reason ! p>ticul> limb ( ! l9e ov] :i* ! select+ impulses are s5t is call$ ! v]tical limb4 ,! o!r limb ( ! l9e is ! "o ov] :i* ! s+le impulse is s5t aft] ea* gr\p ( select+ impulses1 & x is ?is impulse 9 e case :i* causes ! selector swit* to />t rotat+ 9 its hunt = an idle trunk4 ,?is side ( ! l9e is1 !re=e1 call$ rot>y4 ,= ! same reasons ! impulses ov] ! v]tical side ( ! l9e are call$ v]tical impulses & ^? ov] ! rot>y side1 rot>y impulses4 ,! nam+ ( ! limbs ( ! l9e & ( ! curr5t impulses v]tical & rot>y may appe> odd b x is1 to say ! lea/1 conv5i5t & expressive4 ,com+ back to ! functions ( ! ?ird gr\p ( spr+s1 #ac1 #ad1 & #ae1 #ae may be call$ ! v]tical spr+ s9ce x s5ds v]tical impulses2 #ac1 ! rot>y spr+ s9ce x s5ds rot>y impulses2 & #ad1 ! gr\nd spr+ s9ce1 :5 ! hook is up1 x is connect$ ) ! gr\nd4 ,on ! segm5t #c !re are t5 projections or cams #af :i*1 :5 ! dial is mov$1 engage a projection ( ! spr+ #ae4 ,:5 ! dial is be+ pull$ by ! subscrib]'s f+]1 ^! cams engage ! spr+ #ae 9 su* a way z to move x away f ! gr\nd spr+ & no electrical contact is made4 ,on ! return ( ! dial1 h[ev]1 ^! cams engage ! projection on ! spr+ #ae 9 ! opposite way & ! pass+ ( ea* cam =ces ?is v]tical spr+ into engagem5t ) ! gr\nd spr+4 ,x w readily be se51 !re=e1 by a consid]ation ( ! spac+ ( ^! cams on ! segm5t & ! f+] holes 9 ! dial t ! numb] ( cams :i* pass ! v]tical spr+ #ae w correspond to ! numb] on ! hole us$ by ! subscrib] 9 mov+ ! dial4 ,ne> ! upp] "r-h& corn] ( ! segm5t #c1 z %[n 9 ,fig4 #chd1 !re is ano!r projection or cam #ag1 ! function ( :i* is to engage ! rot>y spr+ #ac & press x into contact ) ! gr\nd spr+4 ,?us1 ! fir/ ?+ t happ5s 9 ! movem5t ( ! dial is = ! projection #ag to ride ov] ! hump on ! rot>y spr+ & press ! contact once into engagem5t ) ! gr\nd spr+2 & likewise1 ! la/ ?+ t happ5s on ! return movem5t ( ! dial is = ! rot>y spr+ to be connect$ once to ! gr\nd spr+ aft] ! la/ v]tical impulse has be5 s5t4 ,if bo? ! rot>y & v]tical sides ( ! l9e are connect$ ) ! live side ( ! c5tral-(fice batt]y1 x foll[s t e contact betwe5 ! v]tical & ! gr\nd spr+ or betwe5 ! rot>y & ! gr\nd spr+ w all[ an impulse ( curr5t to fl[ ov] ! v]tical or ! rot>y side ( ! l9e4 ,we may summ>ize ! action ( ^! impulse spr+s by say+ t :5ev] ! dial is mov$ f its normal position1 !re is1 at ! beg9n+ ( ?is movem5t1 a s+le rot>y impulse ov] ! rot>y side ( ! l9e2 & t :ile ! dial returns1 !re is a s]ies ( v]tical impulses ov] ! v]tical side ( ! l9e2 & j be=e ! dial rea*es its normal position1 aft] ! s5d+ ( ! la/ v]tical impulse1 !re is ano!r impulse ov] ! rot>y side ( ! l9e4 ,! me*anical arrangem5ts ( ! int]rupt] segm5t #c & its associat$ p>ts h be5 greatly di/ort$ 9 ,fig4 #chd 9 ord] to make cle> _! mode ( op]ation4 ,?is draw+ has be5 work$ out ) great c>e1 ) ?is 9 m9d1 at a sacrifice ( accuracy 9 reg>d to ! actual /ructural details4 ,r++ ,spr+s3--,! f\r? gr\p ( spr+s 9 ! subscrib]'s telephone is ! r++ gr\p & embraces ! spr+s #ah1 #ai1 & #bj4 ,! spr+s #ai & #bj are normally clos$ & ma9ta9 ! cont9uity ( ! talk+ circuit4 ,:51 h[ev]1 ! button atta*$ to ! spr+ #ai--:i* button may be se5 project+ f ! in/rum5t %[n 9 ,fig4 #chb1 & f ! base ( ! "o %[n 9 ,fig4 #chc--;is press$1 ! cont9uity ( ! talk+ circuit is int]rupt$ & ! v]tical side ( ! l9e is connect$ ) ! gr\nd4 ,x is by ?is op]ation1 aft] ! connection has be5 made ) ! desir$ subscrib]'s l9e1 t ! c5tral-(fice app>atus acts to s5d r++ curr5t out on t l9e4 ,release ,spr+s3--,! fif? set ( spr+s is ! "o %[n at ! left-h& side ( ,fig4 #chd1 embrac+ spr+s #ba1 #bb1 & #bc4 ,! long curv$ spr+ #ba is engag$ by ! project+ lug on ! swit* hook :5 x rises s z to press ?is spr+ away f ! o!r two4 ,on ! return movem5t ( ! hook1 h[ev]1 ?is spr+ is press$ to ! left s z to br+ all ?ree ( !m into contact1 & ?is1 x w be se51 gr\nds bo? limbs ( ! l9e at ! subscrib]'s /ation4 ,?is comb9ation _c be effect$ by any ( ! o!r spr+s at any /age ( _! op]ation1 & x is ! "o :i* results 9 ! en]gization ( su* a comb9ation ( relays & magnets at ! c5tral (fice z w release all p>ts involv$ 9 ! connection & all[ !m to return to _! normal positions ready = ano!r call4 ,sali5t ,po9ts4 ,if ! foll[+ ?+s are borne 9 m9d ab\t ! op]ation ( ! subscrib]'s /ation app>atus1 an und]/&+ ( ! c5tral-(fice op]ations w be facilitat$4 ,fir/1 ! selective impulses always fl[ ov] ! v]tical side ( ! l9e2 !y are always prec$$ & always foll[$ by a s+le impulse ov] ! rot>y side ( ! l9e4 ,! r++ button gr\nds ! v]tical side ( ! l9e & ! release spr+s gr\nd bo? sides ( ! l9e simultane\sly4 ,! ,l9e ,swit*4 ,! fir/ ?+ to be consid]$ 9 connection ) ! c5tral-(fice app>atus is ! l9e swit*4 ,?is1 x w be rememb]$1 is ! device introduc$ into ea* subscrib]'s l9e at ! c5tral (fice = ! purpose ( effect+ a r$uction ( ! numb] ( fir/ selectors requir$ at ! c5tral (fice1 & also = br++ ab\t c]ta9 important functional results 9 connection ) trunk+ betwe5 c5tral & sub-(fices4 ,! function ( ! l9e swit* 9 connection ) ! subscrib]'s l9e1 h[ev]1 is purely t ( r$uc+ ! numb] ( fir/ selectors4 ,! l9e swit*es ( "o hundr$ l9es are all associat$ to =m a s+le unit ( app>atus1 :i*1 besides ! individual l9e swit*es1 includes c]ta9 o!r app>atus common to ^? l9es4 ,su* a gr\p ( "o hundr$ l9e swit*es & associat$ common app>atus is call$ a l9e-swit* unit1 or frequ5tly1 a ,kei? unit4 ,confusion is likely to arise 9 ! m9d ( ! read] betwe5 ! individual l9e swit* & ! l9e-swit* unit1 & to avoid ?is we w ref] to ! piece ( app>atus individual to ! l9e z ! l9e swit*1 & to ! complete unit =m$ ( "o hundr$ ( ^! devices z a l9e-swit* unit4 ,l9e & ,trunk ,contacts4 ,ea* l9e swit* has its own bank ( contacts arrang$ 9 ! arc ( a circle1 & 9 ?is same arc are also plac$ ! contacts ( ea* ( ! t5 individual trunks :i* x is possible = t l9e to appropriate4 ,! contacts individual to ! subscrib]'s l9e 9 ! l9e swit* are all multipl$ toge!r1 ! arrangem5t be+ su* t if a w$ge or plung] is ins]t$ at any po9t1 ! l9e contacts w be squeez$ out ( _! normal position s z to engage ! contacts ( ! trunk correspond+ to ! p>ticul> position 9 ! arc at :i* ! w$ge or plung] is ins]t$4 ,a small plung] individual to ea* l9e is s arrang$ t x may be ?ru/ 9 betwe5 ! contact spr+s 9 ! l9e-swit* bank 9 su* mann] z to connect any "o ( ! trunks ) ! l9e t]m9als repres5t$ 9 t r[1 ! p>ticul> trunk s connect$ dep5d+ on ! portion ( ! arc t[>d :i* ! plung] is po9t$ at ! "t x is ?ru/ 9 ! contacts4 ,^! banks ( l9es & trunk contacts are horizontally arrang$1 & pil$ 9 v]tical columns ( tw5ty-five l9e swit*es ea*4 ,! t5 trunk contacts are multipl$ v]tically ?r\gh ! l9e-swit* banks1 s t ! same t5 trunks are available to ea* ( ! tw5ty-five l9es4 ,we ?us h1 9 effect1 an old /yle1 ,we/]n ,union1 cross-b> swit*bo>d1 ! l9e contacts be+ repres5t$ 9 horizontal r[s & ! trunk contacts 9 v]tical r[s1 ! connection betwe5 any l9e & any trunk be+ complet$ by ins]t+ a plung] at ! po9t ( int]section ( ! horizontal & ! v]tical r[s correspond+ to t l9e & trunk4 ,trunk ,selection4 ,! plung]s by :i* ! l9es & trunks are connect$ are1 z has be5 said1 individual to ! l9e1 & all ( ! tw5ty-five plung]s 9 a v]tical r[ are m\nt$ 9 su* mann] z to be normally held 9 ! same v]tical plane1 & ?is v]tical plane is made to oscillate back & =? by an oscillat+ %aft s z always to po9t ! plung]s t[>d a v]tical r[ ( trunk contacts t repres5t a trunk t is n 9 use at ! "t4 ,! to-&-fro movem5t ( ?is oscillat+ %aft1 call$ ! ma/] b>1 is controll$ by a ma/] swit* & ! function ( ?is ma/] swit* is always to keep ! plung]s po9t$ t[>d ! r[ ( contacts ( an idle trunk4 ,! ?ru/+ movem5t ( ! individual plung]s into ! contact bank is controll$ by magnets individual to ! l9e & "u control ( ! subscrib] 9 initiat+ a call4 ,z soon z ! plung] ( a l9e has be5 ?us ?ru/ into ! contact bank s z to connect ! t]m9als ( t l9e ) a giv5 trunk1 ! plung] is no long] controll$ by ! ma/] b> & rema9s /ation>y4 ,! ma/] b> !n at once moves all ( ! o!r plung]s t are n 9 use s t !y w po9t to ! t]m9als ( ano!r trunk t is n 9 use4 ,! plung]s ( all ! l9e swit*es 9 a gr\p ( tw5ty-five are1 !re=e1 subject to ! oscillat+ movem5ts ( ! ma/] b> :5 ! l9e is n connect$ to a fir/ selector trunk4 ,z soon z a call is orig9at$ on a l9e1 ! correspond+ plung] is =c$ into ! bank & is held /ation>y 9 ma9ta9+ ! connection to a fir/ selector trunk1 & all ( ! o!r plung]s n s engag$1 move on s z to be ready to engage ano!r idle trunk4 ,trunk ,ratio4 ,! assignm5t ( t5 trunks to tw5ty-five l9es w\ld be a great] ratio ( trunks ?an ord9>y traffic conditions require4 ,?is ratio ( trunks to l9es is1 h[ev]1 readily v>i$ by multipl+ ! trunk contacts ( sev]al tw5ty-five l9e gr\ps toge!r4 ,?us1 t5 trunks may be made available to "o hundr$ subscrib]s' l9es by multipl+ ! trunks ( f\r tw5ty-five l9e swit* gr\ps toge!r4 ,9 ?is case ! f\r ma/] b>s correspond+ to ! f\r gr\ps ( tw5ty-five l9e swit*es are all me*anically connect$ toge!r s z to move 9 unison "u ! control ( a s+le ma/] swit*4 ,if m ?an t5 & less ?an tw5ty-"o trunks are assign$ to "o hundr$ l9es1 !n ea* set ( t5 trunks is multipl$ to ! trunk contacts ( fifty l9e swit*es1 ! two ma/] b>s ( ^! swit*es be+ connect$ toge!r & controll$ by a common ma/] swit*4 ,/ructure ( ,l9e ,swit*4 ,! details ( ! p>ts ( a l9e swit* t are individual to ! l9e are %[n 9 ,fig4 #che1 ! l9e & trunk contact bank be+ %[n 9 ! l[] portion ( ?is figure & also 9 a sep>ate view 9 ! deta*$ figure at ! "r4 ,a detail$ gr\p ( sev]al su* l9e swit*es ) ! oscillat+ ma/] b> is %[n 9 ,fig4 #chf4 ,?is figure %[s q cle>ly ! relative arrangem5t ( ! l9e & trunk contact banks1 ! plung]s = ea* bank1 & ! ma/] b>4 ,illu/ration3 ,fig4 #che4 ,l9e ,swit* ,9 practice1 f\r gr\ps ( tw5ty-five l9e swit*es ea* are m\nt$ on a s+le framework & ! gr\p ( "o hundr$ l9e swit*es1 toge!r ) c]ta9 o!r portions ( ! app>atus t w be ref]r$ to lat]1 =m a l9e-swit* unit4 ,a front view ( su* a unit is %[n 9 ,fig4 #chg4 ,9 ord] to give access to all portions ( ! wir+ & app>atus1 ! framework support+ ea* column ( fifty l9e swit*es is h+$ s z to op5 up ! int]ior ( ! device z a :ole4 ,a l9e-swit* unit ?us op5$ out is %[n 9 ,fig4 #chh4 ,illu/ration3 ,fig4 #chf4 ,portion ( ,l9e-,swit* ,unit ,circuit ,op]ation4 ,! mode ( op]ation ( ! l9e swit* may be be/ und]/ood 9 connection ) ,fig4 #chi1 :i* %[s 9 a s*ematic way ! p>ts ( a l9e swit* t are individual to a subscrib]'s l9e1 & also ^? t are common to a gr\p ( fifty or "o hundr$ l9es4 ,^? portions ( ,fig4 #chi :i* are individual to ! l9e are %[n bel[ ! dott$ l9e ext5d+ across ! page4 ,! task ( und]/&+ ! l9e swit* w be made some:at easi] if ,figs4 #che & #chi are consid]$ toge!r4 ,! individual p>ts ( ! l9e swit* are %[n 9 ! same relation to ea* o!r 9 ^! two figures ) ! exception t ! bank ( l9e & trunk spr+s 9 ! l[] "r-h& corn] ( ,fig4 #chi h be5 turn$ ar\nd edgewise s z to make an und]/&+ ( _! circuit connections possible4 ,illu/ration3 ,fig4 #chg4 ,l9e-,swit* ,unit ,illu/ration3 ,fig4 #chh4 ,l9e-,swit* ,unit ,illu/ration3 ,fig4 #chi4 ,circuits ( ,l9e-,swit* ,unit ,! v]tical & rot>y sides ( ! subscrib]'s l9e are %[n ent]+ at ! l[] left-h& corn] ( ?is figure1 & !y pass to ! spr+s ( ! contact bank4 ,imm$iately adjac5t to ^! spr+s are ! trunk contacts f :i* ! v]tical & ! rot>y limbs ( ! fir/ selector trunk proce$4 ,! plung] is indicat$ at #a1 x be+ 9 ! =m ( a :eel ( insulat+ mat]ial4 ,x is c>ri$ on ! rod #b pivot$ on a lev] #c1 :i*1 9 turn1 is pivot$ at #d 9 a /ation>y portion ( ! framework4 ,a spr+ #e1 secur$ to ! und]side ( ! lev] #c & project+ to ! left beyond ! pivot #d ( ?is lev]1 s]ves always to press ! "r-h& portion ( ! lev] #c =w>d 9 su* direction z to t5d to ?ru/ x into ! contact bank4 ,! plung] is normally held out ( ! contact bank by means ( ! lat* #f c>ri$ on ! armature #g ( ! trip magnet4 ,:5 ! trip magnet is en]giz$ x pulls ! armature #g to ! left & ?us releases ! plung] & all[s x to ent] ! contact bank4 ,illu/ration3 ,,p[] ,,swit*bo>d ,,= ,,m$ium-,,siz$ ,,(fice ,m]cury ,arc ,rectifi] ,panel & ,trans=m] at ,"r4 ,! ma/] b> is %[n at #h1 & a fea!r on ?is b> engages a not* 9 ! segm5t atta*$ to ! re> end ( ! plung] rod #b4 ,?is ma/] b> is common to all ( ! plung] rods & by its oscillatory movem5t1 "u ! influ5ce ( ! ma/] swit*1 x always keeps all ( ! idle plung] b>s po9t$ t[>d ! contacts ( an idle trunk4 ,z soon1 h[ev]1 z ! trip magnet is op]at$ to cause ! ins]tion ( a plung] into ! contact bank1 ! fea!r on ! ma/] b> is dis5gag$ by ! not* 9 ! segm5t ( ! plung] rod1 & ! plung] rod is1 !re=e1 no long] subject to ! oscillat+ movem5t ( ! ma/] b>4 ,:5 ! release magnet is en]giz$1 x attracts its armature #i & ?is lifts ! armature #g ( ! trip magnet s t ! lat* #f rides on top ( ! left-h& end ( ! lev] #c4 ,!n1 :5 ! release magnet is de-en]giz$1 ! spr+ #e1 :i* 0 put "u t5sion by ! lat*1 moves ! entire /ructure ( lev]s back to its normal position1 )draw+ ! plung] f ! bank ( contacts4 ,! not* on ! edge ( ! segm5t ( ! plung] rod1 :5 ?us releas$1 w probably n /rike ! fea!r on ! ma/] b>1 & ! plung] rod w ?us n come "u ! control ( ! ma/] b> until ! ma/] b> has mov$1 9 its oscillation1 s t ! fea!r regi/]s ) ! not*1 aft] :i* ?is b> w move ) all ! o!rs4 ,if1 :ile ! plung] is wait+ to be pick$ up by ! ma/] b>1 ! same subscrib] %\ld call aga91 8 l9e w be connect$ ) ! same trunk z be=e4 ,!re is no dang] 9 ?is1 h[ev]1 t ! trunk w be f\nd busy1 because ! ma/] b> w n h occupi$ a position :i* w\ld make x possible = any ( ! l9es to appropriate ?is trunk dur+ ! int]v5+ "t4 ,ma/] ,swit*4 ,associat$ ) ea* ma/] b> !re is a ma/] swit* :i* det]m9es ! position 9 :i* ! ma/] b> %all /op 9 ord] t ! idle plung]s may be po9t$ always to ! contacts ( an idle trunk4 ,! arm #aj ( ?is swit* is atta*$ to ! ma/] b> & oscillates ) x & s]ves to connect ! segm5t #aa successively ) ! contacts #ab1 :i* are connect$ respectively to ! ?ird1 or release wire ( ea* fir/ selector trunk4 ,9 ! figure ! arm #aj is %[n re/+ on ! six? contact ( ! swit* & ?is six? contact is connect$ to a spr+ #ac 9 ! l9e-swit* contact bank t has n yet be5 ref]r$ to4 ,z soon z ! plung] is ins]t$ into ! contact bank1 ! spr+ #ad w be press$ into engagem5t ) ! spr+ #ac1 & ?is spr+ #ad is connect$ ) ! live side ( ! batt]y ?r\gh ! release magnet w9d+4 ,! contact /rip #aa on ! ma/] swit* is ?us connect$ ?r\gh ! release magnet to ! batt]y & f ?is curr5t fl[s ?r\gh ! left-h& w9d+ ( ! ma/]-swit* relay4 ,?is en]gizes ?is relay & causes ! closure ( ! circuit ( ! lock+ magnet :i* magnet unlocks ! ma/] b> to p]mit its fur!r rotation4 ,! unlock+ ( ! ma/] b> br+s ! spr+ #ae into engagem5t ) #af & ?us en]gizes ! ma/] magnet1 ! armature ( :i* vibrates back & =? aft] ! mann] ( an electric-bell armature1 & /eps ! :eel #ag ar\nd4 ,! :eel #ag is me*anically connect$ to ! ma/] b> s t ea* complete revolution ( ! :eel w cause "o complete oscillation ( ! ma/] b>4 ,! ma/] b> w ?us be mov$ s z to cause all ! idle plung]s to sweep ?r\gh an arc & ?is movem5t w /op z soon z ! ma/]-swit* arm #aj connects ! arc #aa ) "o ( ! contacts #ab t is n connect$ to ! live side ( ! batt]y ?r\gh ! spr+s #ac & #ad ( "s o!r l9e swit*4 ,x is by ?is means t ! plung]s ( ! l9e swit*es are always kept po9t+ at ! contacts ( an idle trunk4 ,! way 9 :i* ?is feature has be5 work$ out mu/ dem& admiration & acc\nts = ! m>vel\s quickness ( ?is l9e swit*4 ,! fact t ! plung]s are po9t$ 9 ! "r direction be=e ! "t comes = _! use1 leaves only ! simple ?ru/+ motion ( ! plung] to accompli% ! desir$ connection imm$iately ^u ! initiation ( a call by ! subscrib]4 ,lock+ ,segm5t4 ,x w be und]/ood t ! lock+ segm5t #ah & ! ma/]-swit* contact f+] #aj are bo? rigidly connect$ ) ! ma/] b> #h & move ) x1 ! lock+ segm5t #ah s]v+ always to det]m9e accurately ! angul> position at :i* ! ma/] b> & ! ma/]-swit* arm are br\ght to re/4 ,bridge ,cut-,(f4 ,"o important feature ( automatic swit*+1 p>ticul>ly z exemplifi$ 9 ! sy/em ( ! ,automatic ,electric ,company1 is ! disconnection1 aft] its use1 ( ea* op]at+ magnet ( ea* piece ( app>atus involv$ 9 mak+ a connection4 ,s9ce ^! op]at+ magnets are always bridg$ across ! l9e at ! "t ( _! op]ation & !n cut (f aft] !y h p]=m$ _! function1 ?is feature may be ref]r$ to z ! bridge cut-(f4 ,gu>d+ ,functions4 ,/ill ano!r feature ( importance is ! means = gu>d+ a l9e or a piece ( app>atus t has already be5 appropriat$ or made busy1 s t x w n be appropriat$ or connect$ ) = use 9 "s o!r connection4 ,= ?is latt] purpose contacts & wires are associat$ ) ea* piece ( app>atus1 :i* are multipl$ to simil> contacts on o!r pieces ( app>atus 9 mu* ! same way & = a simil> purpose t ! te/ ?imbles 9 a multiple swit*bo>d are multipl$ toge!r4 ,su* wires & contacts 9 ! ,automatic ,electric ,company's app>atus are call$ private wires & contacts4 ,! bridge cut-(f & gu>d+ functions are provid$ = 9 ! l9e swit* by a bridge cut-(f relay %[n 9 ,fig4 #chi & also 9 ,fig4 #che1 x be+ ! upp] "o ( ! individual l9e relays 9 ea* ( ^? figures4 ,?is bridge cut-(f relay is op]at$ z soon z ! plung] ( ! l9e is ?ru/ into ! bank2 ! contacts #ai & #bj1 clos$ by ! plung]1 s]v+ to complete ! circuit ( ?is relay4 ,to make cle> ! bridge cut-(f feature x w be not$ t ! trip magnet ( a l9e swit* is connect$ 9 a circuit trac$ f ! rot>y side ( ! l9e ?r\gh ! contacts #ba & #bb ( ! bridge cut-(f relay1 !nce ?r\gh ! coil ( ! trip magnet to ! common wire lead+ to ! spr+ #bc ( ! ma/]-b> lock+ device & !nce to ! live side ( ! batt]y4 ,obvi\sly1 !re=e1 z soon z ! bridge cut-(f relay op]ates1 ! trip magnet becomes inop]ative & c cause no fur!r action ( ! l9e swit* because its circuit is brok5 betwe5 ! spr+s #ba & #bb4 ,! private or gu>d+ feature is tak5 c>e ( by ! action ( ! plung] 9 clos+ contacts #ai & #bj1 s9ce ! private wire lead+ to ! bridge cut-(f relay is1 z has already be5 /at$1 connect$ to gr\nd :5 ^! contacts are clos$4 ,?is private wire leads (f & is multipl$ to ! private contacts on all ! connectors t h ! ability to rea* ?is l9e1 & ! fact t ?is wire is gr\nd$ by ! l9e swit* z soon z x becomes busy1 e/abli%es su* conditions at all ( ! connectors t !y w refuse to connect ) ?is l9e z long z x is busy1 9 a way t w be po9t$ out lat] on4 ,relation ( ,l9e ,swit* & ,connectors4 ,! v]tical & rot>y wires ( ! subscrib]'s l9e are %[n lead+ (f to ! connector banks at ! left-h& side ( ,fig4 #chi1 & "o side ( ?is connection passes ?r\gh ! contacts #bd & #be ( ! bridge cut-(f relay on ! l9e swit*4 ,x is ?r\gh ?is pa? t a connection f "s o!r l9e ?r\gh a connector to ?is l9e is e/abli%$ & x is se5 t ?is pa? is held op5 until ! bridge cut-(f relay ( ! l9e swit* is op]at$4 ,= su* a connection to ?is l9e ! bridge cut-(f relay ( ! l9e swit* is op]at$ ov] ! private wire lead+ f ! connector1 & ! op]ation ( ! bridge cut-(f relay at ?is "t s]ves to r5d] inop]ative ! l9e swit*1 s t x w n p]=m its usual functions %\ld ! call$ subscrib] />t to make a call aft] 8 l9e _h be5 seiz$4 ,summ>y ( ,l9e-,swit* ,op]ation4 ,to summ>ize ! op]ation ( a l9e swit* :5 a call is orig9at$ on its l9e1 ! fir/ movem5t ( ! call+ subscrib]'s dial w gr\nd ! rot>y side ( ! l9e & op]ate ! trip magnet4 ,?is w cause ! plung] to be ins]t$ into ! bank1 & ?us ext5d ! l9e to ! fir/ selector trunk ?r\gh ! clos+ ( ! "r-h& set ( spr+s %[n 9 ! l[] "r-h& corn] ( ,fig4 #chi4 ,! ins]tion ( ! plung] w also connect ! batt]y ?r\gh ! left-h& w9d+ ( ! ma/]-swit* relay &1 by ! sequ5ce ( op]ations :i* foll[s1 cause ! ma/] b> to move all ( ! idle plung]s s z to aga9 po9t !m to an idle trunk4 ,! closure ( contacts #ai & #bj by ! plung] causes ! op]ation ( ! bridge cut-(f relay :i* op5s ! circuit ( ! trip magnet1 r5d]+ x inop]ative2 & also e/abli%es gr\nd pot5tial on all ! private wire contacts ( t l9e 9 ! banks ( ! connectors1 s z to gu>d ! l9e & its associat$ app>atus aga9/ intrusion by o!rs4 ,! l9e is cut ?r\gh1 !re=e1 to a fir/ selector & all ( ! l9e-swit* app>atus is completely cut (f f ! talk+ circuit4 ,x mu/ be rememb]$ t all ( ! actions ( ! l9e swit*1 :i* x has tak5 s long to describe1 occur practically in/antane\sly & z a result ( ! fir/ "p ( ! fir/ movem5t ( ! subscrib]'s dial4 ,! l9e swit* has done its "w & gone out ( bus9ess be=e ! selective impulses ( ! fir/ digit beg9 to take place4 ,select+ ,swit*es4 ,! fir/ selector is n[ 9 control ( ! call+ subscrib]4 ,! circuits & elem5ts ( ! fir/ selector swit* are %[n 9 ,fig4 #cij4 ,! g5]al me*anical /ructure ( ! fir/ selectors1 second selectors1 & connectors1 is ! same & may be ref]r$ to briefly "h4 ,fig4 #cia %[s a re> view ( a fir/ selector2 ,fig4 #cib1 a side view ( a second selector2 & ,fig4 #cic1 a front view ( a connector4 ,! arrangem5t ( ! v]tical & rot>y magnets1 ( ! selector %afts1 & ( ! contact banks are id5tical 9 all ?ree ( ^! pieces ( app>atus & all ^! swit*es "w on ! up-&-ar\nd pr9ciple ref]r$ to 9 connection ) ,fig4 #chj4 ,x is ?\ght t ) ! g5]al /ructure %[n 9 ,figs4 #cia1 #cib1 & #cic 9 m9d1 ! actual op]ation may be und]/ood mu* m readily f ,fig4 #cij4 ,f\r magnets--! v]tical1 ! rot>y1 ! private1 & ! release--produce ! swit*+ movem5ts ( ! ma*9e4 ,^! magnets are controll$ by v>i\s comb9ations br\ght ^u ! circuits by ?ree relays--! v]tical1 ! rot>y1 & ! back release4 ,! f\r? relay %[n1 call$ ! (f-normal1 is purely = signal+ purposes1 z w be describ$4 ,side ,swit*4 ,ano!r important elem5t ( ! select+ swit*es is ! s-call$ side swit* :i* might bett] be call$ a pilot swit*--b we are n responsible = its "n4 ,?is side swit* has = its function ! *ang+ ( ! control ( ! subscrib]'s l9e to successive portions ( ! selector me*anism1 r5d]+ inop]ative ^? portions t h already p]=m$ _! functions & t1 !re=e1 are no long] ne$$4 ,?is swit* may be se5 be/ 9 ,fig4 #cib j above ! upp] bank ( contacts4 ,x is %[n 9 ,fig4 #cij greatly di/ort$ me*anically s z to bett] illu/rate its electrical functions4 ,illu/ration3 ,fig4 #cij4 ,circuits ( ,fir/ ,selector ,! contact lev]s #a1 #b1 #c1 & #d ( ! side swit* are c>ri$ ^u ! arm #e :i* is pivot$ at #f4 ,all ( ^! contact lev]s1 !re=e1 move ab\t #f z an axis4 ,! side swit* has ?ree positions & x is %[n1 9 ,fig4 #cij1 9 ! fir/ "o ( ^!4 ,:5 ! private magnet armature is attract$ & releas$ once1 ! escapem5t c>ri$ by x p]mits ! spr+ #g to move ! arm #e s z to br+ ! wip]s ( ! side swit* into its second position2 ! second pull+ up & release ( ! private magnet armature w cause ! movem5t ( ! side swit* wip]s into ! ?ird position4 ,x is to be not$ t ! escapem5t :i* releases ! side swit* arm may be mov$ ei!r by ! private or by ! rot>y magnet1 s9ce ! armature ( ! latt] has a f+] :i* engages ! private magnet armature4 ,illu/ration3 ,fig4 #cia4 ,re> ,view ( ,fir/ ,selector ,functions ( ,side ,swit*4 ,! functions ( ! side swit* may be briefly outl9$ 9 connection ) ! fir/ selector1 z an example4 ,9 ! fir/ position x ext5ds ! control ( ! subscrib]'s signal transmitt] ?r\gh ! fir/ selector trunk & l9e relays to ! v]tical & private magnets s t ^! magnets w be responsive to ! select+ impulses correspond+ to ! fir/ digit4 ,9 its second position x br+s ab\t su* a condition ( affairs t ! rot>y magnet w be br\ght into play & automatically move ! wip]s ov] ! bank contacts 9 se>* ( an idle trunk4 ,9 its ?ird position1 bo? ! v]tical & rot>y relays are cut (f & ! l9e is cut /raight ?r\gh to ! second selector trunk1 & only ^? p>ts ( ! fir/ selector app>atus are left 9 an op]ative /ate :i* h to d ) ! private or gu>d+ circuits & ) ! release4 ,simil> functions are p]=m$ by ! side swit* 9 connection ) ! o!r select+ swit*es4 ,illu/ration3 ,fig4 #cib4 ,side ,view ( ,second ,selector ,release ,me*anism4 ,ano!r "o ( ! features ( ! swit* t ne$s to be consid]$ be=e a detail$ und]/&+ ( its op]ation may be _h1 is ! me*anical relation ( ! hold+ & ! release dog4 ,?is dog is %[n at #h &1 9 ! language ( ! art1 is call$ ! d\ble dog4 ,z w be se51 x has two reta9+ f+]s1 "o adapt$ to engage ! v]tical rat*et & ! o!r1 ! rot>y rat*et on ! selector %aft4 ,?is d\ble dog is pivot$ at #i & is int]l9k$ 9 a peculi> way ) ! armature ( ! v]tical magnet1 ! armature ( ! release magnet1 & ! arm ( ! side swit*4 ,! function ( ?is d\ble dog is to hold ! %aft 9 :atev] v]tical position x is mov$ by ! v]tical magnet & !n1 :5 ! rot>y magnet beg9s to op]ate1 to hold ! %aft 9 its prop] angul> position4 ,x w be not$ t ! fix$ dog #aj is ineffective :5 ! %aft is 9 its normal angul> position4 ,b z soon z ! %aft is rotat$1 ?is fix$ dog #aj becomes ! real hold+ pawl s f> z ! v]tical movem5t is conc]n$4 ,! d\ble dog #h is normally held out ( engagem5t ) ! v]tical & ! rot>y rat*ets by virtue ( ! l9k connection1 %[n at #aa1 betwe5 ! release magnet armature & ! re> end ( ! d\ble dog4 ,on ! previ\s release ( ! swit* ! attraction ( ! release magnet armature p]mitt$ ! l9k #aa to hook ov] ! end ( ! dog #h & ?us1 on its return movem5t1 to pull ?is dog out ( engagem5t ) its rat*ets4 ,?is movem5t also result$ 9 pu%+ on ! l9k #ab :i* is pivot$ to ! side swit* arm #e1 & ?us ! return movem5t ( ! release magnet is made to re/ore ! side swit* to its normal position4 ,9 ord] t ! d\ble dog may be made effective :5 x is requir$1 & 9 ord] t ! side swit* may be free to move "u ! influ5ce ( ! private magnet1 ! d\ble dog is releas$ f its connection ) ! release magnet armature by ! fir/ movem5t ( ! v]tical magnet 9 a mann] :i* is cle> f ! draw+4 ,fir/ ,selector ,op]ation4 ,9 discuss+ ! details ( op]ation ( ! v>i\s selectors x w be f\nd conv5i5t to divide ! discussion accord+ to ! position ( ! side swit*4 ,?is w br+ ab\t a logical arrangem5t because x is really ! side swit* :i* det]m9es by its position ! sequ5ce ( op]ation4 ,illu/ration3 ,fig4 #cic4 ,front ,view ( ,connector ,fir/ ,position ( ,side ,swit*4 ,?is is ! position %[n 9 ,fig4 #cij1 & is ! normal position4 ,! v]tical & ! rot>y l9es ext5d+ f ! call+ subscrib] are cont9u$ by ! lev]s #a & #b ( ! side swit* ?r\gh ! v]tical & ! rot>y relay coils1 respectively1 to ! live side ( batt]y4 ,! lev] #d ( ! side swit* 9 ?is position connects to gr\nd ! circuit lead+ f ! l9e swit* ?r\gh ! release trunk1 & ! w9d+ ( ! (f-normal relay4 ,?is w9d+ is ?us put 9 s]ies ) ! release magnet ( ! l9e swit*1 b on acc\nt ( high resi/ance ( ! (f-normal relay no op]ation ( ! release magnet is caus$4 ,?is w1 h[ev]1 p]mit su* curr5t to fl[ ?r\gh ! release circuit z w en]gize ! s5sitive (f-normal relay & cause x to attract its armature & light ! (f-normal lamp4 ,if ?is lamp rema9s light$ m ?an a brief p]iod ( "t1 x w attract notice & w indicate t ! correspond+ selector has be5 appropriat$ by a l9e swit* & t = "s reason ! selector has gone no fur!r4 ,?is lamp1 !re=e1 is an aid 9 prev5t+ ! cont9uance ( ?is abnormal condition4 ,! fir/ ?+ t happ5s aft] ! l9e swit* has connect$ ! call+ subscrib] ) ! fir/ selector is a succession ( impulses ov] ! v]tical side ( ! l9e1 ?is be+ ! set ( impulses correspond+ 9 numb] to ! ?\s&s digit or to ! (fice1 if !re is m ?an "o4 ,x w be und]/ood t "h we are consid]+ a s+le (fice ( t5-?\s&-l9e capacity or !reab\ts1 & t1 !re=e1 ?is fir/ set ( impulses corresponds to ! ?\s&s digit 9 ! call$ subscrib]'s l9e4 ,ea* "o ( ^! impulses w fl[ f ! batt]y ?r\gh ! v]tical relay & ea* movem5t ( ?is relay armature w close ! circuit ( ! v]tical magnet & cause ! %aft ( ! selector to be /epp$ up to ! prop] level4 ,imm$iately foll[+ ! fir/ s]ies ( select+ impulses f ! subscrib]'s /ation1 a s+le impulse foll[s ov] ! rot>y side ( ! l9e4 ,?is gives ! rot>y relay armature "o impulse & ?is 9 turn closes ! circuit ( ! private magnet once4 ,! s+le movem5t ( ! private magnet armature all[s ! escapem5t f+] on ! arm #e to move "o /ep & ?is br+s ! side swit* contacts into ! second position4 ,second ,position ( ,side ,swit*4 ,9 ?is position lev] #d ( ! side swit* places a gr\nd on ! wire lead+ ?r\gh ! rot>y magnet to a s\rce ( int]rupt$ batt]y curr5t4 ,! impulses :i* ?us fl[ ?r\gh ! rot>y magnet occur at a frequ5cy dep5d5t ^u ! batt]y int]rupt] & ?is is at a rate ( approximately fifte5 impulses p] second4 ,! rot>y magnet w /ep ! selector %aft rapidly ar\nd until some?+ occurs to /op ^! impulses4 ,?is some?+ is ! f9d+ by ! private wip] ( an ungr\nd$ private contact 9 ! bank1 s9ce all ( ! contacts correspond+ to busy trunks are gr\nd$1 z w be expla9$4 ,! action ( ! private magnet ent]s into ?is op]ation 9 ! foll[+ way3 ,a circuit may be trac$ f ! batt]y ?r\gh ! private magnet to ! ?ird side swit* wip] :5 9 its second position1 !nce ?r\gh ! back release relay to ! private wip]4 ,if ! wip] is at ! "t on ! private bank contact ( a busy trunk1 x w f9d t contact gr\nd$ & ! private magnet w be en]giz$4 ,! en]giz+ ( ?is magnet w n1 h[ev]1 cause ! release ( ! side swit*4 ,x mu/ be en]giz$ & de-en]giz$4 ,! private magnet armature w1 !re=e1 be op]at$ by ! f+] ( ! rot>y magnet armature on ! fir/ rot>y /ep4 ,! private magnet w be en]giz$ & hold its armature op]at$ if ! private wip] f9ds a gr\nd on ! fir/ bank contact & w /ay en]giz$ z long z ! private wip] is pass+ ov] private contacts ( busy trunks4 ,its armature w n be all[$ to fall back dur+ ! passage ( ! wip] f "o trunk to ano!r1 because dur+ t int]val ! f+] ( ! rot>y magnet w hold x op]at$4 ,z soon1 h[ev]1 z ! private wip] rea*es ! private bank contact ( an idle trunk1 no gr\nd w be f\nd & ! circuit ( ! private magnet w be left op54 ,:5 ! impulse ?r\gh ! rot>y magnet ceases1 ! private magnet armature w fall back & ! side swit* w be releas$ to its ?ird position4 ,?ird ,position ( ,side ,swit*4 ,! fir/ ?+ to be not$ 9 ?is position is t ! call+ l9e is cut /raight ?r\gh to ! second selector trunk1 ! connection be+ clean ) no magnets bridg$ across or tapp$ (f4 ,! ?ird wip] ( ! side swit*1 :5 9 its ?ird position1 is gr\nd$ & ?is connects ! release wire ( ! second selector trunk1 on :i* ! swit* wip]s re/1 ?r\gh ! private wip]1 ! w9d+ ( ! back release magnet1 & ! ?ird wip] ( ! side swit* to gr\nd4 ,?is e/abli%es a pa? = ! subsequ5t release curr5t ?r\gh ! back release magnet2 &1 ( equal importance1 x places a gr\nd on ! private bank contact ( t trunk s t ! private wip] ( any o!r swit* w be prev5t$ f /opp+ on ! contacts ( ?is trunk 9 ! same mann] t ! wip] ( ?is swit* 0 prev5t$ f /opp+ on o!r trunks t 7 already 9 use4 ,! f\r? lev] on ! side swit*1 :5 9 its ?ird position1 s]ves m]ely to close ! circuit ( ! rot>y (f-normal lamp4 ,?is lamp is = ! purpose ( call+ att5tion to any fir/ selector swit* t has be5 br\ght into connection ) "s second selector trunk & :i*1 = "s reason1 has fail$ 9 its release4 ,^! (f-normal lamps are s arrang$ t !y may be swit*$ (f manually to avoid burn+ !m dur+ ! h\rs ( heavie/ traffic4 ,at night !y af=d a ready means ( te/+ = swit*es t h be5 left (f-normal1 s9ce ! manual swit*es controll+ ^! lamps may !n be clos$1 & any lamps :i* burn w %[ t ! swit*es correspond+ to !m are (f-normal4 ,simple te/s !n suffice to %[ :e!r !y are prop]ly or improp]ly 9 _! (f-normal position4 ,release ( ! ,fir/ ,selector4 ,z w be %[n lat]1 ! normal way ( releas+ ! swit*es is f ! connector back ov] ! release wire4 ,x is suffici5t to say at ?is po9t t :5 ! prop] "t = release comes1 an impulse ( curr5t w come back ov] ! second selector trunk release wire ?r\gh ! private wip]1 to ! back release relay magnet1 & !nce to gr\nd ?r\gh ! ?ird wip] ( ! side swit* :i* is 9 its ?ird position4 ,x may be ask$ :y ! back release magnet 0 n en]giz$ dur+ ! previ\s op]ations describ$1 :5 curr5t pass$ ?r\gh x4 ,! reason = ?is is t 9 ^? previ\s op]ations ! private magnet 0 always includ$ 9 s]ies 9 ! circuit & on acc\nt ( ! high resi/ance ( ! private magnet1 suffici5t curr5t did n pass ?r\gh ! back release magnet to en]gize x4 ,:5 ! back release relay is en]giz$1 x closes ! circuit ( ! release magnet & ?us1 ?r\gh ! l9k #aa1 draws ! d\ble dog away f its engagem5t ) ! %aft rat*ets & at ! same "t1 ?r\gh ! l9k #ab1 re/ores ! side swit* to its normal position4 ,:5ev] ! release magnet is op]at$ x acts z a relay to close a pair ( contacts associat$ ) x & ?us to mom5t>ily gr\nd ! release wire ( ! fir/ selector trunk ext5d+ back to ! l9e swit*4 ,ref]r+ to ,fig4 #chi1 x w be se5 t ?is pa? leads ?r\gh ! contacts #ac & #ad & ! release magnet to ! batt]y4 ,x is by ?is means t ! l9e swit* is releas$1 ! release impulse be+ relay$ back f ! fir/ selector4 ,second ,selector ,op]ation4 ,= ! purpose ( consid]+ ! action ( ! second selector1 we w g back to ! po9t :]e ! fir/ selector _h connect$ ) a second selector trunk & :]e its side swit* _h mov$ into its ?ird position4 ,9 ?is condition1 x w be rememb]$1 ! trunk l9e 0 cut ?r\gh to a second selector trunk & all fir/ selector app>atus cle>$ f ! talk+ circuit4 ,! second selector *os5 is "o correspond+ to ! ?\s&s gr\p z det]m9$ by ! fir/ digit ( ! call$ subscrib]'s numb]4 ,! circuits ( a second selector are %[n 9 ,fig4 #cid & x mu/ be borne 9 m9d t ! me*anical arrangem5ts = produc+ ! v]tical & ! rot>y movem5t ( ! %aft & = op]at+ ! side swit* are practically ! same z ^? ( ! fir/ selector4 ,z 9 ! fir/ selector1 ! sequ5ce ( op]ation is controll$ by ! successive positions ( ! side swit*1 ! fir/ position p]mitt+ ! selection ( ! hundr$s correspond+ to ! v]tical impulses1 ! second position all[+ ! selector to se>* = an idle trunk 9 t hundr$1 & ! ?ird position cutt+ ! trunk ?r\gh & cle>+ ! circuit ( ob/ruct+ app>atus4 ,fir/ ,position ( ,side ,swit*4 ,! fir/ ?+ t happ5s :5 ! subscrib] beg9s to move 8 dial 9 ! transmission ( ! second s]ies ( select+ impulses is ! s5d+ ( a prelim9>y impulse ov] ! rot>y side ( ! l9e4 ,?is1 9 ! case ( ! second selector1 en]gizes ! rot>y relay :i*1 9 turn1 en]gizes ! private magnet2 b ! private magnet 9 ! case ( ! second selector c d no?+ t[>d ! release ( ! side swit* because ! projection #e'1 on ! side swit* arm #e1 meets a projection on ! re> ( ! selector %aft :i* ?us prev5ts ! movem5t ( ! side swit* arm #e until ! selector %aft has be5 mov$ out ( its normal position4 ,imm$iately aft] ! e/abli%m5t ( ! connection to ! selector1 ! second set ( select+ impulses comes 9 ov] ! v]tical wire f ! subscrib]'s /ation4 ,^! impulses1 correspond+ 9 numb] to ! hundr$s digit1 w en]gize ! v]tical relay & cause x1 9 turn1 to en]gize ! v]tical magnet1 /epp+ up ! selector %aft to ! level correspond+ to ! hundr$ s\ght4 ,! s+le rot>y impulse1 :i* foll[s j be=e ! subscrib]'s dial rea*es its normal position1 w en]gize ! rot>y relay ( ! second selector4 ,?is1 9 turn1 en]gizes ! private magnet :i* makes a s+le movem5t ( its armature & all[s ! escapem5t f+] on ! side swit* arm to move "o /ep & br+ ! side swit* contacts into ! second position4 ,illu/ration3 ,fig4 #cid4 ,circuits ( ,second ,selector ,second ,position ( ,side ,swit*4 ,no detail$ discussion ( ?is is necess>y1 s9ce1 ) ! side swit* 9 its second position1 ! actions :i* occur 9 caus+ ! wip]s ( ! second selector to seek & connect ) an idle trunk l9e1 are exactly ! same z 9 ! case ( ! fir/ selector4 ,:5 ! second selector wip]s f9ally rea* a re/+ place on ! bank contacts1 ! private magnet armature1 op]at$ dur+ ! hunt+ process1 is releas$ & ! side swit* is ?us %ift$ into ! ?ird position4 ,?ird ,position ( ,side ,swit*4 ,! mov+ ( ! side swit* into its f9al position br+s ab\t ! same /ate ( affairs ) respect to ! second selector t already exi/s ) respect to ! fir/ selector4 ,! trunk l9e is cut /raight ?r\gh & all bridge circuits or by-pa?s f x are cut (f4 ,! same gu>d+ conditions are e/abli%$ to prev5t o!r l9es or o!r pieces ( app>atus f mak+ connections t w int]f]e ) ! "o be+ e/abli%$1 & ! same provisions are made = work+ ! back release :5 ! prop] impulse comes f ! connector1 & = pass+ ?is back release impulse on to ! fir/ selector 9 ! same way t ! fir/ selector passes x on to ! l9e swit*4 ,! l9e ( ! call+ subscrib] has n[ be5 ext5d$ to a connector1 & t connector is "o ( a gr\p--usually t5--:i* alone has ! ability to rea* ! p>ticul> hundr$ l9es conta9+ ! l9e ( ! desir$ subscrib]4 ,! selection has1 !re=e1 be5 n>r[$ d[n f "o 9 t5 ?\s& to "o 9 "o hundr$4 ,! ,connector--,its ,functions4 ,x has already be5 /at$ t ! connector is ( ! same g5]al type ( app>atus z ! fir/ & ! second selectors4 ,unlike ! fir/ & ! second selectors1 h[ev]1 ! connector is requir$ to make a d\ble selection "u ! guidance ( ! subscrib]4 ,! fir/ selector makes a s+le selection ( a gr\p "u ! guidance ( ! subscrib] & !n an automatic selection 9 t gr\p n controll$ by ! subscrib]4 ,s x is ) ! second selector4 ,! connector1 h[ev]1 makes a selection ( a gr\p ( t5 "u ! guidance ( ! subscrib] & !n1 aga9 "u ! guidance ( ! subscrib]1 x picks out a p>ticul> "o ( t gr\p4 ,! connector also has o!r functions 9 relation to ! r++ ( ! call$ subscrib] & ! giv+ ( a busy signal to ! call+ subscrib] 9 case ! l9e want$ is f\nd busy4 ,x has /ill o!r functions 9 t ! talk+ curr5t1 :i* is f9ally suppli$ to connect$ subscrib]s1 is suppli$ ?r\gh pa?s furni%$ by x4 ,location ( ! ,connectors4 ,connectors are ! only ones ( ! select+ swit*es t are 9 any s5se individual to ! subscrib]s' l9es4 ,none ( !m is individual to a subscrib]'s l9e1 b x may be said t a gr\p ( t5 connectors is individual to a gr\p ( "o hundr$ subscrib]s' l9es4 ,s9ce ea* gr\p ( "o hundr$ l9es has a gr\p ( connectors ( its own & s9ce ea* "o hundr$ l9es also has a l9e-swit* unit ( its own1 & s9ce ! l9es ( ?is gr\p mu/ be multipl$ ?r\gh ! bank contacts ( ! connectors ( ?is individual gr\p & ?r\gh ! bank contacts ( ! l9e swit*es ( ?is p>ticul> unit1 x foll[s t on acc\nt ( ! wir+ problems involv$ !re is good reason = m\nt+ ! connectors 9 close proximity to ! l9e swit*es repres5t+ ! same gr\p ( l9es4 ,"s help 9 ! grasp+ ( ?is ?\ght may result if x be rememb]$ t ! l9e swit* is1 s to speak1 ! po9t ( entry ( a call & t ! connector is ! po9t ( exit1 &1 9 ord] to r$uce ! am\nt ( wir+ & to economize space1 ! po9t ( exit & ! po9t ( entry are made z close toge!r z possible4 ,! relative locations & gr\p+ ( ! l9e swit*es & connectors are cle>ly %[n 9 ,fig4 #cie1 :i* is a re> view ( ! same l9e-swit* unit t 0 illu/rat$ 9 ,figs4 #chg & #chh4 ,illu/ration3 ,,gas ,,eng9e ,,& ,,p[] ,,bo>d ,citiz5s' ,telephone ,co41 ,rac9e1 ,wis4 ,! ,dean ,electric ,co4 ,op]ation ( ! ,connector4 ,! circuits ( ! connector are %[n 9 ,fig4 #cif4 ,9 addition to ! features t h be5 po9t$ out 9 ! fir/ & ! second selectors1 all ( :i* are to be f\nd1 ) "s modifications1 p]haps1 9 ! connector1 !re mu/ be consid]$ ! features 9 ! connector ( busy-signal op]ation1 ( r++ ! call$ subscrib]1 ( batt]y supply to bo? subscrib]s1 & ( ! trunk release op]ation4 ,^! may be be/ und]/ood by trac+ ?r\gh ! op]ations ( ! connector f ! "t x is pick$ up by a second selector until ! connection is f9ally complet$1 or until ! busy signal has be5 giv5 9 case completion 0 f\nd impossible4 ,z 9 ! fir/ & ! second selectors1 ! sequ5ce ( op]ations is det]m9$ by ! position ( ! side swit*4 ,illu/ration3 ,fig4 #cie4 ,connector ,side ( ,l9e-,swit* ,unit ,illu/ration3 ,fig4 #cif4 ,circuits ( ,connector ,fir/ ,position ( ,side ,swit*4 ,! connector 9 a t5-?\s&-l9e sy/em is ! recipi5t ( ! impulses result+ f ! ?ird & f\r? movem5ts ( ! subscrib]'s dial4 ,consid]+ ! ?ird movem5t ( ! subscrib]'s dial1 ! fir/ impulse result+ f x comes ov] ! rot>y side ( ! l9e & results 9 ! rot>y relay attract+ its armature once4 ,?is results 9 a s+le impulse ?r\gh ! private magnet :i*1 h[ev]1 does no?+ because ! projection #e' /rikes aga9/ a projection on ! selector %aft4 ,^! two projections int]f]e only :5 ! selector %aft is 9 its normal position4 ,!n foll[s ! s]ies ( impulses f ! subscrib]'s /ation correspond+ to ! t5s digit 9 ! call$ subscrib]'s numb]4 ,^! pass ov] ! v]tical side ( ! l9e & ?r\gh ! v]tical relay1 en]giz+ t relay a correspond+ numb] ( times4 ,! v]tical magnet1 z 9 ! case ( ! fir/ & ! second selectors1 is includ$ 9 ! circuit controll$ by ! v]tical relay & ?is results 9 ! connector %aft be+ /epp$ up to ! level correspond+ to ! p>ticul> t5s gr\p conta9+ ! call$ subscrib]'s numb]4 ,x w be not$ t ! impulses f ! v]tical side ( ! l9e1 :i* cause ?is selection1 pass ?r\gh "o w9d+ #ac ( ! call+ batt]y supply relay4 ,?is relay is op]at$ by ^! v]tical select+ impulses1 b 9 ?is position ( ! side swit* ! closure ( its local circuits accompli%es no?+4 ,imm$iately aft] ! t5s gr\p ( select+ impulses ov] ! v]tical side ( ! l9e1 !re foll[s a s+le rot>y impulse f ! subscrib]'s /ation :i*1 z 9 ! case ( ! fir/ & ! second selectors1 en]gizes ! rot>y relay & causes x to give "o impulse to ! private magnet4 ,?is impulse is n[ able1 s9ce ! %aft has mov$ f its normal position1 to release ! side swit* arm "o not*1 & ! side swit*1 !re=e1 moves into its second position4 ,second ,position ( ,side ,swit*4 ,x is pr9cipally 9 ?is second position ( ! side swit* t ! connector select+ function diff]s f t ( ! fir/ & ! second selector4 ,!re is no trunk to be hunt$1 b r ! rot>y movem5t ( ! connector wip]s mu/ be made 9 response to ! impulses1 f ! subscrib]'s /ation1 :i* correspond to ! units digit 9 ! select$ numb]4 ,! fir/ impulse correspond+ to ! f\r? movem5t ( ! subscrib]'s dial is a rot>y "o1 &1 z usual1 x passes ?r\gh ! rot>y relay w9d+ & ?is1 9 turn1 gives an impulse to ! private magnet4 ,! private magnet at ?is "t has already releas$ ! side swit* arm to its second position1 b x is unable to release x fur!r because ( a fea!r on ! wip] %aft--:i* projects j f> en\gh to engage ! lug #e'1 :5 ! %aft is 9 its normal angul> position--?us prev5t+ ! side swit* arm f mov+ f>!r ?an its second position4 ,!n foll[s ov] ! v]tical side ( ! l9e ! la/ set ( select+ impulses correspond+ to ! units digit4 ,?is1 z be=e1 en]gizes ! v]tical relay1 b 9 ! second position ( ! side swit*1 x is to be not$1 t ! v]tical relay no long] controls ! v]tical magnet2 ! side swit* has %ift$ ! control ( ! v]tical relay to ! rot>y magnet4 ,! rot>y magnet is1 !re=e1 en]giz$ a numb] ( times correspond+ to ! la/ digit 9 ! call$ numb] & ! wip]s ( ! connectors are ?us br\ght to ! contacts ( ! l9e s\ght--_! f9al goal4 ,at ?is po9t _m ?+s may happ51 & ! ?+s t d happ5 dep5d on :e!r ! call$ subscrib]'s l9e is idle or busy4 ,call$-,l9e ,busy3--,x w fir/ be assum$ t ! call$ l9e is busy4 ,! te/+ op]ation at ! connectors occurs 9 ! second position ( ! side swit*4 ,if ! call$ l9e is busy1 x w be ei!r because x is connect$ to by "s o!r connector or because x has itself made a call4 ,9 ! =m] case ! private contacts ( t l9e 9 ! banks ( all ! connectors s]v+ t hundr$s gr\p ( l9es w be gr\nd$ ?r\gh ! private wip] ( "s o!r connector4 ,t ?is is s1 may be se5 by trac+ ! circuit f ! private wip] on ! %aft to ! ?ird side swit* wip] :i* is gr\nd$ 9 ! ?ird position2 ! o!r connector t has already engag$ ! l9e w1 ( c\rse1 h its side swit* 9 its f9al1 or ?ird position4 ,aga91 if ! l9e call$ is busy1 because a call has already be5 made f ?is l9e to "s o!r l9e1 ! private contacts on ! connectors correspond+ to ! l9e w be gr\nd$1 z w be se5 by trac+ f ! private bank contacts1 :i* are %[n 9 ,fig4 #cif1 ?r\gh ! private wire to ! l9e swit*1 :i* is %[n 9 ,fig4 #chi1 & f !nce to gr\nd ?r\gh ! spr+s #ai & #bj1 :i* are br\ght toge!r :5 ! l9e swit* is op]at$4 ,9 any ev5t1 !re=e1 ! det]m9+ condition ( a busy l9e is t its private bank contacts on all connectors ( its gr\p %all be gr\nd$4 ,"u ! pres5t assum$ condition1 !re=e1 ! connector wip]s1 :i* h be5 br\ght to ! bank contacts ( ! desir$ l9e1 w f9d a gr\nd at ! private bank contact4 ,! connector %aft /ops = an in/ant on ! contacts ( ?is busy l9e & imm$iately !re foll[s ov] ! rot>y side ( ! l9e ! inevitable s+le rot>y impulse4 ,?is en]gizes ! rot>y relay & ?is1 z usual1 en]gizes ! private magnet4 ,rememb]+ n[ t ! connector side swit* is 9 its second position & t ! private wip] ( ! connector has f\nd a gr\nd1 we may trace back f ! private wip] ?r\gh ! ?ird side swit* wip] to its second contact2 !nce ?r\gh ! contact spr+s #ad & #ae1 clos$ by ! private magnet2 !nce ?r\gh ! release magnet2 !nce ?r\gh ! contact spr+s #af & #ag ( ! call+ batt]y supply relay to ! live side ( ! batt]y4 ,?is call+ batt]y supply relay w1 at ?is "t1 h its core en]giz$ because ! coil #ah is 9 s]ies ) ! rot>y relay coil :i*1 z j /at$1 0 en]giz$ by ! la/ rot>y impulse4 ,?is s]ies ( op]ations has l$ to ! en]giz+ ( ! release magnet1 &1 z a result1 ! d\ble dog ( ! connector is pull$ out ( ! connector %aft rat*ets & ! %aft & ! side swit* are re/or$ to _! normal position4 ,busy-,back ,signal3--,! connector has dropp$ back to normal 9 all respects4 ,! call+ subscrib]1 n kn[+ ?is1 presses 8 r++ button4 ,?is gr\nds ! v]tical side ( ! l9e at 8 /ation & op]ates ! v]tical relay at ! connector4 ,?is /eps ! %aft ( ! connector up "o /ep & causes ! closure ( ! contacts #ai & #bj at ! top ( ! connector %aft4 ,?is e/abli%es a connection to a circuit c>ry+ p]iodically int]rupt$ batt]y curr5t on :i* an inductive hum is plac$4 ,?is circuit may be trac$ f ?is s\rce ?r\gh ! spr+s #bj & #ai to ! fir/ wip] ( ! side swit*1 !nce ?r\gh ! normally clos$ contacts ( ! r++ relay to ! rot>y side ( ! l9e1 & ! v>y+ pot5tial to :i* ?is pa? is subject$ produces an inductive fl[ back to ! call+ subscrib]'s telephone1 & gives him ! necess>y signal :i* consi/s ( a hum or buzz+ noise ) :i* all us]s ( automatic sy/ems soon become famili>4 ,release on ,busy ,connection3--,! connector1 s9ce its la/ release1 has be5 /epp$ up "o not* & mu/ aga9 be releas$4 ,:5 ! subscrib] hangs up 8 receiv] aft] receiv+ ! busy signal1 he gr\nds bo? sides ( 8 l9e mom5t>ily by ! action ( ! spr+s #ba1 #bb1 & #bc ( ,fig4 #chd4 ,?is op]ates ! rot>y & ! v]tical relays on ! connector simultane\sly & br+s toge!r = ! fir/ "t ! spr+s #ba & #bb ( ,fig4 #cif4 ,?is e/abli%es a connection f ! batt]y ?r\gh ! spr+s #af & #ag on ! call+ batt]y supply relay1 !nce ?r\gh ! release magnet ( ! connector1 !nce ?r\gh ! spr+s #bb & #ba ( ! v]tical & ! rot>y relay1 !nce ?r\gh ! release trunk back to ! second selector4 ,f "h ! circuit passes ?r\gh ! private wip] ( t selector & ! back release relay to gr\nd ?r\gh ! ?ird side swit* wip] :i* is 9 ! ?ird position4 ,consid]+ ?is circuit 9 respect to its action on ! connector x is obvi\s t x en]gizes ! release magnet on ! connector :i* re/ores ! connector to normal z be=e4 ,at ! second selector ?is circuit pass$ ?r\gh ! back release relay1 :i* clos$ a circuit ?r\gh ! release magnet & ?r\gh ! back release relay contacts1 !nce back ov] ! second selector release trunk to ! back release relay ( ! fir/ selector1 & ?r\gh ! ?ird wip] ( ! side swit* on t selector to gr\nd1 s9ce t side swit* also is 9 its ?ird position4 ,! curr5t ?r\gh ?is circuit en]gizes ! release magnet ( ! second selector & re/ores x to its normal position & also en]gizes ! back release relay ( ! fir/ selector4 ,?is1 9 turn1 closes ! circuit f ! batt]y ?r\gh ! release magnet ( ! fir/ selector & contacts ( ! back release relay to gr\nd4 ,?is works ! release magnet ( ! fir/ selector & re/ores t selector to normal4 ,! contacts on ! fir/ selector release magnet1 %[n 9 ,fig4 #cij1 are clos$ by ! action ( ! release magnet & ?is closes ! pa? f gr\nd back ?r\gh ! fir/ selector release wire1 & ?r\gh ! contacts #ac & #ad ( ! l9e swit*1 ?r\gh ! l9e swit* release magnet to batt]y1 & ?is re/ores ! l9e swit* to normal4 ,! reason = ! t]m back release w n[ be app>5t4 ,! release op]ation at ! connector is relay$ back to ! second selector2 t ( ! second selector back to ! fir/ selector2 & t ( ! fir/ selector back to ! l9e swit*4 ,until ?is plan 0 adopt$1 ! release magnet ( ea* selector & connector involv$ 9 a connection 0 left bridg$ across ! talk+ circuit s z to be available = release2 & x sometimes occurr$ t a fir/ selector w\ld be releas$ be=e a second selector or connector1 :i* latt] swit*es w\ld ?us be left (f-normal until rescu$ by an att5dant4 ,! back release plan makes x impossible = ! connection necess>y = ! release ( a swit* to be torn d[n until ! release is actually accompli%$4 ,call$ ,l9e ,f\nd ,idle3--,x w be rememb]$ t1 be=e ! digression necess>y to trace ?r\gh ! op]ations occurr+ ^u ! f9d+ ( a busy l9e1 ! connector wip]s _h be5 br\ght1 by ! influ5ce ( ! call+ subscrib]'s impulses1 into engagem5t ) ! contacts ( ! desir$ l9e2 t ! connector side swit* 0 9 its second position2 & t ! f9al rot>y impulse foll[+ ! la/ s]ies ( select+ impulses _h n be5 s5t4 ,! condition n[ to be assum$ is t ! call$ subscrib]'s l9e is free & ! private wip]1 !re=e1 has f\nd & re/s on an ungr\nd$ private bank contact4 ,! f9al rot>y impulse :i* imm$iately foll[s w op]ate ! rot>y relay & ?is1 9 turn1 w op]ate ! private magnet4 ,?is happ5$ "u ! assum$ condition t ! l9e 0 busy1 b 9 t case ! release magnet 0 also op]at$ at ! same "t & re/or$ all conditions to normal4 ,"u ! pres5t condition ! op]ation ( ! private magnet w p]=m its usual function & move ! side swit* ( ! connector into its ?ird position4 ,?ird ,position ( ,side ,swit*4 ,:5 ! side swit* ( ! connector moves to its ?ird position1 x1 z usual1 cuts ! talk+ circuit /raight ?r\gh f ! v]tical & ! rot>y sides ( ! trunk lead+ f ! previ\s selector to ! outgo+ t]m9al ( ! subscrib]'s l9e1 :i* may be trac$ ^u ,fig4 #cif back ?r\gh ! l9e swit*1 %[n 9 ,fig4 #chi4 ,sev]al ?+s are to be not$ ab\t ! talk+ circuit s e/abli%$3 ,fir/1 ! inclusion ( ! cond5s]s 9 ! v]tical & ! rot>y sides ( ! connector circuit4 ,! purpose ( ?is w be ref]r$ to lat]4 ,second1 ! inclusion 9 ?is circuit at ! connector ( a pair ( normally clos$ contacts 9 ! r++ relay4 ,x may be said 9 pass+ t ! r++ relay corresponds exactly 9 function to a r++ key 9 a manual swit*bo>d4 ,?ird1 ! talk+ circuit lead+ f ! connector to ! call$ subscrib]'s l9e passes on "o side ?r\gh ! spr+s #bd & #be ( ! bridge cut-(f relay ( ! l9e swit*1 :i* is %[n 9 ,fig4 #chi4 ,^! spr+s are normally op5 & w\ld prev5t ! completion ( ! talk+ circuit b = ! fact t ! bridge cut-(f relay ( ! l9e swit* is en]giz$ ov] ! private wire lead+ to ! connector bank & !n ?r\gh ! connector wip] to ! ?ird side swit* wip] :i*1 at ?is "t1 is 9 its ?ird position4 ,! talk+ circuit is ?us complete4 ,! op]ation ( ?is bridge cut-(f relay on ! l9e swit* has n only complet$ ! talk+ circuit b x has also op5$ ! circuit ( ! trip magnet ( ! l9e swit* s z to prev5t ! op]ation ( ! trip magnet by ! subscrib] on t l9e 9 case he %\ld attempt to make a call dur+ ! int]val betwe5 ! "t :5 8 l9e 0 connect$ ) by ! connector & ! "t :5 he answ]s ! call4 ,! ?ird wip] ( ! connector side swit* :5 mov$ into its ?ird position1 puts ! gr\nd on all ( ! private bank contacts ( ! l9e *os5 & ?us gu>ds t l9e aga9/ connection by o!rs1 z already describ$4 ,x also op]ates ! bridge cut-(f relay ( ! l9e swit* z j m5tion$4 ,! f\r? wip] ( ! side swit*1 :5 mov$ into its ?ird position1 e/abli%es su* a connection z w place ! r++ relay "u ! control ( ! v]tical relay4 ,?is may be se5 by trac+ f gr\nd to ! v]tical relay spr+s #bc & #bd1 !nce ?r\gh ! normally clos$ upp] pair ( contacts on ! private magnet1 !nce ?r\gh ! f\r? wip] on ! side swit* to its ?ird contact1 !nce ?r\gh ! r++ relay magnet1 & ?r\gh ! spr+s #af & #ag ( ! call+ batt]y supply relay & to batt]y4 ,! call+ batt]y supply relay w9d+ be+ 9 s]ies ) ! v]tical relay w9d+1 ! two op]ate toge!r & close ! two normally op5 po9ts 9 ! r++ relay circuit4 ,?is r++ relay acts z an ord9>y r++ key & connects ! g5]ator to ! call$ subscrib]'s l9e 9 an obvi\s mann]1 at ! same "t op5+ ! talk+ circuit back ( ! r++ relay 9 ord] to prev5t ! r++ curr5t *att]+ ! relays 9 ! circuit back ( x4 ,all t rema9s n[ is = ! call$ subscrib] to respond4 ,:5 he does he closes ! metallic circuit ( ! l9e ?r\gh 8 talk+ app>atus4 ,batt]y ,supply to ,connect$ ,subscrib]4 ,?r\gh\t ! :ole process ( build+ up a connection1 x w be rememb]$ t bo? sides ( ! call+ l9e are connect$ ?r\gh ! respective v]tical & rot>y relays involv$ 9 build+ up ! connection ) ! live side ( ! batt]y4 ,at ! "t :5 ! connection is f9ally e/abli%$ & ! call$ subscrib] rung1 bo? sides ( ! call+ l9e are connect$ ?r\gh v>i\s relay w9d+s to ! live side ( ! batt]y4 ,su* a condition leaves bo? sides ( ! l9e at ! same pot5tial &1 !re=e1 !re is no t5d5cy = curr5t to fl[ ?r\gh ! call+ subscrib]'s talk+ app>atus1 ev5 ?\gh x is connect$ across ! circuit ( ! l9e4 ,x rema9s1 !re=e1 to be se5 h[ ^! conditions are s *ang$ aft] ! build+ up ( a connection z to supply ! call+ subscrib] ) talk+ curr5t4 ,! call+ subscrib] c get no curr5t until ! call$ subscrib] responds4 ,:5 ! connection is fir/ made ) ! call$ subscrib]'s l9e1 batt]y connection to 8 l9e is made f ! live side ( batt]y ?r\gh ! normally clos$ contacts ( ! call+ batt]y supply relay1 !nce ?r\gh ! w9d+ #be ( ! call$ batt]y supply relay to ! v]tical side ( ! call$ l9e4 ,! gr\nd$ side ( ! batt]y is connect$ to ! rot>y side ( 8 l9e ?r\gh ! ?ird wip] ( ! connector & ! coil #bf ( ! call$ batt]y supply relay4 ,z a result1 ?is subscrib] receives prop] talk+ curr5t ?r\gh ! coils #be & #bf1 & ?is relay is op]at$ by ! fl[ ( ?is curr5t4 ,! op]ation ( ?is call$ batt]y supply relay m]ely %ifts ! connection ( ! rot>y side ( ! call+ subscrib]'s l9e f its normal batt]y connection1 to gr\nd1 & ?us ! batt]y is plac$ /raight across ! call+ subscrib]'s l9e s z to supply talk+ curr5t4 ,?is supply circuit to ! call+ subscrib] may be trac$ f ! live side ( ! batt]y ?r\gh ! w9d+ #ac ( ! call+ batt]y supply relay & ! w9d+ ( ! v]tical relay to ! v]tical side ( ! l9e1 & f ! gr\nd$ side ( batt]y ?r\gh ! ?ird side swit* wip] 9 its ?ird position to ! n[ clos$ pair ( contacts 9 ! call$ batt]y supply relay ?r\gh ! coil #ah ( ! call+ batt]y supply relay & ! coil ( ! rot>y relay to ! rot>y side ( ! l9e4 ,x w be not$ t ! sy/em ( batt]y supply is t ( ! /&>d cond5s] & ret>dation coil s*eme l>gely employ$ 9 manual practice2 & t aside f ! coils ?r\gh :i* ! batt]y curr5t is suppli$ to ! connect$ subscrib]s1 !re are no taps f1 or bridges across1 ! two sides ( ! talk+ circuit4 ,release aft] ,conv]sation4 ,x rema9s n[ only to secure ! disconnection ( ! subscrib]s aft] !y are ?r\gh talk+4 ,:5 ! call+ subscrib] hangs up1 ! :ole disconnection is br\ght ab\t1 all ( ! app>atus1 includ+ connector1 selectors1 & l9e swit*1 return+ to normal4 ,?is is done by ! back release sy/em & is accompli%$ 9 almo/ ! same way z has already be5 describ$ 9 connection ) ! disconnect aft] an unsuccessful call4 ,!re is ?is diff]5ce1 h[ev]3 aft] an unsuccessful call :5 ! l9e call$ = 0 f\nd busy1 ! release 0 made :ile ! connector side swit* 0 9 its normal position4 ,9 ! pres5t case1 ! release mu/ be made ) ! connector side swit* 9 its ?ird position & ) ! talk+ batt]y bridg$ across ! metallic circuit r ?an connect$ betwe5 ea* limb ( ! l9e & gr\nd4 ,x mu/ be rememb]$ t ! call+ batt]y supply relay1 :ile trav]s$ by curr5t dur+ ! conv]sation1 is n magnetically en]giz$ because1 ) ! curr5t fl[+ ?r\gh ! metallic circuit ( ! l9e1 ! two w9d+s ex]t a diff]5tial effect4 ,z soon1 h[ev]1 z ! call+ subscrib] hangs up 8 receiv]1 ?is diff]5tial action ceases1 due to ! gr\nd+ ( bo? sides ( ! l9e at ! subscrib]'s /ation4 ,?is relay1 !re=e1 op]ates & cuts (f batt]y f ! call$ batt]y supply relay & ?is1 9 turn1 releases its armature & ?us *anges ! connection ( ! rot>y side ( ! call+ l9e f gr\nd to live side ( ! batt]y4 ,! normal condition ( ! batt]y connection n[ be+ re/or$1 bo? ! v]tical & ! rot>y relays at ! connector become op]at$1 due to ! gr\nd on bo? sides ( ! l9e at ! subscrib]'s /ation1 & ?is1 z we h se51 is ! condition :i* br+s ab\t ! op]ation ( ! connector release magnet1 & ! relay+ back ( ! disconnect impulse successively ?r\gh ! selectors to ! l9e swit*4 ,multi-,(fice ,sy/em4 ,9 ex*anges involv+ m ?an "o (fice1 ! same g5]al pr9ciples & mode ( op]ation already outl9$ apply4 ,if ! total numb] ( subscrib]s 9 ! multi-(fice ex*ange is to be less ?an t5 ?\s&1 !n f\r digit numb]s suffice1 & ! fir/ movem5t ( ! dial may be made to select ! (fice into :i* ! connection is to g1 ! subscrib]s' l9es be+ s numb]$ ) respect to ! (fices t ea* (fice w conta9 only c]ta9 ?\s&s4 ,! *oos+ ( ! ?\s& by ! call+ subscrib]1 !re=e1 takes c>e 9 itself ( ! *oice ( (fices4 ,:]e1 h[ev]1 a multi-(fice ex*ange is to provide = connections among a great] numb] ( l9es ?an t5 ?\s& & less ?an "o hundr$ ?\s&1 !n x w take five movem5ts ( ! dial to make ! selection--! five movem5ts correspond+ ei!r to ! five digits 9 a numb] or to ! "n ( an (fice1 z indicat$ on ! dial1 & ! f\r digits ( a small] numb]4 ,! l9es may all c>ry five digit numb]s or1 :at is consid]$ bett] practice1 may be designat$ by an (fice "n foll[$ by a f\r digit numb]4 ,9 ?is latt] case ! numb]s ( ! subscrib]s' l9es w 9 ea* case be conta9$ 9 "o or m ( ! t5s ( ?\s&s gr\ps1 no numb] hav+ m ?an f\r digits4 ,& ! fir/ movem5t ( ! dial1 :e!r ! "n or numb] plan be adopt$1 w select an (fice2 or1 look+ at x ano!r way1 w select a gr\p ( t5 ?\s& & ?is be+ done1 ! next f\r successive movem5ts ( ! dial w select ! numb]s 9 t t5 ?\s& 9 j ! "s way t has be5 already describ$4 ,c]ta9 difficulties arise1 h[ev]1 9 multi-(fice work+ due to ! fact t ! ?ree-wire trunks betwe5 (fices w\ld 9 mo/ cases be objectionable4 ,z long z ! trunks ext5d betwe5 ! v>i\s gr\ps ( app>atus 9 ! same (fice1 x is *eap] to provide ?ree wires = ea* ( !m ?an x is to make any additional complication 9 ! app>atus4 ,:]e ! trunk+ is done betwe5 (fices1 h[ev]1 ! sy/em may be s modifi$ z to "w ov] two wire int]-(fice trunks4 ,! ,trunk ,repeat]4 ,! purpose ( ! trunk repeat] is to enable ! int]-(fice trunk+ to be done ov] two wires4 ,x may be said t ! trunk repeat] is a device plac$ 9 ! outgo+ trunk circuit at ! (fice 9 :i* a call orig9ates1 :i* w d ov] ! two wires ( ! trunk lead+ f x to ! di/ant (fice j ! same ?+ t ! subscrib]'s signal transmitt] does ov] ! two wires ( ! subscrib]'s l9es4 ,x has c]ta9 o!r functions 9 reg>d to fe$+ ! batt]y = talk+ purposes back to ! call+ subscrib]'s l9e1 tak+ ! place 9 ?is respect ( ! call+ batt]y fe$ relay 9 ! connector 9 a s+le (fice ex*ange4 ,illu/ration3 ,fig4 #cig4 ,circuits ( ,trunk ,repeat] ,! circuits ( a trunk repeat] are %[n 9 ,fig4 #cig4 ,9 consid]+ x1 x mu/ be und]/ood t ! ?ree wires ent]+ ! figure at ! left are ! v]tical1 rot>y1 & release wires ( a second selector trunk lead+ f ! fir/ selector banks 9 ! same (fice4 ,! two wires lead+ f ! "r ( ! figure are ^? ext5d+ to ! di/ant (fice1 & t]m9ate !re 9 second selectors4 ,! v]tical & ! rot>y sides ( ?is trunk z %[n at ! left w receive ! impulses f ! subscrib]'s /ation com+ ?r\gh ! l9e swit* & ! fir/ selector1 z usual4 ,! v]tical impulses w pass ?r\gh ! w9d+ ( ! v]tical relay & ?r\gh ! w9d+ #a ( ! call+ batt]y supply relay & !nce to batt]y1 ! same z on a connector4 ,^! impulses w "w ! armatures ( bo? ( ^! relays 9 unison4 ,! movem5ts ( ! v]tical relay armature 9 response to ^! impulses w cause correspond+ impulses to fl[ ov] a circuit :i* may be trac$ f gr\nd1 ?r\gh ! spr+s #c & #b ( ! v]tical relay1 ! spr+s #d & #e ( ! bridg$ relay #f & !nce to ! v]tical side ( ! trunk & to ! di/ant (fice1 :]e x passes into a second selector & ?r\gh its v]tical relay to batt]y4 ,?us ! v]tical impulses are pass$ on ov] ! two-wire trunk to ! second selector at ! di/ant (fice4 ,x becomes necess>y1 h[ev]1 to prev5t ^! impulses f pass+ back ?r\gh ! w9d+ ( ! bridge relay #f & ?is is done by means ( ! sluggi% relay #g4 ,?is relay receives local batt]y impulses 9 unison ) ^? s5t ov] ! trunk by ! v]tical relay1 ^! be+ suppli$ f ! batt]y at ! local (fice ?r\gh ! contacts #h & #i ( ! call+ batt]y supply relay1 :i* works 9 unison ) ! v]tical relay4 ,^! rapidly recurr+ impulses are too fa/ = ! sluggi% relay #g to foll[4 ,& ?is relay m]ely pulls up its armature & cuts (f bo? sides ( ! trunk lead+ back to ! fir/ selector4 ,! rot>y impulses are repeat$ to ! rot>y side ( ! two-wire trunk 9 a simil> way4 ,consid]+ n[ ! op]ation ( ! trunk repeat] 9 ! rev]se direction1 ! action ( ! bridg+ relay #f is ( vital importance4 ,normally bo? sides ( trunk l9e are connect$ to ! live side ( ! batt]y &1 !re=e1 !re is no diff]5ce ( pot5tial betwe5 !m & no t5d5cy to op]ate ! bridg$ relay4 ,:5 ! connection has be5 fully e/abli%$ to ! subscrib] at ! di/ant (fice1 & t subscrib] has respond$1 ! action ( 8 batt]y supply relay w1 z be=e /at$1 *ange ! connection ( ! rot>y side ( ! l9e f batt]y to gr\nd1 & ?us bridge ! batt]y at ! di/ant ex*ange across ! trunk4 ,?is action w pull up ! bridg$ relay #f at ! trunk repeat] & w p]=m exactly ! same function ) respect to ! connection ( ! batt]y ) ! call+ subscrib]'s l9e4 ,9 o!r words1 x w *ange ! connection ( ! rot>y side ( ! call+ l9e f batt]y to gr\nd1 ?us e/abli%+ ! necess>y diff]5ce 9 pot5tial to give ! call+ subscrib] ! necess>y curr5t = transmission purposes4 ,! disconnect feature is ab\t ! same z already describ$4 ,:5 ! call+ subscrib] hangs up 8 receiv] bo? ! v]tical & rot>y relays ( ! trunk repeat] op]ate1 :i* places ! gr\nd on bo? sides ( ! two-wire trunk to ! di/ant (fice1 :i* is ! condition = releas+ all ( ! app>atus !re4 ,= ! purpose ( conv5i5ce ! simplifi$ diagram ( ,fig4 #cih has be5 prep>$1 :i* %[s ! complete connection f a call+ subscrib] to a call$ subscrib] 9 a multi-(fice ex*ange1 :]e9 ! fir/ movem5t ( ! dial is employ$ to e/abli% ! connection to ! prop] (fice & ! f\r succe$+ movem5ts to make a selection among t5 ?\s& l9es 9 t (fice4 ,?is circuit1 !re=e1 employs at ! fir/ (fice ! l9e swit*1 ! fir/ selector1 & ! trunk repeat]2 & at ! second (fice ! second selector1 ?ird selector1 connector1 & l9e swit*4 ,! ?ird selector is omitt$ f ,fig4 #cih1 b ?is w cause no confusion1 s9ce x is exactly l ! second selector4 ,! circuits %[n are exactly l ^? previ\sly describ$ b 9 draw+ !m ! ma9 idea has be5 to simplify ! connections to ! greate/ possible ext5t at a sacrifice 9 ! cle>ness ) :i* ! me*anical int]-relation ( p>ts is %[n4 ,no correct und]/&+ ( ! circuits ( an automatic sy/em is possible )\t a cle> idea ( ! me*anical functions p]=m$ by ! diff]5t p>ts1 &1 !re=e1 we h describ$ :at are app>5tly ! m complex circuit draw+s fir/4 ,x is believ$ t ! /ud5t1 9 attempt+ to ga9 an und]/&+ ( ?is m>vel ( me*anical & electrical intricacy1 w f9d 8 task less burd5some if he w ref] freely to bo? ! simplifi$ circuit draw+ ( ,fig4 #cih & ! m complex ones prec$+ x4 ,by do+ s he w (t5 be enabl$ to cle> up a d\btful circuit po9t f ! simpl] diagram & a d\btful me*anical po9t f ^? diagrams :i* repres5t m cle>ly ! me*anical relation ( p>ts4 ,illu/ration3 ,fig4 #cih4 ,connection betwe5 a ,call+ & a ,call$ ,subscrib] 9 an ,automatic ,sy/em ,automatic ,sub-,(fices4 ,obvi\sly1 ! sy/em ( trunk+ employ$ 9 automatic ex*anges l5ds itself ) great facility to ! subdivision ( an ex*ange into a l>ge numb] ( comp>atively small (fice di/ricts & ! e/abli%m5t ( bran* (fices or sub-(fices at ! c5t]s ( ^! di/ricts4 ,! trunk+ betwe5 l>ge (fices has already be5 describ$4 ,an attractive feature ( ! automatic sy/em is ! e/abli%m5t ( s-call$ sub-/ations or sub-(fices4 ,:]e !re is1 9 an outly+ di/rict1 a di/9ct gr\p ( subscrib]s ^: l9es may readily be c5t]$ at a common po9t )9 t di/rict & :]e ! numb] ( su* subscrib]s & l9es is insuffici5t to e/abli% a fully equipp$ (fice1 x is possible to e/abli% a s-call$ sub-/ation or sub-(fice connect$ ) ! ma9 (fice ( t di/rict by trunk l9es4 ,at ?is sub-(fice !re are plac$ only l9e swit*es & connectors4 ,:5 a call is orig9at$ on "o ( ^! sub-(fice l9es1 ! l9e swit* acts in/antly to connect t l9e ) "o ( ! trunks lead+ to ! ma9 (fice ( t di/rict1 at :i* ?is trunk t]m9ates 9 a fir/ selector4 ,f !re on1 ! connection is ! same z t 9 a sy/em 9 :i* no sub-(fices are employ$4 ,calls com+ into ?is sub-(fice ov] trunk l9es f ! ma9 (fice are receiv$ on ! connectors at ! sub-(fice & ! connection is made ) ! sub-(fice l9e by ! connector 9 ! usual mann]4 ,?is arrangem5t1 x is se51 am\nts m]ely to a /ret*+ ( ! connector trunks = a giv5 gr\p ( l9es s t !y w rea* out f a ma9 (fice to a sub-(fice1 x be+ m economical to l5g!n ! small] numb] ( trunks & by s do+ to decrease 9 l5g? ! l>g] numb] ( subscrib]s' l9es4 ,! ,rot>y ,connector4 ,= c]ta9 purposes x becomes desirable 9 automatic "w to employ a special =m ( connector :i* w h 9 itself a c]ta9 ability to make automatic selection ( "o ( a gr\p ( previ\sly *os5 trunks 9 mu* ! same mann] z ! fir/ & second selectors automatically *oose ! fir/ idle "o ( a gr\p ( trunks4 ,su* a use is dem&$ 9 private bran*-ex*ange work+ :]e a giv5 bus9ess e/abli%m5t1 = in/ance1 has a plurality ( l9es connect+ its own private swit*bo>d ) ! c5tral (fice4 ,! directory numb] ( all ^! l9es is1 = conv5i5ce1 made ! same1 & x is important1 !re=e1 t :5 a p]son attempts to make a connection ) ?is e/abli%m5t1 he w n fail to get 8 connection simply because ! fir/ "o ( ^! l9es happ5s to be busy4 ,= su* use a giv5 horizontal r[ ( connector t]m9als or a "p ( su* a r[ is assign$ to ! l9es lead+ to ! private bran* ex*ange & ! connector is s modifi$ z to h a c]ta9 discretion>y p[] ( its own4 ,z a result1 :5 ! common numb] ( all ^! l9es is call$1 ! connector w *oose ! fir/ "o1 if x is n already engag$ by "s o!r connector1 b if x is1 x w pass on to ! next1 & s on until an idle "o is f\nd4 ,x is only :5 ! connector has hunt$ ?r\gh ! entire gr\p ( l9es & f\nd !m all busy t x w refuse to connect & w give ! busy signal to ! call+ subscrib]4 ,p>ty ,l9es4 ,! description ( ?is sy/em z giv5 above has be5 conf9$ entirely to direct l9e work+2 h[ev]1 p>ty l9es may be & are frequ5tly employ$4 ,! circuits & app>atus us$ ) direct l9es are1 ) slight modifications1 applicable to use ) p>ty l9es4 ,! h>monic me?od ( r++ is employ$ & ! /ations are s arrang$ ) respect to ! connectors t ^? requir+ ! same frequ5cy = r++ ! bells are 9 gr\ps s]v$ by ! same set ( connectors4 ,illu/ration3 ,,p[] ,,ma*9]y ,citiz5s' ,telephone ,company1 ,rac9e1 ,wis4 ,! ,dean ,electric ,co4 ,! p>ty l9es are op]at$ on ! pr9ciple commonly kn[n 9 manual practice z ! jack p] /ation arrangem5t4 ,ea* p>ty l9e w1 !re=e1 h sets ( t]m9als appe>+ 9 sep>ate hundr$s2 ! connectors associat$ ) ea* ( ^! hundr$s be+ s arrang$ z to impress ! prop] frequ5cy ( r++ curr5t on ! l9e4 ,f ! subscrib]s' /&po9t ! op]ation is ! same z = direct l9es1 z ! p>ticul> hundr$s digit ( a numb] s]ves to select "o ( a gr\p ( connectors capable ( connect+ ! prop] r++ curr5t to ! l9e4 ,to avoid confusion1 :i* w\ld be caus$ by a subscrib] on a p>ty l9e attempt+ to make a call :5 ! l9e is already 9 use by "s o!r subscrib]1 ! subscrib]s' /ations are s arrang$ t :5 ! l9e is 9 use all o!r /ations on ! l9e are lock$ out4 ,illu/ration3 ,fig4 #cii4 ,wall ,set = ,two-,wire ,sy/em ,! ,two-,wire ,automatic ,sy/em4 ,! two-wire sy/em t has rec5tly be5 introduc$ by ! ,automatic ,electric ,company br+s ab\t ! v important result ( accompli%+ all ( ! automatic swit*+ ov] metallic circuit l9es )\t ! use ( gr\nd or common returns4 ,! sy/em is ?us reliev$ ( ! di/urb+ influ5ces to :i* ! ?ree-wire sy/em is sometimes subject$1 due to diff]5ces 9 e>? pot5tial betwe5 v>i\s portions ( ! sy/em1 :i* may add to or subtract f ! batt]y pot5tial & alt] ! net pot5tial available betwe5 two di/ant po9ts4 ,! introduction ( ?is sy/em has also made possible c]ta9 o!r incid5tal features ( advantage1 "o ( :i* is a great simplification & r$uction 9 size ( ! subscrib]'s /ation signal-transmitt+ app>atus4 ,) ! do+ away ( ! gr\nd z a return circuit1 x becomes impossible to s5d v]tical impulses ov] "o side ( ! l9e & to foll[ !m by s+le rot>y impulses ov] ! o!r side ( ! l9e4 ,yet x becomes necess>y to di/+ui% betwe5 ! pure selective impulses & ^? impulses :i* dictate a *ange ( function at ! c5tral (fice4 ,! plan has1 !re=e1 be5 adopt$ ( accompli%+ ! selection 9 ea* case by %ort & rapidly recurr+ impulses & ( accompli%+ ^? functions =m]ly br\ght ab\t by ! s+le impulse ov] ! rot>y side ( ! l9e by a pause betwe5 ! respective s]ies ( selective impulses4 ,?is is accompli%$ at ! c5tral (fice by replac+ ! v]tical & ! rot>y relays ( ! ?ree-wire sy/em by a quick-act+ & a sluggi% relay1 respectively2 ! quick-act+ relay p]=m+ ! functions previ\sly c>ri$ out by ! v]tical relay1 & ! sluggi% relay act+ only dur+ ! pauses betwe5 ! successive s]ies ( quick impulses to d ! ?+s =m]ly done by ! rot>y relay4 ,?is has result$ 9 a delightful simplification ( subscrib]'s app>atus1 s9ce x is n[ necess>y only to provide a device :i* w connect ! two sides ( ! l9e toge!r ! requir$ numb] ( times 9 quick succession & !n all[ a pause ) ! circuit clos$ :ile ! subscrib] is gett+ ready to transmit ano!r set ( impulses correspond+ to ano!r digit4 ,! call+ device has no me*anical function co-act+ ) any ( ! o!r p>ts ( ! telephone & may be consid]$ z a sep>ate me*anical device electrically connect$ ) ! l9e4 ,! transmitt+ device is n mu* l>g] ?an a l>ge wat* & a good idea ( x may be _h f ,fig4 #cii1 :i* %[s ! late/ wall set1 & ,fig4 #djj1 :i* %[s ! late/ desk set ( ! ,automatic ,electric ,company4 ,we regret ! fact t ?is company has made ! reque/ t ! complete details ( _! two-wire sy/em be n publi%$ at ?is "t4 ,illu/ration3 ,fig4 #djj4 ,desk ,/& = ,two-,wire ,sy/em ,,*apt] ,,xxx ,,! ,,lorim] ,,automatic ,,sy/em ,! ,lorim] automatic telephone sy/em has n be5 comm]cially us$ 9 ?is c\ntry b is 9 comm]cial op]ation 9 a few places 9 ,canada4 ,x is int]e/+ f sev]al po9ts ( view4 ,x 0 inv5t$1 built1 & in/all$ by ! ,lorim] ,bro!rs--,hoyt1 ,george ,william1 & ,egb]t--( ,brant=d1 ,ont>io4 ,^! "y m5 )\t previ\s telephonic tra9+ &1 accord+ to _! /atem5ts1 )\t ev] hav+ se5 ! inside ( a telephone (fice1 conceiv$ & develop$ ?is sy/em & put x 9 practical op]ation4 ,) ! /ruggles & ef=ts ( ^! "y m5 9 accompli%+ ?is feat we h "s famili>ity1 & x impresses u z "o ( ! mo/ rem>kable inv5tive a*ievem5ts t has come to our att5tion1 reg>dless ( :atev] ! m]its or dem]its ( ! sy/em may be4 ,! ,lorim] sy/em is int]e/+ also f ! fact t1 9 mo/ cases1 x repres5ts ! me*anical r ?an ! electrical way ( do+ ?+s4 ,! swit*es are p[] driv5 & electrically controll$ r ?an electrically driv5 & electrically controll$1 z 9 ! sy/em ( ! ,automatic ,electric ,company4 ,! subscrib]'s /ation app>atus consi/s ( ! usual receiv]1 spee* transmitt]1 call bell1 & hook swit*1 & 9 addition a signal transmitt] arrang$ to be manipulat$ by ! subscrib] s z to control ! op]ation ( ! c5tral-(fice app>atus 9 connect+ ) any desir$ l9e 9 ! sy/em4 ,! c5tral-(fice app>atus is design$ ?r\gh\t ^u ! pr9ciple ( swit*+ by means ( p[]-driv5 swit*es :i* are "u ! control ( ! signal transmitt]s ( ! call+ subscrib]'s /ation4 ,! swit*es employ$ 9 mak+ a connection are all s arrang$ ) respect to con/antly rotat+ %afts t ! movable memb] ( su* swit*es may be connect$ to ! %afts by means ( electromagnets controll$ directly or indirectly by relays1 :i*1 9 turn1 are br\ght "u ! control ( ! signal transmitt]s4 ,! circuits are s design$ 9 _m in/ances t ! *anges necess>y = ! diff]5t /eps are br\ght ab\t by ! movem5t ( ! swit*es !mselves1 ?us p]mitt+ ! use ( circuits :i* are r simple4 ,! swit*es employ$ are all ( a rot>y type2 ! co-ord9ate selection1 :i* is accompli%$ 9 ! ,automatic ,electric ,company's sy/em by a v]tical & rot>y movem5t1 be+ br\ght ab\t 9 ?is sy/em by ! indep5d5t rotation ( two swit*es4 ,subscrib]'s ,/ation ,equipm5t4 ,a subscrib]'s desk-/& set1 except ! call bell1 is %[n 9 ,fig4 #dja1 & a wall set complete 9 ,fig4 #djb4 ,9 bo? ( ^! illu/rations may be se5 ! famili> transmitt]1 receiv]1 & hook swit*1 & 9 ! wall set1 ! call bell4 ,! portion ( ^! telephone sets :i* is unfamili> at pres5t is ! "p :i* is enclos$ 9 ! enl>g$ base ( ! desk /& & ! protrud+ device bel[ ! spee* transmitt] 9 ! wall set--! signal transmitt] ref]r$ to e>li] 9 ! *apt]4 ,! small pu% button & small plate ?r\gh :i* ! numb] may be se5 directly bel[ ! transmitt] 9 ,fig4 #djb1 are = ! purpose ( regi/]+ calls4 ,illu/ration3 ,fig4 #dja4 ,lorim] ,automatic ,desk ,/& ,! signal transmitt] is a device ^: function is to record me*anically ! numb] ( ! subscrib]'s /ation ) :i* connection is desir$1 & to transmit t record to ! c5tral (fice by a sy/em ( electrical impulses ov] ! l9e conductors4 ,in/ead ( op]at+ by its own initiative1 ! signal transmitt] is adapt$ to respond to c5tral-(fice control 9 transmitt+ electrically ! numb] :i* has be5 record$ me*anically ^u x4 ,! signal transmitt] %[n remov$ f ! base ( ! desk /& at ! left 9 ,fig4 #djc comprises 9 "p f\r sets ( contact p9s hav+ t5 p9s 9 ea* set1 "o set = ea* ( ! digits ( a f\r-digit numb]4 ,!re are also sev]al additional contact p9s = signal+ & auxili>y controll+ purposes4 ,all ( ^! contact p9s are arrang$ ^u ! circumf]5ce ( a circle & a movable bru% m\nt$ ^u a %aft at ! c5t] ( ! circle is adapt$ to be rotat$ by a clock spr+ & to make contact ) ea* ( ! p9s successively4 ,! call is />t$1 aft] ! numb] desir$ has be5 set on ! dial1 by giv+ ! crank at ! "r ( ! signal transmitt] a complete turn & ?us w9d+ ! spr+4 ,! %aft c>ry+ ! signal transmitt] bru% c>ries also an escapem5t :eel1 ! pallet ( :i* is directly controll$ by an electromagnet4 ,illu/ration3 ,fig4 #djb4 ,lorim] ,automatic ,wall ,set ,! f\r dials ) ! num]als pr9t$ on !m are atta*$ to f\r lev]s1 respectively1 & are mov$ by _! lev]s opposite w9d[s1 ne> ! top ( ! cas+4 ,?r\gh ea* ( ^! w9d[s a s+le num]al may be se5 on ! correspond+ "o ( ! dials4 ,! dials may be adju/$ s t ! f\r num]als se5 w read f left to "r to correspond to ! numb] ( ! l9e ) :i* connection is desir$4 ,! sett+ ( ! dials s t ! numb] desir$ %[s at ! small circul> op5+ results 9 connect+ ! e>? or a common return conductor to "o p9 ( ea* set ( t5 p9s1 ! p9 gr\nd$ 9 ea* set dep5d+ ^u ! num]ical value ( ! digit = :i* ! dial is set4 ,! circle ( contact p9s is set 9 an insulat+ disk1 ! signal transmitt+ bru% op]ates ^u ! p9s on "o side ( ! disk1 & electrical f+]s atta*$ to ! dials op]ate ^u ! p9s on ! o!r side ( ! disk4 ,! escapem5t :eel is a s+le too!d disk atta*$ directly to ! %aft :i* c>ries ! signal bru% & its pallet is atta*$ rigidly to ! magnet armature4 ,illu/ration3 ,fig4 #djc4 ,desk ,/& ) ,signal ,transmitt] ,remov$ ,once a call has be5 turn$ 91 ! entire subscrib]'s /ation equipm5t is lock$ beyond p[] ( ! subscrib] to tamp] ) x 9 any way1 r5d]+ x impossible ei!r to defeat ! call :i* has be5 />t$ or to prev5t ! subscrib]'s /ation z a :ole f return+ completely to normal position & ?us re/or+ itself = regul> s]vice4 ,! key %[n j bel[ ! signal transmitt] 9 ! case ( ! desk /&1 & at ! "r 9 ! wall set1 is = ! purpose ( op]at+ a relay at ! c5tral (fice :i*1 9 turn1 connects r++ curr5t to ! l9e ( ! subscrib] ) :i* connection has be5 made1 & ?us actuates ! call bell4 ,z ! numb] set up at ! signal transmitt] rema9s 9 full view until reset = "s o!r numb]1 x is easily *eck$ by inspection & also less5s ! labor involv$ 9 mak+ a second call = ! same l9e1 :i* is frequ5tly necess>y :5 ! l9e is f\nd busy ! fir/ "t call$4 ,c5tral-,(fice ,app>atus4 ,! subscrib]'s l9es are divid$ into gr\ps ( "o hundr$ l9es ea* at ! c5tral (fice1 ea* gr\p be+ s]v$ by a s+le unit ( c5tral-(fice app>atus4 ,9 a c5tral-(fice unit !re is sectional app>atus :i* appe>s b once = ! unit ( "o hundr$ l9es2 divisional app>atus :i* appe>s a numb] ( times = ea* unit1 dep5d+ ^u ! traffic2 & l9e app>atus :i* appe>s "o hundr$ times = ea* unit or once = ea* l9e4 ,! sectional app>atus comprises devices ^: duties are1 fir/1 to detect a call+ l9e1 & second1 to assign to ! call+ l9e a set ( idle divisional app>atus :i* s]ves to p]=m ! necess>y swit*+ functions & complete ! connection4 ,! sets ( divisional app>atus1 or1 z call$ 9 ?is sy/em1 divisions1 are common to a section & are employ$ 9 a mann] simil> to ! connect+ cords ( a manual swit*bo>d4 ,! numb] ( ^! divisions provid$ = ea* section is1 !re=e1 det]m9$ by ! numb] ( simultane\s connections result+ f calls orig9at+ 9 ! section4 ,x has be5 ! cu/om 9 build+ ?is app>atus to provide ea* section ) sev5 divisions or connective elem5ts4 ,! l9e app>atus comprises "o relay1 hav+ a s+le w9d+1 & two pairs ( contacts op]at$ by its armature4 ,?is device is sub/antially ! well kn[n cut-(f relay almo/ univ]sally employ$ 9 common-batt]y sy/ems4 ,! fix$ multiple contacts ( ! l9es 9 ! swit*+ banks ( ! connect+ app>atus are consid]$ z p]ta9+ to ! v>i\s pieces ( app>atus on :i* !y are f\nd r ?an to _! respective l9es4 ,a good idea may be obta9$ ( ! arrangem5t ( ! sectional & divisional app>atus by ref]r+ to ,fig4 #djd1 :i* is "o unit ( a ?\s&-l9e equipm5t4 ,! app>atus 9 ! v]tical r[ at ! extreme left ( ! illu/ration is ! sectional app>atus1 :ile ! rema9+ sev5 v]tical r[s ( app>atus are ! divisions4 ,! ,section4 ,! sectional app>atus = ea* unit consi/s ( ?ree sep>ate devices call$ = conv5i5ce a decimal indicator1 a division />t]1 & a decimal-regi/] controll]4 ,all ( ^! devices are normally motionless :5 idle4 ,! en]gization ( ! decimal indicator1 9 response to ! inauguration ( a call at a subscrib]'s /ation1 results imm$iately 9 an action ( ! division />t] :i* />ts a division to connect ) ! l9e call+4 ,x results also 9 ! />t+ ( ! decimal-regi/] controll]1 ! rema9+ unit ( sectional app>atus4 ,x is ?us se5 t ^u ! />t+ ( a call by a subscrib]1 all ( ! sectional app>atus belong+ to 8 "o hundr$ l9es imm$iately becomes active1 ! division />t] act+ to />t a division1 ! decimal indicator becom+ en]giz$ to indicate ! t5s gr\p 9 :i* ! call has appe>$1 & ! decimal-regi/] controll] becom+ active to adju/ ! decimal regi/] ( ! division assign$ by ! division />t]4 ,! division />t] hav+ assign$ a division = ! exclusive use ( ?is p>ticul> call1 passes to a position f :i* x may />t a simil> idle division :5 ! next call is receiv$4 ,! decimal regi/] controll] makes its half revolution = ! call & comes to re/1 await+ a subsequ5t call1 & ! decimal indicator cont9ues en]giz$ b only mom5t>ily1 s9ce x is releas$ by ! action ( ! cut-(f relay :5 ! call is tak5 9 *>ge by ! divisional connective devices4 ,calls may foll[ ea* o!r rapidly1 ! connective devices be+ entirely indep5d5t ( ea* o!r aft] hav+ be5 assign$ to ! respective call+ l9es4 ,z has be5 describ$1 ! decimal indicator />ts ! division />t] & ! decimal-regi/] controll] 9 quick succession4 ,! division />t]1 %[n at ! extreme bottom ( ! left-h& r[ ( ,fig4 #djd1 is a cyl9d] swit* ( ! same g5]al type z us$ ?r\gh\t ?is sy/em4 ,9 x ! t]m9als ( a swit* 9 ea* division appe> z fix$ contact po9ts 9 a circle ov] :i* move ! bru%es ( ! division />t]4 ,! decimal-regi/] controll] has ! duties ( transmitt+ to ! divisional app>atus a s]ies ( curr5t impulses correspond+ 9 numb] to ! num]ical value ( ! t5s digit ( ! call+ l9e4 ,?is is effect$ by provid+ be=e a movable bru% t5 contacts f :i* ! bru% may receive curr5t4 ,^! contacts are normally n connect$ to batt]y1 s t ! bru% 9 pass+ ov] !m does n receive curr5t f !m2 h[ev]1 :5 ! bru% has rea*$ ! contact correspond+ 9 numb] to ! t5s digit ( ! call+ l9e1 a relay associat$ ) ! decimal-regi/] controll] *>ges ! contacts ) ! pot5tial ( ! ma9 batt]y1 & ea* ( ! rema9+ contacts pass$ ov] by ! bru% s5ds a curr5t impulse to a device design$ to indicate on ! division select$ = ! call ! t5s digit ( ! call+ l9e4 ,! ,connective ,division4 ,! connective division1 sev5 ( :i* are %[n 9 ,fig4 #djd1 is an assemblage ( swit*es compris+1 z a :ole1 a set suitable = a complete connection f call+ to call$ subscrib]4 ,ea* connective division 9 ! unit illu/rat$ is completely equipp$ to c>e = a call$ numb] ( ?ree digits1 i4 e41 ea* division w connect its call+ l9e ) any "o ( "o ?\s& l9es :i* may be call$4 ,by a sy/em ( int]connect+ betwe5 divisions1 ea* division may be equipp$ ) int]connect+ app>atus s z to make x possible to complete a call ) any "o ( t5 ?\s& l9es4 ,ea* connect+ division ( a t5-?\s&-l9e ex*ange comprises six major swit*es4 ,( ! six major swit*es1 "o is t]m$ a second>y connector1 ano!r an int]connector1 & ! f\r rema9+ are t]m$ ! prim>y portion ( ! division4 ,illu/ration3 ,fig4 #djd4 ,unit ( ,swit*+ ,app>atus ,be=e tak+ up ! op]ation ( ! swit*es1 ! me*anical nature ( ! swit*es !mselves w be describ$4 ,! swit*es are built ) a contact bank cyl9drical 9 =m & ) int]nal movable bru%es travel+ 9 a rot>y mann] 9 circul> pa?s ^u horizontal r[s ( contacts fix$ 9 ! cyl9drical banks4 ,= driv+ ^! bru%es a con/antly rotat+ ma9 p[]-driv5 %aft is provid$4 ,betwe5 ea* %aft & ! rotat+ bru%es ( ea* major swit* is an electric clut*1 :i*1 by ! movem5t ( an armature1 causes ! bru%es ( ! swit* to p>take ( ! motion ( ! %aft & by ! return ( ! armature to come aga9 to re/4 ,! motion ( ! bru%es ( ! major swit*es1 or cyl9d] swit*es1 z !y are frequ5tly call$ because ( _! =m1 is con/antly 9 ! same direction4 ,!y h a normal position ^u a set ( ! cyl9d] contacts4 ,!y leave _! normal position & take any pr$et]m9$ position z controll$ by ! magnets ( ! clut*1 &1 hav+ s]v$ ! transi5t purpose1 !y return to _! normal position by trav]s+ ! rema9d] ( _! complete revolution & /opp+ 9 _! position ( re/ or idl5ess4 ,! me*anical con/ruction ( ea* ( ! cyl9d] swit*es is su* t x may dis5gage its clut* & br+ its bru%es to re/ only ) ! bru%es 9 "s "o ( a numb] ( pr$et]m9$ positions4 ,! locations ( ! bru%es 9 ^! positions ( re/1 or /op positions1 z !y are call$1 may diff] ) ! diff]5t cyl9d] swit*es1 accord+ to ! nature ( ! duty requir$ ( ! swit*1 & ! total numb] ( /op positions also may v>y4 ,! prim>y & second>y connectors1 ! int]connector selectors1 & ! int]connectors ea* h elev5 /op positions2 ! rot>y swit* has eight /op positions2 ! signal-transmitt] controll] has b two4 ,9 ! six cyl9d] swit*es mak+ up a connective division & requir$ = any conv]sation1 9 a t5-?\s&-l9e ex*ange "s ( ! swit*es are set to positions :i* are det]m9$ by ! control ( ! call+ subscrib] & repres5t by _! selective positions ! value ( "s digit ( ! call+ or call$ subscrib]'s numb]4 ,o!rs are swit*es controll+ ! call 9 its progress & controll+ ! swit*es responsive to ! call4 ,^! latt] swit*es take positions indep5d5t ( ! numb]s4 ,9 addition to ! major swit*es1 !re are ^u ea* division f\r m9or swit*es t]m$ regi/]s4 ,ea* consi/s ( an arc ( fix$ contacts accompani$ by a set ( bru%es :i* sweep ov] ! contacts4 ,in/ead ( be+ driv5 by an electromagnet1 ! regi/] bru%es are plac$ "u t5sion ( a spr+ :i* t5ds at all times to draw !m =w>d4 ,!y are !n re/ra9$ by an escapem5t device simil> to a pallet escapem5t 9 a clock1 ! pallet be+ controll$ by ! regi/]'s magnets4 ,:5 a s]ies ( impulses are receiv$ by ! regi/] magnets1 ! pallet is actuat$ a correspond+ numb] ( times & ! regi/] bru%es are p]mitt$ to move =w>d "u t5sion ( _! p[]ful propell+ spr+4 ,ea* regi/] is associat$ ) a major swit*1 & ! regi/] bru%es are engag$ by a cam ^u ! associat$ major swit*1 & are re/or$ to normal position aga9/ ! t5sion ( _! propell+ spr+1 ! =ce ( re/oration be+ obta9$ f ! ma9 %aft4 ,! electrical clut*es :i* connect & disconnect ! movable bru%es ( ! major swit*es f ! ma9 driv+ %aft are controll$ 9 all in/ances by circuits local to ! c5tral (fice4 ,9 "s in/ances ^! circuits include relay contacts & are controll$ by a relay4 ,9 o!r in/ances !y are =m$ solely ?r\gh swit* contacts4 ,9 all cases ! control1 :5 f a di/ance1 is receiv$ ^u relays suitable = be+ controll$ by ! small curr5ts :i* are adapt$ to fl[ ov] long l9es4 ,9 all in/ances ! p[] = mov+ a bru% is d]iv$ f ! ma9 %aft & only ! control ( ! movem5t is d]iv$ f electromagnets1 relays1 or o!r electric s\rces4 ,9 _m in/ances ! clut* circuit is clos$ ?r\gh contacts ( its own swit* &1 !re=e1 may be clos$ only :5 its swit* is 9 "s pr$et]m9$ position4 ,all ( ! swit*es are me*anically p[]ful & design$ p>ticul>ly to su/a9 ! we> ( long-cont9u$ & (t-repeat$ usage4 ,?is is true also ( ! mov+ p>ts :i* c>ry ! bru%es & ( ! j\rnals su/a9+ ^? p>ts4 ,! ,swit*es ( ! ,connective ,division4 ,! six major swit*es ( ! connect+ division are z foll[s3 ,! ,prim>y ,connector3--,! function ( ?is swit* is to connect ! conductors ( ! call+ l9e ) ! swit*+ devices ( ! connective division4 ,associat$ ) ?is swit* is a regi/] t]m$ ! decimal regi/]4 ,! "o hundr$ l9es ( ! section are t]m9at$ 9 fix$ multiple contacts 9 ! cyl9d] swit* ( ! prim>y connector4 ,! call+ l9e is select$ & connect$ ) by adju/+ ! decimal regi/] to a position correspond+ to ! call+ l9e's t5s digit & adju/+ ! bru%es ( ! cyl9d] swit* to a position correspond+ to ! call+ l9e's unit digit4 ,! ,rot>y ,swit*3--,?is is a ma/] swit*1 or pilot swit*1 consi/+ ( a cyl9d] swit* )\t regi/]4 ,its duty is ! control ( o!r swit*es & ! completion ( circuits =m$ 9 "p ?r\gh o!r swit*es4 ,x is ! pilot swit* & ! swit* ( initiative & control = ! entire connective division4 ,signal-,transmitt] ,controll]3--,! prim>y function ( ?is swit* is ! g5]ation ( signal+ impulses ( two classes4 ,impulses ( ! fir/ class pass ov] c5tral-(fice circuits only & are effective ^u magnets ( ! div]s major & m9or swit*es2 impulses ( ! second class pass ov] a l9e conductor ( ! call+ l9e & are effective ^u ! signal transmitt] at ! subscrib]'s /ation4 ,! impulses s5t out ov] ! l9e to ! subscrib]'s /ation cause ! bru% to pass ov] ! contacts & !reby indicate ! num]ical values ( ! v>i\s digits set by ! dials4 ,?is swit* also ent]s 9 an important mann] into ! circuits involv$ 9 ! te/+ ( ! call$ l9e = ! busy condition4 ,x is controll$ by ! rot>y swit*4 ,int]connector ,selector3--,9 an ex*ange us+ f\r digits 9 ! numb]s1 ! regi/] ( ! int]connector selector is adju/$ 9 ea* call to a position correspond+ to ! num]ical value ( ! ?\s&s digit ( ! call$ numb]4 ,! cyl9d] swit* !n acts to select an idle trunk4 ,! swit* is controll$ by ! rot>y swit* 9 connection ) ! signal transmitt] controll]4 ,int]connector3--,?is swit* is simil> to ! int]connector selector 9 design & 9 function4 ,x is a cyl9d] swit* ) regi/]4 ,! regi/] is adju/$ 9 ea* call to a position correspond+ to ! num]ical value ( ! hundr$s digit ( ! numb] call$ & ! cyl9d] swit* !n op]ates to select an idle trunk4 ,! swit* is controll$ by ! rot>y swit* 9 connection ) ! signal transmitt] controll]4 ,second>y ,connector3--,?is swit* conta9s 9 its cyl9d] bank ( contacts ! multiple po9ts ( "o hundr$ subscrib]s' l9es & its function is to connect ! conductors ( ! call$ l9e to ! conductors ( ! connective division4 ,?is is accompli%$ by adju/+ ! regi/] to correspond to ! value ( ! t5s digit ( ! l9e desir$ & by adju/+ ! cyl9d] bru%es to correspond to ! value ( ! units digit ( ! l9e4 ,! swit* is controll$ by ! rot>y swit* 9 connection ) ! signal-transmitt] controll]4 ,op]ation4 ,a brief description ( ! progress ( a call f its in/itution to ! complete connection & subsequ5t disconnection beg9s ) ! adju/m5t ( ! dial indicators ( ! telephone set & ! turn+ ( ! crank ( ! signal transmitt] "o revolution4 ,?is act1 p]=m$ by ! call+ subscrib]1 connects "o ( ! l9e conductors to e>?4 ,imm$iately ! decimal indicator associat$ ) ! section 9 :i* ! call+ l9e t]m9ates is en]giz$ & />ts ! division />t]4 ,! division />t] in/antly />ts ! rot>y swit* ( an idle division4 ,! rot>y swit* n[ />ts ! decimal-regi/] controll] & connects to x ! decimal regi/] ( ! prim>y connector ( ! division select$4 ,all ( ! above acts 9 ! c5tral (fice occur practically simultane\sly4 ,! impulses g5]at$ by ! controll] are effective ^u ! decimal regi/] ( ! />t$ division &1 !re=e1 adju/ t regi/] to a position correspond+ to ! t5s value ( ! call+ l9e4 ,! rot>y swit* n[ disconnects ! t5s regi/] & />ts ! cyl9d] bru%es ( ! prim>y connector :i* automatically /op :5 !y enc\nt] ! call+ l9e4 ,at ?is in/ant ! cut-(f relay ( ! l9e is en]giz$ & ! decimal indicator is releas$4 ,! call n[ is cle> ( all sectional app>atus & ano!r call may come ?r\gh imm$iately1 be+ assign$ 9 *>ge ( ano!r idle division4 ,! total "t 9 :i* any call is 9 *>ge ( ! sectional app>atus1 i4 e41 ! total "t f ! gr\nd+ ( ! l9e conductor at ! sub-/ation until ! l9e has be5 connect$ ) by ! prim>y connector ( "s division ( t section & ! sectional app>atus has be5 releas$ by ! op]ation ( ! cut-(f relay1 approximates two-fif?s ( a second4 ,! next op]ation initiat$ by ! rot>y swit* is ! />t+ ( ! signal-transmitt] controll] ( ! connective division1 :i*1 9 turn1 adju/s ! regi/] ( ! int]connector selector to a position correspond+ to ! ?\s&s digit ( ! numb] ( ! call$ l9e z indicat$ by ! signal transmitt] at ! call+ /ation4 ,?is selects an int]connector s]v+ ! l9es ( ! select$ ?\s&4 ,?is initial selection be+ complet$ ! rot>y swit* readju/s ! circuits ( ! connective division 9 su* mann] t 9 ! fur!r progress ( ! signal-transmitt] controll]1 its impulses w be effective ^u ! regi/] ( ! select$ int]connector4 ,9 ?is mann]1 ! regi/] ( ! int]connector1 :i* may be ^u ! same connective division z ! rot>y swit* h&l+ ! call1 or :i* may be ! int]connector ( "s o!r division1 z det]m9$ by ! numb] ( ! call$ subscrib]1 is adju/$ to a position correspond+ to ! second or hundr$s digit ( ! numb] call$4 ,! cyl9d] swit* ( ! int]connector !n selects & appropriates an idle trunk ext5d+ to a second>y connector ^u "s connective division s]v+ ! hundr$ select$4 ,! rot>y swit* aga9 %ifts ! circuits ( ! connective division 9 su* mann] t ! signal-transmitt] controll] is effective ^u ! second>y connector1 bo? regi/] & cyl9d]1 & adju/s ! regi/] & cyl9d]1 respectively1 ) _! bru%es 9 contact ) ! t5s & units digits1 respectively1 ( ! numb] ( ! call$ l9e4 ,! conductors ( ! call$ l9e n[ are connect$ ?r\gh ! second>y connector1 ! int]connector1 & ! int]connector selector to ! rot>y swit*2 ! conductors ( ! call+ l9e are connect$ ?r\gh ! prim>y connector to ! rot>y swit*2 ?us completely connect+ ! l9es except at ! rot>y swit*4 ,to effect ! connect+ toge!r ( ! two l9es1 bo? rot>y swit* & signal-transmitt] controll] mu/ pass =w>d into _! next positions1 ! connection :5 ?us effect$ be+ made ?r\gh conductors conta9+ a repeat+ coil & ma9 batt]y connection = supply+ talk+ curr5t to ! two l9es & conta9+ also r++ & sup]visory relays4 ,! call$ l9e is te/$ to det]m9e if busy dur+ ! %ort int]val 9 :i* ! rot>y swit* takes a %ort /ep to connect ! call+ & ! call$ l9es4 ,9 ?is /ep ( ! rot>y swit* ! busy-te/ relay is connect$ to ! gu>d wire or busy-te/ wire ( ! call$ l9e1 & if t l9e be busy1 ! relay int]f]es ) ! control ex]cis$ by ! rot>y swit* ^u ! signal-transmitt] controll]1 & ! controll] is prev5t$ f tak+ ! /ep requir$ to connect ! l9e4 ,?us1 :5 a busy l9e is enc\nt]$1 ! f9al /ep ( ! rot>y swit* is tak5 to set up ! conv]sation conditions1 b ! signal-transmitt] controll] does n take its f9al /ep2 by ?is failure ( ! signal-transmitt] controll] due to ! action ( ! busy-te/ relay1 ! call+ l9e is n connect$ to ! call$ l9e b is connect$ to a busy-back tone g5]ator in/ead4 ,:e!r ! l9e enc\nt]$ be busy or idle1 ! connective division rema9s 9 its condition z !n adju/$ until ! subscrib] hangs 8 receiv] ^u ! hook swit* to obta9 disconnection4 ,! r++ ( ! bell ( ! call$ /ation is done directly by ! call+ subscrib] 9 press+ ! r++ key4 ,! disconnection is effect$1 :5 ! receiv] ( ! call+ l9e is hung up1 by ! sup]visory relay 9 ! c5tral (fice1 ^: w9d+ is includ$ 9 ! l9e circuit1 & ^: contacts act directly to />t ! rot>y swit*4 ,9 disconnect+1 ! rot>y swit* />ts ! prim>y & ! second>y connectors & ?us in/antly releases bo? ! call+ & ! call$ l9es4 ,!reaft] ! rot>y swit* 9 pass+ f position to position re/ores swit* aft] swit* ( ! connective division to normal & f9ally itself returns to normal 9 prep>ation = its assignm5t to s]vice 9 answ]+ a subsequ5t call4 ,,*apt] ,,xxxi ,,! ,,automanual ,,sy/em ,two sy/ems ( telephony are n[ 9 common use 9 ?is c\ntry--! manual sy/em & ! automatic4 ,) ! gr[? ( ! automatic1 & ! gradually rip5+ conviction1 :i* is n[ fully matur$ 9 ! m9ds ( mo/ telephone eng9e]s1 t automatic swit*+ is practical1 !re has be5 a gr[+ t5d5cy t[>d do+ automatically _m ( ! ?+s t _h previ\sly be5 done manually4 ,"o ( ! results ( ?is t5d5cy has be5 ! production ( ! automanual sy/em1 ! inv5tion ( ,edw>d ,e4 ,clem5t1 an eng9e] & pat5t attorney1 ( ,wa%+ton1 ,d4 ,c4 ,9 connection ) ,mr4 ,clem5t's "n1 z inv5tor1 mu/ be m5tion$ t ( ,*>les ,h4 ,nor?1 ^: excell5t "w z a design] & manufactur] has contribut$ mu* t[>d ! pres5t excell5ce ( ?is highly int]e/+ sy/em4 ,*>act]i/ics ( ,sy/em4 ,! "n automanual is co9$ f ! two words1 automatic & manual1 & is int5d$ to sugge/ ! idea t ! sy/em p>takes 9 "p ( ! features ( ! automatic sy/em & 9 "p ( ^? ( ! manual sy/em4 ,we regret t nei!r space nor ! pr(essional relation :i* we h _h ) ! developm5t ( ?is sy/em w p]mit u to make public an ext5d$ & detail$ description ( its app>atus & circuits4 ,only ! g5]al features ( ! sy/em may1 !re=e1 be dealt )4 ,illu/ration3 ,,p[] ,,app>atus ,,= ,,common-,,batt]y ,,manual ,,(fice ,,( ,,m$ium ,,size ,! und]ly+ idea ( ! automanual sy/em is to relieve ! subscrib] ( all "w 9 connection ) ! build+ up ( 8 connection1 except ! ask+ = x2 to complicate ! subscrib]'s /ation equipm5t 9 no way1 x be+ left ! same z 9 ! common-batt]y manual sy/em2 to d away ) manual app>atus1 su* z jacks1 cords & plugs1 at ! c5tral (fice1 & to sub/itute = x automatic swit*+ app>atus :i* w be guid$ 9 its movem5ts1 n by ! subscrib]1 b by a v mu* small] numb] ( op]ators ?an w\ld be necess>y to manipulate a manual swit*bo>d4 ,g5]al ,features ( ,op]ation4 ,a broad view ( ! op]ation ( ! sy/em is ?is4 ,! subscrib] desir+ to make a call takes d[n 8 receiv]1 & ?is causes a lamp to light 9 front ( an op]ator4 ,! op]ator presses a button & is 9 telephonic communication ) ! subscrib]4 ,receiv+ ! numb] desir$1 ! op]ator sets x up on a keybo>d 9 j ab\t ! same way t a typi/ w set up ! lett]s ( a %ort ^w on a typewrit+ ma*9e4 ,! sett+ up ( ! numb] on ! keybo>d be+ accompli%$1 ! prop] condition ( control ( ! associat$ automatic app>atus at ! c5tral (fice is e/abli%$ & ! op]ator has no fur!r connection ) ! call4 ,! automatic swit*+ app>atus guid$ by ! conditions set up on ! op]ator's keybo>d proce$s to make ! prop] selection ( trunks & to e/abli% ! prop] connections ?r\gh !m to build up a talk+ circuit betwe5 ! call+ subscrib] & ! call$ & to r+ ! call$ subscrib]'s bell1 or1 if 8 l9e is f\nd busy1 ! app>atus refuses to connect ) x & s5ds a busy signal back to ! call+ subscrib]4 ,! op]ator p]=ms no "w 9 disconnect+ ! subscrib]s1 t be+ automatically tak5 c>e ( :5 !y hang up _! receiv]s at ! close ( ! conv]sation4 ,f ! =ego+ x w be se5 t !re is ?is fundam5tal diff]5ce betwe5 ! automatic & ! automanual--! automatic sy/em disp5ses entirely ) ! c5tral-(fice op]ator = all ord9>y swit*+ functions2 ! automanual employs op]ators b attempts to s facilitate _! "w t !y may h&le v _m m calls ?an w\ld be possible 9 a manual sy/em1 & at ! same "t secures ! advantages ( secrecy :i* ! automatic sy/em secures to its subscrib]s4 ,subscrib]'s ,app>atus4 ,"o ( ! ma9 po9ts 9 ! controv]sy conc]n+ automatic v]sus manual sy/ems is :e!r or n x is desirable to h ! subscrib] ask = 8 connection or to h him make c]ta9 simple movem5ts ) 8 f+]s :i* w lead to 8 secur+ x4 ,! develop]s ( ! automanual sy/em h tak5 ! position t ! mo/ desirable way1 s f> z ! subscrib] is conc]n$1 is to let him ask = x4 ,x is probable t ?is po9t w n be a decid+ "o 9 ! *oice ( future sy/ems1 s9ce x already seems to be prov5 t ! subscrib]s 9 automatic sy/ems are will+ to g ?r\gh ! necess>y movem5ts to me*anically set up ! call4 ,! advantage :i* ! automanual sy/em %>es ) ! manual1 h[ev]1 9 ! great] simplicity ( its subscrib]'s /ation app>atus1 _c be ga9said4 ,illu/ration3 ,fig4 #dje4 ,op]ators' ,key ,tables ,illu/ration3 ,fig4 #djf4 ,top ,view ( ,key ,table ,op]ator's ,equipm5t4 ,! g5]al =m ( ! op]ator's equipm5t is %[n 9 ,fig4 #dje4 ,a clos] view ( ! top ( "o ( ! key tables is %[n 9 ,fig4 #djf4 ,z w be se51 ! equipm5t on ea* op]ator's position consi/s ( ?ree sep>ate sets ( pu%-button keys closely resembl+ 9 ext]nal appe>ance ! keys ( a typewrit] or add+ ma*9e4 ,imm$iately above ea* set ( keys are ! signal lamps belong+ to t set4 ,! op]ator's keys are arrang$ 9 /rips ( t51 plac$ across r ?an l5g?wise on ! key %elf4 ,"o ( ^! /rips is %[n 9 ,fig4 #djg4 ,!re are z _m /rips ( keys 9 ea* set z !re are digits 9 ! subscrib]s' numb]s1 i4 e41 ?ree 9 a sy/em hav+ a capacity ( less ?an "o ?\s&2 f\r 9 a sy/em ( less ?an t5 ?\s&2 & s on4 ,9 addition to ! numb] keys ( ea* set is a p>tial r[ ( keys1 includ+ :at is call$ a />t+ key & also keys = mak+ ! p>ty-l9e selection4 ,illu/ration3 ,fig4 #djg4 ,/rip ( ,select+ ,keys ,illu/ration3 ,fig4 #djh4 ,wir+ ( ,key ,%elf ,! simplicity ( ! op]ator's key equipm5t is "o ( its attractive features4 ,fig4 #djh %[s "o ( ! key %elves op5$ s z to expose to view all ( ! app>atus & wir+ t is plac$ be=e ! op]ator4 ,! reason = provid+ m ?an "o key set on ea* op]ator's position is1 t aft] a call has be5 set up on "o key set1 a few seconds is requir$ be=e ! automatic app>atus controll$ by ! key set c d its "w & release ! key set ready = ano!r call4 ,! provision ( m ?an "o key set makes x possible = ! op]ator to />t sett+ up ano!r call on ano!r key set )\t wait+ = ! fir/ to be releas$ by ! automatic app>atus4 ,illu/ration3 ,fig4 #dji4 ,swit* ,room ( ,automanual ,c5tral ,(fice ,automatic ,swit*+ ,equipm5t4 ,a g5]al view ( ! arrangem5t ( automatic swit*es 9 an ex*ange e/abli%$ by ! ,nor? ,electric ,company at ,a%tabula1 ,ohio1 is %[n 9 ,fig4 #dji4 ,! desk 9 ! =egr\nd is t ( ! wire *ief4 ,?is automatic app>atus consi/s l>gely ( relays & automatic select+ swit*es4 ,! swit*es are ( ! /ep-by-/ep type1 hav+ v]tical & rot>y movem5ts1 & an idea ( "o ( !m1 m9us its contact banks1 is giv5 9 ,fig4 #daj4 ,! control ( ! automatic swit*es by ! op]ator's key sets is ?r\gh ! m$ium ( a p[]-driv51 impulse-s5d+ ma*9e4 ,f ?is ma*9e impulses are tak5 correspond+ to ! numb]s ( ! keys depress$4 ,illu/ration3 ,fig4 #daj4 ,select+ ,swit* ,automatic ,di/ribution ( ,calls4 ,a feature ( great int]e/ 9 ?is sy/em is ! mann] 9 :i* ! incom+ calls are di/ribut$ among ! op]ators4 ,f ea* key set an op]ator's trunk is ext5d$ to :at is call$ a second>y selector swit*1 ?r\gh :i* x may be connect$ to a prim>y selector trunk & call+ l9e4 ,:5 a subscrib] calls by tak+ d[n 8 receiv]1 8 l9e relay pulls up & causes a prim>y selector swit* to connect 8 l9e ) an idle local trunk or l9k circuit1 at ! same "t />t+ up a second>y selector swit* :i* imm$iately connects ! prim>y trunk & ! call+ l9e to an op]ator's idle key set4 ,if an op]ator is at ! "t engag$ 9 sett+ up a call on a key set1 or if t key set is /ill act+ to control ! s5d+ ( impulses to ! automatic swit*es1 x may be said to be busy1 & x is n select$ by ?is prelim9>y select+ app>atus 9 response to an incom+ call4 ,z soon1 h[ev]1 z ! necess>y impulses h be5 tak5 f ! key set by ! automatic app>atus1 t key set is releas$ & is aga9 ready to receive a call4 ,9 ?is way ! calls come be=e ea* op]ator only z t op]ator is able & ready to receive !m4 ,sett+ up a ,connection4 ,z soon z ! key-set lamp lights1 9 response to su* an incom+ call1 ! op]ator presses a li/5+ button1 receives ! numb] f ! subscrib]1 & depresses ! correspond+ numb] buttons on t key set1 !reby det]m9+ ! numb]s 9 ea* ( ! s]ies ( impulses to be s5t to ! selector & ! connector swit*es to make ! desir$ connection4 ,! op]ator repeats ?is numb] to ! call+ subscrib] z %e sets x up1 & !n presses ! />t+ button1 :]eupon h] "w is done s f> z t call is conc]n$4 ,if1 ^u repeat+ ! call to ! subscrib]1 ! op]ator f9ds t %e is 9 error1 %e may *ange ! numb] set up at any "t be=e %e has press$ ! />t+ button4 ,build+ up a ,connection4 ,! keys s set up det]m9e ! numb] ( impulses t w be transmitt$ by ! impulse-s5d+ ma*9e to ! selector & ! connector swit*es4 ,^! swit*es1 impell$ by ^! impulses1 e/abli% ! connection if ! l9e call$ = is n already connect$ to4 ,if a p>ty-l9e /ation is call$ =1 ! prop] /ation on x w be selectively rung z det]m9$ by ! p>ty-l9e key depress$ by ! op]ator4 ,if ! l9e is f\nd busy1 ! connector swit* refuses to make ! connection & places a busy-back signal on ! call+ l9e4 ,spe$ 9 ,h&l+ ,calls4 ,?is necess>ily brief outl9e gives an idea only ( ! m /rik+ features ( ! automanual sy/em4 ,a /udy ( ! rapidity ) :i* calls may be h&l$ 9 actual practice %[s rem>kable results z comp>$ ) manual me?ods ( op]at+4 ,! op]ators set up ! numb] keys correspond+ to a call$ numb] ) ! same rapidity t ! keys ( a typewrit] are press$ 9 spell+ a ^w4 ,9 fact1 ev5 great] spe$ is possible1 s9ce x is notic$ t ! op]ators frequ5tly w depress all ( ! keys ( a numb] at once1 z by a s+le /rik+ movem5t ( ! f+]s4 ,! rapidity ) :i* ?is is done defies accurate tim+ by a /op wat* 9 ! h&s ( an exp]t4 ,x is practically true1 !re=e1 t ! "t consum$ by ! op]ator 9 h&l+ any "o call is t :i* is tak5 9 gett+ ! numb] f ! subscrib] & 9 repeat+ x back to him4 ,,table ,,xi ,total ,"t ,consum$ by ,op]ator 9 ,h&l+ ,calls on ,automanual ,sy/em ---------------------------------------- ------------------------- ,fir/ #ajj ,calls ---------------------------------------- ------------------------- ,longe/ ,individual ,p]iod #ab4dj seconds ,av]age five longe/ ,individual ,p]iods #g4dd seconds ,av]age t5 longe/ ,individual ,p]iods #f4cd seconds ,%orte/ ,individual ,p]iod #a4fj seconds ,av]age five %orte/ ,individual ,p]iods #a4ib seconds ,av]age t5 %orte/ ,individual ,p]iods #a4if seconds ,av]age ,entire #ajj ,calls #c4cif seconds ,h\rly ,rate at :i* calls 7 be+ h&l$ #ajfj ---------------------------------------- ------------------------- ---------------------------------------- ------------------------- ,second #ajj ,calls ---------------------------------------- ------------------------- ,longe/ ,individual ,p]iod #g4fj seconds ,av]age five longe/ ,individual ,p]iods #e4eb seconds ,av]age t5 longe/ ,individual ,p]iods #e4cd seconds ,%orte/ ,individual ,p]iod #b4jj seconds ,av]age five %orte/ ,individual ,p]iods #b4jd seconds ,av]age t5 %orte/ ,individual ,p]iods #b4ah seconds ,av]age ,entire #ajj ,calls #c4cgd seconds ,h\rly ,rate at :i* calls 7 be+ h&l$ #ajfg ---------------------------------------- ------------------------- ---------------------------------------- ------------------------- ,?ird #ajj ,calls ---------------------------------------- ------------------------- ,longe/ ,individual ,p]iod #e4dj seconds ,av]age five longe/ ,individual ,p]iods #e4cb seconds ,av]age t5 longe/ ,individual ,p]iods #d4dd seconds ,%orte/ ,individual ,p]iod #a4fj seconds ,av]age five %orte/ ,individual ,p]iods #a4fe seconds ,av]age t5 %orte/ ,individual ,p]iods #a4hj seconds ,av]age ,entire #ajj ,calls #c4afj seconds ,h\rly ,rate at :i* calls 7 be+ h&l$ #aaci ---------------------------------------- ------------------------- ,ow+ to ! difficulty ( secur+ accurate traffic data by means ( a /op wat*1 an automatic1 electrical tim+ device1 capable ( regi/]+ seconds & hundr$?s ( a second1 has be5 us$ 9 /udy+ ! p]=mance ( ?is sy/em 9 regul> op]ation at ,a%tabula ,h>bor4 ,! op]ators 7 n in=m$ t ! records 7 be+ tak51 & ! data tabulat$ repres5ts ! "w ( two op]ators 9 h&l+ regul> subscrib]s' calls4 ,! figures 9 ,table ,,xi are giv5 by ,c4 ,h4 ,nor? z repres5t+ ! total "t consum$ by ! op]ator f ! "t h] l9e lamp 0 light$ until h] "w 9 connection ) ! call 0 f9i%$1 & x includ$1 !re=e1 ! press+ ( ! li/5+ button1 ! receiv+ ( ! numb] f ! subscrib]1 repeat+ x back to him1 sett+ up ! connection on ! keys1 & press+ ! />t+ key4 ,x w be se5 t ! av]age "t = ea* #ajj calls is q uni=m & is slightly ov] ?ree seconds4 ,! consid]able v>iation 9 ! individual calls1 rang+ f a maximum ( #ab4dj seconds d[n to a m9imum ( #a4fj seconds1 is due almo/ entirely to ! diff]5ce betwe5 ! subscrib]s 9 ! spe$ ) :i* !y c give _! numb]s4 ,^! figures indicate t1 9 ea* ( ! te/s1 calls 7 be+ h&l$ at ! rate ( m ?an "o ?\s& p] h\r by ea* op]ator4 ,! te/ ( ! subscrib]'s wait+ "t1 i4 e41 ! "t t he wait$ = ! op]ator to answ]1 = "o hundr$ calls made )\t ! k ( ! op]ator1 %[$ ! results z giv5 9 ,table ,,xii1 9 :i* a split second /op wat* 0 us$ 9 mak+ ! obs]vations4 ,,table ,,xii ,subscrib]s' ,wait+ ,"t ---------------------------------------- ------------------ ,numb] ( ,calls ,te/$ #ajj ,longe/ ,individual ,p]iod #e4bj seconds ,av]age #e ,longe/ ,individual ,p]iods #d4fd seconds ,av]age #aj ,longe/ ,individual ,p]iods #c4hj seconds ,%orte/ ,individual ,p]iod #a4jj seconds ,av]age #e ,%orte/ ,individual ,p]iods #a4bh seconds ,av]age #aj ,%orte/ ,individual ,p]iods #a4cd seconds ,av]age ,entire #ajj ,calls #b4jg seconds ---------------------------------------- ------------------ ,! l5g? ( "t :i* ! subscrib] has to wait be=e receiv+ an answ] f ! op]ator is1 ( c\rse1 "o ( ! factors t ent]s into ! giv+ ( good telephone s]vice1 & ! times %[n by ?is te/ are consid]ably %ort] ?an ord9>ily ma9ta9$ 9 manual practice4 ,! wait+ "t ( ! subscrib] is n1 ( c\rse1 a "p ( ! "t t is consum$ by ! op]ator1 & ! real economy s f> z ! op]ator's "t is conc]n$ is %[n 9 ! te/s record$ 9 ,table ,,xi4 ,,*apt] ,,xxxii ,,p[] ,,plants ,! p[] plant is an organization ( devices to furni% to a telephone sy/em ! sev]al k9ds ( curr5t1 at prop] pressures1 = ! p]=mance ( ! sev]al g5]al electrical tasks )9 ! ex*ange4 ,k9ds ( ,curr5ts ,employ$4 ,s\rces ( bo? direct & alt]nat+ curr5t are requir$ & a s+le ex*ange may employ ^! = "o or m ( ! foll[+ purposes3 ,direct ,curr5t4 ,curr5t :i* fl[s always 9 "o direction :e!r /eady or v>y+1 is ref]r$ to z direct curr5t1 & may be requir$ = transmitt]s1 = relays1 = l9e1 sup]visory1 & auxili>y signals1 = busy te/s1 = automatic swit*es1 = call regi/]s1 = telegraphy1 & 9 ! =m ( pulsat+ curr5t = ! r++ ( bias$ bells4 ,alt]nat+ ,curr5t4 ,s\rces ( alt]nat+ curr5t are requir$ = ! r++ ( bells1 = busy-back & o!r automatic signals to subscrib]s1 = h[l] signals to attract ! att5tion ( subscrib]s :o h left _! receiv]s (f _! hooks1 & = signal+ ov] composite l9es4 ,types ( ,p[] ,plants4 ,cle>ly ! requirem5ts = curr5t supply diff] greatly = magneto & common-batt]y sy/ems4 ,!re is1 h[ev]1 no great diff]5ce betwe5 ! p[] plants requir$ = ! automatic & ! manual common-batt]y sy/ems4 ,9 ! simple/ =m ( telephone sy/em--two magneto telephones on a private l9e--! p[] plant at ea* /ation consi/s ( two elem5ts3 "o1 ! magneto g5]ator1 :i* is a translat+ device = turn+ h& p[] into alt]nat+ curr5t = r++ ! bell ( ! di/ant /ation2 & ! o!r1 a prim>y batt]y :i* furni%es curr5t to en]gize ! transmitt]4 ,9 su* a sy/em1 !re=e1 ea* telephone has its own p[] plant4 ,! t]m p[] plant1 h[ev]1 z commonly employ$ 9 telephone "w1 ref]s m p>ticul>ly to ! organization ( devices at ! c5tral (fice = furni%+ ! requir$ k9ds ( curr5t1 & x is to p[] plants 9 ?is s5se t ?is *apt] is devot$4 ,magneto ,sy/ems4 ,if magneto l9es be connect$ to a swit*bo>d1 ! curr5t = ?r[+ ! drop at ! swit*bo>d is furni%$ by ! subscrib]'s g5]ator1 & ! curr5t = en]giz+ ! subscrib]'s transmitt] is furni%$ by ! local batt]y at 8 /ation2 b s\rces ( curr5t mu/ be provid$ = enabl+ ! c5tral-(fice op]ator to signal or talk to ! subscrib]s4 ,^! are ab\t ! only ne$s = :i* curr5t mu/ be furni%$ 9 an ord9>y magneto c5tral (fice4 ,if a multiple bo>d is employ$1 direct curr5t is also ne$$ = ! purpose ( ! busy te/ & also = op]at+ ! drop re/or+ circuits1 if ! electrical me?od ( re/or+ ! drops is employ$4 ,common-,batt]y ,sy/ems4 ,9 common-batt]y sy/ems ! requirem5ts are v mu* m ext5sive4 ,! subscrib]s' telephones h no p[] plants ( _! own1 b are provid$ ) a common s\rce ( direct curr5t locat$ at ! c5tral (fice = supply+ ! talk+ curr5t1 & = op]at+ ! c5tral-(fice signals1 & ! op]ators are provid$ ) "o or m common s\rces ( alt]nat+ or pulsat+ curr5t = r++ ! subscrib]s' bells4 ,common-batt]y equipm5t requires ! use ( curr5ts ( diff]5t k9ds = a great] numb] ( auxili>y purposes ?an does magneto equipm5t4 ,^! facts make ! p[] plant 9 a common-batt]y (fice mu* m important ?an 9 a magneto (fice4 ,op]ators' ,transmitt] ,supply4 ,9 a small magneto ex*ange1 ! transmitt] curr5t may be _h f prim>y batt]ies1 a sep>ate batt]y be+ employ$ = ea* op]ator's set4 ,:5 !re are m ?an ?ree or f\r op]ators1 h[ev]1 x is usual1 ev5 9 magneto (fices1 to obta9 ! transmitt] curr5t f a common /orage batt]y4 ,a /orage batt]y has ! =tunate quality ( v l[ int]nal resi/ance1 !re=e a numb] ( op]ators' transmitt]s may be actuat$ by "o s\rce )\t introduc+ cross-talk4 ,9 o!r words1 a /orage batt]y is a curr5t-furni%+ device ( good regulation1 ! v>iation ( consumption 9 "o circuit lead+ f x caus+ slight v>iation 9 ! curr5ts ( o!r circuits lead+ f x4 ,if ?is 7 n s1 cross-talk w\ld exi/ betwe5 ! telephones ( ! op]ators' positions connect$ to ! same batt]y4 ,?is regulat+ quality enables ! multiple fe$+ ( telephone circuits to be c>ri$ fur!r ?an ! m]e supply+ ( op]ators' sets & is ! quality :i* makes possible ! successful use ( a /orage batt]y z ! s+le s\rce ( transmitt] curr5t = common-batt]y c5tral-(fice equipm5t4 ,9 furni%+ a plurality ( op]ators' transmitt]s f a common batt]y1 ! importance ( l[ resi/ance & inductance 9 ! portion ( ! pa? t is common to all ( ! circuits mu/ n be ov]look$4 ,n only is a batt]y ( extremely l[ resi/ance requir$1 b also conductors lead+ f x t are common to two or m ( ! circuits %\ld be ( v l[ resi/ance & consequ5tly l>ge 9 cross-section & z %ort z possible4 ,9 common-batt]y (fices !re is obvi\sly no ne$ ( employ+ a sep>ate batt]y = ! op]ators' transmitt]s1 s9ce !y may readily be suppli$ f ! common /orage batt]y :i* supplies direct curr5t to ! subscrib]s' l9es4 ,r++-,curr5t ,supply4 ,magneto ,g5]ators4 ,z a c5tral-(fice equipm5t is requir$ to r+ _m subscrib]s' bells1 only ! small ones f9d x conv5i5t to r+ !m by means ( h&-op]at$ magneto g5]ators4 ,small magneto swit*bo>ds are usually equipp$ s t ea* op]ator is provid$ ) a h&-g5]ator1 b ev5 :]e su* is ! case "s s\rce ( r++ curr5t n manually op]at$ is desirable4 ,9 l>g] swit*bo>ds ! h& g5]ators are entirely disp5s$ )4 ,! magneto g5]ator may be driv5 by a belt f any conv5i5t con/antly mov+ pulley1 & ! e>ly telephone ex*anges 7 (t5 equipp$ ) su* g5]ators hav+ bett] be>+s & m curr5t capacity ?an ^? 9 magneto telephones4 ,^! 7 adapt$ to be run con/antly f "s s\rce ( p[]1 deliv]+ r++ curr5t to ! op]ators' keybo>ds at f #af to #bj cycles p] second4 ,pole ,*ang]s4 ,vibrat+ pole *ang]s 7 also us$ 9 ! e>ly ex*anges1 b pass$ out ( use1 p>tly because ( poor design1 b m because ( ! abs5ce ( good =ms ( prim>y batt]ies = vibrat+ !m & = furni%+ ! direct curr5ts to be trans=m$ into alt]nat+ l9e curr5t = r++ ! bells4 ,! pole *ang] 0 r$esign$ aft] ! beg9n+ ( ! great spread ( telephony 9 ! ,unit$ ,/ates 9 #ahic4 ,today x is firmly e/abli%$ z an elem5t ( good telephone practice4 ,fig4 #daa illu/rates ! pr9ciple ^u :i* "o ( ! well-kn[n pole *ang]s--! ,w>n]--op]ates4 ,9 ?is #a is an electromagnet suppli$ by a con/ant-curr5t batt]y #b to keep ! vibratory sy/em cont9ually 9 motion4 ,?is motor magnet & its batt]y "w 9 a local circuit & cause vibration 9 exactly ! same mann] z ! armature ( an ord9>y electric door bell is caus$ to vibrate4 ,! batt]y f :i* ! r++ curr5t is d]iv$ is indicat$ at #c1 & ! poles ( ?is are connect$1 respectively1 to ! vibrat+ contacts #d & #e4 ,^! contacts are m]ely ! mov+ memb]s ( a pole *ang+ swit*1 & a /udy ( ! action w readily %[ t :5 ^! mov+ p>ts engage ! "r-h& contacts1 curr5t w fl[ to ! l9e suppos$ to be connect$ to ! t]m9als #f & #g 9 "o direction1 :ile1 :5 ^! p>ts engage ! left-h& contacts1 curr5t w fl[ to ! l9e 9 ! rev]se direction4 ,! circuit ( ! cond5s] %[n is controll$ by ! armature ( ! relay #h4 ,! w9d+ ( ?is relay is put directly 9 ! circuit ( ! ma9 batt]y #c1 s t :5ev] curr5t is drawn f ?is batt]y to r+ a di/ant bell1 ?is relay w be op]at$ & w bridge ! cond5s] across ! circuit ( ! l9e4 ,! purpose ( ! cond5s] is to make ! impulses fl[+ f ! pole *ang] less abrupt1 & ! reason = hav+ its bridg$ circuit normally brok5 is to prev5t a wa/e ( curr5t f ! batt]y #c1 due to ! en]gy :i* w\ld o!rwise be consum$ by ! cond5s] if x 7 left p]man5tly across ! l9e4 ,illu/ration3 ,fig4 #daa4 ,w>n] ,pole ,*ang] ,illu/ration3 ,fig4 #dab4 ,pole ,*ang]s = ,h>monic ,r++ ,pole *ang]s = r++ bells ( h>monic p>ty l9es are requir$ to produce alt]nat+ curr5ts ( practically con/ant frequ5cies4 ,! ideal arrangem5t is to cause ! direct curr5ts f a /orage batt]y to be alt]nat$ by means ( ! pole *ang]s1 & !n trans=m$ into high] voltages requir$ = r++ purposes1 ! trans=m] also s]v+ to smoo? ! curr5t wave1 mak+ x m suitable = r++ purposes4 ,9 ,fig4 #dab su* an arrangem5t1 adapt$ to develop curr5ts = h>monic r++ on p>ty l9es1 is %[n4 ,! regul> common batt]y ( ! c5tral (fice is indicat$ at #a1 #b be+ an auxili>y batt]y ( dry cells1 ! purpose ( :i* w be pres5tly ref]r$ to4 ,at ! "r ( ! batt]y #a !re is %[n ! call+ plug ) its associat$ p>ty-l9e r++ keys adapt$ to impress ! sev]al frequ5cies on ! subscrib]s' l9es4 ,! me?od by :i* ! curr5t f ! ma9 /orage batt]y passes ?r\gh ! motor magnets ( ! sev]al vibrators1 & by :i* ! prim>y curr5ts ?r\gh ! trans=m]s are made to alt]nate at ! respective frequ5cies ( ^! vibrators1 w be obvi\s f ! draw+4 ,x is also cle> t ! second>y curr5ts develop$ 9 ^! trans=m]s are l$ to ! sev]al r++ keys s z to be available = connection ) ! subscrib]s' l9es at ! w ( ! op]ator4 ,! cond5s]s are bridg$ across ! prim>y w9d+s ( ! trans=m]s = ! purpose ( aid+ 9 smoo?+ out ! curr5t waves4 ,! use ( ! auxili>y batt]y #b & ! ret>dation coil #c 9 ! ma9 supply lead is = ! purpose ( prev5t+ ! pulsat+ curr5ts drawn f ! ma9 batt]y #a f mak+ ! batt]y noisy4 ,^! two batt]ies h l poles connect$ to ! supply lead1 & ! auxili>y batt]y furni%es no curr5t to ! sy/em except :5 ! electromotive =ce ( ! impulse fl[+ f ! ma9 batt]y is *ok$ d[n by ! imp$ance coil & ! defici5cy is !n mom5t>ily suppli$ = ea* wave by ! auxili>y batt]y4 ,?is is ! me?od develop$ by ! ,dean ,electric ,company = prev5t+ ! pole-*ang] sy/em f caus+ di/urbances on l9es suppli$ f ! same ma9 batt]y4 ,illu/ration3 ,fig4 #dac4 ,multi-,cyclic ,g5]ator ,set ,r++ ,dynamos4 ,alt]nat+ & pulsat+ curr5ts = r++ purposes are also l>gely furni%$ f alt]nat+-curr5t dynamos simil> to ^? us$ 9 comm]cial p[] & light+ "w1 b specially design$ to produce r++ curr5ts ( prop] frequ5cy & voltage4 ,^! are usually driv5 by electric motors d]iv+ _! curr5t ei!r f ! comm]cial supply ma9s or f ! c5tral-(fice batt]y4 ,9 l>ge ex*anges h>monic r+]s are usually op]at$ by alt]nat+-curr5t g5]ators driv5 by motors1 a sep>ate dynamo be+ provid$ to furni% ! curr5t ( ea* frequ5cy4 ,fig4 #dac %[s a set ( f\r su* g5]ators directly connect$ to a common motor4 ,z no s\rce ( comm]cial p[] = driv+ su* g5]ators is absolutely uni=m1 & s9ce ! frequ5cy ( ! r++ curr5t mu/ rema9 v close to a con/ant pr$et]m9$ rate1 "s means mu/ be employ$ = hold+ ! g5]ators at a con/ant spe$ ( revolution1 & ?is is done by means ( a gov]nor %[n at ! "r-h& end ( ! %aft 9 ,fig4 #dac4 ,! pr9ciple ( ?is gov]nor is %[n 9 ,fig4 #dad4 ,a weight$ spr+ acts1 by c5trifugal =ce1 to make a contact aga9/ an adju/able screw1 :5 ! spe$ ( ! %aft rises a pr$et]m9$ am\nt4 ,?is spr+ & its contact are connect$ to two collector r+s #a & #b on ! motor %aft1 & connection is made ) ^! by ! bru%es #c & #d4 ,! clos+ ( ! gov]nor contact s]ves1 !re=e1 m]ely to %ort-circuit ! resi/ance #e1 :i* is normally includ$ 9 ! %unt field ( ! motor4 ,?is gov]nor is bas$ on ! pr9ciple t weak5+ ! field increases ! spe$4 ,x acts to ins]t ! resi/ance 9 s]ies ) ! field w9d+ :5 ! spe$ falls1 & ?is1 9 turn1 results 9 re/or+ ! spe$ to normal4 ,illu/ration3 ,fig4 #dad4 ,gov]nor = ,h>monic ,r++ ,g5]ators ,auxili>y ,signal+ ,curr5ts4 ,alt]nat+ curr5ts1 su* z ^? employ$ = busy signals to subscrib]s 9 automatic sy/ems1 ^? = caus+ l\d tones 9 receiv]s :i* h be5 left (f ! hook swit*1 & ^? = produc+ l\d tones 9 call+ receiv]s connect$ to composite l9es1 all ne$ to be ( mu* high] frequ5cy ?an alt]nat+ curr5t = r++ bells4 ,! simple/ way ( produc+ su* tones is by means ( an int]rupt] l t ( a vibrat+ bell2 b ?is is n ! mo/ reliable way & x is usual to produce busy or busy-back curr5ts by rotat+ commutators to int]rupt a /eady curr5t at ! requir$ rate4 ,z ! usual busy-back signal is a s]ies ( recurr5t tones ab\t "o-half second long1 int]sp]s$ ) p]iods ( sil5ce1 ! rapidly commut$ direct curr5t is requir$ to be fur!r commut$ at a sl[ rate1 & ?is is conv5i5tly done by associat+ a high-spe$ commutator ) a l[-spe$ "o4 ,su* an arrangem5t may be se5 at ! left-h& end ( ! multicyclic alt]nat+ ma*9e %[n 9 ,fig4 #dac4 ,?is commut+ device is usually associat$ ) ! r++ ma*9e because t is ! "o ?+ ab\t a c5tral (fice t is available = imp>t+ cont9u\s rot>y motion4 ,prim>y ,s\rces4 ,mo/ telephone p[] plants consume comm]cial electric p[] & deliv] special electric curr5t4 ,usually "s translat+ device1 su* z a motor-g5]ator or a m]cury-arc rectifi]1 is employ$ to trans=m ! comm]cial curr5t into ! specializ$ curr5t requir$ = ! imm$iate uses ( ! ex*ange4 ,*>g+ f ,direct-,curr5t ,ma9s4 ,9 "s cases comm]cial direct curr5t is us$ to *>ge ! /orage batt]ies )\t ! int]v5tion ( ! translat+ devices1 resi/ances be+ us$ 9 s]ies ) ! batt]y to regulate ! am\nt ( curr5t4 ,comm]cial direct curr5t usually is available at pressures f #aaj volts & upw>d1 :ile telephone p[] plants conta9 /orage batt]ies r>ely ( pressures high] ?an #ej volts4 ,to *>ge a #ej-volt /orage batt]y direct f #aaj-volt ma9s results 9 ! loss ( ab\t half ! en]gy pur*as$1 ?is lo/ en]gy be+ set free 9 ! =m ( heat g5]at$ 9 ! resi/ance devices4 ,not)/&+ ?is1 x is sometimes economical to *>ge directly f ! comm]cial direct-curr5t p[] ma9s1 b only 9 small (fices :]e ! total am\nt ( curr5t consum$ is n l>ge & :]e ! greate/ simplicity 9 equipm5t is desirable4 ,x is bett]1 h[ev]1 9 ne>ly all cases1 to conv]t ! pur*as$ p[] f ! receiv$ voltage to ! requir$ voltage by "s =m ( translat+ device1 su* z a rot>y conv]t] or a m]cury-arc rectifi]4 ,rot>y ,conv]t]s4 ,broadly speak+1 a rot>y conv]t] consi/s ( a motor adapt$ to ! voltage & k9d ( curr5t receiv$1 me*anically c\pl$ to a g5]ator adapt$ to produce curr5t ( ! requir$ k9d & voltage4 ,! h>monic r++ ma*9e %[n 9 ,fig4 #dac is an example ( ?is1 ?is p>ticul> "o be+ adapt$ to receive direct curr5t at ord9>y comm]cial pressure & to deliv] f\r diff]5t alt]nat+ curr5ts ( suitable pressures & frequ5cies4 ,x is to be und]/ood1 h[ev]1 t ! conv]sion may be f direct curr5t to direct curr5t1 f alt]nat+ to direct1 or f direct to alt]nat+4 ,su* a device :]e ! motor is a sep>ate & di/9ct ma*9e f ! g5]ator or g5]ators is call$ a motor-g5]ator4 ,x is usual to connect ! motors & ! g5]ators toge!r directly by a c\pl+ hav+ "s flexibility1 z %[n 9 ,fig4 #dac1 s z to prev5t undue friction 9 ! be>+s4 ,illu/ration3 ,,! ,,p[] ,,& ,,wire ,,*ief',s ,,room ,,( ,,! ,,ex*ange ,,at ,,webb ,,city1 ,,miss\ri ,z an alt]native to ! conv]t+ device made up ( a motor c\pl$ to a g5]ator1 bo? motor & g5]ator w9d+s may be comb9$ on ! same core & rotate )9 ! same field4 ,su* a rot>y conv]t] has be5 call$ a dynamotor4 ,z a rule ! dynamotor is only suitable = small p[]-plant "w4 ,x has ! foll[+ objectionable features3 7a7 ,x is difficult to regulate its output1 s9ce ! same field s]ves = bo? ! motor & ! dynamo w9d+s4 ,= ?is reason its ma9 use is z a r++ ma*9e :]e ! regulation ( ! output is n an important factor4 7b7 ,fur!rmore1 ! fact t ! motor & dynamo armature w9d+s are on ! same core makes x difficult to gu>d aga9/ breakd[ns ( ! insulation betwe5 ! two w9d+s1 especially :5 ! driv+ curr5t is ( high voltage4 ,*>g+ ,dynamos4 ,! dynamo = *>g+ ! /orage batt]y is1 ( c\rse1 a direct-curr5t ma*9e & may be a "p ( a motor g5]ator or x may d]ive its p[] f "s o!r ?an an electric motor1 su* z a gas or /eam eng9e4 ,x %\ld be able to develop a voltage slightly above t ( ! voltage ( ! /orage batt]y :5 at its maximum *>ge1 s z always to be able to deliv] curr5t to ! *>g+ batt]y reg>dless ( ! /ate ( *>ge4 ,a #cj-volt g5]ator1 = example1 c *>ge elev5 cells 9 s]ies economically2 a #fj-volt g5]ator c *>ge tw5ty-five cells 9 s]ies economically4 ,batt]y-*>g+ g5]ators are controll$ z to _! output by v>y+ a resi/ance 9 s]ies ) _! fields4 ,su* ma*9es are usually %unt-w\nd4 ,sometimes !y are comp\nd-w\nd1 b comp\nd+ is less important 9 telephone g5]ators ?an 9 "s o!r uses4 ,a feature ( great importance 9 ! design ( *>g+ g5]ators is smoo?ness ( curr5t4 ,if x 7 possible to design g5]ators to produce absolutely ev5 or smoo? curr5t1 ! /orage batt]y w\ld n be su* an ess5tial feature to common-batt]y ex*anges1 because !n ! g5]ator might deliv] its curr5t directly to ! bus b>s ( ! (fice )\t any /orage-batt]y connection & )\t caus+ noise on ! l9es4 ,su* g5]ators h be5 built 9 small units4 ,ev5 if ^! smoo? curr5t g5]ators 7 comm]cially develop$ to a degree to produce absolutely no noise on ! l9es1 ! /orage batt]y w\ld /ill be us$1 s9ce its action z a res]voir = electrical en]gy is important4 ,x n only disp5ses ) ! necessity ( runn+ ! g5]ators cont9u\sly1 b x also af=ds a safegu>d aga9/ breakd[ns :i* is "o ( its important uses4 ,! ability to c>ry ! load ( a c5tral (fice directly on ! *>g+ g5]ator )\t ! use ( a /orage batt]y is ( no importance except 9 an em]g5cy :i* takes ! /orage batt]y :olly out ( s]vice4 ,s9ce ! beg9n+ ( common-batt]y work+ su* em]g5cies h happ5$ a negligible numb] ( times4 ,f> m communities h lack$ telephone s]vice because ( accid5ts beyond human control ?an because ( /orage-batt]y failures4 ,9 p[] plants s]v+ l>ge (fices1 ! dem& ^u ! /orage batt]y is great en\gh to require l>ge plate areas 9 ea* cell4 ,! int]nal resi/ance1 !re=e1 is small & consid]able fluctuations may exi/ 9 ! *>g+ curr5t )\t _! be+ he>d 9 ! talk+ circuits4 ,! am\nt ( noise to be he>d dep5ds also on ! type ( *>g+ g5]ator4 ,increas+ ! numb] ( armature coils & commutator segm5ts increases ! smoo?ness ( ! *>g+ curr5t4 ,! %ape ( ! g5]ator pole pieces is also a factor 9 secur+ su* smoo?ness4 ,if1 ) a giv5 ma*9e & /orage batt]y1 ! talk+ circuits are di/urb$ by ! *>g+ curr5t1 relief may be obta9$ by ins]t+ a l>ge imp$ance 9 ! *>g+ circuit4 ,?is imp$ance requires to be ( l[ resi/ance1 because :atev] heat is develop$ 9 x is lo/ en]gy4 ,?is means t ! be/ conditions exi/ :5 ! resi/ance is l[ & ! inductance l>ge4 ,^! conditions are satisfi$ by us+ 9 ! imp$ance coil _m turns ( l>ge wire & an ample iron core4 ,dynamotors are n g5]ally suitable = *>g+ purposes4 ,n only is ! difficulty 9 regulat+ _! output a disadvantage1 b ! fact t ! prim>y & second>y w9d+s are s closely associat$ on ! armature core makes !m c>ry into ! *>g+ curr5t1 n only ! commutator noises ( ! g5]ator end1 b ( ! motor end z well4 ,m]cury-,arc ,rectifi]s4 ,9 common-batt]y (fices s]v+ a few hundr$ l9es1 & :]e ! comm]cial supply is alt]nat+ curr5t1 x is good practice to trans=m x into direct-batt]y *>g+ curr5t by means ( a m]cury-arc rectifi]4 ,x is a device broadly simil> to ! m]cury-arc lamp produc$ by ,pet] ,coop] ,hewitt4 ,x conta9s no mov+ p>ts & op]ates at high effici5cy )\t introduc+ noises into ! telephone l9es4 ,x requires little c>e & has good l5g? ( life4 ,illu/ration3 ,fig4 #dae4 ,m]cury-,arc ,rectifi] ,circuits ,! circuit ( a m]cury-arc rectifi] *>g+ outfit is %[n 9 ,fig4 #dae4 ,! m]cury-arc rectifi] prop] consi/s ( a glass bulb conta9+ vacuum & a small am\nt ( m]cury4 ,:5 its t]m9als are connect$1 z indicat$--! two anodes across an alt]nat+-curr5t s\rce & ! ca?ode ) a circuit t is to be suppli$ ) direct curr5t--?is device has ! peculi>ity ( action t curr5t w fl[ alt]nately f ! two anodes always to ! ca?ode & nev] f x4 ,! ca?ode1 !re=e1 becomes a s\rce ( positive pot5tial &1 z su*1 is us$ 9 *>g+ ! /orage batt]y ?r\gh ! s]ies reactance coil & ! comp5sat+ reactances1 z indicat$4 ,! l9e trans=m] %[n at ! upp] portion ( ,fig4 #dae1 is ! "o = conv]t+ ! high-pot5tial alt]nat+ curr5t to ! comp>atively l[-pot5tial curr5t requir$ = ! action ( ! rectifi]4 ,! trans=m] bel[ ?is has a "o-to-"o ratio1 & is call$ ! insulat+ trans=m]4 ,its purpose is to safegu>d ! telephone app>atus & circuits aga9/ abnormal pot5tials f ! l9e1 & also to prev5t ! gr\nd1 :i* is commonly plac$ on ! neutral wire ( trans=m]s on comm]cial light+ circuits1 f int]f]+ ) ! gr\nd t is commonly plac$ on ! positive pole ( ! c5tral-(fice batt]y4 ,provision ,aga9/ ,breakd[n4 ,9 ord] to provide aga9/ breakd[n ( s]vice1 a well-design$ telephone p[] plant %\ld h available m ?an "o prim>y s\rce ( p[] & m ?an "o *>g+ unit & r++ unit4 ,duplicate ,prim>y ,s\rces4 ,9 l>ge cities :]e ! comm]cial p[] s]vice is highly develop$ & a breakd[n ( ! g5]at+ /ation is practically impossible1 x is cu/om>y to dep5d on t s]vice alone4 ,9 ord] to insure aga9/ loss ( p[] due to an accid5t to portions ( ! di/ribut+ sy/em1 x is ! common cu/om to run two entirely sep>ate p[] leads into ! (fice1 com+1 if possible1 f diff]5t p>ts ( ! sy/em s t a breakd[n on "o section w n deprive ! telephone ex*ange ( prim>y p[]4 ,9 small] places :]e ! comm]cial s]vice is n s reliable1 x is usual to provide1 9 addition to ! comm]cial electric-p[] s]vice1 an indep5d5t s\rce ( p[] 9 ! =m ( a gas or /eam eng9e4 ,?is may be run z a regul> s\rce1 ! comm]cial s]vice be+ employ$ z an em]g5cy or vice v]sa1 z economy may dictate4 ,9 provid+ a gas eng9e = driv+ *>g+ dynamos1 x is important to obta9 "o hav+ z good regulation z possible1 9 ord] to obta9 a *>g+ curr5t ( practically con/ant voltage4 ,duplicate ,*>g+ ,ma*9es4 ,! /orage batt]ies ( telephone ex*anges are usually provid$ ( suffici5t capacity to supply ! direct-curr5t ne$s ( ! (fice = tw5ty-f\r h\rs aft] a full *>ge has be5 giv5 !m4 ,?is 9 itself is a /rong safegu>d aga9/ breakd[n4 ,9 addition to ?is ! *>g+ ma*9es %\ld be 9 duplicate1 s t a burnt-out armature or o!r damage to "o ( ! *>g+ units w n disable ! plant4 ,duplicate ,r++ ,ma*9es4 ,x is equally important t ! r++ ma*9es1 :e!r ( ! rot>y or vibrat+ type1 be 9 duplicate4 ,= l>ge ex*anges ! r++ ma*9es are usually dynamos1 & x is n unusual to h "o ( ^! driv5 f ! comm]cial p[] ma9s & ! o!r f ! /orage batt]y4 ,) ?is arrangem5t complete failure ( all s\rces ( prim>y p[] w\ld /ill leave ! ex*ange op]ative z long z suffici5t *>ge rema9s 9 ! /orage batt]y4 ,capacity ( ,p[] ,units4 ,9 design+ telephone swit*bo>ds x is ! common practice to s design ! frameworks t ! space = multiple jacks is 9 excess ( t requir$ = ! orig9al in/allation4 ,9 a l mann]1 ! p[] plant is also design$ ) a view ( be+ readily increas$ 9 capacity to an am\nt suffici5t to provide curr5t = ! ultimate numb] ( subscrib]s' l9es = :i* ! swit*bo>d is design$4 ,! motor g5]ators1 or :atev] means are provid$ = *>g+ ! /orage batt]ies1 are usually in/all$ ( suffici5t size to c>e = ! ultimate requirem5ts ( ! (fice4 ,! r++ ma*9es are also provid$ = ! ultimate equipm5t4 ,h[ev]1 9 ! case ( ! /orage batt]y1 x is common practice to provide ! batt]y tanks ( suffici5t size to c>e = ! ultimate capacity1 :ile ! plates are in/all$ = a capacity only slightly 9 excess ( t requir$ = ! orig9al in/allation4 ,z ! equipm5t ( subscrib]s' l9es is increas$1 additional plates may1 !re=e1 be add$ to ! cells )\t replac+ ! /orage batt]y z a :ole1 & )\t mak+ extraord9>y provisions to prev5t ! int]ruption ( s]vice4 ,x is also cu/om>y to provide *>g+ & supply leads f ! /orage batt]y ( c>ry+ capacity suffici5t = ! ultimate requirem5ts ( ! (fice4 ,/orage ,batt]y4 ,! /orage batt]y is ! p[] plant elem5t :i* has made common-batt]y sy/ems possible4 ,! common-batt]y sy/em is ! elem5t :i* has made ! pres5t wide developm5t ( telephony possible4 ,a /orage-batt]y cell is an electro-*emical device 9 :i* a *emical /ate is *ang$ by ! passage ( curr5t ?r\gh ! cell1 ?is /ate t5d+ to rev]t :5 a curr5t is all[$ to fl[ 9 ! opposite direction4 ,a /orage cell consi/s ( two conductors 9 a solution1 ! nature & ! relation ( ^! ?ree elem5ts be+ su* t :5 a direct curr5t is made to pass f "o conductor to ! o!r ?r\gh ! solution1 ! compell$ *emical *ange is proportional to ! product ( ! curr5t & its duration4 ,:5 ! two conductors are jo9$ by a pa? ov] :i* curr5t may fl[1 a curr5t does fl[ 9 ! opposite direction to t :i* *>g$ ! cell4 ,all /orage batt]ies s f> 9 ext5sive use 9 telephone sy/ems are compos$ ( lead plates 9 a solution ( sulphuric acid 9 wat] call$ ! electrolyte4 ,9 *>g+1 ! curr5t t5ds to oxidize ! lead ( "o plate & de-oxidize ! o!r4 ,9 dis*>g+1 ! t5d5cy is t[>d equilibrium4 ,! conta9]s1 employ$ 9 telephone "w1 = ! plates & electrolyte are ei!r ( glass or wood ) a lead l9+1 ! glass j>s be+ us$ = ! small] siz$ plates ( small capacity cells1 :ile ! lead-l9$ wood5 tanks are employ$ ) ! l>g] capacity cells4 ,! pot5tial ( a cell is slightly ov] two volts & is indep5d5t ( ! %ape or size ( ! plates = a giv5 type ( batt]y4 ,! /orage capacity ( a cell is det]m9$ by ! size & ! numb] ( plates4 ,!re=e1 by increas+ ! numb] ( plates & ! areas ( _! surfaces1 ! amp]e-h\r capacity ( ! cell is correspond+ly increas$4 ,! desir$ pot5tial ( ! batt]y is obta9$ by connect+ ! prop] numb] ( cells 9 s]ies4 ,/orage-batt]y cells us$ 9 telephone "w v>y f #b plates hav+ an area ( #ab squ>e in*es ea*1 to cells hav+ ov] #ej plates1 ea* plate hav+ an area ( #bdj squ>e in*es4 ,! amp]e-h\r capacity ( ^! batt]ies v>ies f #f amp]e h\rs to #d1jjj amp]e h\rs1 respectively1 :5 us$ at an av]age #h-;h\r dis*>ge rate4 ,9 ,fig4 #daf is illu/rat$ a /orage cell employ+ a glass conta9] & hav+ fifte5 plates4 ,ea* plate is #aa in*es high & #aj-a_/b in*es wide1 ) an area1 !re=e1 ( #aae4e squ>e in*es4 ,su* a cell has a normal capacity ( #efj amp]e h\rs4 ,! type illu/rat$ is "o made by ! ,electric ,/orage ,batt]y ,company ( ,philadelphia1 ,pa4,a ,illu/ration3 ,fig4 #daf4 ,/orage ,cell ,in/allation4 ,9 in/all+ ! glass j>s x is cu/om>y to place !m 9 trays p>tially fill$ ) s&4 ,!y are1 h[ev]1 at times in/all$ on insulators s design$ z to prev5t moi/ure f caus+ leakage betwe5 ! cells4 ,! cells us+ wood5 tanks are plac$ on glass or porcela9 insulators1 & ! tanks are plac$ ) en\gh cle>ance betwe5 !m to prev5t ! lead l9+ ( adjac5t tanks f be+ 9 contact & !reby %ort-circuit+ ! cells4 ,aft] ! positive & ! negative plates h be5 in/all$ 9 ! tanks1 _! respective t]m9als are connect$ to bus b>s1 ^! bus b>s be+1 = ! small types ( batt]y1 lead-cov]$ clamp+ bolts1 :ile 9 ! l>g] types re9=c$ lead bus b>s are employ$1 to :i* ! plates are securely jo9$ by a process call$ lead burn+4 ,?is process consi/s 9 melt+ a portion ( ! bus b> & ! t]m9al lug ( ! plate by a flame ( v high temp]ature1 ?us fus+ ea* individual plate to ! prop] bus b>4 ,! plates ( adjac5t cells are connect$ to ! same bus b>1 ?us elim9at+ ! necessity ( any o!r connection betwe5 ! cells4 ,initial ,*>ge4 ,z soon z ! plates h be5 in/all$ 9 ! tanks & weld$ to ! bus b>s1 ! cell %\ld be fill$ ) electrolyte hav+ a specific gravity ( #a4ahj to #a4aij to "o-half in* above ! tops ( ! plates & !n ! *>ge %\ld be imm$iately />t$ at ab\t ! normal rate4 ,9 ! case ( a batt]y consi/+ ( cells ( l>ge capacity1 x is cu/om>y to place ! electrolyte 9 ! cells z ne>ly simultane\sly z possible r ?an to completely fill ! cells 9 consecutive ord]4 ,:5 ! electrolyte is plac$ 9 ! cells simultane\sly1 ! *>ge is />t$ at a v mu* r$uc$ rate be=e ! cells are completely fill$1 ! rate be+ increas$ z ! cells are fill$1 ! normal rate ( *>ge be+ rea*$ :5 ! cells are completely fill$4 ,read+s %\ld be tak5 h\rly ( ! specific gravity & temp]ature ( ! electrolyte1 voltage ( ! cells1 & amp]age ( *>g+ curr5t4 ,a record or log %\ld be kept ( ! specific gravity & voltage ( ea* ( ! cells ( ! batt]y regul>ly dur+ ! life ( ! batt]y & x is well to comm5ce ?is record ) ! initial *>ge4 ,! initial *>ge %\ld be ma9ta9$ = at lea/ t5 h\rs aft] ! "t :5 ! voltage & specific gravity h rea*$ a maximum4 ,if = any reason x is impractical to cont9ue ! initial *>ge un9t]rupt$1 ! fir/ p]iod ( *>g+ %\ld be at lea/ f twelve to fifte5 h\rs4 ,h[ev]1 e ef=t %\ld be made to h ! initial *>ge cont9u\s1 z an int]ruption t5ds to increase ! "t necess>y = ! initial *>ge1 & if ! "t be too long betwe5 ! p]iods ( ! initial *>ge1 ! effici5cy & capacity ( ! cells are liable to be affect$4 ,9 case ( a l>ge batt]y1 precaution %\ld be tak5 to insure t ! v5tilation is exceptionally good1 because if x is n good ! temp]ature is liable to increase consid]ably & !reby cause an undue am\nt ( evaporation f ! cells4 ,! object ( ! temp]ature read+s tak5 dur+ ! *>ge is to enable corrections to be made to ! specific gravity read+s z obta9$ by ! hydromet]1 9 ord] t ! correct specific gravity may be asc]ta9$4 ,?is correction is made by add+ 4#jja specific gravity = ea* ?ree degrees 9 temp]ature above #gj deg4 ,fahr5heit1 or subtract+ ! same am\nt = ea* ?ree degrees bel[ #gj deg4 ,fahr5heit4 ,at ! "t ! cells beg9 to gas !y %\ld be gone ov] c>efully to see t !y gas ev5ly1 & also to detect & rem$y e>ly 9 ! *>g+ p]iod any defects :i* may exi/4 ,if !re is any d\bt 9 reg>d to ! "t at :i* ! cells rea* a maximum voltage & specific gravity1 ! *>ge %\ld be cont9u$ suffici5tly long be=e ! la/ t5 h\rs ( ! *>ge are comm5c$ to elim9ate any su* d\bt1 z 9 _m cases poor effici5cy & l[ capacity ( a cell lat] 9 its life may be trac$ to an insuffici5t initial *>ge4 ,op]ation4 ,aft] ! batt]y has be5 put 9 commission ! p]iodic *>ges %\ld be c>efully wat*$1 z excessive *>g+ causes dis9tegration & decreases ! life & capacity ( ! batt]y2 :ile1 on ! o!r h&1 und]*>g+ w result 9 sulphat+ ( ! plates & decrease ( capacity1 &1 if ! und]*>ge be great1 w result 9 a dis9tegration ( ! plates4 ,x is1 !re=e1 ess5tial t ! batt]y be *>g$ regul>ly & at ! rate specifi$ = ! p>ticul> batt]y 9 "q4 ,9 ord] to m9imize ! *ance ( ei!r cont9u\sly ov]*>g+ or und]*>g+ ! batt]y1 ! *>ges are divid$ into two classes1 namely1 regul> *>ges & ov]*>ges4 ,! regul> *>ges are ! p]iodic *>ges = ! purpose ( re/or+ ! capacity ( ! batt]y aft] dis*>ge4 ,! ov]*>ges1 :i* %\ld occur once a week or once 9 e two weeks1 accord+ to ! use ( ! batt]y1 are = ! purpose ( insur+ t all cells h receiv$ _! prop] *>ge1 = r$uc+ su* sulphat+ z may h occurr$ on cells und]*>g$1 & = keep+ ! plates1 9 g5]al1 9 a heal?y condition4 ,! specific gravity ( ! electrolyte1 ! voltage ( ! batt]y1 & ! am\nt ( gas+ obs]v$ are all indications ( ! am\nt ( *>ge :i* ! batt]y has receiv$ & %\ld all be consid]$ :5 practicable4 ,ei!r ! specific gravity or voltage may be us$ z ! r\t9e me?od ( det]m9+ ! prop] *>ge1 b1 h[ev]1 if ! prop] *>ge is det]m9$ by ! voltage read+s1 ?is %\ld be frequ5tly *eck$ by ! specific gravity1 & vice v]sa4 ,dur+ ! *>g+ & dis*>g+ ( a batt]y ! level ( ! electrolyte 9 ! cells w fall4 ,z ! portion ( ! electrolyte :i* is evaporat$ is ma9ly wat]1 ! electrolyte may be readily re/or$ to its normal level by add+ di/ill$ wat] or c>efully collect$ ra9 wat]4 ,pilot ,cell4 ,z ! specific gravity ( all ! cells ( a batt]y1 aft] hav+ once be5 prop]ly adju/$1 w v>y ! same 9 all ! cells dur+ use1 x has be5 f\nd satisfactory to use "o cell1 commonly t]m$ ! pilot cell1 = tak+ ! regul> specific gravity read+s & only read+ ! specific gravity ( all ! cells occasionally or on ! ov]*>ge4 ,?is cell mu/ be repres5tative ( all ! cells ( ! batt]y1 & if ! batt]y is s subdivid$ 9 use t sev]al sets ( cells are liable to receive diff]5t usage1 a pilot cell %\ld be select$ = ea* gr\p4 ,ov]*>ge4 ,if ! batt]y is *>g$ daily1 x %\ld receive an ov]*>ge once a week1 or if *>g$ less frequ5tly1 an ov]*>ge %\ld be giv5 at lea/ once e two weeks4 ,9 mak+ an ov]*>ge ?is %\ld be done at a con/ant rate & at a rate specifi$ = ! batt]y4 ,dur+ ! ov]*>ge ! voltage ( ! batt]y & ! specific gravity ( ! pilot cell %\ld be tak5 e fifte5 m9utes f ! "t ! gas+ beg9s4 ,! *>ge %\ld be cont9u$ until five consecutive1 specific-gravity read+s are practically ! same4 ,! voltage ( ! batt]y %\ld n increase dur+ ! la/ h\r ( ! *>ge4 ,z ! pr9cipal object ( ! ov]*>ge is to insure t all ( ! cells h receiv$ ! prop] *>ge1 x mu/1 !re=e1 be cont9u$ long en\gh to n only prop]ly *>ge ! mo/ effici5t cells1 b also to prop]ly *>ge ^? :i* are l[] 9 effici5cy4 ,! long] ! int]val betwe5 ov]*>ges1 ! great] w be ! v>iation betwe5 ! cells &1 !re=e1 x is necess>y to cont9ue ! ov]*>ge long] :5 ! int]val betwe5 ov]*>ges is z great z two weeks4 ,be=e ! ov]*>ge is made ! cells %\ld be c>efully inspect$ = %ort circuits & o!r abnormal conditions4 ,^! inspections may be/ be made by subm]g+ an electric lamp 9 ! cell1 if ! cell be ( wood1 or ( all[+ x to %9e ?r\gh f ! outside1 if x be ( glass4 ,by ?is means any =eign mat]ial may be readily detect$ & remov$ be=e s]i\s damage is caus$4 ,9 mak+ ^! inspections x mu/ be borne 9 m9d t :atev] tools or implem5ts are us$ mu/ be non-metallic & ( "s insulat+ mat]ial4 ,regul> ,*>ge4 ,regul> *>ges are ! p]iodic *>ges = re/or+ ! capacity ( ! batt]y1 & %\ld be made z frequ5tly z ! use ( ! batt]y dem&s4 ,! voltage ( ! cells is a good guide = det]m9+ :5 ! batt]y %\ld be re*>g$4 ,! voltage ( a cell %\ld nev] be all[$ to drop bel[ #a4h volts1 & x is usually consid]$ bett] practice to re*>ge :5 ! batt]y has rea*$ #a4i volts4 ,if a batt]y is to rema9 idle = ev5 a %ort "t1 x %\ld be left 9 a completely *>g$ condition4 ,! regul> *>ges = cells completely equipp$ ) plates %\ld be cont9u$ until ! specific gravity ( ! pilot cell has ris5 to five po9ts bel[ ! maximum atta9$ on ! prec$+ ov]*>ge1 or1 if only p>tially equipp$ ) plates1 until x has ris5 to ?ree po9ts bel[ ! previ\s maximum4 ,! voltage p] cell at ?is "t %\ld be f 4#je volts to 4#a volts bel[ t obta9$ on ! previ\s ov]*>ge4 ,at ?is "t all ! cells %\ld be gas+1 b n z freely z on an ov]*>ge4 ,l[ ,cells4 ,an unheal?y condition 9 a cell usually manife/s itself 9 "o ( ! foll[+ ways3 ,fall+ (f 9 specific gravity or voltage relative to ! re/ ( ! cells1 lack ( gas+ :5 *>g$1 & color ( ! plates1 ei!r noticeably light] or d>k] ?an ^? ( o!r cells ( ! batt]y4 ,:5 any ( ! above conditions are f\nd 9 a cell1 ! cell %\ld receive imm$iate att5tion1 z a delay may mean s]i\s tr\ble4 ,! cell %\ld be ?or\ghly inspect$ to det]m9e if a %ort-circuit exi/s1 ei!r caus$ by "s =eign sub/ance1 by an excess ( s$im5t 9 ! bottom ( ! tank1 or by portions ( ! plates !mselves4 ,if su* a condition is f\nd1 ! cause %\ld be imm$iately remov$ &1 if ! defect has be5 ( %ort duration1 ! next ov]*>ge w probably re/ore x to normal condition4 ,if ! defect has exi/$ = "s "t1 x is (t5 necess>y to give ! cell a sep>ate *>ge4 ,?is may be done by connect+ x directly to ! *>g+ g5]ator ) tempor>y leads & ?us br+ x back to its normal condition4 ,x is sometimes f\nd necess>y to replace ! cell 9 ord] to re/ore ! batt]y to its normal condition4 ,s$im5t4 ,! cells ( ! batt]y %\ld be c>efully wat*$ to prev5t ! s$im5t :i* collects 9 ! bottom ( ! j> or tank dur+ use f rea*+ ! bottom ( ! plates1 !reby caus+ %ort circuits betwe5 !m4 ,:5 ! s$im5t 9 ! cell has rea*$ )9 "o-half in* ( ! bottom ( ! plates1 x %\ld be remov$ at once4 ,) small cells us+ glass j>s ?is c mo/ easily be done directly aft] an ov]*>ge by c>efully draw+ (f ! electrolyte )\t di/urb+ ! s$im5t & !n remov+ x f ! j>4 ,! plates & electrolyte %\ld be replac$ 9 ! j> z soon z conv5i5t to prev5t ! plates f becom+ dry4 ,if ! plates are l>ge & 9 wood5 tanks1 ! s$im5t c mo/ easily be remov$ by means ( a scoop made especially = ! purpose4 ,! pref]able "t to clean ! tanks is j be=e an ov]*>ge4 ,replac+ ,batt]ies4 ,!re comes a "t 9 ! life ( ne>ly e c5tral-(fice equipm5t :5 ! /orage batt]y mu/ be completely r5ew$4 ,?is is due to ! fact t ! life ( ev5 ! be/ ( /orage batt]ies is n z great z ! life ( ! av]age swit*bo>d equipm5t4 ,x may also be due to ! necessity = great] capacity ?an c be secur$ ) ! exi/+ batt]y tanks1 usually caus$ by und]e/imat+ ! traffic ! (fice w be requir$ to h&le4 ,aga91 x is sometimes necess>y to make ext5sive alt]ations 9 an exi/+ batt]y1 p]haps due to ! necessity = *ang+ its location4 ,to *ange a batt]y "o cell at a "t1 keep+ ! o!rs 9 commission mean:ile1 has (t5 be5 done1 b x is always exp5sive & unsatisfactory & is likely to %ort5 ! life ( ! batt]y1 due to improp] & irregul> =m+ ( ! plates dur+ ! initial *>ge4 ,! adv5t ( ! electric automobile indu/ry has br\ght ) x a conv5i5t means = ov]com+ ?is difficulty4 ,portable /orage cells = automobile use are available 9 almo/ e locality & may (t5 be r5t$ at small co/4 ,a suffici5t numb] ( su* cells may be tempor>ily in/all$1 en\gh ( !m be+ plac$ 9 multiple to give ! necess>y output4 ,by float+ a tempor>y batt]y s =m$ across ! *>g+ ma9s & runn+ ! g5]ators cont9u\sly1 a tempor>y s\rce ( curr5t supply may be _h at small exp5se = runn+ ! ex*ange dur+ ! p]iod requir$ = alt]ations4 ,usually a "t ( l[ traffic is *os5 = mak+ ! *anges1 su* z f ,saturday ev5+ to ,monday morn+4 ,v l>ge c5tral-(fice batt]ies1 s]v+ z _m z #f1jjj l9es1 h ?us be5 tak5 out ( s]vice & replac$ )\t int]f]+ ) ! traffic & ) ! use ( b a comp>atively few portable cells4 ,"o precaution has to be obs]v$ 9 su* "w1 & t is n to subject ! portable cells to too great an ov]*>ge1 due to ! great excess ( g5]ator ov] batt]y capacity4 ,?is is easily avoid$ by wat*+ ! ammet]s to see t ! input is n 9 too great excess ( ! output1 & if necess>y1 by frequ5tly /opp+ ! ma*9es to avoid ?is4 ,p[] ,swit*bo>d4 ,! cle>+-h\se ( ! telephone p[] plant is ! p[] bo>d4 ,9 mo/ cases1 x c>ries swit*es1 met]s1 & protective devices4 ,swit*es4 ,! swit*es mo/ ess5tial are ^? = op5+ & clos+ ! motor & ! g5]ator circuits ( ! *>g+ sets & ) ^! usually are associat$ ! />t+ rheo/ats ( ! motors & ! field rheo/ats ( ! g5]ators4 ,! />t+ rheo/ats are adapt$ to all[ resi/ance to be remov$ f ! motor armature circuit1 all[+ ! armature to ga9 spe$ & increase its c\nt]-electromotive =ce )\t ov]heat+4 ,! accept$ type has means = op5+ ! driv+ circuit automatically 9 case its voltage %\ld fall1 ?us prev5t+ a tempor>y int]ruption ( driv+ curr5t f damag+ ! motor armature on its return to normal voltage4 ,illu/ration3 ,fig4 #dag4 ,p[]-,plant ,circuits ,met]s4 ,! met]s usually are voltmet]s & ammet]s1 ! =m] be+ adapt$ to read ! sev]al voltages ( direct curr5ts 9 ! p[] plant4 ,an important "o to be kn[n is ! voltage ( ! g5]ator be=e beg9n+ a batt]y *>ge1 s t ! g5]ator may n be ?r[n on ! /orage batt]y :ile g5]at+ a voltage less ?an t ( ! batt]y4 ,if ?is 7 done1 ! batt]y w\ld dis*>ge ?r\gh ! g5]ator armature4 ,! voltmet] enables ! voltage ( ! *>g+ g5]ator to be kept above t ( ! batt]y1 z ! latt] rises dur+ *>ge4 ,x enables ! p]=mance ( sev]al cells ( ! batt]y to be obs]v$4 ,a conv5i5t way is to connect ! t]m9als ( ! sev]al cells to jacks on ! p[] bo>d & to t]m9ate ! voltmet] 9 a plug4 ,! ammet]1 ) suitable connections1 enables ! batt]y-*>ge rate to be kept normal & ! batt]y dis*>ge to be obs]v$4 ,9 ord] to economize p[]1 x is be/ to *>ge ! batt]y dur+ ! h\rs ( heavy load4 ,! g5]ator output !n divides1 ! swit*bo>d tak+ :at ! load requires1 ! batt]y receiv+ ! rema9d]4 ,9 sy/ems requir+ ! t]m9al voltage ( ! equipm5t to be kept con/ant )9 close limits1 ei!r x is necess>y to use two batt]ies--nev] draw+ curr5t f a batt]y dur+ *>ge--or to provide means ( comp5sat+ = ! rise ( voltage :ile ! batt]y is "u *>ge4 ,! latt] is ! m mod]n me?od & is done ei!r by us+ few] cells :5 ! voltage p] cell is high] or by ins]t+ c\nt]-electromotive =ce cells 9 ! dis*>ge leads1 oppos+ ! dis*>ge by m or few] cells z ! voltage ( ! batt]y is high] or l[]4 ,9 ei!r me?od1 swit*es on ! p[] bo>d enable ! ins]tion & removal ( ! necess>y end cells or c\nt]-electromotive =ce cells4 ,protective ,devices4 ,! protective devices requir$ on a p[] bo>d are pr9cipally circuit-break]s & fuses4 ,circuit-break]s are adapt$ to op5 motor & g5]ator circuits :5 _! curr5ts are too great1 too small1 or 9 ! wrong direction4 ,fuses are adapt$ to op5 circuits :5 ! curr5ts 9 !m are too great4 ,! be/ type is t 9 :i* ! op]ation ( ! fuses s\nds or %[s an al>m1 or bo?4 ,p[]-,plant ,circuits4 ,! circuit arrangem5t ( c5tral-(fice p[] plants is subject to wide v>iation accord+ to conditions4 ,! type ( telephone swit*bo>d equipm5t1 :e!r magneto or common-batt]y1 automatic or manual1 w1 ( c\rse1 l>gely affect ! circuit arrangem5t ( ! p[] plant4 ,fig4 #dag %[s a typical example ( good practice 9 ?is respect = use ) a common-batt]y manual swit*bo>d equipm5t4 ,besides %[+ ! swit*es = h&l+ ! v>i\s ma*9es & ! *>ge-&-dis*>ge leads f ! /orage batt]y1 ?is diagram %[s h[ curr5t f ! /orage batt]y is deliv]$ to v>i\s p>ts ( ! c5tral-(fice equipm5t4 ,footnote ,a3 ,! in/ructions giv5 lat] 9 ?is *apt] are = batt]ies ( ?is make1 al?\gh !y are applicable 9 _m respects to all types commonly us$ 9 telephone "w4 ,,*apt] ,,xxxiii ,,h\s+ ,,c5tral-,,(fice ,,equipm5t ,! ,c5tral-,(fice ,build+4 ,prop] arrangem5t ( ! c5tral-(fice equipm5t dep5ds l>gely ^u ! design ( ! c5tral-(fice build+4 ,! problem involv$ %\ld n be solv$ by ! ar*itect alone4 ,! mo/ c>eful co-op]ation betwe5 ! eng9e] & ! ar*itect is necess>y 9 ord] t ! v>i\s p>ts ( ! telephonic equipm5t may be prop]ly relat$1 & t ! wires connect+ !m ) ea* o!r & ) ! outside l9es be dispos$ ( ) due reg>d to safety1 economy1 & conv5i5ce4 ,s _m factors ent] into ! design ( a c5tral-(fice build+ t x is impossible to lay d[n m ?an ! mo/ g5]al rules4 ,! atta9m5t ( an ideal is (t5 impossible1 because ( ! fact t ! build+ is usually 9 conge/$ di/ricts1 & its v %ape & size mu/ be gov]n$ by ! lot on :i* x is built1 & by ! imm$iate surr\nd+s4 ,frequ5tly1 also1 ! build+ mu/ be us$ = o!r purposes ?an ^? ( a telephone (fice1 s t ! sev]al purposes mu/ be consid]$ 9 its design4 ,aga91 old build+s1 design$ = o!r purposes1 mu/ sometimes be alt]$ to meet ! requirem5ts ( a telephone (fice1 & ?is is p]haps ! mo/ difficult problem ( all4 ,! ext]ior ( ! build+ is a matt] t may be l>gely decid$ by ! ar*itect & own] aft] ! g5]al "* ( ! build+ has be5 det]m9$4 ,"o important feature1 h[ev]1 & "o t has be5 ov]look$ 9 _m cases t we "k (1 is to s arrange ! build+ t swit*bo>d sections & o!r bulky portions ( ! app>atus1 :i* are necess>ily assembl$ at ! factory r ?an on ! site1 may be br\ght into ! build+ )\t te>+ d[n ! walls4 ,fire ,haz>d4 ,! app>atus to be h\s$ 9 a c5tral-(fice build+ (t5 repres5ts a co/ runn+ into ! hundr$s ( ?\s&s ( doll>s2 b :e!r ( l>ge or small fir/ co/1 x is evid5t t its de/ruction might incur a v mu* great] loss ?an t repres5t$ by its replacem5t value4 ,9 gu>d+ ! c5tral-(fice equipm5t aga9/ de/ruction by fire or o!r causes1 ! telephone company is conc]n$ to a v mu* great] ext5t ?an ! m]e co/ ( ! physical prop]ty2 s9ce x is gu>d+ ! ?+ :i* makes x possible to d bus9ess4 ,:ile ! co/ ( ! c5tral (fice & its cont5ts may be small 9 comp>ison ) ! total inve/m5t 9 outside plant & o!r portions ( ! equipm5t1 x is yet true t ^! l>g] portions ( ! inve/m5t become useless ) ! loss ( ! c5tral (fice4 ,!re is ano!r consid]ation1 & t is ! moral obligation ( ! op]at+ company to ! public4 ,a complete breakd[n ( telephone s]vice = any consid]able p]iod ( "t 9 a l>ge city is 9 ! nature ( a public calamity4 ,= ^! reasons ! safegu>d+ ( ! c5tral (fice aga9/ damage by fire & wat] %\ld be 9 all cases a feature ( fundam5tal importance1 & %\ld influ5ce n only ! "* ( ! build+ itself1 b 9 _m cases ! *oice ( its location4 ,size ( ,build+4 ,x goes )\t say+ t ! build+ mu/ be l>ge en\gh to accommodate ! swit*bo>ds & o!r app>atus t is requir$ to be in/all$4 ,! requirem5t does n end "h1 h[ev]4 ,telephone ex*ange sy/ems h1 ) few exceptions1 gr[n v mu* fa/] ?an 0 expect$ :5 !y 7 orig9ally in/all$4 ,_m build+s h _h to be ab&on$ because outgr[n4 ,9 plann+ ! build+1 !re=e1 ! eng9e] %\ld always h 9 m9d its ultimate requirem5ts4 ,x is n always necess>y t ! build+ %all be made l>ge en\gh at ! outset to take c>e ( ! ultimate requirem5ts1 b :]e ?is is n done1 ! way %\ld be left cle> = add+ to x :5 necessity dem&s4 ,illu/ration3 ,,r++ ,,& ,,*>g+ ,,ma*9es ,,& ,,p[] ,,bo>d ,plaza ,(fice1 ,new ,york ,telephone ,co4 ,/r5g? ( ,build+4 ,! major portion ( telephone c5tral-(fice app>atus1 :e!r automatic or manual1 is n ( su* weight z to dem& excessive /r5g? 9 ! floors & walls ( build+s4 ,exceptions to ?is may be f\nd 9 ! /orage batt]y1 9 ! p[] ma*9]y1 especially :]e subject to vibration1 & 9 c]ta9 cases 9 ! cable runs4 ,aft] ! ultimate size ( ! equipm5t has be5 det]m9$1 ! eng9e] & ! ar*itect %\ld conf] on ?is po9t1 p>ticul>ly ) ref]5ce to ! heavi] portions ( ! app>atus1 to make sure t adequate /r5g? is provid$4 ,! approximate weights ( all p>ts ( c5tral-(fice equipm5ts may readily be asc]ta9$ f ! manufactur]s4 ,provision = ,employes4 ,9 manual (fices p>ticul>ly x has be5 f\nd to be n only humane1 b economical to provide adequate qu>t]s = ! employes1 bo? 9 ! op]at+ rooms & places :]e !y actually p]=m _! "w1 & 9 ! places :]e !y may assemble = recreation & re/4 ,! "w ( ! telephone op]ator1 p>ticul>ly 9 l>ge cities1 is ( su* a nature z (t5 to dem& frequ5t p]iods ( re/4 ,?is is true n only on acc\nt ( ! n]v\s /ra9 on ! op]ator1 b also on acc\nt ( ! necessity1 br\ght ab\t by ! dem&s ( economy1 = v>y+ ! numb] ( op]ators 9 accordance ) ! traffic load4 ,^! features acc5tuate ! dem& = prop] rooms :]e recreation1 re/1 & n\ri%m5t may be _h4 ,provision = ,cable ,runways4 ,9 v small (fices no special /ructural provision ne$ be made 9 ! design ( ! build+ itself = ! entrance ( ! outside cables1 & = ! disposal ( ! cables & wires lead+ betwe5 v>i\s portions ( ! app>atus4 ,= l>ge (fices1 h[ev]1 ?is mu/ necess>ily ent] z an important feature 9 ! /ructure ( ! build+ itself4 ,x is important t ! cables be arrang$ sy/ematically & 9 su* a way t !y w be protect$ aga9/ injury & at ! same "t be accessible ei!r = repairs or replacem5t1 or = ! addition ( new cables to provide = gr[?4 ,disord]ly arrangem5t ( ! wires or cables results 9 disord] inde$1 ) increas$ ma9t5ance co/1 uneconomical use ( space1 inaccessibility1 liability to injury1 & g5]al unsightl9ess4 ,! c>ry+ ( cables f ! basem5t to ! upp] floors or betwe5 floors else:]e mu/ be provid$ = 9 a way t w n be wa/eful ( space1 & arrangem5ts mu/ be made = support+ ! cables 9 _! v]tical runs4 ,9 ! aggregate _! weight may be great1 & fur!rmore ea* individual cable mu/ be s support$ t its %ea? w n be subject to undue /ra94 ,ano!r factor :i* mu/ be consid]$ 9 v]tical cable runs is ! gu>d+ aga9/ su* runs =m+ natural flues ?r\gh :i* flames or heat$ gases w\ld pass1 9 ! ev5t ( ev5 an unimportant fire at _! l[] ends4 ,arrangem5t ( ,app>atus 9 ,small ,manual ,(fices4 ,:]e a common-batt]y multiple swit*bo>d equipm5t is us$1 at lea/ ?ree pr9cipal rooms %\ld be provid$--"o = ! multiple swit*bo>d prop]2 "o = ! t]m9al & p[] app>atus1 includ+ ! di/ribut+ frames1 racks1 & p[] ma*9]y2 & ! ?ird = ! /orage batt]y4 ,^! %\ld adjo9 ea* o!r = purposes ( conv5i5ce & ( economy 9 wir+4 ,illu/ration3 ,fig4 #dah4 ,typical ,small ,(fice ,floor ,plan ,floor ,plans = ,small ,manual ,(fices4 ,z 0 po9t$ out1 !re are sev]al plans ( dispos+ ( ! ma9 & int]m$iate di/ribut+ frames & ! l9e & cut-(f relay racks4 ,! "o mo/ practic$ is to m\nt ! relay rack alongside ! ma9 & int]m$iate di/ribut+ frame 9 ! t]m9al room4 ,a typical floor plan ( su* an arrangem5t = a small (fice1 employ+ z a maximum five sections ( multiple swit*bo>ds1 is %[n 9 ,fig4 #dah4 ,?is is an ideal arrangem5t well adapt$ = a rectangul> floor space & on t acc\nt may (t5 be put into effect4 ,x %\ld be not$ t ! swit*bo>d gr[s f left to "r1 & t alt]native arrangem5ts are %[n = dispos+ ( ^? sections beyond ! second4 ,! cable turn+ section ?r\gh :i* ! multiple & answ]+ jacks are l$ to ! t]m9al frames is plac$ z close z possible to ! t]m9al frames4 ,?is results 9 a consid]able sav+ 9 cable4 ,an int]e/+ feature ( ?is floor plan is ! arrangem5t ( unit>y sections ( ma9 & int]m$iate frames & relay racks1 repres5t+ rec5t practice ( ! ,we/]n ,electric ,company4 ,! iron "w ( ! ?ree racks is built 9 sections & ^! are /ructurally connect$ across s t ! fir/ section ( ! ma9 frame1 ! int]m$iate frame1 & ! relay rack =m "o unit1 ! /ructural iron "w :i* ties !m toge!r =m+ ! runway = ! cables betwe5 !m4 ,b two ( ^! units1 includ+ two sections ( ea* frame1 are %[n in/all$1 ! provision = gr[? be+ indicat$ by dott$ l9es4 ,! batt]y room 9 ?is case provides = ! disposal ( ! batt]y cells 9 two ti]s4 ,?is room is m]ely p>tition$ (f f ! di/ribut+ or t]m9al room4 ,:]e ?is is done ! p>tition walls %\ld be pla/]$ on bo? sides s z to prev5t1 z f> z possible1 ! entrance ( any batt]y fumes into ! app>atus rooms4 ,! wire *ief's desk1 z w be not$1 is locat$ 9 su* a position z to give easy access f x n only to ! di/ribut+ frames & relay rack1 b to ! p[] app>atus z well4 ,comb9$ ,ma9 & ,int]m$iate ,frames4 ,= use 9 small ex*anges1 ! ,we/]n ,electric ,company has rec5tly put on ! m>ket a comb9$ ma9 & int]m$iate di/ribut+ frame4 ,?is is con/ruct$ ab\t ! same z an ord9>y ma9 frame1 ! protectors be+ on "o side & ! l9e & int]m$iate frame t]m9als on ! o!r4 ,! l[] half ( ! t]m9als on ea* v]tical bay is devot$ to ! outside l9e t]m9als & ! upp] half is devot$ to int]m$iate frame t]m9als4 ,?is arrangem5t is indicat$ 9 ! elevation 9 ,fig4 #dai4 ,) ! use ( ?is comb9$ ma9 & int]m$iate frame1 ! floor plan ( ,fig4 #dah may be modifi$1 z %[n 9 ,fig4 #dbj4 ,illu/ration3 ,fig4 #dai4 ,comb9$ ,ma9 & ,int]m$iate ,frames ,illu/ration3 ,fig4 #dbj4 ,small ,(fice ,floor ,plan ,illu/ration3 ,fig4 #dba4 ,t]m9al ,app>atus--,small ,(fice ,9 ,fig4 #dba is giv5 an excell5t idea ( t]m9al-room app>atus c>ri$ out 9 accordance ) ! m usual plan ( employ+ sep>ate ma9 & int]m$iate di/ribut+ frames4 ,at ! extreme "r ( ?is figure ! protector side ( ! ma9 frame is %[n4 ,x w be und]/ood t ! l9e cables t]m9ate on ! horizontal t]m9al /rips on ! o!r side ( ?is frame & are connect$ ?r\gh ! horizontal & v]tical runways ( ! frame to ! protector t]m9als4 ,! int]m$iate frame is %[n 9 ! c5tral portion ( ! figure1 ! side t[>d ! left conta9+ ! answ]+-jack t]m9als1 & ! side t[>d ! "r ! multiple jack t]m9als1 ^! latt] be+ arrang$ horizontally4 ,?is horizontal & v]tical arrangem5t ( ! t]m9als on ! ma9 & int]m$iate di/ribut+ frames has be5 ! di/+ui%+ feature betwe5 ! ,bell & ,indep5d5t practice1 ! ,bell ,companies adh]+ to ! horizontal & v]tical arrangem5t1 :ile ! ,indep5d5t ,companies h employ$ ! v]tical arrangem5t on bo? sides4 ,we are in=m$ t 9 ! future ! new small] in/allations ( ! ,bell ,companies w be made l>gely ) ! v]tical arrangem5t on bo? sides4 ,at ! left ( ,fig4 #dba is %[n ! relay rack 9 two sections ( two bays ea*4 ,?is illu/ration also gives a good idea ( ! common practice 9 dispos+ ( ! cables betwe5 ! frames 9 iron runways j bel[ ! ceil+ ( ! t]m9al room4 ,types ( ,l9e ,circuits4 ,! design ( ! t]m9al-room floor plan w dep5d l>gely on ! arrangem5t ( app>atus 9 ! subscrib]s' l9e circuits ) respect to ! di/ribut+ frames & relay racks4 ,! ,bell practice 9 ?is respect has already be5 ref]r$ to & is illu/rat$ 9 ,fig4 #cdh4 ,9 ?is ! l9e & cut-(f relays are p]man5tly associat$ ) ! answ]+ jacks & lamps1 result+ 9 ! answ]+-jack equipm5t be+ subject to *ange ) respect to ! multiple & ! l9e ?r\gh ! jump]s ( ! int]m$iate frame4 ,! practice ( ! ,kellogg ,company1 on ! o!r h&1 has be5 illu/rat$ 9 ,fig4 #cec1 & 9 ?is ! l9e & cut-(f relays are p]man5tly associat$ ) ! multiple & ) ! l9e1 only ! answ]+ jacks & lamps be+ subject to *ange ?r\gh ! jump] wires on ! int]m$iate frame4 ,?is latt] arrangem5t has l$ to a v desirable p>allel arrangem5t ( ! two di/ribut+ frames & ! relay rack4 ,^! are made ( equal l5g? s z to correspond bay = bay1 & are plac$ side by side ) only en\gh space betwe5 !m = ! passage ( workm5--! relay rack ly+ betwe5 ! ma9 & int]m$iate frames4 ,9 ?is s*eme all ! multiple & answ]+-jack cables run f ! int]m$iate di/ribut+ frame1 & ! cabl+ betwe5 ! int]m$iate frame & ! relay rack & betwe5 ! relay rack & ! ma9 frame is run /raight across f "o rack to ! o!r4 ,?is results 9 a great sav+ ( cable )9 ! t]m9al room1 ov] t arrangem5t :]e9 ! cabl+ f "o frame to ano!r is necess>ily l$ along ! l5g? ( ! frame to its end & !n passes ?r\gh a s+le runway to ! end ( ! o!r frame4 ,l>ge ,manual ,(fices4 ,= purposes ( illu/rat+ ! practice 9 h\s+ ! app>atus 9 v l>ge (fices equipp$ ) manual swit*bo>ds1 we h *os5 ! ,*elsea (fice ( ! ,new ,york ,telephone ,company z an excell5t example ( mod]n practice4 ,illu/ration3 ,fig4 #dbb4 ,floor ,plan1 ,op]at+ ,room1 ,*elsea ,(fice1 ,new ,york ,city ,! gr\nd plan ( ! build+ is ,u-%ap$1 9 ord] to provide ! necess>y light ov] ! r l>ge floor areas4 ,! plan ( ! op]at+ floor--! six? floor ( ! build+--is %[n 9 ,fig4 #dbb4 ,z w be se51 ?is con/itutes a s+le op]at+ room1 ! ,a-bo>d be+ locat$ 9 ! "r w+ & ! ,b-bo>d 9 ! left4 ,! po9t f :i* bo? bo>ds gr[ is ne> ! c5t] ( ! front ( ! build+1 ! bo>ds com+ toge!r at ?is po9t 9 a common cable turn+ section4 ,! disposal ( ! v>i\s desks = ! manag]1 *ief op]ator1 & monitors is indicat$4 ,^? swit*bo>d sections :i* are %[n 9 full l9es are ! ones at pres5t in/all$1 ! provision = gr[? be+ indicat$ 9 dott$ l9es4 ,illu/ration3 ,fig4 #dbc4 ,t]m9al ,room & ,op]ators' ,qu>t]s1 ,*elsea ,(fice1 ,new ,york ,city ,! fif? floor is devot$ to ! t]m9al room & op]ators' qu>t]s1 ! t]m9al room occupy+ ! left-h& w+ & ! major portion ( ! front ( ! build+1 & ! op]ators' qu>t]s ! "r-h& w+4 ,! l9e & ! trunk cables come up f ! basem5t ( ! build+ at ! extreme left1 be+ support$ directly on ! outside wall ( ! build+4 ,arriv+ at ! fif? floor1 !y turn horizontally & are l$ "u a false floor+ provid$ ) trap doors1 to ! protector side ( ! ma9 frame4 ,! disposal ( ! cables betwe5 ! v>i\s frames w be m readily und]/ood by ref]5ce to ! foll[+ photographs4 ,a g5]al view ( a portion ( ! ,a-bo>d ( ! ,*elsea (fice is %[n 9 ,fig4 #dbd1 ?is view be+ tak5 f a po9t 9 ! left-h& w+ look+ t[>d ! front4 ,9 ,fig4 #dbe is %[n a clos] view ( a small] portion ( ! bo>d4 ,fig4 #dbf gives an excell5t idea ( ! re> ( ?is swit*bo>d & ( ! disposal ( ! cables & wires4 ,! ma9 mass ( cables at ! top are ^? ( ! multiple4 ,imm$iately bel[ ^! may be se5 ! outgo+ trunk cables4 ,! =ms ( ! answ]+-jack cables lie bel[ ^! & are n s readily se51 b ! cables lead+ f ^! =ms are l$ d[n to ! runway at ! bottom ( ! sections1 & !nce along ! l5g? ( ! bo>d to ! int]m$iate di/ribut+ frame on ! floor bel[4 ,! lay] ( cables1 support$ on ! iron rack imm$iately above ! answ]+-jack cable runway1 %[n at ! extreme bottom ( ! view1 are ^? conta9+ ! wires lead+ f ! repeat+ coils to ! cord circuits4 ,an int]e/+ feature ( ?is bo>d is ! provisions = protection aga9/ injury by fire & wat]4 ,on top ( ! bo>ds ?r\gh\t _! entire l5g? !re is laid a heavy t>paul9 curta9 ) /raps t]m9at+ 9 h&les hang+ d[n f its edges4 ,^! may be se5 9 ,fig4 #dbf & also 9 ,fig4 #dbe4 ,! idea ( ?is is t if ! bo>d is expos$ to a wat] haz>d1 z 9 ! case ( fire1 ! bo>d may be completely cov]$1 front & re>1 ) ?is t>paul9 curta91 by m]ely pull+ ! /raps4 ,! entire =ce--bo? op]ators & repairm5--is drill$ to assure ! c>ry+ out ( ?is plan4 ,! re> ( ! bo>ds is adapt$ to be enclos$ by wood5 curta9s1 simil> to ^? employ$ 9 roll-top desks4 ,^! are all rais$ 9 ! re> view ( ,fig4 #dbf1 ! h\s+ = ! roll$-up curta9 be+ %[n at ! extreme top ( ! sections4 ,9 ord] to gu>d ! multiple cables & ! multiple jacks aga9/ fire :i* might orig9ate 9 ! cord-circuit wir+1 a heavy asbe/os p>tition is plac$ imm$iately above ! cord racks & is cle>ly %[n 9 ,fig4 #dbf4 ,illu/ration3 ,fig4 #dbd4 ,subscrib]s' ,bo>d4 ,*elsea ,(fice1 ,new ,york ,city ,illu/ration3 ,fig4 #dbe4 ,subscrib]s' ,bo>d4 ,*elsea ,(fice1 ,new ,york ,city ,illu/ration3 ,fig4 #dbf4 ,re> ,view ,*elsea ,swit*bo>d ,illu/ration3 ,fig4 #dbg4 ,t]m9al & ,p[] ,app>atus4 ,*elsea ,(fice ,a view ( ! t]m9al & p[] room is %[n 9 ,fig4 #dbg4 ,9 ! upp] left-h& corn] ! cables may be se5 9 _! passage d[nw>d f ! cable turn+ section betwe5 ! ,a- & ,b-bo>ds4 ,! l>ge gr\p ( cables %[n at ! extreme left is ! ,a-bo>d multiple4 ,?is passes d[n & !n along ! horizontal %elves ( ! int]m$iate frame1 :i* is ! frame 9 ! extreme left ( ?is view4 ,! ,b-bo>d multiple comes d[n ?r\gh ano!r op5+ 9 ! floor1 & z is %[n1 aft] pass+ "u ! ,a-bo>d multiple jo9s x 9 ! same v]tical run f :i* x passes to ! int]m$iate frame4 ,! cord-circuit cables lead d[n ?r\gh ! same op5+ z t occupi$ by ! ,a-bo>d multiple & pass (f to ! "r-h& "o ( ! racks %[n1 :i* conta9s ! repeat+ coils4 ,! cables lead+ f ! op5+ 9 ! ceil+ to ! "r-h& side ( ! int]m$iate di/ribut+ frame are ! answ]+-jack cables1 & f ! t]m9als on ?is side ( ?is frame o!r cables pass 9 small] gr\ps to ! relay t]m9als on ! relay racks :i* lie betwe5 ! int]m$iate frame & ! coil rack4 ,! p[] bo>d is %[n at ! extreme "r4 ,! fuse panel at ! left ( ! p[] bo>d conta9s 9 its l[] portion fuses = ! batt]y supply leads to ! op]ator's position & to private-bran* ex*anges1 & 9 its upp] portion lamps & fuses = ! r++ g5]ator circuits = ! v>i\s op]ators' positions & also = private-bran* ex*anges4 ,at ! l[] left-h& portion ( ?is view is %[n ! batt]y cab9et4 ,x is ! practice ( ! ,new ,york ,telephone ,company n to employ sep>ate batt]y rooms1 b to locate its /orage batt]ies directly 9 ! t]m9al room & to enclose !m1 z %[n1 9 a wood5 cab9et ) glass panels1 :i* is v5tilat$ by means ( a lead pipe ext5d+ to a flue 9 ! wall4 ,"o unit ( *>g+ ma*9es1 consi/+ ( motor & g5]ator1 is %[n 9 ! imm$iate =egr\nd4 ,a duplicate ( ?is unit is employ$ b is n %[n 9 ?is view4 ,! v>i\s r++ & message regi/] ma*9es are %[n beyond ! *>g+ ma*9es4 ,?ree ( ^! small] ma*9es are = supply+ r++ curr5t & ! rema9d] are = supply+ #cj-volt direct curr5t = op]at+ ! message regi/]s4 ,"o ( ! ma*9es ( ea* set is w\nd to run f ! ma9 /orage batt]y 9 case ( a failure ( ! g5]al light+ s]vice f :i* ! curr5t = op]at+ is normally drawn4 ,illu/ration3 ,fig4 #dbh4 ,t]m9al ,app>atus4 ,*elsea ,(fice ,illu/ration3 ,fig4 #dbi4 ,floor ,plan1 ,automatic ,(fice1 ,lans+1 ,mi*igan ,ano!r view ( ! t]m9al-room app>atus is giv5 9 ,fig4 #dbh4 ,?is is tak5 f ! po9t m>k$ ,b on ! floor plan ( ,fig4 #dbc4 ,at ! "r may be se5 ! message regi/]s on :i* ! calls ( ! subscrib]s 9 ?is (fice are c\nt$ z a basis = ! bills = _! s]vice4 ,at ! extreme left is %[n ! private-l9e te/ bo>d4 ,?r\gh ?is bo>d run all ( ! l9es leas$ = private use1 & also all ( ! ord] wire or call l9es pass+ ?r\gh ?is (fice4 ,! purpose ( su* an arrangem5t is to facilitate ! te/+ ( su* l9e wires4 ,at ! "r ( ?is private-l9e te/ bo>d is %[n a f\r-position wire *ief's desk1 ^u :i* are provid$ facilities = mak+ all ( ! te/s inside & outside4 ,illu/ration3 ,fig4 #dcj4 ,l9e-,swit* ,units ,illu/ration3 ,fig4 #dca4 ,automatic ,app>atus at ,lans+ ,(fice ,! ma9 frame is %[n at ! "r ( ,fig4 #dbh1 j to ! "r ( a gall]y f :i* a /ep-ladd] leads4 ,! left-h& side ( ?is frame is ! l9e or protector side1 b ! portion t[>d ! obs]v] 9 ?is picture is unequipp$4 ,^! equipp$ protector /rips c>ry #djj pairs ( t]m9als ea*1 & ! consequ5t l5g? ( ^! /rips makes necess>y ! gall]y %[n1 9 ord] t all ( !m may be readily accessible4 ,illu/ration3 ,fig4 #dcb4 ,ma9 ,di/ribut+ ,frame1 ,lans+ ,(fice ,illu/ration3 ,fig4 #dcc4 ,l9e ,swit*es ,illu/ration3 ,,p[] ,,plant ,,= ,,automatic ,,swit*bo>d ,,equipm5t ,bay ,cities ,home ,telephone ,company1 ,b]keley1 ,cal4 ,illu/ration3 ,fig4 #dcd4 ,second>y ,l9e ,swit*es & ,fir/ ,selectors ,automatic ,(fices4 ,!re is no great diff]5ce 9 ! am\nt ( floor space requir$ 9 c5tral (fices employ+ automatic & manual equipm5t4 ,:atev] diff]5ce !re is1 is likely to be 9 favor ( ! automatic4 ,! fact t no su* rigid requirem5t exi/s 9 ! arrangem5t ( automatic app>atus1 z t :i* makes x necess>y to place ! sections ( a multiple bo>d all 9 "o r[1 makes x possible to utilize ! available space m economically ) automatic ?an ) manual equipm5t4 ,illu/ration3 ,fig4 #dce4 ,second ,selectors ,illu/ration3 ,fig4 #dcf4 ,toll ,di/ribut+ ,frame & ,h>monic ,conv]t]s ,9 manual practice x is necess>y to place ! di/ribut+ frames & p[] app>atus 9 a sep>ate room f t conta9+ ! swit*bo>d1 b 9 an automatic ex*ange no su* necessity exi/s2 9 fact1 s f> z ! di/ribut+-frame equipm5t is conc]n$1 x is consid]$ desirable to h x locat$ 9 ! same room z ! automatic swit*es4 ,! batt]y room 9 an automatic ex*ange %\ld be entirely sep>ate f ! op]at+ room1 s9ce ! fumes f ! batt]y w\ld be fatal to ! prop] work+ ( ! automatic swit*es4 ,typical ,automatic ,(fice4 ,! floor-plan & views ( a m$ium-siz$ automatic (fice at ,lans+1 ,mi*igan1 h be5 *os5 z repres5t+ typical practice4 ,! floor plan is %[n 9 ,fig4 #dbi4 ,! app>atus indicat$ 9 full l9es repres5ts ! pres5t equipm5t1 & t 9 dott$ l9es ! space t w be requir$ by ! expect$ future equipm5t4 ,9 ,fig4 #dcj is %[n a gr\p ( five l9e-swit* units1 repres5t+ a total ( five hundr$ l9es4 ,! l5g? ( su* a unit is practically f\rte5 feet & ! bread? ov] all ab\t tw5ty-two in*es4 ,fig4 #dca %[s a g5]al view ( ?is ,lans+ (fice1 tak5 f a po9t ( view indicat$ at ,a on ! floor plan ( ,fig4 #dbi4 ,fig4 #dcb %[s ! ma9 di/ribut+ frame1 :i* is ( ord9>y type2 ,fig4 #dcc %[s a clos] view ( "s ( ! prim>y l9e swit*es2 ,fig4 #dcd is a view ( ! second>y l9e swit*es & fir/ selectors1 ! latt] be+ on ! "r2 ,fig4 #dce is a view ( ! frequ5cy selectors & second selectors1 ! =m] be+ us$ 9 connection ) p>ty-l9e "w2 & ,fig4 #dcf is a view ( ! toll di/ribut+ frame & h>monic conv]t]s = p>ty-l9e r++4 ,a g5]al view ( ! ma9 swit*+ room 9 ! ,grant ,av5ue (fice ( ! ,home ,telephone ,company ( ,san ,francisco is giv5 9 ,fig4 #dcg1 ?is be+ tak5 be=e ! "w ( in/allation _h be5 fully complet$4 ,! pres5t capacity ( ! equipm5t is #f1jjj & ! ultimate #ab1jjj l9es4 ,?is (fice is "o ( a numb] ( simil> ones rec5tly in/all$ = ! ,home ,telephone ,company 9 ,san ,francisco1 ! comb9ation ( :i* =ms by f> ! l>ge/ automatic ex*ange yet in/all$4 ,! scope ( ! plans is su* z to enable #abe1jjj subscrib]s to be s]v$ )\t any *ange 9 ! fundam5tal design1 & by means m]ely ( addition 9 equipm5t & l9es z dem&$ by ! future subscriptions = telephone s]vice4 ,illu/ration3 ,fig4 #dcg4 ,grant ,av5ue ,(fice--,san ,francisco ,,*apt] ,,xxxiv ,,private ,,bran* ,,ex*anges ,def9itions4 ,a telephone ex*ange devot$ to ! purely local uses ( a private e/abli%m5t su* z a /ore1 factory1 or bus9ess (fice1 is a private ex*ange4 ,if1 9 addition to be+ us$ = su* local communication1 x s]ves also = communication ) ! subscrib]s ( a city ex*ange1 x becomes 9 effect a bran* ( ! city ex*ange &1 !re=e1 a private bran* ex*ange4 ,! t]m ,p4 ,b4 ,x4 has become a "p ( ! telephone man's vocabul>y z an abbreviation = private bran* ex*ange4 ,private ex*anges = purely local use require no sep>ate treatm5t z any ( ! types ( swit*+ equipm5ts = int]connect+ ! l9es = communication1 t h be5 or t w be describ$ h]e91 may be us$4 ,! problem becomes a special "o1 h[ev]1 :5 communication mu/ also be _h ) ! subscrib]s ( a public ex*ange1 s9ce !n trunk+ is involv$ 9 :i* ! conditions diff] mat]ially f ^? enc\nt]$ 9 trunk+ betwe5 ! sev]al (fices 9 a multi-(fice ex*ange4 ,= su* communication "o or m trunk l9es are l$ f ! private bran* (fice usually to ! ne>e/ c5tral (fice ( ! public ex*ange & su* trunks are call$ private bran*-ex*ange trunks4 ,!y are ! pa?s = communication betwe5 ! private ex*ange & ! public ex*ange4 ,= e/abli%+ ! connections ei!r betwe5 ! local l9es !mselves or betwe5 ! local l9es & ! trunks1 & = p]=m+ o!r duties t w be ref]r$ to1 "o or m private bran*-ex*ange op]ators are employ$ at ! swit*bo>d ( ! private e/abli%m5t4 ,! private bran* ex*ange may op]ate 9 conjunction ) a manual or an automatic public ex*ange1 b :e!r manual or automatic1 ! private ex*ange is usually manually op]at$1 al?\gh x is q possible to make a private bran* ex*ange t is :olly automatic & w1 !re=e1 involve no op]ator at all4 ,functions ( ! ,private ,bran*-,ex*ange ,op]ator4 ,x is possible1 z j /at$1 entirely to disp5se ) ! private bran*-ex*ange op]ator s f> z ! m]e connection & disconnection ( ! l9es is conc]n$4 ,b ! real function ( ! private bran*-ex*ange op]ator is a broad] "o ?an ?is & x is = ?is reason t ev5 9 connection ) automatic public ex*anges1 op]ators are desirable at ! private bran*es4 ,! private bran*-ex*ange op]ator is1 z x 71 ! doorkeep] ( ! telephone entrance to ! private e/abli%m5t4 ,%e is ! p]son fir/ met by ! public 9 ent]+ ?is telephone door4 ,!re is ! same reason1 !re=e1 :y %e %\ld be intellig5t1 c\rte\s1 & oblig+ z t ! ord9>y doorkeep] %\ld possess ^! *>act]i/ics4 ,z to incom+ traffic to a private bran* ex*ange1 an intellig5t op]ator may d mu* t[>d direct+ ! calls to ! prop] dep>tm5t or p]son1 ev5 ?\gh ! p]son call+ may h little idea z to :om he desires to rea*4 ,?is saves ! "t ( ! p]son :o makes ! call z well z t ( ! p at ! private bran* /ations1 s9ce x prev5ts _! be+ unnecess>ily call$4 ,! functions ( ! private bran*-ex*ange op]ator are no less important ) respect to outgo+ calls4 ,x is ! duty ( ! op]ator to obta9 connections ?r\gh ! city ex*ange = ! private bran* subscrib]1 :o m]ely asks = a c]ta9 connection & hangs up 8 receiv] to await h] call :5 %e %all h obta9$ x4 ,?is sav+ ( "t ( busy p by hav+ ! bran*-ex*ange op]ator make _! calls = !m has "o att5d+ disadvantage1 :i* is t ! p]son 9 ! city ex*ange :o is call$ does n1 :5 he answ]s 8 telephone1 f9d ! real p>ty ) :om he is to conv]se1 b has to wait until t p>ty responds to ! private bran* op]ator's call4 ,?is is ak9 to ask+ a p]son to call at "o's (fice & !n be+ out :5 he gets !re4 ,?is drawback is greatly acc5tuat$ :]e bo? ! p>ties t are to be involv$ 9 ! connection are p high 9 au?ority 9 c]ta9 e/abli%m5ts at private bran* ex*anges4 ,"s bus9ess h\ses h made ! rule t ! private bran* op]ator %all n connect ) _! l9es until %e has actually he>d ! voice ( ! prop] p>ty at ! o!r end4 ,:5 two subscrib]s 9 two diff]5t private bran* ex*anges :]e ?is rule is en=c$1 attempt to get into communication ) ea* o!r1 ! possibilities ( tr\ble are obvi\s4 ,all t may be said on ?is matt] is t ! p]son :o calls ano!r by telephone %\ld ext5d t p]son ! same c\rtesies t he w\ld _h he call$ him 9 p]son to 8 (fice2 & t a p]son :o is call$ by telephone by ano!r %\ld meet him ) ! same consid]ation z if he _h receiv$ a p]sonal call at 8 (fice or home4 ,! arbitr>y rul+ made by "s corporations & p]sons1 :i* results always 9 ! o!r fell['s do+ ! wait+1 is n e?ically correct nor is x good policy4 ,private ,bran* ,swit*bo>ds4 ,private bran* swit*bo>ds may be ( common-batt]y or magneto types reg>dless ( :e!r !y "w 9 conjunction ) ma9 (fice equipm5ts hav+ common-batt]y or magneto equipm5ts4 ,usually a magneto private bran* ex*ange works 9 conjunction ) a magneto ma9 (fice1 b ?is is n always true4 ,!re are cases :]e ! private bran* equipm5t ( mod]n common-batt]y type works 9 conjunction ) ma9 (fice equipm5t ( ! magneto type2 & 9 "s ( ^! cases ! private bran* ex*ange has a mu* l>g] numb] ( subscrib]s ?an ! ma9 (fice4 ,?is is likely to be true 9 l>ge summ] resort hotels locat$ 9 small & o!rwise unimportant rural di/ricts4 ,9 "o su* case )9 our k ! private bran* ex*ange has a l>g] numb] ( /ations ?an ! total c5sus population ( ! t[n1 result+ 9 an app>5t telephone developm5t consid]ably great] ?an "o hundr$ p] c5t4 ,magneto ,type4 ,:]e bo? ! private bran* & ! ma9 (fice equipm5ts are ( ! magneto type1 ! private bran* requirem5ts are met by a simple magneto swit*bo>d ( ! requisite size1 & ! trunk+ conditions are met by r+-d[n trunks ext5d+ to ! ma9 (fice4 ,9 ?is case ! sup]vision is t ( ! ord9>y cle>+-out drop type1 ! op]ators work+ toge!r z be/ !y may4 ,common-,batt]y ,type4 ,! cases :]e ! private bran* bo>d is ( common-batt]y type & ! ma9 (fice ( magneto type are comp>atively s few t !y ne$ n be treat$ "h4 ,:]e !y d occur !y dem& special treatm5t because ! ma9 portion ( ! traffic ov] ! trunk l9es to ! city or t[n c5tral (fice is likely to be toll traffic ?r\gh t (fice ov] long-di/ance l9es4 ,! pr9cipal reason :y ! equipm5t ( ! t[n (fices "u su* conditions is magneto r ?an common batt]y is t ! traffic conditions are ^? ( %ort season & heavy toll1 & common-batt]y swit*+ equipm5t at ! ma9 (fice has no especial advantages = toll "w4 ,illu/ration3 ,fig4 #dch4 ,desk ,type1 ,private ,bran* ,bo>d ,= small private bran* ex*anges ! desk type ( swit* bo>d1 %[n 9 ,fig4 #dch1 is l>gely us$4 ,! op]ator frequ5tly has o!r "w to d & ! desk is1 !re=e1 a conv5i5ce4 ,9 l>g] private ex*anges1 su* z ^? requir+ m ?an "o op]ator1 "s =m ( upright cab9et is employ$1 & if1 z sometimes occurs1 ! bran* ex*ange is ( su* size z to dem& a multiple bo>d1 !n ! g5]al =m ( ! bo>d does n diff] mat]ially f ! /&>d types ( multiple bo>d employ$ 9 regul> c5tral (fice "w4 ,! mo/ common private bran*-ex*ange condition is t ( a common-batt]y bran* work+ into a common-batt]y ma9 (fice4 ,9 su* ! ma9 po9t to be consid]$ is t ( sup]vision ( trunk-l9e connections4 ,cord ,type4 ,= ! l>g] sizes ( bran* ex*ange swit*bo>ds1 ! swit*+ app>atus is practically ! same z t ( ord9>y manual swit*bo>ds :]e9 ! connections are made betwe5 ! v>i\s l9es by means ( pairs ( cords & plugs4 ,! private bran*-ex*ange trunk l9es usually t]m9ate on ! private bran* bo>d 9 jacks b 9 "s cases plug-end$ trunks are us$4 ,illu/ration3 ,fig4 #dci4 ,key ,type1 ,private ,bran* ,bo>d ,! l9e signals may consi/ 9 me*anical visual signals or 9 lamps1 ! *oice betwe5 ^! dep5d+ l>gely on ! s\rce ( batt]y supply at ! bran* ex*ange1 a matt] :i* w be consid]$ lat]4 ,! trunk-l9e signals at ! private bran* bo>d are usually ord9>y drops :i* are ?r[n :5 ! ma9-ex*ange op]ator r+s on ! l9e z %e w\ld on an ord9>y subscrib]'s l9e4 ,frequ5tly1 h[ev]1 lamp signals are us$ = ?is purpose1 be+ op]at$ by lock+ relays en]giz$ :5 ! ma9-(fice op]ator r+s or1 9 "s cases1 op]at$ at ! "t :5 ! ma9-(fice op]ator plugs into ! trunk-l9e jack4 ,illu/ration3 ,fig4 #ddj4 ,circuits1 ,key-,type ,bo>d ,key ,type4 ,= small private bran*-ex*ange swit*bo>ds1 a type employ+ no cords & plugs has come into great favor dur+ rec5t ye>s4 ,in/ead ( connect+ ! l9es by jacks & plugs1 !y are connect$ by means ( keys closely resembl+ ord9>y r++ & li/5+ keys4 ,su* a swit*bo>d is %[n 9 ,fig4 #dci1 ?is hav+ a capacity ( ?ree trunks1 sev5 local l9es1 & ! equival5t ( five cord circuits4 ,! drops associat$ ) ! ?ree trunks may be se5 9 ! upp] left-h& side ( ! face ( ! swit*bo>d4 ,imm$iately bel[ ^! 9 ?ree v]tical r[s are ! keys :i* are us$ 9 connect+ ! trunks ) ! cord circuits or connect+ bus wires4 ,at ! "r ( ! drop associat$ ) ! trunks are sev5 visual signals1 ^! be+ ! call+ signals ( ! local l9es4 ,! sev5 v]tical r[s ( keys1 imm$iately to ! "r ( ! ?ree trunk-l9e r[s1 are ! l9e keys4 ,! ?r[+ ( any "o ( ^! keys & ( a trunk-l9e key 9 ! same horizontal r[ 9 ! same direction w connect a l9e ) a trunk ?r\gh ! correspond+ bus wires1 leav+ "o ( ! sup]visory visual signals1 %[n at ! extreme top ( ! bo>d1 connect$ ) ! circuit4 ,! keys 9 a s+le r[ at ! "r are ^? by means ( :i* ! op]ator may bridge h] talk+ set across any ( ! cord circuits4 ,! circuits ( ?is p>ticul> bo>d are %[n 9 ,fig4 #ddj4 ,?is is equipp$ = common-batt]y work+1 ! batt]y fe$ wires be+ %[n at ! left4 ,sup]vision ( ,private ,bran* ,connections4 ,at ! ma9 (fice :]e common-batt]y equipm5t is us$1 ! private bran* trunks t]m9ate be=e ! ,a-op]ators exactly 9 ! same way z ord9>y subscrib]s' l9es1 i4 e41 ea* 9 an answ]+ jack & lamp at "o position & 9 a multiple jack on ea* section4 ,x goes )\t say+1 !re=e1 t ! h&l+ ( a private bran* call1 ei!r incom+ or outgo+1 %\ld be done by ! ,a-op]ator 9 ! same mann] z a call on an ord9>y subscrib]'s l9e1 & t ! sup]vision ( ! connection %\ld impose no special duties on ! ,a-op]ator4 ,!re has be5 mu* discussion1 & no f9al agreem5t1 z to ! prop] me?od ( controll+ ! sup]visory lamp at ! ma9 (fice ( a cord t is1 at ! "t1 connect$ to a private bran* trunk4 ,?ree g5]al me?ods h be5 practic$3 ,! fir/ me?od is to h ! private bran* subscrib] directly control ! sup]visory lamp at ! ma9 (fice )\t produc+ any effect ^u ! private bran* sup]visory signal2 ?is latt] signal be+ display$ only aft] ! connection has be5 tak5 d[n at ! ma9 (fice & 9 response to ! )drawal ( ! ma9 (fice plug f ! private bran* jack4 ,?is is good practice s f> z ! ma9-(fice discipl9e is conc]n$ b x results 9 a consid]able disadvantage to bo? ! city & private bran* subscrib]s 9 t x is impossible = ! private bran* subscrib]1 :5 connect$ to ! o!r1 to re-signal ! private bran* op]ator )\t ! connection be+ fir/ tak5 d[n4 ,! second me?od is to h ! private bran* subscrib] control bo? ! sup]visory signal at ! private bran* bo>d & at ! ma9 bo>d4 ,?is has ! disadvantage ( br++ bo? op]ators 9 on ! circuit :5 ! private bran* subscrib] signals4 ,! ?ird me?od1 & "o t seems be/1 is to place ! sup]visory lamp ( ! private bran* bo>d alone "u ! control ( ! private bran* subscrib]1 s t he may attract ! att5tion ( ! private bran* op]ator )\t di/urb+ ! sup]visory signal at ! ma9 (fice4 ,! sup]visory signal at ! ma9 (fice 9 ?is case is display$ only :5 ! private bran* op]ator takes d[n ! connection4 ,?is practice results 9 a me?od ( op]ation at ! ma9 (fice t involves no special action on ! "p ( ! ,a-op]ator4 ,%e takes d[n ! connection only :5 ! ma9-(fice subscrib] has hung up 8 telephone & ! private bran* subscrib] has disconnect$ f ! trunk4 ,:atev] me?od is employ$1 private bran* disconnection is usually sl[1 & = ?is reason _m op]at+ companies in/ruct ! ,a-op]ators to disconnect on ! light+ ( ! sup]visory lamp ( ! city subscrib]4 ,) ,automatic ,(fices4 ,private bran* ex*anges mo/ us$ 9 connection ) automatic (fices employ manual swit*bo>ds1 ) ! cord circuits ( :i* is associat$ a signal transmitt+ device by :i* ! op]ator in/ead ( ! subscrib] may manipulate ! automatic app>atus ( ! public ex*ange by impulses s5t ov] ! private bran*-ex*ange trunk l9es4 ,! subscrib]'s equipm5t at ! private bran* /ations may be ei!r automatic or manual4 ,frequ5tly ! same private bran* ex*ange w conta9 bo? k9ds4 ,) ! manual sub-/ation equipm5t ! op]ation is exactly ! same z 9 a private bran* ( a manual ex*ange1 except t ! private bran* op]ator by means ( h] dial makes ! c5tral-(fice connection in/ead ( tell+ ! ma9-(fice op]ator to d s = h]4 ,) automatic sub-/ation equipm5t at ! private bran* ! subscrib]s1 by remov+ _! receiv]s f _! hooks1 call ! att5tion ( ! private bran* op]ator1 :o may receive _! ord]s & make ! desir$ c5tral-(fice connection = !m1 or :o may plug _! l9es ?r\gh to ! c5tral (fice & all[ ! subscrib]s to make ! connection !mselves ) _! own dials4 ,9 automatic equipm5t ( ! common-batt]y type1 "s *ange always takes place 9 ! call+ l9e at ! "t ! call$ subscrib] answ]s4 ,9 ! ?ree-wire sy/em dur+ ! "t ( call+1 bo? wires are ( ! same pol>ity ) respect to e>?4 ,at ! "t ( ! answ]+ ( ! call$ subscrib]1 ! two wires assume diff]5t pol>ities1 "o be+ positive to ! o!r4 ,su* a *ange is suffici5t = ! actuation ( devices local to ! private ex*ange swit*bo>d & may be int]pret$ ?r\gh ! call+ sup]visory signal 9 su* a way z to all[ x to gl[ dur+ call+ & n to gl[ aft] ! call$ subscrib] has answ]$4 ,9 ! two-wire automatic sy/em a simil> *ange c be arrang$ =1 ) simil> advantage\s results4 ,secrecy4 ,9 private ex*anges op]at+ 9 connection ) automatic c5tral (fices1 ! secret feature ( individual l9es may or may n be c>ri$ into ! private ex*ange equipm5t4 ,"s patrons ( automatic ex*anges set a high value on ! abs5ce ( any op]ator 9 a connection & transact bus9ess ov] su* l9es :i* !y w\ld n transact at all ov] manual l9es or w\ld n transact 9 ! same way ov] manual l9es4 ,to "s su* patrons1 ! pres5ce ( a private ex*ange op]ator1 ev5 ?\gh employ$ & sup]vis$ by !mselves1 seems to be a disadvantage4 ,to meet su* a feel+1 x is n difficult to arrange ! circuits ( a private ex*ange swit*bo>d s t ! op]ator may li/5 9 ^u a cord circuit at any "t & ov]he> :at is be+ said ^u x s long z two subscrib]s are n 9 communication on t cord circuit4 ,t is1 %e may answ] a call & may speak to ! call+ p]son at any "t %e wi%es until ! call$ p]son answ]s4 ,:5 he does answ] & conv]sation c take place1 "s device op]ates to disconnect h] li/5+ circuit f ! cord circuit1 n to be connect$ aga9 until at lea/ "o ( ! subscrib]s has hung up 8 receiv]4 ,) private ex*ange app>atus s arrang$1 ! secrecy ( ! sy/em is complete4 ,batt]y ,supply4 ,!re are ?ree available me?ods ( supply+ direct curr5t = talk+ & signal+ purposes to private bran* ex*anges1 ea* ( :i* repres5ts good practice "u c]ta9 conditions4 ,fir/1 by means ( pairs ( wires ext5d$ f ! c5tral-(fice batt]y2 second1 by means ( a local /orage batt]y at ! private bran* ex*ange *>g$ ov] wires f ! c5tral (fice2 & ?ird1 by means ( a local /orage batt]y at ! private ex*ange *>g$ f a local s\rce4 ,! *oice ( ^! ?ree me?ods dep5ds always on ! local conditions & x is a desirable feature1 to be employ$ by l>ge op]at+ companies1 to h all private bran*-ex*ange swit*bo>ds provid$ ) simple conv]tible features conta9$ )9 ! swit*bo>d = adapt+ x to any "o ( ^! me?ods ( supply+ curr5t4 ,if a direct-curr5t p[] circuit is available at ! private bran* ex*ange1 x may be us$ = *>g+ ! local /orage batt]y by ins]t+ m]e resi/ance devices 9 ! *>g+ leads4 ,if ! local p[] circuit c>ries alt]nat+ curr5t1 a conv]t+ device ( "s sort mu/ be us$ & = ?is purpose1 if ! ex*ange is l>ge en\gh to w>rant x1 a m]cury rectifi] is an economical & simple device4 ,! supply ( curr5t to private bran* ex*anges ov] wires lead+ to ! c5tral-(fice batt]y has ! disadvantage ( requir+ "o or sev]al pairs ( wires 9 ! cables c>ry+ ! trunk wires4 ,no special wires are run1 regul> pairs 9 ! pap] insulat$ l9e or trunk cables be+ admirably suit$ = ! purpose4 ,suffici5t conductivity may be provid$ by plac+ sev]al su* pairs 9 multiple4 ,if ! am\nt ( curr5t requir$ by ! private ex*ange w>rants x1 pairs ( *>g+ wires f ! c5tral (fice may be few] if a batt]y is *>g$ ov] !m ?an if !y are us$ direct to ! bus b>s ( ! private ex*ange swit*bo>d4 ,if !y are us$ 9 ! latt] way1 & ?is is simpl] = reasons ( ma9t5ance1 "s means mu/ be provid$ to prev5t ! consid]able resi/ance ( ! supply wires f introduc+ cross-talk into ! circuit ( ! private ex*ange4 ,?is is accompli%$ by bridg+ a consid]able capacity across ! supply pairs at ! private ex*ange--t5 to twelve micr(>ads usually suffice4 ,?is po9t has already be5 ref]r$ to & illu/rat$ 9 connection ) ,fig4 #ada4 ,! numb] ( pairs ( wires1 or1 9 o!r words1 ! am\nt ( copp] 9 ! batt]y lead betwe5 ! c5tral (fice & ! private bran*-ex*ange swit*bo>d ne$s to be prop]ly det]m9$ n only to elim9ate cross-talk :5 ! prop] cond5s]s are us$ ) !m1 b to furni% ! prop] diff]5ce ( pot5tial at ! private ex*ange bus b>s1 s t ! l9e & sup]visory signals w receive ! prop] curr5t4 ,x is a conv5i5ce 9 in/all+ & ma9ta9+ private ex*ange swit*bo>ds ( ?is k9d to prep>e tables %[+ ! numb] ( pairs ( ,no4 #ai gauge & ,no4 #bb gauge wires requir$ = a private ex*ange at a giv5 di/ance f its c5tral (fice & ( a probable am\nt ( traffic4 ,! traffic may be express$ 9 ! maximum numb] ( pairs ( cords :i* w be 9 use at "o "t4 ,) ?is fact & ! di/ance1 ! numb] ( pairs ( wires requir$ may be det]m9$4 ,r++ ,curr5t4 ,! r++ curr5t may be provid$ 9 two ways3 ov] pairs ( wires f ! city-(fice r++ ma*9es or by means ( a local h& g5]ator1 or bo?4 ,a key %\ld enable ei!r ( ^! s\rces ( r++ curr5t to be *os5 at w4 ,m>k+ ( ,app>atus4 ,all app>atus %\ld be m>k$ ) p]man5t & cle> labels4 ,t private ex*ange swit*bo>d is be/ at :i* an almo/ un9=m$ op]ator c\ld sit & op]ate x at once4 ,x is n difficult to lay out a s*eme ( labels :i* w enable su* a bo>d to be op]at$ )\t any detail$ in/ructions be+ giv54 ,desirable ,features4 ,! bo>d %\ld conta9 means ( connect+ c]ta9 ( ! local private ex*ange l9es to ! c5tral-(fice trunks :5 ! bo>d is unatt5d$4 ,also1 x is desirable t x %\ld conta9 means :]eby any local private ex*ange l9e may be connect$ to ! trunk s t its /ation w act z an ord9>y subscrib]'s /ation4 ,:e!r ! trunks ( ! private ex*ange lead to a manual or an automatic equipm5t1 x (t5 is desir$ to connect a local l9e ?r\gh 9 t way1 ei!r s t ! call+ p]son may make 8 calls )\t ! k ( ! private ex*ange op]ator1 because he wi%es to make a l>ge numb] ( calls 9 succession1 or because = "s o!r reason he pref]s to transact 8 bus9ess directly ) or ?r\gh ! ex*ange ?an to entru/ x to 8 op]ator4 ,,*apt] ,,xxxv ,,int]communicat+ ,,sy/ems ,def9ition4 ,! t]m int]communicat+ has be5 giv5 to a specializ$ type ( telephone sy/em :]e9 ! l9e belong+ to ea* /ation is ext5d$ to ea* ( ! o!r /ations1 result+ 9 all l9es ext5d+ to all /ations4 ,ea* /ation is provid$ ) app>atus by means ( :i* ! telephone us] !re may connect 8 own telephone ) ! l9e ( ! /ation ) :i* he wi%es to communicate1 enabl+ him to signal & talk ) ! p]son at t /ation4 ,limitations4 ,! idea is simple4 ,ea* p]son does 8 own swit*+ directly1 & no op]ator is requir$4 ,x is easy to see1 h[ev]1 t ! sy/em has limitations4 ,! am\nt ( l9e wire necess>y 9 ord] to run ea* l9e to ea* /ation is relatively great1 & becomes prohibitive except 9 ex*anges involv+ a v small numb] ( subscrib]s1 none ( :i* is remote f ! o!rs4 ,aga91 ! am\nt ( swit*+ app>atus requir$ becomes prohibitive = any b a small numb] ( /ations4 ,z a result1 tw5ty-five or ?irty /ations are consid]$ ! usual practical limit = int]communicat+ sy/ems4 ,types4 ,an int]communicat+ sy/em may be ei!r magneto or common-batt]y1 accord+ to :e!r x uses magneto or common-batt]y telephones4 ,! =m] is ! simpl]2 ! latt] is ! m g5]ally us$4 ,illu/ration3 ,,we/]n ,,electric ,,company ,,batt]y ,,room ,,at ,,monm\?1 ,,ill9ois ,simple ,magneto ,sy/em4 ,! s*ematic circuit arrangem5t ( an excell5t =m ( magneto int]communicat+ sy/em is giv5 9 ,fig4 #dda4 ,9 ?is1 five metallic circuit l9es are l$ to z _m /ations1 an ord9>y two-contact op5 jack be+ tapp$ (f ( ea* l9e at ea* /ation4 ,a magneto bell ( ! bridg+ type is p]man5tly bridg$ across ea* l9e at ! /ation to :i* t l9e belongs4 ,! telephone at ea* /ation is an ord9>y bridg+ magneto set except t its bell is1 9 ea* case1 connect$ to ! l9e z j /at$4 ,ea* telephone is connect$ ?r\gh a flexible cord to a two-contact plug adapt$ to fit into any ( ! jacks at ! same /ation4 ,! op]ation is almo/ obvi\s4 ,if a p]son at ,/ation ,a desires to call ,/ation ,e1 he ins]ts 8 plug into ! jack ( l9e ,e at 8 /ation & turns 8 g5]ator crank4 ,! bell ( ,/ation ,e r+s reg>dless ( :]e ! plug ( t /ation may be4 ,! p]son at ,/ation ,e responds by ins]t+ 8 own plug 9 ! jack ( l9e ,e1 aft] :i* ! two p>ties are enabl$ to conv]se ov] a metallic circuit4 ,x makes no diff]5ce :e!r ! p]sons1 aft] talk+1 leave ^! plugs 9 ! jacks or take !m out1 s9ce ! position ( ! plug does n alt] ! relation ( ! bell ) ! l9e4 ,illu/ration3 ,fig4 #dda4 ,magneto ,int]communicat+ ,sy/em ,?is sy/em has ! advantage ( great simplicity & ( be+ ab\t z fool pro( z possible4 ,x is1 h[ev]1 n q z conv5i5t to use z ! lat] common-batt]y sy/ems :i* require no turn+ ( a g5]ator crank4 ,common-,batt]y ,sy/ems4 ,9 ! m popul> common-batt]y sy/ems two g5]al plans ( op]ation are 9 vogue1 "o employ+ a plug & jacks at ea* /ation = swit*+ ! home in/rum5t into circuit ) any l9e1 & ! o!r employ+ m]ely pu% buttons = do+ ! same ?+4 ,^! may be ref]r$ to z ! plug type & ! pu%-button type1 respectively4 ,illu/ration3 ,fig4 #ddb4 ,plug ,type ( ,common-,batt]y ,int]communicat+ ,sy/em ,kellogg ,plug ,type4 ,! circuits ( a plug type ( int]communicat+ sy/em1 z manufactur$ by ! ,kellogg ,company1 are %[n 9 ,fig4 #ddb4 ,:ile only ?ree /ations are %[n1 ! me?od ( connect+ m w be obvi\s4 ,?is sy/em requires z _m pairs ( wires runn+ to all /ations z !re are /ations1 & 9 addition1 two common wires = r++ purposes4 ,! talk+ batt]y fe$ is ?r\gh ret>dation coils to ea* l9e4 ,:5 all ! hooks are d[n1 ea* call bell is connect$ betwe5 ! l[] common wire & ! tip side ( ! talk+ circuit individual to ! correspond+ /ation4 ,! r++ buttons at ea* /ation are connect$ betwe5 ! tip ( ! plug at t /ation & ! upp] common wire4 ,z a result1 :5 a p]son at "o /ation desires to call ano!r1 x is only necess>y = him to ins]t 8 plug 9 ! jack ( ! desir$ /ation & press 8 r++ button2 ! circuit be+ trac$ f "o pole ( ! r++ batt]y ?r\gh ! upp] common r++ wire1 r++ key ( ! /ation mak+ ! call1 tip ( plug1 tip conductor ( call$ /ation's l9e1 bell ( call$ /ation1 & back to ! r++ batt]y ?r\gh ! l[] common r++ wire4 ,illu/ration3 ,fig4 #ddc4 ,pu%-,button ,wall ,set ,kellogg ,pu%-,button ,type4 ,fig4 #ddc %[s a ,kellogg wall-type int]communicat+ set employ+ ! pu%-button me?od ( select+1 & ,fig4 #ddd %[s ! int]nal arrangem5t ( ?is set4 ,illu/ration3 ,fig4 #ddd4 ,pu%-,button ,wall ,set ,we/]n ,electric ,sy/em4 ,! me?od ( op]ation ( ! pu%-button key employ$ 9 ! int]communicat+ sy/em ( ! ,we/]n ,electric ,company is well %[n 9 ,fig4 #dde4 ,:5 ! button is depress$ all ! way d[n1 z %[n 9 ! c5t] cut ( ,fig4 #dde1 :i* repres5ts ! r++ position ( ! key1 contact is made ) ! l9e wires ( ! /ation call$1 & r++ curr5t is plac$ on ! l9e4 ,:5 ! pressure is releas$1 ! button assumes an int]m$iate position1 z %[n 9 ! "r-h& cut1 :i* repres5ts ! talk+ position ( ! key & 9 :i* ! r++ contacts #a & #b are op51 b contact ) ! l9e = talk+ purposes is ma9ta9$4 ,! key is automatically held 9 ?is int]m$iate position by lock+ plate #c until ?is plate is actuat$ by ! op]ation ( ano!r button :i* releases ! key s t x assumes its normal position z %[n 9 ! left-h& cut4 ,:5 a button is depress$ to call a /ation1 x fir/ connects ! call$ /ation's l9e to ! call+ /ation ?r\gh ! two pairs ( contacts #d & #e & !n connects ! r++ batt]y to t l9e by caus+ ! spr+ #a to engage ! contact #b4 ,! r++ curr5t !n passes ?r\gh ! bell at ! call$ /ation1 ?r\gh ! back contacts ( ! swit* hook at t /ation1 ov] "o side ( ! l9e1 & ?r\gh ! way-d[n contact #a ( ! button at ! call+ /ation1 !nce ov] ! o!r side ( ! batt]y l9e back to ! r++ batt]y1 op]at+ ! bell at ! call$ /ation4 ,illu/ration3 ,fig4 #dde4 ,pu%-,button ,action1 ,we/]n ,electric ,sy/em ,! circuits ( ! ,we/]n ,electric sy/em are simil> to ^? ( ,fig4 #ddb1 b adapt$1 ( c\rse1 to ! pu%-button arrangem5t ( swit*es4 ,two batt]ies are employ$1 "o = r++ & ! o!r = talk+1 talk+ curr5t be+ f$ to ! l9es ?r\gh ret>dation coils to prev5t int]f]5ce or cross-talk f o!r /ations :i* might be connect$ toge!r at ! same "t4 ,mon>* ,sy/em4 ,z ! mak+ ( connections 9 an int]communicat+ sy/em is entirely 9 ! h&s ( ! us]1 x is desirable t ! op]ation be simple & t c>elessness on ! "p ( ! us] result 9 z few evil effects z possible4 ,= in/ance1 ! leav+ ( ! receiv] (f its hook w1 9 _m sy/ems1 result 9 su* a dra9 on ! batt]y z to greatly %ort5 its life4 ,! sy/em ( ! ,mon>* ,company has c]ta9 di/9ctive features 9 ?is respect4 ,x is ( ! pu%-button type & z 9 ! sy/em j discuss$1 "o pressure ( ! f+] on "o button cle>s ! /ation ( previ\s connections1 r+s ! /ation call$1 & e/abli%es a talk+ connection betwe5 ! call]'s telephone & ! l9e desir$4 ,9 addition to ?is1 ! sy/em is design$ to elim9ate batt]y wa/e by s arrang+ ! circuits t ! batt]y curr5t does n fl[ ?r\gh ei!r call$ or call+ in/rum5t until a complete connection is made--! call+ button d[n at "o /ation1 ! home button d[n at ! call$ /ation1 & bo? receiv]s (f ! hook4 ,x does n hurt ! batt]ies1 !re=e1 if "o neglects to hang up 8 receiv]4 ,illu/ration3 ,fig4 #ddf4 ,pu%-,button ,wall ,set ,illu/ration3 ,fig4 #ddg4 ,pu%-,button ,action1 ,mon>* ,sy/em ,?ree views ( ! wall set ( ?is sy/em are %[n 9 ,fig4 #ddf1 :i* illu/rates h[ bo? ! door & ! conta9+ box are sep>ately h+$ = easy access to ! app>atus & connect+ rack4 ,z 9 ! ,we/]n ,electric & ,kellogg pu%-button sy/ems1 ea* pu%-button key has ?ree positions1 z %[n 9 ,fig4 #ddg4 ,! fir/ button %[s all ! spr+s op51 ! normal position ( ! key4 ,! second button is 9 ! half-way or talk+ position ) all ! spr+s1 except ! r++ spr+1 9 contact4 ,! ?ird button %[s ! spr+s all 9 contact1 ! condition :i* exi/s :5 r++ a /ation4 ,! me*anical con/ruction ( ! key is %[n 9 ,fig4 #ddh4 ,ea* button has a sep>ate frame ^u :i* ! spr+s are m\nt$4 ,any "o ( ! frames ) its gr\p ( contact spr+s may be remov$ )\t int]f]+ ) ei!r ! electrical or ! me*anical op]ation ( ! o!rs4 ,?is is a conv5i5t feature1 mak+ possible ! in/allation ( z few /ations z are ne$$ at fir/1 & ! subsequ5t addition ( buttons z o!r /ations are add$4 ,illu/ration3 ,fig4 #ddh4 ,pu%-,button ,keys ,! re/or+ feature is a horizontal metal c>riage1 9 con/ruction v mu* l a ladd]--"o r\nd press+ aga9/ ea* key frame1 due to ! t5sion on ! c>riage ex]t$ by a s+le flat spr+4 ,! plung] ( ea* button is equipp$ ) a %\ld]1 :i* normally is above ! r\nd ( ! ladd]4 ,:5 ! button is op]at$1 ?is %\ld] presses aga9/ a r\nd ( ! c>riage =c+ x ov] f> en\gh s t ! %\ld] c slip by4 ,! upp] surface ( ! %\ld] is flat1 & on pass+ bel[ ! p91 all[s ! c>riage to slip back into its normal position & ! p9 re/s on ! top ( ! %\ld] hold+ ! plung] d[n4 ,?is position places ! talk+ spr+s 9 contact4 ,! r++ spr+s are op5 until ! plung] is press$ all ! way d[n1 !n ! r++ contact is made4 ,:5 ! pressure is releas$1 ! plung] comes back to ! half-way or talk+ position1 leav+ ! r++ contacts op5 aga94 ,:5 ano!r button is press$1 ! same op]ation takes place &1 by virtue ( ! c>riage be+ tempor>ily displac$1 ! orig9al key is left free to spr+ back to its normal position4 ,ea* /ation is provid$ ) a button = ea* o!r /ation & a home button4 ,! sali5t feature ( ! sy/em is t be=e a connection may be e/abli%$1 ! button at ! call+ /ation correspond+ to ! /ation call$ & also ! home button ( ! /ation call$ mu/ be depress$1 if x is n already d[n4 ,! home key at any /ation1 :5 depress$1 transposes ! sides ( ! l9e ) respect to ! talk+ app>atus4 ,! home key also has a spr+ :i* *anges ! normal connection ( ! l9e at t /ation f ! negative to ! positive side ( ! talk+ batt]y4 ,unless1 !re=e1 a connection betwe5 two /ations is made ?r\gh ! call+ key at "o /ation & ! home key at ! o!r1 no curr5t c fl[ ev5 ?\gh bo? receiv]s are (f _! hooks1 because 9 t case no connection w exi/ ) ! positive side ( ! batt]y4 ,?is relation is %[n 9 ,fig4 #ddi1 :i* gives a simplifi$ circuit arrangem5t = two connect$ /ations4 ,illu/ration3 ,fig4 #ddi4 ,mon>* ,int]communicat+ ,sy/em ,ref]r+ to ,fig4 #ddi1 :5 ! /ation call$ depresses ! home button ! talk+ circuit is !n complet$ aft] ! hook swit* is rais$4 ,?is is because ! talk+ batt]y is controll$ by ! home key4 ,conductors f bo? ! negative & ! positive sides ( ! batt]y ent] ?is key4 ,9 ! normal position ( ! spr+s1 ! negative side ( ! batt]y is 9 contact ) ! ma/] spr+ 9 ! home key & ?r\gh ^! spr+s ! negative batt]y is appli$ to all ! call+ keys1 & f !re on to ! hook swit*4 ,:51 h[ev]1 ! home button is op]at$1 ! spr+ :i* c>ries ! negative batt]y to ! home key is op5$1 & ! spr+ :i* c>ries ! positive batt]y is clos$4 ,?is puts ! positive batt]y on at ! hook swit* in/ead ( ! negative batt]y1 z 9 its normal condition4 ,9 ?is sy/em x is se5 t a sep>ate pair ( l9e wires is us$ = ea* /ation1 & 9 addition to ^!1 two common pairs are run to all /ations1 "o = r++ & "o = talk+ batt]y connections4 ,= ,private ,bran* ,ex*anges4 ,s f> ! int]communicat+ sy/em has be5 discuss$ only ) respect to its use 9 small isolat$ plants4 ,x has a field ( usefulness 9 connection ) city ex*ange "w1 z x may be made to s]ve admirably z a private bran* ex*ange4 ,:]e ?is is done1 "o or m trunk l9es lead+ to an (fice ( ! city ex*ange are run ?r\gh ! int]communicat+ sy/em exactly z a local l9e 9 t sy/em1 be+ tapp$ to a jack or pu% button at e /ation4 ,a p]son at any "o ( ! /ations may orig9ate a call to ! ma9 (fice by ins]t+ 8 plug 9 ! trunk jack1 or pu%+ 8 trunk pu% button4 ,also any /ation1 )9 he>+ or sight ( ! trunk-l9e signal f ! ma9 (fice1 may answ] a ma9-(fice call 9 ! same way4 ,9 ord] t ! conv5i5ce ( a private bran* ex*ange may be fully realiz$1 h[ev]1 x is cu/om>y to provide an att5dant's /ation at :i* is plac$ ! drop or bell on :i* ! incom+ trunk signal is receiv$4 ,! duty ( ?is att5dant dur+ bus9ess h\rs is to answ] trunk calls f ! ma9 (fice & f9d+ out :at p>ty is desir$1 call up ! prop] /ation on ! int]communicat+ sy/em4 ,! p>ty at t /ation may !n connect himself ) ! trunk4 ,! practice ( ! ,dean ,company1 = in/ance1 is z foll[s 9 reg>d to trunk+ betwe5 int]communicat+ sy/ems & ma9 (fices ) common-batt]y equipm5t4 ,! att5dant's /ation telephone cab9et conta9s1 besides ! pu%-button keys = local & trunk connections1 a drop signal & release key1 toge!r ) relays 9 ea* trunk circuit4 ,! latt] are us$ to hold ! trunks until ! desir$ p>ty responds4 ,! ma9-ex*ange trunk l9es1 besides t]m9at+ at ! att5dant's /ation1 are wir$ ?r\gh ! complete int]communicat+ sy/em s t any int]communicat+ telephone c be connect$ direct to ! c5tral (fice by depress+ ! trunk key1 :i* is provid$ ) a button ( di/9ctive color4 ,! press+ ( ! trunk key all[s ! telephone to take its curr5t f ! ma9-(fice /orage batt]y & to op]ate ! ma9-(fice l9e & sup]visory signals direct1 )\t mak+ x necess>y to call on ! att5dant to set up ! connection4 ,illu/ration3 ,fig4 #dej4 ,junction ,box ,illu/ration3 ,fig4 #dea4 ,typical ,arrangem5t ( ,int]communicat+ ,sy/em ,incom+ calls f ! common-batt]y ma9 (fice to ! int]communicat+ sy/em are all h&l$ by ! att5dant4 ,! ma9-(fice op]ator signals ! int]communicat+ sy/em by r++1 ! same z = a regul> subscrib]'s l9e4 ,?is w op]ate a drop 9 ! att5dant's /ation cab9et1 & ?r\gh an armature contact1 give a signal on a l[-pit*$ buzz]4 ,?is al>m buzz] op]ates only :5 ! ma9 ex*ange is r++ &1 !re=e1 does n require t ! drop %utt] be re/or$ imm$iately4 ,an extra key may be provid$ = an ext5sion night-al>m bell1 = use :]e ! att5dant also does "w 9 a room sep>ate f t conta9+ ! att5dant's /ation telephone equipm5t4 ,! att5dant op]ator answ]s ! ma9-l9e signal by press+ ! prop] trunk button1 z designat$ by ! op]at$ drop on ! att5dant's cab9et4 ,! answ]+ ( ! trunk connects a lock+ relay across ! circuit s t ! att5dant may call ! desir$ p>ty on ! int]communicat+ sy/em )\t hav+ to hold ! trunk manually4 ,! p>ty desir$ is !n notifi$ :i* trunk to use & ! att5dant op]ator hangs up h] receiv]1 no fur!r att5tion be+ necess>y on h] "p4 ,! trunk-hold+ relay is automatically releas$ :5 ! desir$ p>ty 7) ! telephone receiv] (f ! hook7 depresses ! prop] trunk button1 ?us cle>+ ! trunk l9e ( all bridg$ app>atus & mak+ ! talk+ circuit ! same z 9 ! regul> type ( private bran*-ex*ange swit*bo>d4 ,! mo/ conv5i5t way ( in/all+ ! wires ( an int]communicat+ sy/em is to run a cable conta9+ ! prop] numb] ( pairs to provide = ! ultimate numb] ( /ations to all ! /ations1 tapp+ (f f ! conductors 9 ! cable to ! jacks or pu% buttons at ea* /ation4 ,^! tap connections are be/ made by means ( junction boxes :i* conta9 t]m9als = all ! conductors4 ,su* a junction box1 ) ! ?r\gh cable & ! tap cable 9 place1 is illu/rat$ 9 ,fig4 #dej4 ,a s*ematic lay-out ( ! v>i\s p>ts ( a ,dean int]communicat+ sy/em1 provid$ ) an att5dant's /ation & ) trunks to a city (fice1 is giv5 9 ,fig4 #dea4 ,,*apt] ,,xxxvi ,,long-,,di/ance ,,swit*+ ,def9itions4 ,telephone messages betwe5 communities are call$ long-di/ance messages4 ,!y are also call$ toll messages4 ,almo/ all long-di/ance traffic is h&l$ by message-rate 7measur$-s]vice7 me?ods ( *>ge4 ,all measur$-s]vice messages are toll messages1 :e!r !y are complet$ )9 a giv5 community or betwe5 communities4 ,! t]m long-di/ance1 !re=e1 is m descriptive ?an ! t]m toll4 ,! subject ( local & long-di/ance measur$ s]vice is treat$ exhau/ively 9 a *apt] ( its own4 ,"s telephone-ex*ange op]at+ companies call _! own int]-city bus9ess toll1 & use ! t]m long-di/ance = bus9ess c>ri$ betwe5 ex*anges = !m by ano!r company4 ,! di/9ction seems to be unw>rant$4 ,use ( ,repeat+ ,coil4 ,mo/ long-di/ance l9es are magneto circuits4 ,if !y are swit*$ to gr\nd$ circuits1 repeat+ coils ne$ to be ins]t$4 ,toll swit*+ equipm5ts conta9 means ( ins]t+ repeat+ coils 9 ! connect+ cords :5 requir$4 ,_! use r$uces ! volume ( transmitt$ spee*1 b (t5 is ess5tial ev5 9 connect+ metallic circuit l9es1 z a quiet local metallic circuit may h a gr\nd ^u x :i* w cause excessive noises :5 a quiet long-di/ance l9e is connect$ to x4 ,swit*+ ?r\gh ,local ,bo>d4 ,9 ! simple/ =m ( long-di/ance swit*+1 ! l9es t]m9ate 9 swit*bo>ds ) local l9es & may be connect$ ) ea* o!r & ) ! local l9es ?r\gh ! regul> cord circuits1 if ! equipm5t be ( ! magneto type4 ,! way/ations on su* a l9e are equipp$ ) magneto g5]ators4 ,^! way/ations may signal ea* o!r by bell r++2 ! c5tral (fice may call any way/ation by r++ ! prop] signal & may sup]vise 9 a way all traffic on su* l9es by not+ ! calls = o!r /ations ?an ! sup]vis+ ex*ange4 ,op]ators' ,ord]s4 ,by ,call ,circuits4 ,:]e ! long-di/ance traffic betwe5 two communities is l>ge1 economy requires t ! s5d+ ( signals by r++ ov] ! l9e1 wait+ = an answ]1 & !n recit+ ! details ( ! call1 be improv$ ^u4 ,if ! traffic is l>ge & ! di/ance betwe5 communities small1 call circuits are e/abli%$ 9 ! same way z betwe5 ! swit*bo>ds 9 sev]al manual c5tral (fices ( an ex*ange4 ,! long-di/ance op]ator h&l+ ! orig9at+ call passes ! necess>y details to ! di/ant op]ator by telephone ov] ! call circuit4 ,su* circuits also are kn[n z ord] circuits4 ,!y are accessible to orig9at+ op]ators at keys & are connect$ directly & p]man5tly to ! telephone sets ( receiv+ op]ators4 ,"o call circuit c h&le ! ord]s = a l>ge numb] ( actual conv]sation circuits4 ,! op]ator at ! receiv+ end designates ! conv]sation circuit :i* %all be us$1 ! orig9at+ op]ator foll[+ t in/ruction4 ,by ,telegraph4 ,:]e traffic & di/ance are l>ge1 conv]sation l9es co/ m ?an 9 ! case la/ assum$4 ,x !n is ( great] importance to use all ! possible talk+ circuits = actual conv]sations 9 ord] t ! rev5ue may be z high z possible4 ,a phantom circuit good en\gh = call circuit purposes w\ld be good en\gh = actual comm]cial messages1 !re=e1 x is cu/om>y to furni% su* orig9at+ & receiv+ op]ators ) ,morse telegraph sets4 ,! l9es are obta9$ by apply+ composite app>atus to ! conv]sation circuits4 ,two ,morse circuits c be _h f ea* long-di/ance l9e )\t impair+ any quality ( t l9e except ! ability to r+ ov] x4 ,z "o ,morse circuit c c>ry in=mation en\gh betwe5 two op]ators to enable !m to keep _m telephone circuits busy1 !y d n ne$ to r+ ^u ! composit$ l9es1 s t no?+ is lo/ :ile rev5ue is ga9$4 ,two-,numb] ,calls4 ,9 cases :]e ! traffic betwe5 communities is l>ge1 :]e ! rate is small1 & :]e ! conv]sations are %ort & m on ! g5]al ord] ( local calls1 x is usual to h&le ! swit*es exactly z local calls are trunk$ betwe5 c5tral (fices ( ! same ex*ange4 ,t is1 ! subscrib]'s op]ator :o answ]s ! call trunks x1 by ! assi/ance ( a call circuit & an incom+ trunk op]ator4 ,! subscrib]'s op]ator records only ! numb]s ( ! call+ & call$ subscrib]s4 ,no long-di/ance op]ators at all assi/ 9 ^! connections4 ,!y are kn[n z two-numb] calls4 ,! call+ subscrib] rema9s at 8 telephone until ! conv]sation is f9i%$4 ,p>ticul>-,p>ty-,calls4 ,9 cases :]e ! traffic is small]1 & :]e ! rate is l>ge1 x is cu/om>y to h&le ! calls ?r\gh long-di/ance op]ators4 ,! ticket records ! p>ticul> p>ty wi%$1 & ! calls are nam$ p>ticul> p>ty calls4 ,9 su* connections ! call+ patron is all[$ to hang up 8 receiv]1 aft] 8 call is record$1 & is call$ aga9 :5 8 correspond5t is f\nd & is ready to talk4 ,?is makes all calls = conv]sations outgo+ ones4 ,only record+ op]ators receive calls f patrons4 ,l9e op]ators make calls to patrons4 ,trunk+4 ,long-di/ance l9es ent]+ a city usually t]m9ate 9 "o (fice only1 no matt] h[ _m (fices ! local ex*ange may h4 ,x is possible to t]m9ate ^! long-di/ance l9es on a position ( ! multiple swit*bo>d = local l9es4 ,= a v>iety ( reasons ?is is n practic$ except 9 special cases4 ,! usual me?od is to t]m9ate !m 9 a special long-di/ance bo>d & to provide trunk l9es f ?is bo>d to ! "o or m local swit*bo>ds ( ! ex*ange4 ,9 common-batt]y sy/ems ^! toll trunks are s arrang$ t ! call$ local subscrib] receives transmitt] curr5t f ! (fice ne>e/ to him1 yet is able to %[ ! long-di/ance op]ator ! position ( 8 swit* hook & is able to be call$ by ! long-di/ance op]ator )\t ! int]v5tion ( ! swit*+ op]ator 9 ! local (fice1 ev5 ?\gh two repeat+ coils may be 9 ! trunk circuit4 ,?r\gh ,r++4 ,!re is a di/9ct traffic advantage 9 hav+ ! r++ ( ! subscrib] "u ! control ( ! long-di/ance op]ator4 ,! latt] may call = ! subscrib] by /at+ h] wi% ov] ! call circuit associat$ ) ! long-di/ance trunk4 ,! connection hav+ be5 made by ! swit*+ op]ator1 ! long-di/ance op]ator may )hold r++ ! subscrib]'s bell until all is 9 read9ess = ! conv]sation4 ,high-,voltage ,toll ,trunks4 ,9 "s sy/ems1 ! long-di/ance trunks are fur!r specializ$ by be+ enabl$ to furni% transmitt] curr5t to subscrib]s at a high] voltage ?an is us$ 9 local conv]sations4 ,) a giv5 con/ruction ( transmitt]s !re is a critical maximum curr5t :i* c be c>ri$ by ! granul> c>bon ( ! in/rum5t )\t excessive heat+1 consequ5t noises1 & p]man5t damage4 ,! %orte/ l9es & ! longe/ l9es ( an ex*ange di/rict be+ s]v$ by a s\rce ( curr5t common to all1 ! /&>d pot5tial ( ?is s\rce mu/ be su* z to give ! longe/ l9es curr5t en\gh )\t giv+ ! %orte/ l9es too mu*4 ,! v longe/ local l9es1 h[ev]1 d n receive curr5t en\gh f ! /&>d pot5tial to give maximum effici5cy :5 talk+ ov] long di/ances1 ?\gh !y get en\gh = local conv]sations4 ,by provid+ a batt]y ) a voltage twice t us$ = local conv]sations & connect+ x into ! curr5t supply elem5t ( ! toll trunk ?r\gh non-inductive resi/ances1 n too mu* curr5t may be giv5 to ! %orte/ l9es & consid]ably m ?an normal curr5t to ! longe/ l9es4 ,ticket ,pass+4 ,:5 only "o op]ator is necess>y 9 a t[n1 h] duty be+ to swit* bo? local & long-di/ance l9es1 %e may write h] own tickets & execute !m entire4 ,9 l>g] communities ) l>g] long-di/ance traffic1 ! duties ne$ to be specializ$4 ,! subscrib]s' wants z to long-di/ance connections are giv5 by !mselves to record+ long-di/ance op]ators1 :o write !m on tickets & pass ^! to op]ators :o get ! p>ties toge!r4 ,! problem ( ticket-pass+ becomes important & _m me*anical c>ri]s h be5 tri$1 culm9at+ 9 ! sy/em :i* utilizes vacuum tubes4 ,?is is 9 "s ways simil> to vacuum or compress$-air tube sy/ems = c>ry+ ca% 9 retail /ores4 ,! ticket is c>ri$1 h[ev]1 )\t any enclos+ case & ! tubes are flat in/ead ( r\nd1 i4 e41 !y are rectangul> 9 section4 ,by suitable means a vacuum is ma9ta9$ 9 a l>ge common tube hav+ a tap to a box-l valve at ea* l9e op]ator's position4 ,a ticket tube connects ?is valve ) a di/ribut+ table at or ne> :i* ! tickets are writt54 ,! tickets are ( uni=m size & are s made z to enable a flap to be b5t up easily along "o edge4 ,! di/ribut+ op]ator has m]ely to ins]t ! ticket1 b5t edge =emo/1 9 ! op5 end ( ! tube1 :]eupon ! air pressure beh9d x w drive x ?r\gh to its de/9ation1 ne> by or f> away4 ,! tickets travel ?irty feet a second4 ,! tube may be b5t into almo/ any requir$ =m4 ,! ticket1 on arriv+ at a l9e op]ator's position1 slides betwe5 two spr+s1 break+ a %unt ar\nd a relay & all[+ ! latt] to light ! lamp4 ,way/ations4 ,way/ations on long-di/ance l9es may be equipp$ 9 sev]al ways4 ,mo/ ( !m h magneto sets & c r+ ea* o!r4 ,"s are equipp$ ) common-batt]y sets & get all curr5t = signal+ & transmission f a t]m9al c5tral (fice4 ,9 ! latt] case1 !re is ! advantage t ! r+]s are 9 s]ies ) cond5s]s1 assi/+ greatly 9 te/s = fault locations4 ,su* te/s are h9d]$ by ! pres5ce ( r+] bridges across ! l9e1 z 9 magneto practice4 ,cond5s]s c be ins]t$ 9 s]ies ) r+]s ( magneto sets if ! te/+ advantage is valu$ highly en\gh4 ,a disadvantage ( ! use ( common-batt]y sets 9 way/ations on long-di/ance l9es is ! less5$ transmission volume ( ! /ations f>!/ f ! curr5t s\rce4 ,c5t] ,*eck+4 ,an op]at+ advantage ( common-batt]y sets on long-di/ance l9es is t all calls are =c$ to be answ]$ by ! t]m9al /ation4 ,way/ations c n call ea* o!r1 z !y h no call+ means4 ,) magneto sets1 way/ation ag5ts sometimes call ea* o!r direct & neglect to record ! call & to remit its price4 ,:5 !y c n call ea* o!r direct1 ! rev5ues ( ! company increase4 ,a traffic me?od :i* requires all calls f way/ations to be made to a c5tral swit*+ (fice is call$ a c5t]-*eck+ sy/em4 ,x is s call$ because all *eck+ = /ations s swit*$ is done at ! c5tral po9t in/ead ( ea* way/ation keep+ its own records ( calls s5t & receiv$4 ,9 su* practice x is usual to bill ea* /ation once a mon? = ! messages x s5t4 ,:]e c5t] *eck+ is n practic$1 ! ag5t makes a report & s5ds a remittance4 ,c5t] *eck+ comes ab\t naturally = way/ations hav+ no r++ equipm5t4 ,c5t] *eck+ orig9at$ long be=e ! inv5tion ( common-batt]y sy/ems4 ,x requires m]ely t no way/ation %all h a g5]ator :i* c r+ a bell4 ,! me?od mo/ widely us$ is to equip ! way/ations ) magneto g5]ators :i* produce direct curr5ts only2 su* a g5]ator _c op]ate a pol>iz$ r+]4 ,x is n usual to produce ! direct curr5t by actually rectify+ ! alt]nat+ curr5t1 b m]ely by omitt+ half ! impulses1 s5d+ to ! l9e only alt]nate half-cycles ( ! curr5t g5]at$4 ,any drop or relay adapt$ to respond to regul> r++ curr5t w respond to ?is modifi$ =m ( g5]ator4 ,,*apt] ,,xxxvii ,,telephone ,,traffic ,! t]m traffic1 ) ref]5ce to telephone s]vice1 has come to mean ! gross transaction ( communication betwe5 telephone us]s4 ,?is traffic may be express$ 9 :atev] t]ms are f\nd conv5i5t = ! p>ticul> phase consid]$4 ,unit ( ,traffic4 ,) ref]5ce to paym5t = local telephone s]vice1 ! conv]sation is ! unit ( traffic4 ,9 ! daily op]ations ( telephone sy/ems !re are few] conv]sations ?an !re are connections & few] connections ?an !re are calls1 because l9es are f\nd busy & all calls to subscrib]s are n answ]$4 ,= ^! reasons1 9 traffic inquiries :i* h to d ) ! am\nt ( bus9ess :i* subscrib]s attempt to transact1 ! total traffic 9 a giv5 "t usually is consid]$ z s _m calls orig9at$ by ! subscrib]s 9 ! community4 ,f ?is condition arises ! t]m orig9at+ calls4 ,= ! reason t ! purpose ( ! swit*+ equipm5t 9 a c5tral (fice is to make connections1 ! abilities ( op]ators & ( equipm5ts frequ5tly are measur$ 9 t]ms ( connections p] h\r or p] o!r unit ( "t4 ,= ! reason t 9 *>g+ = s]vice all unavail+ calls are omitt$1 ! conv]sation is ! unit ( traffic4 ,traffic ,v>iations4 ,telephone-ex*ange traffic is subject to su* g5]al v>iations z are not$ 9 ! way a compass ne$le po9ts nor?1 ! migrations ( birds1 ! bl[+ ( ! trade w9ds1 & o!r natural ph5om5a4 ,!re are v>iations 9 traffic :i* occur ea* day1 o!rs :i* *ange ) ! seasons1 & /ill o!rs :i* are relat$ to holidays & o!r special comm]cial & social ev5ts4 ,= in/ance1 ! day be=e ,?anksgiv+ ,day1 9 _m regions1 is ! busie/ telephone traffic day 9 ! ye>4 ,illu/ration3 ,,we/]n ,,electric ,,motor-,,g5]ator ,,*>g+ ,,set ,! daily v>iations 9 telephone traffic are closely relat$ to comm]cial activities & c]ta9 g5]al features ( ?is daily v>iation are common to all telephone sy/ems ev]y:]e4 ,fig4 #deb is a typical graphic record ( ! traffic ( a telephone ex*ange & repres5ts :at happ5s 9 almo/ e t[n or city4 ,! total calls 9 ?is figure are n giv5 z absolute units b w\ld v>y to adapt ! figure to a p>ticul> case4 ,! figure %[s pr9cipally t ! traffic 9 ! night is light2 t x rises to its maximum height some:]e betwe5 #aj o'clock ,a4,m4 & noon2 t ?\gh x is nev] z high aga9 dur+ t day1 ! aft]noon peak is ov] #hj p] c5t z great2 & t two m9or peaks appe> ab\t ! d9n] h\r & aft] ev5+ ent]ta9m5ts4 ,illu/ration3 ,fig4 #deb4 ,load ,curve ,busy-,h\r ,ratio4 ,if ! /ory told by ,fig4 #deb 7 to be turn$ into a table ( calls p] h\r1 ! busie/ h\r ( ! day w\ld be f\nd to correspond to ! highe/ portion ( ! figure1 & 9 t busie/ h\r ( ! day1 if a numb] ( select$ days 7 to be comp>$1 w\ld be f\nd a v con/ant traffic4 ,! numb] ( calls made1 or ! numb] ( connections complet$1 9 t p>ticul> h\r1 day by day1 w\ld be f\nd to be mu* ! same4 ,! ratio ( ! numb] ( units 9 t h\r to ! numb] ( units 9 t entire day w\ld be f\nd to be practically ! same ratio day by day4 ,?is ratio ( busy h\r to total day w\ld be f\nd to be mu* m ne>ly con/ant ?an ! gross numb] ( calls p] h\r or p] day4 ,9 a l>ge1 busy city1 ab\t "o-eigh? ( ! total daily calls are 9 "s "o h\r2 9 a small]1 less active city1 probably "o-t5? are s conge/$4 ,?is is reasonable :5 "o rememb]s t 9 ! l>g] city ! active bus9ess ( ! day beg9s lat] & ends e>li]4 ,importance ( ,traffic ,/udy4 ,a k ( ! am\nt ( traffic 9 an ex*ange1 & its di/ribution z to "t & z to ! divisions ( ! ex*ange1 is important = a numb] ( reasons4 ,traffic k is ess5tial 9 ord] t ! equipm5t may be design$ & plac$ 9 ! prop] way & ! total load di/ribut$ prop]ly on t app>atus & its op]ators4 ,= example1 9 an (fice equipp$ ) a manual multiple swit*bo>d1 ! l5g? ( ! swit*bo>d is gov]n$ entirely by ! numb] ( op]ators :o mu/ "w be=e x4 ,x is me*anically possible to make a swit*bo>d = t5 ?\s& l9es only #ae feet long1 seat+ sev5 op]ators4 ,! entire multiple ( t5 ?\s& l9es c\ld appe> ?ree times 9 su* a swit*bo>d4 ,! sev5 op]ators c\ld n h&le ! traffic we "k w\ld be orig9at$ by t5 ?\s& l9es1 ) any pres5t sy/em ( *>g+ = s]vice4 ,ev5 a r\gh k ( ! probable traffic w\ld enable u to approximate ! numb] ( op]ators ne$$ & to equip ea* position1 n only ) access to ! t5 ?\s& l9es to be call$1 b also ) j en\gh keybo>d equipm5t1 s]v+ z tools1 & j en\gh answ]+ jacks1 s]v+ z means ( br++ ! traffic to h]4 ,x is =ekn[l$ge ( traffic :i* enables a swit*bo>d to fit ! task x is to p]=m4 ,rates ( ,call+4 ,! rates ( call+ ( diff]5t k9ds ( l9es v>y4 ,! l9es ( bus9ess /ations orig9ate m calls ?an d ! l9es ( resid5ces4 ,"s k9ds ( bus9ess orig9ate m calls ?an o!rs4 ,"s k9ds ( bus9ess h a high] rate ( call+ 9 "o season ?an 9 o!rs4 ,flat-rate l9es orig9ate m calls ?an d message-rate l9es4 ,:5 a l9e *anges f a flat rate to a message rate1 ! numb] ( orig9at+ calls p] day decreases4 ,an op]ator's position1 h&l+ message-rate l9es only1 c s]ve m l9es ?an if all ( !m 7 at flat rates4 ,! numb] ( message-rate or co9-prepaym5t l9es :i* an op]ator's position c c>e = dep5ds n only on ! traffic b on ! me?od ( *>g+ = s]vice1 :e!r by tickets or met]s & ^u ! k9d ( met]s2 or x dep5ds on ! me?od ( collect+ ! co9s4 ,9 "s regions1 ! rate ( call+1 on ! introduction ( a complete measur$-s]vice plan1 has be5 r$uc$ to "o-f\r? ( :at x 0 on ! flat-rate plan4 ,9 manual swit*bo>ds ( e>ly types1 :]e9 ! position ( ! subscrib]'s answ]+ jack 0 fix$ by 8 telephone numb]1 ! inequality ( traffic became a s]i\s problem4 ,mo/ ( ! subscrib]s :o fir/ in/all$ telephones :5 ! ex*ange 0 small1 reta9$ _! telephones & numb]s2 z _! use ( ! telephone grew ) _! bus9ess1 x 0 cu/om>y to f9d ! positions answ]+ ! l[] numb]s mu* m busy ?an ! positions answ]+ ! high] numb]s1 ! latt] belong+ to lat] & usually less active bus9ess places4 ,functions ( ,int]m$iate ,di/ribut+ ,frame4 ,! int]m$iate di/ribut+ bo>d 0 inv5t$ to meet ^! conditions ( unequal traffic ^u l9es & ( v>iations 9 traffic ) *anges ( seasons & ( *>ges4 ,! int]m$iate di/ribut+ bo>d enables a l9e to reta9 its numb] & its position 9 ! multiple1 b to keep its answ]+ jack & lamp signal 9 any desir$ position4 ,if a flat-rate subscrib] *anges to a message rate1 8 l9e may be mov$ to a message-rate position & be answ]$1 9 company ) o!rs l x1 by an op]ator s]v+ _m m l9es ?an %e c\ld s]ve if all ( !m 7 flat rate4 ,me?ods ( ,traffic ,/udy4 ,! be/ way to le>n traffic facts = ! purposes ( design+ & op]at+ equipm5t is to conduct sy/ematic s]ies ( obs]vations 9 all ex*anges2 to record !m 9 company ) all relat$ facts2 & to comp>e !m f "t to "t1 record+ ! results ( ! comp>isons4 ,!n :5 x is requir$ to solve a new problem1 ! traffic data w enable ! probable future conditions to be kn[n ) z great exactness z is possible 9 /udies ) relation to transportation or any o!r human activity4 ,,table ,,xiii ,call+ ,rates ---------------------------------------- ---------------- ,,calls ,,p] ,,day ,,) ,,diff]5t ,,k9d ,,( ,,s]vice ,,me?ods ,,( ,,*>ge ------------------------------ ,,flat ,,rate ,,message ,,rate ---------------------------------------- --------------- ,resid5ce #h #d ,bus9ess #ab to #bj #h to #ad ,private ,ex*ange ,trunk #dj #be ,hotel ,ex*ange ,trunk #ej #cj ,ap>tm5t ,h\se ,trunk #cj #ah ---------------------------------------- --------------- ,!re are ?ree g5]al ways ( obs]v+ traffic4 ,a record ( orig9at+ calls is kn[n z a peg c\nt1 because ! c\nt+ =m]ly 0 done by mov+ a peg f place to place 9 a s]ies ( holes4 ,! simple/ exact way is to provide ea* op]ator ) a small me*anical c\nt]1 ! key ( :i* %e c depress once = ea* call to be c\nt$4 ,a second way is to det]m9e a ratio :i* exi/s1 = ! p>ticul> "t & place1 betwe5 ! numb] ( calls 9 a giv5 p]iod & ! av]age numb] ( cord circuits 9 use4 ,kn[+ ?is ratio1 ! cord circuits c be c\nt$1 ! ratio appli$1 & ! probable total kn[n4 ,! ?ird me?od1 :i* is applicable to (fices hav+ s]vice met]s on all l9es1 is to associate "o ma/] met] p] position or gr\p ( l9es ) all ! met]s ( t position or gr\p1 s t ea* "t any s]vice met] ( t position is op]at$1 ! ma/] met] w c\nt "o unit4 ,?is me?od applies to ei!r manual or automatic equipm5ts4 ,repres5tative ,traffic ,data4 ,= purposes ( comp>ison1 ! foll[+ are repres5tative facts z to c]ta9 traffic conditions4 ,call+ ,rates4 ,! numb] ( calls orig9at$ p] day by diff]5t k9ds ( l9es ) diff]5t me?ods ( *>ge are %[n 9 ,table ,,xiii4 ,op]ators' ,loads4 ,! abilities ( subscrib]s' op]ators to swit* ^! calls dep5d on ! type ( equipm5t us$1 on ! k9d ( managem5t ex]cis$1 & on ! individual skill ( op]ators4 ,) manual multiple equipm5t ( ! common-batt]y type1 & good managem5t1 ! numb]s ( orig9at+ calls p] busy h\r giv5 9 ,table ,,xiv c be h&l$ by an av]age op]ator4 ,! numb] ( calls p] op]ator p] busy h\r dep5ds ^u ! am\nt ( trunk+ to o!r (fices :i* t op]ator is requir$ to d4 ,9 a small city1 = example1 :]e all ! l9es are h&l$ by "o swit*bo>d1 !re is no local swit*+ problem except to complete ! connection 9 ! multiple be=e ea* position4 ,9 a l>ge city1 :]e wire economy & me*anical consid]ations compel ! l9es to be h&l$ by a numb] ( (fices ) manual equipm5t1 "s portion ( ! total orig9at+ load ( ea* (fice mu/ be trunk$ to o!rs4 ,table ,,xiv %[s t an increase ( #ij p] c5t 9 ! am\nt ( out-trunk+ has decreas$ ! op]ator's ability to less ?an #gj p] c5t ( ! possible maximum4 ,,table ,,xiv ,effect ( ,out-,trunk+ on ,op]ator's ,capacity ---------------------------------------- --------------------------- ,,p] ,,c5t ,,orig9at+ ,,calls ,,capacity ,,( ,,subscrib]s' ,,op]ator',s ,,trunk$ ,,to ,,o!r ,,(fices ,,position ,,9 ,,calls ,,p] ,,busy ,,h\r ---------------------------------------- --------------------------- #j #bdj #aj #bcj #cj #bjj #ej #ahe #ge #agj #ij #afe ---------------------------------------- --------------------------- ,trunk+ ,factor4 ,9 provid+ ! sy/em ( trunks int]connect+ ! (fices1 :e!r ! equipm5t be manual or automatic1 x is ess5tial to "k n only h[ mu* traffic orig9ates 9 ea* (fice1 b h[ mu* ( x w be trunk$ to ea* o!r (fice & h[ _m trunks w be requir$4 ,an int]e/+ phase ( telephone traffic /udies is t x is possible to det]m9e 9 advance ! am\nt ( traffic :i* c be complet$ directly 9 ! multiple ( t (fice & h[ mu* mu/ be trunk$ else:]e4 ,!oretical consid]ations w\ld indicate t if ! local multiple conta9s "o-eigh? ( ! total l9es ( ! city1 "o-eigh? ( ! calls orig9at+ 9 t (fice c\ld be complet$ locally & sev5-eigh?s w\ld be trunk$ out4 ,9 almo/ all cases1 h[ev]1 x is f\nd t m ?an ! !oretical p]c5tage ( orig9at+ calls are = ! neighborhood ( t (fice & c be complet$ 9 ! multiple4 ,?is results 9 ! det]m9ation ( a factor by :i* ! !oretical out-trunk+ c be multipli$ to det]m9e ! probable real out-trunk+4 ,9 mo/ cases1 ! ratio ( actual to !oretical out-trunk+ is #ge p] c5t1 or approximately t4 ,9 special cases1 x may be f> f #ge p] c5t4 ,trunk ,effici5cy4 ,! capacities ( trunks v>y ) _! me?ods ( op]ation & ) ! numb] ( trunks 9 a gr\p4 ,= example1 9 ! manual sy/em :]e trunk op]ators 9 di/ant (fices are in/ruct$ ov] call circuits & make disconnections 9 response to lamp signals1 su* an incom+ trunk op]ator c complete f #bej to #ejj connections p] busy h\r4 ,! actual ability dep5ds ^u ! numb] ( di/ant (fices s]v$ by t op]ator & ^u ! am\nt ( "w %e has to p]=m on ea* call4 ,! numb] ( messages :i* c be h&l$ by "o trunk 9 ! busy h\r w dep5d ^u ! numb] ( trunks 9 ! gr\p & ^u ! sy/em employ$4 ,x appe>s t ! ability ( trunks 9 ?is reg>d is high] 9 ! automatic sy/em ?an 9 ! manual sy/em4 ,= ! latt]1 ,table ,,xv gives repres5tative facts4 ,,table ,,xv ,messages p] ,trunk 9 ,manual ,sy/em ---------------------------------------- ------------ ,,numb] ,,( ,,trunks ,,9 ,,gr\p1 ,,messages ,,p] ,,trunk ,,p] ,,manual ,,sy/em ,,busy ,,h\r ---------------------------------------- ------------ #e #g #aj #i #bj #ab #dj #ae #fj #ah ---------------------------------------- ------------ ,"s ( ! reasons = ! high] effici5cies ( trunks 9 ! automatic sy/em are n well def9$1 b unque/ionably exi/4 ,!y h to d p>tly ) ! prompt] answ]+ obs]vable 9 automatic sy/ems4 ,! op]ation ( call+ be+ simple1 a call$ subscrib] seems to fe> t unless he answ]s promptly ! call+ p>ty w disconnect & p]haps may call a competitor4 ,! introduction ( ma*9e-r++ on automatic l9es1 :]e exi/+ 9 competition ) manual r++ on manual l9es1 seems to enc\rage subscrib]s to answ] ev5 m promptly4 ,! l5g? ( conv]sation 9 automatic sy/ems seems to be %ort] ?an 9 manual sy/ems4 ,/ill m important1 disconnection 9 automatic sy/ems is in/antane\s dur+ all h\rs1 :]eas 9 manual sy/ems x is less prompt 9 ! busie/ & lea/ busy h\rs ?an 9 ! h\rs ( int]m$iate conge/ion4 ,! practical results ( trunk effici5cies 9 automatic sy/ems are giv5 9 ,table ,,xvi4 ,,table ,,xvi ,messages p] ,trunk 9 ,automatic ,sy/em ---------------------------------------- ------------ ,,numb] ,,( ,,trunks ,,9 ,,gr\p1 ,,messages ,,p] ,,trunk ,,p] ,,automatic ,,sy/em ,,busy ,,h\r ---------------------------------------- ------------ #e #ae #aj #bb #bj #bh #dj #cb #fj #cd ---------------------------------------- ------------ ,toll ,traffic4 ,toll or long-di/ance traffic foll[s ! g5]al laws ( local or ex*ange traffic4 ,conv]sations are ( great] av]age l5g? 9 long-di/ance traffic4 ,! long-di/ance l9e is held long] = an av]age conv]sation ?an is a local-ex*ange l9e4 ,! local trunks :i* connect long-di/ance l9es ) ex*ange l9es = conv]sation are held long] ?an are ! actual long-di/ance trunks betwe5 cities4 ,kn[+ ! probable traffic to be br\ght to ! long-di/ance swit*+ c5t] by ! long-di/ance trunks f ex*ange c5t]s1 ! numb] ( trunks requir$ may be det]m9$ by kn[+ ! capacity ( ea* trunk4 ,^! trunk capacities v>y ) ! me?od ( h&l+ ! traffic & !y v>y z d local trunks ) ! numb] ( trunks 9 a gr\p4 ,table ,,xvii illu/rates ?is v>iation ( capacity ) sizes ( gr\ps4 ,,table ,,xvii ,messages p] ,trunk 9 ,long-,di/ance ,gr\ps ---------------------------------------- ----------- ,,numb] ,,( ,,long-,,di/ance ,,messages ,,p] ,,trunk ,,p] ,,trunks ,,9 ,,gr\p ,,busy ,,h\r ---------------------------------------- ----------- #e #b #aj #c #bj #c4b #dj #c4e #fj #d #ajj #d4f ---------------------------------------- ----------- ,quality ( ,s]vice4 ,! quality ( telephone s]vice r5d]$ by a p>ticul> equipm5t manag$ 9 a p>ticul> way dep5ds on a great v>iety ( elem5ts4 ,! h&l+ ( ! traffic pres5t$ by patrons is a true manufactur+ problem4 ,! quality ( ! s]vice r5d]$ requires cont9u\s te/+ 9 ord] t ! managem5t may "k :e!r ! s]vice is rea*+ ! /&>d2 :e!r ! /&>d is high en\gh2 :e!r ! co/ ( produc+ x c be r$uc$ )\t l[]+ ! quality2 & :e!r ! patrons are gett+ f x z mu* value z !y might4 ,9 manual sy/ems1 ! quality ( telephone s]vice dep5ds ^u a numb] ( elem5ts4 ,! foll[+ are "s pr9cipal ones3 #a4 ,prompt answ]+4 #b4 ,prompt disconnection4 #c4 ,fre$om f errors 9 connect+ ) ! call$ l9e4 #d4 ,promptness 9 connect+ ) ! call$ l9e4 #e4 ,c\rtesy & ! use ( =m4 #f4 ,fre$om f failure by busy l9es & failure to answ]4 #g4 ,cle> enunciation4 #h4 ,team "w4 ,answ]+ ,"t4 ,!re is an int]relation betwe5 ^! elem5ts4 ,team "w assi/s bo? answ]+ & prompt disconnection4 ,! quality ( telephone s]vice c n be measur$ alone 9 t]ms ( prompt answ]+4 ,=m]ly telephone s]vice 0 boa/$ ( z be+ ?ree-second s]vice if mo/ ( ! orig9at+ calls 7 answ]$ 9 ?ree seconds4 ,(t5 su* prompt answ]+ reacts to prev5t prompt disconnect+4 ,pati5t1 sy/ematic "w is requir$ to le>n ! real quality ( ! s]vice4 ,z to answ]+1 ! cle>e/1 true/ /atem5t conc]n+ manual s]vice is f\nd by mak+ te/ calls to ea* position1 divid+ !m into gr\ps ( v>i\s numb]s ( :ole seconds ea*1 & comp>+ ! p]c5tage ( ^! gr\ps to ! :ole numb] ( telephones to t position4 ,= example1 assume ea* ( ! calls to a giv5 position to h be5 answ]$ 9 t5 seconds or less1 9 :i* #ajj p] c5t are answ]$ 9 t5 seconds or less2 #hj p] c5t 9 eight seconds or less2 #fj p] c5t 9 six seconds or less4 ,x is probable t a reasonably uni=m manual s]vice w %[ only a small p]c5tage answ]$ 9 ?ree seconds or "u4 ,su* p]c5tages may be drawn 9 ! =m ( curves1 s t at a glance "o may le>n effici5cy 9 t]ms ( prompt answ]+4 ,disconnect+ ,"t4 ,prompt disconnection 0 improv$ enorm\sly by ! introduction ( relay manual bo>ds4 ,j be=e ! in/allation ( relay bo>ds 9 ,new ,york ,city1 ! av]age disconnect+ "t 0 ov] sev5te5 seconds4 ,on ! completion ( an entire relay equipm5t1 ! av]age disconnect+ "t 0 f\nd to be "u ?ree seconds4 ,! introduction ( relay manual app>atus has l$ subscrib]s to a l>g] traffic & to ! mak+ ( calls :i* succe$ ea* o!r v closely4 ,a mo/ important rule is1 t disconnect signals %all be giv5 prompt att5tion ei!r by ! op]ator :o made ! connection1 by an op]ator adjac5t1 or by a monitor :o may be assi/+2 & ano!r1 /ill m important "o is1 t a fla%+ keybo>d lamp indicat+ a recall %all be giv5 prec$5ce ov] all orig9at+ & all o!r disconnect signals4 ,accuracy & ,promptness4 ,promptness & accuracy 9 connect+ ) ! call$ l9e are vital1 & yet a l>ge p]c5tage ( errors 9 ^! elem5ts might exi/ 9 an ex*ange hav+ a v high av]age spe$ ( answ]+ ! orig9at+ call4 ,inde$1 x seems q ! rule t :]e ! ef=t ( ! managem5t is devot$ t[>d secur+ & ma9ta9+ extreme spe$ ( orig9al answ]+1 all ! o!r elem5ts suff] 9 due proportion4 ,c\rtesy & ,=m4 ,x goes )\t say+ t op]ators %\ld be c\rte\s2 b x is necess>y to say x1 & keep say+ x 9 ! mo/ effective =m1 9 ord] to prev5t human nature "u ! mo/ exasp]at+ circum/ances f laps+ a little f ! /&>d1 h[ev] high4 ,! use ( =m assi/s bo? ! op]ators & ! subscrib]s1 because 9 all matt]s ( /rict r\t9e x is mu* easi] to secure high spe$ & great accuracy by mak+ z _m z possible ( ! op]ations automatic4 ,! use ( ! ^w numb] & o!r well-accept$ =malities has assi/$ greatly 9 secur+ spe$1 cle> und]/&+1 & accurate p]=mance4 ,! simple exp$i5t ( spell+ numb]s by repeat+ ! figures 9 a deta*$ =m--z #a-b-e = #abe--;has taught subscrib]s ! same exp$i5t1 & ! p]c5tage ( possible error is mat]ially r$uc$ by go+ "o /ep fur!r & hav+ ! op]ator1 9 repeat+1 use always ! opposite =m f t spok5 by ! call+ subscrib]4 ,busy & ,don't ,answ] ,calls4 ,not)/&+ ! old impression ( ! public to ! contr>y1 ! op]ator has no control ov] ! busy l9e & don't answ] situation4 ,x is1 h[ev]1 ( high importance t ! managem5t %\ld "k1 by ! analysis ( repeat$ & exhau/ive te/s ( ! s]vice1 to :at ext5t ^! tr\bles are degrad+ x4 ,9 addition to improv+ ! s]vice by ! elim9ation ( busy reports1 !re is no means ( increas+ rev5ue :i* is s easy & s c]ta9 z t :i* comes f foll[+ up ! tabulat$ results ( busy calls4 ,enunciation4 ,x mu/ be rememb]$ t cle> enunciation = telephone purposes is a matt] :olly relative1 & ! ability ( an op]ator 9 ?is reg>d c be det]m9$ only by a close analysis ( _m obs]vations f ! /&po9t ( a subscrib]4 ,a trick ( spee* r ?an a pleasant voice & an easy address has made ! answ]+ ability ( _m an op]ator captivat+ to a gr\p ( satisfi$ subscrib]s4 ,team ,"w4 ,by team "w is meant ! ability ( a gr\p ( op]ators1 seat$ side by side1 to "w toge!r z a unit 9 c>+ = ! s]vice br\ght to !m by ! answ]+ jacks )9 _! rea*4 ,9 swit*bo>ds ( ! con/ruction usual today1 a call be=e any op]ator may be answ]$ by h]1 or by ! op]ator at ei!r ! "r or ! left ( h] position4 ,9 _m ex*anges ?is advantage is :olly ov]look$4 ,9 ! p]iod ( g5]al re-design ( c5tral-(fice equipm5ts ab\t f\rte5 ye>s ago1 a swit*bo>d 0 in/all$ ) me*anical visual signals & answ]+-jacks on a flat-top bo>d1 & an arrangem5t ( op]ators su* t ! signal ( any call 0 extremely prom95t & 9 easy rea* ( ea* "o ( f\r or possibly five op]ators4 ,associat$ ) ! l9e signals )9 ! rea* ( su* a gr\p 0 an auxili>y lamp signal :i* w\ld light :5 a call 0 made by any ( ! l9es s t]m9at+4 ,x 0 f\nd t ) ?is arrangem5t ! calls 7 answ]$ 9 a /rictly ev5 mann]1 special ru%es be+ c>$ = by ! jo9t ef=ts ( ! gr\p r ?an s]v+ to swamp ! op]ator :o happ5$ to be 9 *>ge ( ! p>ticul> section affect$ by ! ru%4 ,?is pr9ciple has be5 tri$ out 9 s _m ways t x is a/oni%+ t x is n recogniz$ z be+ a vital "o4 ,! :ole matt] is accompli%$ by impress+ ^u ea* op]ator t h] duty is1 n to answ] ! calls ( a specific numb] ( l9es be=e h]1 b to answ]1 ) su* promptness z is possible1 any call :i* is )9 ! rea* ( h] answ]+ equipm5t4 ,obs]vation ( ,s]vice4 ,all t is requir$ to be kn[n conc]n+ ! =m ( address & c\rtesy may be le>n$ by a close obs]vation ( ! op]ators' "w by ! *ief op]ators & monitors1 & by ! use ( li/5+ circuits p]man5tly connect$ to ! op]ators' sets4 ,x is naturally necess>y t ! use ( ^! li/5+ circuits by ! *ief op]ator or h] assi/ants mu/ n be kn[n to ! op]ators at ! times ( use1 ev5 ?\gh !y may "k ( ! exi/5ce ( su* facilities4 ,) a well-design$ & prop]ly ma9ta9$ automatic equipm5t1 ! eight elem5ts ( good manual s]vice r$uce !mselves to only "o or two4 ,fre$om f failure by busy l9es & failure to answ] are s]vice-qualities indep5d5t ( ! k9d ( swit*+ app>atus4 ,too great a p]c5tage ( busy calls = a giv5 l9e indicates t ! telephone facilities = calls incom+ to t subscrib] are inadequate4 ,! be/ condition w\ld be = ea* subscrib] to h l9es en\gh s t none ( !m ev] w\ld be f\nd busy4 ,?is is ! condition ! telephone company tries to e/abli% betwe5 its v>i\s (fices4 ,9 manual practice x is possible to keep su* records z w enable ! traffic dep>tm5t to "k :5 ! l9es to a subscrib] are insuffici5t = ! traffic try+ to rea* him4 ,z soon z su* facts are kn[n1 !y c be laid be=e ! subscrib] s t he may arrange = additional incom+ l9es4 ,9 automatic practice ?is is n s simple1 z ! s\rce & de/9ation ( traffic 9 g5]al is n s cle>ly kn[n to ! traffic dep>tm5t4 ,automatic record]s ( busy calls are necess>y to enable ! facts to be tabulat$4 ,,*apt] ,,xxxviii ,,measur$ ,,s]vice ,9 ! comm]cial relation betwe5 ! public & a telephone sy/em1 ! commodity :i* is produc$ by ! latt] & consum$ by ! =m] is telephone s]vice4 ,us]s (t5 consid] t paym5t is made = r5tal ( telephone app>atus & to "s p]sons ! paym5t p] mon? seems l>ge = ! r5tal ( a m]e telephone :i* c\ld be b\ght outright = a few doll>s4 ,! telephone in/rum5t is b a small "p ( ! physical prop]ty us$ by a patron ( a telephone sy/em4 ,ev5 ! entire gr\p ( prop]ty elem5ts us$ by a patron 9 receiv+ telephone s]vice repres5ts mu* less ?an :at really is 8 proportion ( ! s]vice-r5d]+ ef=t4 ,:at ! patron receives is s]vice & its value dur+ a "t dep5ds l>gely on h[ mu* ( x he uses 9 t "t1 & less on ! numb] ( telephones he c call4 ,! co/ ( telephone s]vice v>ies z ! am\nt ( use4 ,x is j1 !re=e1 t ! sell+ price %\ld v>y z ! am\nt ( use4 ,rates4 ,!re are two g5]al me?ods ( *>g+ = telephone s]vice & ( nam+ rates = ?is *>ge4 ,^! are call$ flat rates & measur$-s]vice rates4 ,! latt] are also kn[n z message rates1 because ! message or conv]sation is ! unit4 ,flat rates are ^? :i* are also kn[n z r5tals4 ,! s]vice furni%$ "u flat rates is also kn[n z unlimit$ s]vice1 = ! reason t "u x a patron pays ! same am\nt ea* mon? & is entitl$ to hold z _m conv]sations--s5d z _m messages & make z _m calls--z he wi%es1 )\t any additional paym5t4 ,9 ! measur$-s]vice plan1 ! am\nt ( paym5t 9 a mon? v>ies 9 "s way ) ! am\nt ( use1 dep5d+ on ! plan adopt$4 ,! patron may pay a fix$ base am\nt p] mon?1 entitl+ him to h equipm5t = telephone s]vice & to receive messages1 b be+ requir$ to pay1 9 addition to ?is base am\nt1 a sum :i* is det]m9$ by ! numb] ( messages :i* he s5ds4 ,or he may pay a base am\nt p] mon? & be entitl$ to h ! equipm5t1 to receive calls1 & to s5d a c]ta9 numb] ( messages1 pay+ specifically 9 addition only = messages exce$+ t c]ta9 numb]4 ,:e!r flat rates or measur$-s]vice rates are practic$1 ! g5]al t5d5cy is to e/abli% l[] rates = s]vice 9 homes ?an 9 bus9ess places4 ,?is is ano!r recognition ( ! ju/ice ( graduat+ ! rates 9 accordance ) ! am\nt ( use4 ,units ( ,*>g+4 ,:ile bo? ! flat-rate & ! measur$-rate me?ods ( *>g+ = unlimit$ & measur$ s]vice are practic$ 9 local ex*anges1 long-di/ance s]vice univ]sally is sold at message rates4 ,! unit ( message rates 9 long-di/ance s]vice is "t4 ,! *>ge = a message betwe5 two po9ts jo9$ by long-di/ance l9es usually is a c]ta9 sum = a conv]sation ?ree m9utes long plus a c]ta9 sum = ea* additional m9ute or fraction ( a m9ute4 ,9 local s]vice1 ! message-rate "t *>ge p] message takes less acc\nt ( ! "t unit4 ,! conv]sation is almo/ univ]sally ! unit 9 ex*anges4 ,"s managem5ts re/rict messages ( multi-p>ty l9es to five m9utes p] conv]sation1 because ( ! desire to avoid )hold+ ! l9e f o!r p>ties ^u x = too long p]iods4 ,s]vice sold at public /ations simil>ly is re/rict$ z to "t1 ev5 ?\gh ! message be local to ! ex*ange4 ,?ree to five m9utes local conv]sation is sold g5]ally = five c5ts 9 ! ,unit$ ,/ates4 ,! "t ( ! av]age local message1 c\nt+ actual conv]sation "t only1 is "o hundr$ seconds4 ,toll ,s]vice4 ,long ,haul4 ,9 long-di/ance s]vice1 !re are two g5]al me?ods ( h&l+ traffic1 z to ! relations betwe5 ! call+ & ! call$ /ations4 ,= ! great] di/ances1 z betwe5 cities n closely relat$ because n belong+ to "o g5]al community1 ! call+ patron calls a p>ticul> p]son & pays no?+ unless he holds conv]sation ) t p]son4 ,9 ?is me?od1 ! op]ator records ! "n ( ! p]son call$ =2 ! "n1 telephone numb]1 or bo?1 ( ! p]son call+2 ! names ( ! t[ns :]e ! message orig9at$ & end$2 ! date1 ! "t conv]sation began1 & ! l5g? ( "t x la/$4 ,%ort ,haul4 ,:]e t[ns are closely relat$ 9 comm]cial & social ways & :]e ! traffic is l>ge & approa*es local s]vice 9 "*1 & yet :]e conv]sations betwe5 !m are *>g$ at diff]5t rates ?an are local calls )9 !m1 a m rapid sy/em ( toll *>g+ ?an t j describ$ is ( advantage4 ,9 ^! conditions1 patrons are n sold a s]vice :i* all[s a p>ticul> p>ty to be nam$ & f\nd1 nor is ! id5tity ( ! call+ p]son requir$4 ,! op]ator ne$s to "k m]ely ( ^! calls t !y orig9ate at a c]ta9 telephone & are = a c]ta9 o!r4 ,! facts %e mu/ record are few] & h] "w is simpl]4 ,!re=e1 ! co/ ( su* swit*+ is less ?an = true long-di/ance calls & x c be le>n$ by c>eful audit+ j :5 traffic betwe5 po9ts becomes great en\gh to w>rant swit*+ !m 9 ?is way4 ,su* swit*+1 = example1 exi/s betwe5 ,new ,york & ,brooklyn1 betwe5 ,*icago & suburbs ar\nd x :i* h names ( _! own b really are "p ( ! community ( ,*icago1 & betwe5 ,san ,francisco & o!r cities :i* clu/] ar\nd ,san ,francisco ,bay4 ,calls ( ! long-haul class are kn[n z p>ticul> p]son or p>ticul> p>ty calls1 :ile %ort-haul calls are kn[n z two-numb] long-di/ance calls4 ,x is cu/om>y to h&le p>ticul> p>ty calls on long-di/ance swit*bo>ds & to h&le two-numb] calls 9 manual sy/ems on subscrib]s' swit*bo>ds exactly l local calls1 except t ! two-numb] calls are ticket$4 ,x is cu/om>y 9 automatic sy/ems to h&le two-numb] calls by means ( ! regul> automatic equipm5t plus ticket+ by a suburban or two-numb] op]ator4 ,tim+ ,toll ,connections4 ,x =m]ly 0 cu/om>y to measure ! "t ( long-di/ance conv]sations by not+ on ! ticket ! "t ( its beg9n+ & ! "t ( its end+1 ! op]ator read+ ! "t f a clock4 ,= human & physical reasons1 su* tim+ seems n to be consid]$ infallible by ! patron :o pays ! *>ge1 & 9 cases ( dispute conc]n+ ov]time *>ges s tim$1 telephone companies f9d x wise/ to make concessions4 ,! physical cause ( error 9 read+ "t f a clock is t ( p>allax2 t is1 ! error :i* arises f ! fact t ! m9ute h& ( a clock is "s di/ance f ! surface ( ! dial s t "o c look "u x4 ,on an ord9>y clock hav+ a l>ge face & its m9ute h& po9t+ upw>d or d[nw>d1 five p /&+ 9 a r[ c\ld read five diff]5t times f x at ! same in/ant4 ,! middle p]son might see ! m9ute h& po9t+ at #f1 indicat+ ! "t to be half-pa/ some?+2 :]eas1 p]son ,no4 #a & p]son ,no4 #e 9 ! r[ might read ! "t respectively #bi & #ca m9utes pa/ some?+4 ,op]ators f> to ! "r or to ! left ( a clock w get diff]5t read+s1 & an op]ator bel[ a clock w get diff]5t k9ds ( read+s at diff]5t times & correct read+s at few times4 ,tim+ ,ma*9es3--,ma*9es :i* record "t directly on long-di/ance tickets are ( value & ma*9es :i* automatically compute ! "t elaps+ dur+ a conv]sation are ( mu* great] value4 ,! calculagraph is a ma*9e ( ! latt] class4 ,! use ( "s su* ma*9e uni=mly r$uces controv]sy z to "t :i* really elaps$4 ,p>allax errors are avoid$4 ,! record possesses a dignity :i* c>ries conviction4 ,illu/ration3 ,fig4 #dec4 ,calculagraph ,records ,calculagraph records are %[n 9 ,fig4 #dec4 ,9 ! "o %[n 9 ! upp] portion ( ?is figure1 ! conv]sation began at #aj4dd ,p4,m4 ,?is is %[n by ! "r-h& dial ( ! ?ree :i* con/itute ! record4 ,! m9utes pa/ #aj o'clock are %[n by ! h& )9 ! dial & ! h\r #aj is %[n by ! triangul> m>k j outside ! dial betwe5 ,x & ,,xi4 ,! duration ( ! conv]sation is %[n by ! middle & ! left-h& dials4 ,! figures on bo? ^! dials indicate m9utes4 ,! middle dial indicates r\ghly t ! conv]sation la/$ = a "t betwe5 #j & #e m9utes4 ,! left-h& dial indicates ) great] exactness t ! conv]sation la/$ "o & "o-qu>t] m9utes4 ,! h& ( ! left-h& dial makes "o revolution 9 five m9utes2 ( ! middle dial1 "o revolution 9 an h\r4 ,! middle dial tells h[ _m full p]iods ( five m9utes h elaps$ & ! left-h& dial %[s ! excess ov] ! five-m9ute int]val4 ,! l[] portion ( ,fig4 #dec is a simil> record beg9n+ at ! same "t ( day1 b la/+ ab\t five & "o-half m9utes4 ,z be=e1 ! read+s ( ! two dials are add$ to get ! elaps$ "t4 ,illu/ration3 ,fig4 #ded4 ,relative ,position ( ,h&s & ,dials ,! "r-h& dial1 %[+ m]ely "t ( day1 /&s /ill :ile its h&s revolve4 ,! dies :i* pr9t ! dials & h&s ( ! middle & ! left-h& records rotate toge!r4 ,exam9+ ! ma*9e1 "o f9ds t ! h&s ( ^! dials always po9t to z]o4 ,! middle dial & h& make "o complete revolution 9 an h\r2 ! left-h& dial & h&1 "o 9 five m9utes4 ,9 mak+ ! records1 ! dials are pr9t$ at ! beg9n+ & ! h&s at ! end ( ! conv]sation4 ,!re=e1 ! h&s w h mov$ =w>d dur+ ! conv]sation--/ill po9t+ to z]o 9 bo? cases--b :5 pr9t$ ! h&s w po9t to "s o!r place ?an !y 7 po9t+ :5 ! dials 7 pr9t$4 ,9 ?is way1 _! angul> di/ances truly indicate ! lapse ( "t4 ,fig4 #ded %[s ! relative position ( ! h&s & dials )9 ! ma*9e at all times4 ,x w be not$ t ! arr[ ( ! left-h& dial does n po9t exactly to z]o4 ,?is is due to ! fact t ! dials & h&s are pr9t$ by sep>ate op]ations & _c be pr9t$ simultane\sly4 ,illu/ration3 ,,we/]n ,,electric ,,r++ ,,ma*9e ,ano!r me?od ( tim+ toll connections has be5 develop$ by ! ,mon>* ,telephone ,manufactur+ ,company4 ,?is employs a ma/] clock ( great accuracy1 :i* may be m\nt$ on ! wall any:]e 9 ! build+ or ano!r build+ if desir$4 ,a circuit leads f ?is clock to a "t-/amp device on ! op]ator's key %elf1 & ! clock closes ?is circuit e qu>t] m9ute4 ,! impulses ?us s5t ov] ! circuit en]gize ! magnet ( ! "t /amp1 :i* /eps a tra9 ( pr9t+ :eels ar\nd s z always to keep !m set 9 su* position z to prop]ly pr9t ! correct "t on a ticket :5ev] ! head ( ! /amp is mov$ by ! op]ator into contact ) ! ticket4 ,a l>ge numb] ( su* /amps may be op]at$ f ! same ma/] clock4 ,by pr9t+ ! />t+ "t ( a connection bel[ ! f9i%+ "t ! computation ( laps$ "t becomes a matt] ( subtraction4 ,a typical toll ticket ) ! beg9n+ & end+ "t pr9t$ by ! "t /amp 9 ! upp] left-h& corn] & ! elaps$ "t record$ by h& 9 ! upp] "r-h& corn] is %[n 9 ,fig4 #dee4 ,x is se5 t ?is /amp records 9 ! ord] m5tion$ ! mon?1 ! day1 ! h\r1 ! m9ute & qu>t] m9ute1 ! ,a4,m4 & ,p4,m4 division ( ! day1 & ! ye>4 ,illu/ration3 ,fig4 #dee4 ,toll ,ticket ,us$ ) ,mon>* ,sy/em ,an int]e/+ feature ( ?is sy/em is t ! same ma/] clock may be made 9 a simil> mann] to actuate second>y clocks plac$ at subscrib]s' /ations1 ! impulses be+ s5t ov] wires 9 ! same cables z ^? conta9+ ! subscrib]s' l9es4 ,?is sy/em1 !re=e1 s]ves n only z a means = tim+ ! toll tickets & op]at+ "t /amps :]ev] !y are requir$ 9 ! bus9ess ( ! telephone company1 b also to supply a g5]al clock & "t-/amp s]vice to ! patrons ( ! telephone company z a by-product ( ! g5]al telephone bus9ess4 ,ex*ange s]vice is measur$ 9 t]ms ( conv]sations )\t mu* reg>d to _! l5g?4 ,! paym5t = ! s]vice may be made at ! "t x is receiv$1 z 9 public /ations & at telephones equipp$ ) co9 prepaym5t devices2 or ! calls f a telephone may be record$ & collection = !m made at agre$ int]vals4 ,9 ! prepaym5t me?od ! price p] call is uni=m4 ,9 ! def]r$ paym5t me?od ! calls are record$ z !y are made1 _! numb] summ$ up at int]vals1 & ! am\nt due det]m9$ by ! price p] call4 ,! price p] call may v>y ) ! numb] ( calls sold4 ,a l>ge us] may h a l[] rate p] call ?an a small us]4 ,local ,s]vice4 ,ticket ,me?od4 ,measur$ local s]vice sometimes is record$ by means ( tickets1 simil>ly to ! describ$ me?od ( *>g+ long-di/ance calls1 except t ! "t ( day & ! duration ( conv]sation are n s important4 ,:]e local ticket+ is practic$1 x is usual to write on ! ticket only ! numb] ( ! call+ telephone & ! date1 & to pass into ! records only ^? tickets :i* repres5t actual conv]sations1 keep+ out tickets repres5t+ calls = busy l9es & calls :i* 7 n answ]$4 ,met] ,me?od4 ,! requirem5ts ( spe$ 9 good local s]vice are oppos$ to ! ticket+ me?od4 ,:]e measur$ s]vice is suppli$ to a sub/antial proportion ( ! l9es ( a l>ge ex*ange1 electro-me*anical s]vice met]s are atta*$ to ! l9es4 ,^! s]vice met]s regi/] z a consequ5ce ( "s act on ! "p ( ! swit*bo>d op]ator1 or may be caus$ to regi/] by ! answ]+ ( ! call$ subscrib]4 ,illu/ration3 ,fig4 #def4 ,connection ,met] ,9 manual practice1 met]s ( ! type %[n 9 ,fig4 #def are associat$ ) ! l9es z 9 ,fig4 #deg4 ,! met]s are m\nt$ sep>ately f ! swit*bo>d1 ne$+ only to be connect$ to ! te/-/r& ( ! l9e by cabl$ wires4 ,if desir$1 ! met] may be m\nt$ on racks 9 qu>t]s especially devot$ to !m1 & ! cases 9 :i* ! racks are m\nt$ may be kept lock$4 ,9 su* an arrangem5t ! met]s are read f "t to "t ?r\gh ! glass doors ( ! cases4 ,! met]s are caus$ to op]ate by pressure on ! met] key ,,mk1 associat$ ) ! answ]+ cord z 9 ,fig4 #deh4 ,?is increases ! normal pot5tial to #cj volts4 ,:5 ! armature ( ! met] has made a "p ( its /roke1 x closes a contact :i* places its #dj-ohm w9d+ 9 %unt ) its #ejj-ohm w9d+1 ?us furni%+ ample p[] = turn+ ! met] :eels4 ,illu/ration3 ,fig4 #deg4 ,we/]n ,electric ,l9e ,circuit & ,s]vice ,met] ,su* met]s are 9 common use 9 l>ge ex*anges1 notable examples be+ ! cities ( ,new ,york & ,london4 ,9 ,london1 !re is a zone )9 :i* ! price p] call is "o p5ny & betwe5 :i* & o!r zones ! price is twop5ce4 ,calls )9 ! zone ei!r are complet$ by ! answ]+ op]ator directly 9 ! multiple be=e h] or are trunk$ to o!r (fices 9 t zone4 ,calls = po9ts outside ( t zone are trunk$ to o!r (fices & 9 giv+ ! ord] ! op]ator f9ds t ! call circuit key lights a special signal lamp be=e h]4 ,?is rem9ds h] t ! call is at a twop5ce price1 s 9 record+ x %e presses ! met] key twice4 ,?is c\nts two units on ! met] & ! units are bill$ at a p5ny ea*4 ,9 automatic sy/ems x is n possible to op]ate a met] sy/em 9 :i* ! op]ator w press a key = ea* call to be *>g$1 because !re is no op]ator4 ,9 su* sy/ems--a notable example be+ ! measur$-s]vice automatic sy/em 9 ,san ,francisco--! met] regi/]s only ^u ! answ]+ ( ! call$ subscrib]4 ,calls = l9es f\nd busy & calls :i* are n answ]$ d n regi/]4 ,calls = long-di/ance record+ op]ators1 two-numb] ticket op]ators1 in=mation1 compla9t1 & o!r company dep>tm5ts are n regi/]$4 ,9 ! ,*9at[n qu>t] ( ,san ,francisco1 :]e mo/ calls beg9 & end 9 ! neighborhood1 s]vice is sold at an unlimit$ flat rate = neighborhood calls & at a message rate = o!r calls4 ,! met] sy/em recognizes ?is condition & does n regi/] calls f ,*9ese subscrib]s = ,*9ese subscrib]s1 ?\gh x does regi/] calls f ,*9ese subscrib]s to ,caucasian subscrib]s4 ,! nature ( ! sy/em is su* z to enable x to discrim9ate z to races1 localities1 or o!r peculi>ities z may be desir$4 ,illu/ration3 ,fig4 #deh4 ,we/]n ,electric ,cord ,circuit & ,s]vice ,met] ,key ,9 ! manual met] circuits ( ,figs4 #deg & #deh1 ! met] w9d+s h no relation to ! l9e conductors4 ,9 ! automatic arrangem5t j describ$1 !re are met] w9d+s 9 ! l9e dur+ times ( call+1 b none 9 ! l9e dur+ times ( conv]sation4 ,! balance ( ! l9e1 !re=e1 is undi/urb$ at all times :]e9 balance is ( any importance4 ,9 bo? sy/ems j describ$1 ! met]s ( all l9es are 9 _! respective c5tral (fices4 ,met]s = use at subscrib]s' /ations h be5 devis$ & !re is no fundam5tal reason :y ! record might n be made at ! subscrib]'s /ation in/ead (1 or 9 addition to1 a c5tral-(fice record4 ,exp]i5ce has %[n t confid5ce 9 a met] sy/em c be secur$ if ! met]s be positive1 accurate1 & reliable4 ,! labor ( read+ ! met]s is mu* less :5 !y are kept 9 c5tral (fices4 ,subscrib]s may h access to !m if !y wi%4 ,prepaym5t ,me?od4 ,prepaym5t measur$-s]vice me*anisms p]mit a co9 or tok5 to be dropp$ into a ma*9e at ! subscrib]'s telephone at ! "t ! conv]sation is held4 ,a v>iety ( =ms ( telephone co9 collectors are 9 use1 _! op]ations be+ fundam5tally ei!r electrical or me*anical4 ,electrically op]at$ co9 collectors require ei!r t ! co9 be dropp$ into ! ma*9e 9 ord] to enable ! c5tral (fice to be signal$ 9 manual sy/ems1 or ! swit*es to be op]at$ 9 automatic sy/ems1 or !y require t ! co9 be dropp$ into ! ma*9e aft] call+1 b be=e ! conv]sation is p]mitt$4 ,we/]n ,electric ,company co9 collectors1 %[n 9 ,fig4 #dei1 may be op]at$ 9 ei!r way 9 connection ) manual sy/ems4 ,! usual way is to require ! co9 to be dropp$ be=e ! c5tral-(fice l9e lamp c gl[4 ,! op]ator !n r+s ! call$ subscrib] & ^u 8 answ]+ places a suffici5t pot5tial ^u ! call+ l9e to op]ate ! pol>iz$ relay & to drop ! co9 into ! ca% box4 ,if ! call$ subscrib] does n answ] or 8 l9e is busy1 pot5tial is plac$ on ! call+ l9e1 mov+ ! pol>iz$ relay 9 ! o!r direction & dropp+ ! co9 into a return *ute s t ! subscrib] may take x4 ,if x is pref]r$ t ! co9 be paid only on ! reque/ ( ! op]ator1 ! return feature ne$ n be provid$4 ,9 bo? =ms ( op]ation1 ! ,we/]n ,electric co9 collector is adapt$ to bridge its pol>iz$ relay betwe5 "o limb ( ! l9e & gr\nd dur+ ! "t a co9 re/s on ! p9s1 z %[n 9 ,fig4 #dei4 ,:5 no co9 is on ! p9s--i4 e41 be=e call+ & aft] ! call$ /ation responds--! relay is n s bridg$4 ,illu/ration3 ,fig4 #dei4 ,pr9ciple ( ,we/]n ,electric ,co9 ,collector ,! armature ( ! relay responds only to a high pot5tial & ?is is appli$ by ! op]ator4 ,if ! co9 is to be tak5 by ! company1 "o pol>ity is s5t2 if x is to be return$ to ! patron1 ! o!r pol>ity is s5t4 ,^! pol>ities are appli$ to a limb ( ! l9e prop]4 ,x w be recall$ t pressures to actuate s]vice met]s are appli$ to ! te/-/r&4 ,if wi%$1 keys may be arrang$ s z to apply #cj volts to ! te/-/r& & ! collect+ pot5tial to ! l9e at ! same op]ation4 ,?is enables ! s]vice met] to c\nt ! tok5s plac$ 9 ! ca% box ( ! co9 collector1 & s]ves z a valuable *eck4 ,9 automatic sy/ems1 9 "o arrangem5t1 co9 collectors are arrang$ s t no impulses c be s5t unless a co9 has be5 deposit$1 ! co9 automatically pass+ to ! ca% box :5 ! call$ subscrib] answ]s1 or to ! patron if x is n answ]$4 ,9 ano!r arrangem5t1 calls are made exactly z 9 unlimit$ s]vice1 b a co9 mu/ be deposit$ be=e a conv]sation c be held4 ,! call+ p]son c he> ! call$ p>ty speak & may speak himself b c n be he>d until ! co9 is deposit$4 ,no co9-return me*anism is requir$ 9 ?is me?od4 ,co9 collectors ( ^! types usually are adapt$ to receive only "o k9d ( co91 ^!1 9 ! ,unit$ ,/ates1 be+ ei!r nickels or dimes4 ,= long-di/ance s]vice1 :]e ! *>ges v>y1 x is necess>y to signal to an op]ator j :at co9s are paid4 ,x is uni=mly cu/om>y to s5d ^! signals by s\nd1 ! collector be+ s arrang$ t ! co9s /rike gongs4 ,9 co9 collectors ( ! ,gray ,telephone ,pay/ation ,company1 ! co9s /rike ^! gongs by _! own weight 9 fall+ ?r\gh *utes4 ,9 co9 collectors ( ! ,baird ,electric ,company1 ! p[] = ! signals is provid$ by h& p[]1 a lev] be+ pull$ = ea* co9 deposit$4 ,bo? me?ods are 9 wide use4 ,,*apt] ,,xxxix ,,phantom1 ,,simplex1 ,,& ,,composite ,,circuits ,def9itions4 ,phantom circuits are arrangem5ts ( telephone wires :]eby m work+1 non-int]f]+ telephone l9es exi/ ?an !re are sets ( actual wires4 ,:5 f\r wires are arrang$ to provide ?ree metallic circuits = telephone purposes1 two ( ! l9es are physical circuits & "o is a phantom circuit4 ,simplex & composite circuits are arrangem5ts ( wires :]eby telephony & telegraphy c take place at ! same "t ov] ! same wires )\t int]f]5ce4 ,illu/ration3 ,fig4 #dfj4 ,phantom ,circuit ,phantom4 ,9 ,fig4 #dfj f\r wires jo9 two (fices4 ,,rr are repeat+ coils1 design$ = effici5t trans=m+ ( bo? talk+ & r++ curr5ts4 ,! devices m>k$ ,a 9 ?is & ! foll[+ figures are air-gap arre/]s4 ,curr5ts f ! telephones connect$ to ei!r physical pair ( wires pass1 at any in/ant1 9 opposite directions 9 ! two wires ( ! pair4 ,! phantom circuit uses "o ( ! physical pairs z a wire ( its l9e4 ,x does ?is by tapp+ ! middle po9t ( ! l9e side ( ea* ( ! repeat+ coils4 ,! imp$ance ( ! repeat+-coil w9d+ is l[]$ because1 all ! w9d+s be+ on ! same core1 ! phantom l9e curr5ts pass f ! middle to ! out] connections s z to neutralize ea* o!r's influ5ce4 ,! curr5ts ( ! phantom circuit1 unlike ^? ( ! physical circuits1 are 9 ! same direction 9 bo? wires ( a pair at any in/ant4 ,_! pot5tials1 !re=e1 are equal & simultane\s4 ,a phantom circuit is =m$ mo/ simply :5 bo? physical l9es end 9 ! same two (fices4 ,if "o physical l9e is long] ?an ! o!r1 a phantom circuit may be =m$ z 9 ,fig4 #dfa1 :]e9 ! repeat+ coil is ins]t$ 9 ! long] l9e :]e x passes ?r\gh a t]m9al /ation ( ! %ort]4 ,illu/ration3 ,fig4 #dfa4 ,phantom f ,two ,physical ,circuits ( ,unequal ,l5g? ,illu/ration3 ,fig4 #dfc4 ,two ,phantoms ,jo9$ by ,physical ,circuit ,a circuit may be built up by add+ a physical circuit to a phantom4 ,a circuit may be made up ( two or m phantom circuits1 jo9$ by physical ones4 ,9 ,fig4 #dfb a phantom circuit is ext5d$ by ! use ( a physical circuit1 :ile 9 ,fig4 #dfc1 two phantom circuits are jo9$ by plac+ betwe5 !m a physical circuit4 ,illu/ration3 ,fig4 #dfb4 ,phantom ,ext5d$ by ,physical ,circuit ,transpositions4 ,9 phantom circuits =m$ m]ely by ins]t+ repeat+ coils 9 physical circuits & do+ no?+ else1 an exact balance ( ! sides ( ! phantom circuit is lack+4 ,! resi/ances1 insulations1 & capacities to e>? ( ! sides may be equal1 b ! exposures to adjac5t telephone & telegraph circuits & to p[] circuits w n be equal unless ! phantom circuits are transpos$4 ,to transpose a set ( l9es ( two physical wires ea*1 is n complicat$1 ?\gh x mu/ be done ) c>e & 9 accordance ) a def9ite1 =ekn[n plan4 ,transpos+ phantom circuits is less simple1 h[ev]1 z f\r wires p] circuit h to be transpos$1 in/ead ( two4 ,illu/ration3 ,fig4 #dfd4 ,transposition ( ,phantom ,circuits ,9 ,fig4 #dfd1 ! g5]al spac+ ( transposition sections is ! usual "o1 #a1cjj feet1 ( ! ,,abcb sy/em widely 9 use4 ,! pole circuit1 on p9s #e & #f ( ! upp] arm1 is transpos$ once ea* two miles4 ,! pole circuit ( ! second arm transposes ei!r once or twice a mile4 ,b nei!r pole circuit diff]s 9 transposition f any o!r regul> s*eme except 9 ! frequ5cy ( transposition4 ,all ! o!r wires ( ea* arm1 h[ev]1 are s arrang$ t ea* wire on ei!r side ( ! pole circuit moves f p9 to p9 at section-ends1 till x has complet$ a cycle ( *anges ov] all f\r ( ! p9s on its side4 ,9 do+ s1 ea* phantom circuit is transpos$ ) prop] reg>d to ea* ( ! o!r ?ree on t tw5ty-wire l9e4 ,! new transposition lett]+ 9 ,fig4 #dfd is = ! purpose ( id5tify+ ! exact s*eme ( wir+ ea* transposition pole4 ,! complication ( wir+ at ea* transposition pole is increas$ by ! adoption ( phantom circuits4 ,ma9t5ance ( all ! circuits is made m co/ly & less easy unless ! "w at po9ts ( transposition is done ) c>e & skill4 ,phantom circuits1 to be always successful1 require t ! physical circuits be balanc$ & kept s4 ,transmission ov] ,phantom ,circuits4 ,"u prop] conditions phantom circuits are bett] ?an physical circuits1 & 9 ?is respect x may be not$ t "s long-di/ance op]at+ companies in/ruct _! op]ators always to give pref]5ce to phantom circuits1 because ( ! bett] transmission ov] !m4 ,! use ( phantom circuits is conf9$ almo/ :olly to op5-wire circuits2 & :ile ! capacity ( ! phantom circuit is some:at great] ?an t ( ! physical circuit1 its resi/ance is consid]ably small]4 ,9 ! actual wire ! phantom loop is only half ! resi/ance ( ei!r ( ! physical l9es f :i* x is made1 = x conta9s twice z mu* copp]4 ,! resi/ance ( ! repeat+ coils1 h[ev]1 is to be add$4 ,simplex4 ,simplex telegraph circuits are made f metallic circuit telephone l9es1 z %[n 9 ,fig4 #dfe4 ,! pr9ciple is id5tical ) t ( phantom telephone circuits4 ,! pot5tials plac$ on ! telephone l9e by ! telegraph op]ations are equal & simultane\s4 ,!y cause no curr5t to fl[ ar\nd ! telephone loop1 only along x4 ,if all qualities ( ! loop are balanc$1 ! telephones w n ov]he> ! telegraph impulses4 ,9 ! figure1 ,,aa are arre/]s1 z be=e1 ,,gg are ,morse relays2 a #b-micr(>ad cond5s] is %unt$ ar\nd ! contact ( ea* ,morse key ,f to qu5* ! noises due to ! sudd5 *anges on op5+ ! keys betwe5 dots & da%es4 ,illu/ration3 ,fig4 #dfe4 ,simplex ,telegraph ,circuit ,a simplex arrangem5t ev5 m simple sub/itutes imp$ance coils = ! repeat+ coils ( ,fig4 #dfe4 ,! op]ation ( ! ,morse circuit is ! same4 ,an advantage ( su* a circuit1 z %[n 9 ,fig4 #dff1 is t ! telephone circuit does n suff] f ! two repeat+-coil losses 9 s]ies4 ,a disadvantage is1 t 9 r++ on su* a l9e ) a gr\nd$ g5]ator1 ! ,morse relays are caus$ to *att]4 ,illu/ration3 ,fig4 #dff4 ,simplex ,telegraph ,circuit ,! circuit ( ,fig4 #dfe may be made to fit ! condition ( a ?r\gh telephone l9e & a way telegraph /ation4 ,! midway ,morse app>atus ( ,fig4 #dfg is loop$ 9 by a comb9ation ( imp$ance coils & cond5s]s4 ,! plans ( ,figs4 #dfe & #dff "h are comb9$1 ) ! fur!r idea ( /opp+ direct & pass+ alt]nat+ curr5ts1 z is s well accompli%$ by ! use ( cond5s]s4 ,illu/ration3 ,fig4 #dfg4 ,simplex ,circuit ) ,way/ation ,illu/ration3 ,fig4 #dfh4 ,composite ,circuit ,composite4 ,composite circuits dep5d on ano!r pr9ciple ?an t ( produc+ equal & simultane\s pot5tials on ! two wires ( ! telephone loop4 ,! opposition ( imp$ance coils to alt]nat+ curr5ts & ( cond5s]s to direct curr5ts are ! fundam5tals4 ,! e>ly "w 9 ?is art 0 done by ,van ,rysselb]ghe1 ( ,belgium4 ,9 ,fig4 #dfh1 "o telephone circuit =ms two ,morse circuits1 two wires c>ry+ ?ree s]vices4 ,ea* ,morse circuit w be se5 to include1 s]ially1 two #ej-ohm imp$ance coils1 & to h %unts ?r\gh cond5s]s to gr\nd4 ,! #ej-ohm coils are connect$ diff]5tially1 (f]+ l[ consequ5t imp$ance to ,morse impulses1 ^: frequ5cy ( int]ruption is n great4 ,z ! imp$ance coils are l>ge1 h cores ( consid]able l5g?1 & are w\nd ) two sep>ate ?\gh s]ially connect$ w9d+s ea*1 _! imp$ance to voice curr5ts is great4 ,!y act z ?\gh !y 7 n connect$ diff]5tially1 s f> z voice curr5ts are conc]n$4 ,because ( ! cond5s]s s]ially 9 ! telephone l9e1 voice curr5ts c pass ?r\gh x1 b direct curr5ts c n4 ,impulses due to dis*>ges ( cores1 coils1 & capacities 9 ! ,morse circuit c\ld make s\nds 9 ! telephones1 b ^! are *ok$ out1 or l$ to e>? by ! #cj-ohm imp$ance coils & ! heavy ,morse cond5s]s4 ,r++4 ,r++ ov] simplex circuits is done 9 ! way usual :]e no telegraph s]vice is add$4 ,bo? telegraphy & telephony ov] simplex circuits foll[ _! usual practice 9 ! way ( call+ & conv]s+4 ,9 composite work+1 h[ev]1 r++ by usual me?ods ei!r is impossible because ( heavy gr\nds & %unts1 or if x is possible to get r++ signals ?r\gh at all1 ! relays ( ! ,morse app>atus w *att]1 int]f]+ ) ! prop] use ( ! telegraph portion ( ! s]vice4 ,x is cu/om>y1 !re=e1 ei!r to equip composite circuits ) special signal+ devices by :i* high-frequ5cy curr5ts pass ov] ! telephone circuits1 op]at+ relays :i* 9 turn op]ate local r++ signals2 or to refra9 f r++ on composite circuits & to transmit ord]s = connections by telegraph4 ,! latt] is :olly satisfactory ov] composite l9es betwe5 po9ts hav+ heavy telegraph traffic1 & x is betwe5 su* po9ts z ^! t composite practice is mo/ g5]al4 ,phantoms f ,simplex & ,composite ,circuits4 ,phantom & simplex pr9ciples are id5tical1 & by add+ ! composite pr9ciple1 two simplex circuits may h a phantom sup]add$1 z 9 ,fig4 #dfi4 ,simil>ly1 z 9 ,fig4 #dgj1 two composite circuits c be phantom$4 ,?is case gives sev5 di/9ct s]vices ov] f\r wires3 ?ree telephone loops--two physical & "o phantom--& f\r ,morse l9es4 ,illu/ration3 ,fig4 #dfi4 ,phantom ( ,two ,simplex ,circuits ,illu/ration3 ,fig4 #dgj4 ,phantom ( ,two ,composite ,circuits ,railway ,composite4 ,! =ego+ are problems ( mak+ telegraphy a by-product ( telephony4 ,) s _m telegraph wires on poles ov] ! c\ntry1 x has seem$ a pity n to turn ! ?+ ar\nd & provide = telephony z a by-product ( telegraphy4 ,?is has be5 accompli%$1 & ! result is call$ a railway composite sy/em4 ,= ! reason t ! telegraph circuits are n 9 pairs1 accurately mat*$ "o wire aga9/ ano!r1 & are n always uni=m z to mat]ial1 x has n be5 possible to secure z good telephone circuits f telegraph wires z telegraph circuits f telephone wires4 ,practical results are secur$ by adaptation ( ! orig9al pr9ciple ( diff]5t frequ5cies4 ,a /udy ( ,fig4 #dfh %[s t ov] su* a composite circuit ! usual me?od ( r++ f /ation to /ation ov] ! telephone circuit by an alt]nat+ curr5t ( a frequ5cy ( ab\t sixte5 p] second is practically impossible4 ,?is is because ( ! heavy %ort-circuit provid$ by ! two #cj-ohm *oke coils at ea* ( ! /ations1 ! heavy %unt ( ! l>ge cond5s]s1 & ! gr\nd+ ?r\gh ! #ej-ohm *oke coils4 ,if high-frequ5cy spee* curr5ts c pass ov] ^! circuits ) a v small loss1 o!r high-frequ5cy circuits %\ld f9d a good pa?4 ,!re are _m easy ways ( mak+ su* curr5ts1 b =m]ly none v simple = receiv+ !m4 ,fig4 #dga %[s "o simple obs]v] ( su* high-frequ5cy curr5ts1 x be+ m]ely an adaptation ( ! famili> pol>iz$ r+] us$ 9 e subscrib]'s telephone4 ,9 ei!r position ( ! armature x makes contact ) "o or ! o!r ( two /uds connect$ to ! batt]y1 s t 9 all times ( re/ ! relay ,a is en]giz$4 ,:5 a high-frequ5cy curr5t passes ?r\gh ?is pol>iz$ relay1 h[ev]1 !re is en\gh "t 9 :i* ! armature is out ( contact ) ei!r /ud to r$uce ! total en]gy ?r\gh ! relay ,a & all[ its armature to fall away1 r++ a vibrat+ bell or giv+ "s o!r signal4 ,illu/ration3 ,fig4 #dga4 ,r++ ,device = ,composite ,circuits ,fig4 #dgb %[s a =m ( app>atus = produc+ ! high-frequ5cy curr5t necess>y = signal+4 ,x is evid5t t if a magneto g5]ator1 su* z is us$ 9 ord9>y magneto telephones1 c\ld be made to drive its armature fa/ en\gh1 x also might furni% ! high-frequ5cy curr5t necess>y = signal+ ?r\gh cond5s]s & pa/ heavy imp$ances4 ,illu/ration3 ,fig4 #dgb4 ,r++ ,curr5t ,device ,apply+ ^! pr9ciples ( high-frequ5cy signals s5t & receiv$ to a s+le-wire telegraph circuit1 ! arrangem5t %[n 9 ,fig4 #dgc results1 ?is be+ a type ( railway composite circuit4 ,! pr9cipal po9ts ( int]e/ h]e9 are ! ins]tion ( imp$ances 9 s]ies ) ! telegraph l9es1 ! %unt+ ( ! telegraph relays by small cond5s]s1 ! fur!r %unt+ ( ! :ole telegraph me*anism ( a /ation by ano!r cond5s]1 & ?us keep+ out ( ! l9e circuit *anges 9 curr5t values :i* w\ld be he>d 9 ! telephones if viol5t1 & might be inaudible if o!rwise4 ,illu/ration3 ,fig4 #dgc4 ,railway ,composite ,circuit ,illu/ration3 ,,front ,,( ,,long-,,di/ance ,,p[] ,,bo>d ,u4,s4 ,telephone ,company1 ,clevel&1 ,ohio4 ,! ,dean ,electric ,co4 ,a fur!r int]e/+ elem5t is ! v heavy %unt+ ( ! telephone receiv] by means ( an inductive coil4 ,?is %unt is appli$ = by-pa? purposes s t heavy di/urb+ curr5ts may be kept out ( ! receiv] :ile a suffici5t am\nt ( voice curr5t is div]t$ ?r\gh ! receiv]4 ,x is well to h ! inductance ( ?is %unt made adju/able by provid+ a movable iron core = ! %unt w9d+4 ,:5 ! core is drawn out ( ! coil1 its imp$ance is dim9i%$ because ! inductance is dim9i%$4 ,?is r$uces ! am\nt ( di/urb+ noise 9 ! receiv]4 ,! core %\ld be )drawn z little z ! am\nt ( di/urbance p]mits1 z ?is also dim9i%es ! l\dness ( ! receiv$ spee*4 ,because ! signal+ ov] l9es equipp$ ) ?is =m ( composite work+ results 9 ! r++ ( a bell by means ( local curr5t1 x is ( p>ticul> advantage 9 cases :]e ! bell ne$s to r+ l\dly4 ,swit* /ations1 cross+s1 & simil> places :]e ! att5dant is n con/antly ne> ! telephone c be equipp$ ) ?is type ( composite app>atus & x s (f]s a valuable sub/itute = regul> railway telegraph equipm5t1 ) :i* ! att5dant may n be famili>4 ,! success ( ! local bell-r++ arrangem5t1 h[ev]1 dep5ds on accurate relay adju/m5t & on ! ma9t5ance ( a prim>y batt]y4 ,! dra9 on ! r++ batt]y is great] ?an on ! talk+ batt]y4 ,a good sub/itute = ! bell signal on railway composite circuits is a telephone receiv] respond+ directly to high-frequ5cy curr5ts ov] ! l9e4 ,! receiv] is design$ specially = ! purpose & is kn[n z a h[l]4 ,its signal c be easily he>d ?r\gh a l>ge room4 ,! cond5s] 9 s]ies ) x is ( small capacity1 limit+ ! dra9 ^u ! l9e4 ,usually ! h[l] is deta*$ by ! swit* hook dur+ conv]sation f a /ation4 ,railway ,composite ,set4 ,! circuit ( a set utiliz+ su* an arrangem5t toge!r ) o!r details ( a complete railway composite set is %[n 9 ,fig4 #dgd4 ,! draw+ is arrang$ ?us1 9 ! hope ( simplify+ ! und]/&+ ( its pr9ciples4 ,x w be se5 t ! induction coil s]ves z an int]rupt] z well z = transmission4 ,all ( ! contacts are %[n 9 ! position !y h dur+ conv]sation4 ,! lett]s ,hc#a1 ,hc#b1 etc41 & ,kc#a1 ,kc#b1 etc41 ref] to hook contacts & key contacts1 respectively1 ( ! numb]s giv54 ,! arrangem5ts ( ! hook & key spr+s are %[n at ! "r ( ! figure4 ,,rr repres5t imp$ance coils connect$ s]ially 9 ! l9e & plac$ at t]m9al /ations4 ,! composite telephone sets are bridg$ f ! l9e to gr\nd at any po9ts betwe5 ! t]m9al imp$ance coils4 ,! direct curr5ts ( telegraphy are prev5t$ f pass+ to gr\nd ?r\gh ! telephone set dur+ conv]sation by ! #b-micr(>ad cond5s] :i* is 9 s]ies ) ! receiv]4 ,!y are prev5t$ f pass+ to gr\nd ?r\gh ! telephone set :5 ! receiv] is on ! hook by a 4#je micr(>ad cond5s] 9 s]ies ) ! h[l]4 ,! alt]nat+ curr5ts ( spee* & int]rupt] signal+ are kept f pass+ to gr\nd at t]m9als by ! imp$ance coils4 ,signals are s5t f ! set by press+ ! key ,k4 ,?is op]ates ! vibrator by clos+ contacts ,kc#f & ,kc#g4 ,! h[l] is cut (f & ! receiv] is %ort-circuit$ by ! same op]ation ( ! key4 ,! imp$ance ( ! coil ,i is *ang$ by mov+ its adju/able core4 ,illu/ration3 ,fig4 #dgd4 ,railway ,composite ,set ,applications4 ,a *ief use ( composite & simplex circuits is = ticket wire purposes4 ,^! are circuits ov] :i* long-di/ance op]ators in/ruct ea* o!r z to connect+ & disconnect+ l9es1 ! r\t+ ( calls1 & ! mak+ ( appo9tm5ts4 ,"o su* wire w c>e = all ! bus9ess ( _m long-di/ance trunks4 ,! public also absorbs ! telegraph product ( telephone l9es4 ,su* telegraph s]vice is leas$ to brok]s1 manufactur]s1 m]*ants1 & newspap]s4 ,railway companies use portable telephone adjuncts to telegraph circuits on tra9s = s]vice f /ations n able to support telegraph att5dants1 & 9 a limit$ degree = ! dispat*+ ( tra9s4 ,telephone tra9 dispat*+1 h[ev]1 m]its bett] equipm5t ?an a railway composite sy/em af=ds4 ,,*apt] ,,xl ,,telephone ,,tra9 ,,dispat*+,a ,x has be5 only )9 ! pa/ ?ree few t ! telephone has begun to replace ! telegraph = h&l+ tra9 movem5ts4 ,! telegraph & ! railroads h gr[n up toge!r 9 ?is c\ntry s9ce #ahej1 & 9 view ( ! excell5t results t ! telegraph has giv5 9 tra9 dispat*+ & ( ! close alliance t has always naturally exi/$ betwe5 ! railway & ! telegraph1 x has be5 difficult = ! telephone1 :i* came mu* lat]1 to ent] ! field4 ,rapid ,gr[?4 ,! telephone has be5 9 g5]al use among ! railroads = _m ye>s1 b only on a few %ort l9es has x be5 us$ = dispat*+ tra9s4 ,9 ^! cases ! ord9>y magneto circuit & in/rum5ts h be5 employ$1 diff]+ 9 no respect f ^? us$ 9 comm]cial s]vice at ! pres5t "t4 ,code r++ 0 us$ & ! numb] ( /ations on a circuit 0 limit$ by ! same causes t limit ! telephones on comm]cial p>ty l9es at pres5t4 ,! pres5t type ( telephone dispat*+ sy/ems1 h[ev]1 diff]s ess5tially f ! sy/ems us$ 9 comm]cial "w1 & is1 9 fact1 a highly specializ$ p>ty-l9e sy/em1 arrang$ = selective r++ & _m /ations4 ,! fir/ ( ! pres5t type 0 in/all$ by ! ,new ,york ,c5tral & ,hudson ,riv] ,railroad 9 ,octob]1 #aijg1 betwe5 ,albany & ,fonda1 ,new ,york1 a di/ance ( #dj miles4 ,?is section ( ! road is on ! ma9 l9e & has f\r tracks controll$ by block signals4 ,! ,*icago1 ,burl+ton1 & ,qu9cy ,railroad 0 ! second to in/all tra9-dispat*+ circuits4 ,9 ,decemb]1 #aijg1 a portion ( ! ma9 l9e f ,aurora to ,m5dota1 ,ill9ois1 a di/ance ( #df miles1 0 equipp$4 ,?is 0 foll[$ 9 quick succession by v>i\s o!r circuits rang+1 9 g5]al1 9 l5g?s ov] #ajj miles4 ,at ! pres5t "t !re are ov] #bj tra9-dispat*+ circuits on ! ,*icago1 ,burl+ton1 & ,qu9cy ,railroad cov]+ #abe miles ( d\ble track1 #bh miles ( multi-track1 & #a1cha miles ( s+le track1 & connect+ ) #bhf /ations4 ,o!r railroads ent]$ ?is field 9 quick ord] aft] ! initial in/allations1 & at ! pres5t "t ne>ly e l>ge railroad sy/em 9 ! ,unit$ ,/ates is equipp$ ) sev]al telephone tra9-dispat*+ circuits & all ( ^! seem to be ext5d+ _! sy/ems4 ,9 #aiaj1 sev]al railroads1 includ+ ! ,delaw>e1 ,lackawanna1 & ,we/]n1 _h _! total mileage equipp$ ) telephone dispat*+ circuits4 ,! ,at*ison1 ,topeka1 & ,santa ,fe ,railroad is equipp+ its :ole sy/em z rapidly z possible & already is ! l>ge/ us] ( ?is equipm5t 9 ?is c\ntry4 ,f late/ in=mation1 ov] #ee railroads h ent]$ ?is field1 ) ! result t ! telephone is n[ 9 use 9 railroad s]vice on ov] #bi1jjj miles ( l9e4 ,causes ( ,its ,introduction4 ,! reasons lead+ to ! introduction ( ! telephone into ! dispat*+ field 7 ( ?is nature3 ,fir/1 & mo/ important1 0 ! enactm5t ( ,/ate & ,f$]al ,laws limit+ to n9e h\rs ! work+ day ( railroad employes transmitt+ or receiv+ ord]s p]ta9+ to ! movem5t ( tra9s4 ,! second1 :i* is directly dep5d5t ^u ! fir/1 0 ! inability ( ! railroads to obta9 ! additional numb] ( telegraph op]ators :i* 7 requir$ "u ! provisions ( ! new laws4 ,x 0 e/imat$ t #ae1jjj additional op]ators w\ld be requir$ to ma9ta9 s]vice 9 ! same fa%ion aft] ! new laws w5t into effect 9 #aijg4 ,! increas$ annual exp5se occasion$ by ! employm5t ( ^! additional op]ators 0 r\ghly e/imat$ at #aj1jjj1jjj4 ,a ?ird reason is f\nd 9 ! decreas$ effici5cy ( ! av]age railway & comm]cial telegraph op]ator4 ,!re is a v g5]al compla9t among ! railroads today reg>d+ ?is p>ticul> po9t1 & _m ( !m welcome ! telephone1 because1 if = no o!r reason1 x r5d]s !m indep5d5t ( ! telegraph]4 ,:at has occasion$ ?is decrease 9 effici5cy x is n easy to say1 b !re is a /rong t5d5cy to lay x1 9 "p1 to ! attitude ( ! telegraph]s' organization t[>d ! /ud5t op]ator4 ,x is a fact1 too1 t ! limits :i* ^! organizations h plac$ on /ud5t op]ators 7 directly responsible = ! lack ( available m5 :5 !y 7 ne$$4 ,advantages4 ,9 mak+ ?is radical *ange1 railroad (ficials 7 mo/ cauti\s1 & yet we "k ( no case :]e ! introduction ( ! telephone has be5 foll[$ by its ab&onm5t1 ! t5d5cy hav+ be5 9 all cases t[>d fur!r in/allations & m equipm5t ( ! mod]n type4 ,! reasons = ?is are cle>1 = :]e ! telephone is us$ x does n require a highly specializ$ man z /ation op]ator & consequ5tly a mu* broad] field is op5 to ! railroads f :i* to draw op]ators4 ,?is1 we ?9k1 is ! mo/ f>-rea*+ advantage4 ,! telephone me?od also is fa/]4 ,on an ord9>y tra9-dispat*+ circuit x n[ requires f #j4a ( a second to #e seconds to call any /ation4 ,9 case a plurality ( calls is desir$1 ! dispat*] calls "o /ation aft] ano!r1 gett+ ! answ] f "o :ile ! next is be+ call$1 & s on4 ,by speak+ into a telephone _m m words may be transmitt$ 9 a giv5 "t ?an by ,morse telegraphy4 ,x is possible to s5d fifty words a m9ute by ,morse1 b su* spe$ is exceptional4 ,less ?an half t is ! rule4 ,! ga9 9 high spe$1 !re=e1 :i* is obta9$ is obvi\s & x has be5 f\nd t ?is is a mo/ important feature on busy divisions4 ,x is true t 9 ! issuance ( ord]s1 ! spe$1 9 telephonic tra9 dispat*+1 is limit$ to t requir$ to write ! words 9 longh&4 ,b all directions ( a collat]al "*1 ! receipt ( important in=mation1 & ! in/antane\s descriptions ( em]g5cy situations c be giv5 & receiv$ at a spe$ limit$ only by t ( human spee*4 ,! dispat*] is also br\ght into a clos] p]sonal relation ) ! /ation m5 & tra9m51 & ?is feature ( direct p]sonal communication has be5 f\nd to be ( importance 9 br++ ab\t a high] degree ( co-op]ation & bett] discipl9e 9 ! s]vice4 ,telephone dispat*+ has features peculi> to itself :i* are important 9 improv+ ! class ( s]vice4 ,"o ( ^! is ! answ]-back automatically giv5 to ! dispat*] by ! way/ation bell4 ,?is in=ms ! dispat*] :e!r or n ! bell at ! /ation rang1 & excuses by ! op]ators t x did n1 are elim9at$4 ,anyone c answ] a telephone call 9 an em]g5cy4 ,! /ation op]ator is frequ5tly ag5t also1 & 8 duties (t5 take him out ( he>+ ( ! telegraph s\nd]4 ,! selector bell us$ ) ! telephone c be he>d = a di/ance ( sev]al hundr$ feet4 ,9 addition1 x is q likely t anyone 9 ! neighborhood w\ld recognize t ! /ation 0 want$ & ei!r notify ! op]ator or answ] ! call4 ,9 cases ( em]g5cy ! tra9 crews c get into direct communication ) ! dispat*] imm$iately1 by means ( portable telephone sets :i* are c>ri$ on ! tra9s4 ,x is a well-kn[n fact t e m9ute a ma9 l9e is block$ by a wreck c be reckon$ z great loss to ! railroad4 ,x is also possible to in/all sid+ telephone sets locat$ ei!r 9 boo?s or on poles along ! "r-(-way4 ,^! are 9 g5]al s]vice today at sid+s1 cross+s1 drawbridges1 wat] tanks1 & su* places1 :]e x may be ess5tial = a tra9 crew to rea* ! ne>e/ way/ation to give or receive in=mation4 ,! advantage ( ^! sid+ sets is com+ m & m to be realiz$4 ,) ! telegraph me?od ( dispat*+1 a tra9 is ord]$ to pass ano!r tra9 at a c]ta9 sid+1 let u say4 ,x rea*es ?is po9t1 & to use a railroad expression1 goes into ! hole4 ,n[1 if any?+ happ5s to ! second tra9 :]eby x is delay$1 ! fir/ tra9 rema9s ti$ up at t sid+ )\t ! possibility ( ei!r rea*+ ! dispat*] or be+ rea*$ by him4 ,) ! telephone /ation at ! sid+1 :i* requires no op]ator1 ?is is avoid$4 ,if a tra9 f9ds itself wait+ too long1 ! conductor goes to ! sid+ telephone & talks to ! dispat*]1 possibly gett+ ord]s :i* w advance him _m miles t w\ld o!rwise h be5 lo/4 ,x is no long] necess>y = a way/ation op]ator to call ! dispat*]4 ,:5 "o ( ^! op]ators wi%es to talk to ! dispat*]1 he m]ely takes 8 telephone receiv] (f ! hook1 presses a button1 & speaks to ! dispat*]4 ,) ! telephone x is a simple matt] to arrange = provision s t ! *ief dispat*]1 ! sup]9t5d5t1 or any o!r (ficial may li/5 9 at w ^u a tra9 circuit to obs]ve ! "* ( ! s]vice4 ,! fact t ?is c be done & t ! op]ators "k x c be done has a v /rong t5d5cy to improve ! discipl9e4 ,! dispat*]s are s reliev$1 by ! elim9ation ( ! /ra9 ( cont9u\s telegraph+1 & c h&le _! "w s mu* m quickly ) ! telephone1 t 9 _m cases x has be5 f\nd possible to increase ! l5g? ( _! divisions f #cj to #ej p] c5t4 ,railroad ,conditions4 ,"o ( ! ma9 reasons t delay$ ! telephone = s _m ye>s 9 its entrance to ! dispat*+ field is t ! conditions 9 ?is field are l no?+ :i* has yet be5 met ) 9 comm]cial telephony4 ,!re 0 no sy/em develop$ = meet+ !m1 al?\gh ! elem5ts 7 at h&4 ,a railroad is divid$ up into a numb] ( divisions or dispat*]s' di/ricts ( v>y+ l5g?s4 ,^! l5g?s are dep5d5t on ! d5sity ( ! traffic ov] ! division4 ,9 "s cases a dispat*] w h&le n m ?an #be miles ( l9e4 ,9 o!r cases ?is di/rict may be #cjj miles long4 ,ov] ! l5g? ( "o ( ^! divisions ! telephone circuit ext5ds1 & ?is circuit may h ^u x #e or #ej /ations1 all ( :i* may be requir$ to li/5 ^u ! l9e at ! same "t4 ,x w be se5 f ?is t ! telephone dispat*+ circuit p>takes some:at ( ! nature ( a long-di/ance comm]cial circuit 9 its l5g?1 & x also resembles a rural l9e 9 t x has a l>ge numb] ( telephones ^u x4 ,reg>d+ ?ree o!r *>act]i/ics1 namely1 t _m ( ^! /ations may be requir$ to be 9 on ! circuit simultane\sly1 t !y mu/ all be signal$ selectively1 & t x mu/ also be possible to talk & signal on ! circuit simultane\sly1 a telephone tra9-dispat*+ circuit resembles no?+ 9 ! comm]cial field4 ,^! requirem5ts are ! ones :i* h necessitat$ ! developm5t ( special equipm5t4 ,transmitt+ ,ord]s4 ,! me?od ( giv+ ord]s is ! same z t foll[$ ) ! telegraph1 ) "o important exception4 ,:5 ! dispat*] transmits a tra9 ord] by telephone1 he writes out ! ord] z he speaks x into 8 transmitt]4 ,9 ?is way ! spe$ at :i* ! ord] is giv5 is regulat$ s t ev]yone receiv+ x c easily get x all d[n1 & a copy ( ! transmitt$ ord] is reta9$ by ! dispat*]4 ,all figures & prop] names are spell$ out4 ,!n aft] an ord] has be5 giv51 x is repeat$ to ! dispat*] by ea* man receiv+ x1 & he und]l9es ea* ^w z x comes 94 ,?is is n[ done s rapidly t a man c repeat an ord] m quickly ?an ! dispat*] c und]l9e4 ,! d\bt z to ! accuracy ) :i* x is possible to transmit in=mation by telephone has be5 dispell$ by ?is me?od ( proc$ure1 & ! safety ( telephone dispat*+ has be5 fully e/abli%$4 ,app>atus4 ,! app>atus :i* is employ$ at way/ations may be divid$ into two gr\ps--! selector equipm5t & ! telephone equipm5t4 ,! selector is an electro-me*anical device = r++ a bell at a way/ation :5 ! dispat*] op]ates a key correspond+ to t /ation4 ,at fir/1 z 9 telegraphy1 ! selector magnets 7 connect$ 9 s]ies 9 ! l9e1 b today all sy/ems bridge ! selectors across ! telephone circuit 9 ! same way & = ! same reasons t x is done 9 bridg+ p>ty-l9e "w4 ,!re are at ! pres5t "t ?ree types ( selectors 9 g5]al use1 & ! mileage op]at$ by means ( ^! is probably consid]ably ov] #ie p] c5t ( ! total mileage s op]at$ 9 ! c\ntry4 ,illu/ration3 ,fig4 #dge4 ,we/]n ,electric ,selector ,illu/ration3 ,fig4 #dgf4 ,we/]n ,electric ,selector ,! ,we/]n ,electric ,selector4 ,?is selector is ! late/ & p]haps ! simple/4 ,fig4 #dge %[s x ) its glass du/-pro( cov] on1 & ,fig4 #dgf %[s x ) ! cov] remov$4 ,?is selector is adapt$ = op]at+ at high spe$1 /ations be+ call$ at ! rate ( t5 p] second4 ,! op]at+ me*anism1 :i* is m\nt$ on ! front ( ! selector s z to be readily accessible1 works on ! c5tral-en]gy pr9ciple--! batt]y = its op]ation1 z well z = ! op]ation ( ! bell us$ 9 connection ) x1 bo? be+ locat$ at ! dispat*]'s (fice4 ,! bell batt]y may1 h[ev]1 be plac$ at ! way/ation if ?is is desir$4 ,! selector consi/s ( two electromagnets :i* are bridg$ 9 s]ies across ! telephone circuit & are ( v high imp$ance4 ,x is possible to place z _m ( ^! selectors z may be desir$ across a circuit )\t s]i\sly affect+ ! telephonic transmission4 ,direct-curr5t impulses s5t out by ! dispat*] op]ate ^! magnets1 "o ( :i* is sl[ & ! o!r quick-act+4 ,! fir/ impulse s5t out is a long impulse & pulls up bo? armatures1 !reby caus+ ! pawls above & bel[ ! small rat*et :eel1 %[n 9 ,fig4 #dgf1 to engage ) ?is :eel4 ,! rema9+ impulses op]ate ! quick-act+ magnet & /ep ! :eel ar\nd ! prop] numb] ( tee?1 b d n affect ! sl[-act+ magnet :i* rema9s held up by !m4 ,! pawl connect$ to ! sl[-act+ magnet m]ely s]ves to prev5t ! rat*et :eel f turn+ back4 ,atta*$ to ! rat*et :eel is a contact ^: position c be v>i$ 9 relation to ! /ation>y contact on ! left ( ! selector ) :i* ?is engages4 ,?is contact is set s t :5 ! :eel has be5 rotat$ ! desir$ numb] ( tee?1 ! two contacts w make & ! bell be rung4 ,any selector may ?us be adju/$ = any /ation1 & ! selectors are ?us int]*angeable4 ,:5 ! curr5t is remov$ f ! l9e at ! dispat*]'s (fice1 ! armatures fall back & ev]y?+ is re/or$ to normal4 ,an answ]-back signal is provid$ ) ?is selector dep5d5t ^u ! op]ation ( ! bell4 ,:5 ! selector at a /ation op]ates1 ! bell normally r+s = a few seconds4 ,! dispat*]1 h[ev]1 c hold ?is r+ = any l5g? ( "t desir$4 ,! keys employ$ at ! dispat*]'s (fice = op]at+ selectors are %[n 9 ,fig4 #dgg4 ,!re is "o key = ea* way/ation on ! l9e & ! dispat*] calls any /ation by m]ely giv+ ! correspond+ key a qu>t] turn to ! "r4 ,fig4 #dgh %[s ! me*anism ( "o ( ^! keys & ! means employ$ = s5d+ out curr5t impulses ov] ! circuit4 ,! key is adju/able & may be arrang$ = any /ation desir$ by means ( ! movable cams %[n on ! re> 9 ,fig4 #dgh1 ^! cams1 :5 occupy+ diff]5t positions1 s]v+ to cov] diff]5t numb]s ( ! tee? ( ! impulse :eel :i* op]ate ! impulse contacts4 ,illu/ration3 ,fig4 #dgg4 ,dispat*]'s ,keys ,illu/ration3 ,fig4 #dgh4 ,dispat*]'s ,key ,me*anism ,! ,gill ,selector4 ,! second type ( selector 9 ext5sive use ?r\gh\t ! c\ntry today is kn[n z ! ,gill1 aft] its inv5tor4 ,x is manufactur$ = bo? local-batt]y & c5tral-en]gy types1 ! latt] be+ ! late/ developm5t ( ?is selector4 ,) ! local-batt]y type1 ! way/ation bell r+s until /opp$ by ! dispat*]4 ,) ! c5tral-en]gy type x r+s a def9ite l5g? ( "t & c be held = a long] p]iod z is ! case ) ! ,we/]n ,electric selector4 ,! selector is op]at$ by comb9ations ( direct-curr5t impulses :i* are s5t out ov] ! l9e by keys 9 ! dispat*]'s (fice4 ,illu/ration3 ,fig4 #dgi4 ,gill ,selector ,! dispat*] has a key cab9et1 & calls 9 ! same way z already describ$1 b ^! keys in/ead ( s5d+ a s]ies ( quick impulses1 s5d a succession ( impulses ) int]vals betwe5 correspond+ to ! p>ticul> arrangem5t ( tee? 9 ! correspond+ way/ation selector :eel4 ,ea* key1 !re=e1 belongs def9itely ) a c]ta9 selector & c be us$ 9 connection ) no o!r4 ,a concrete example may make ?is cle>]4 ,! dispat*] may op]ate key ,no4 #adba4 ,?is key />ts a clockwork me*anism :i* impresses at regul> int]vals1 on ! telephone l9e1 direct-curr5t impulses1 ) int]vals betwe5 z foll[s3 #a-d-b-a4 ,!re is on ! l9e "o selector correspond+ to ?is comb9ation & x alone1 ( all ! selectors on ! circuit1 w /ep its :eel cle> ar\nd s t contact is made & ! bell is rung4 ,9 all ! o!rs1 ! pawls w h slipp$ out at "s po9t ( ! revolution & ! :eels w h return$ to _! normal positions4 ,! ,gill selector is %[n 9 ,fig4 #dgi4 ,x conta9s a d\ble-w\nd relay :i* is bridg$ across ! telephone circuit & op]ates ! selector4 ,?is relay has a resi/ance ( #d1ejj ohms & a high imp$ance1 & op]ates ! selector me*anism :i* is a special modification ( ! rat*et & pawl pr9ciple4 ,! ess5tial features ( ?is selector are ! /ep-up selector :eel & a "t :eel1 normally held at ! bottom ( an incl9$ track4 ,! op]ation ( ! selector magnet pu%es ! "t :eel up ! track & all[s x to roll d[n4 ,if ! magnet is op]at$ rapidly1 ! :eel does n get cle> d[n be=e be+ pu%$ back aga94 ,a small p9 on ! side ( ! pawl1 engag+ ! selector :eel normally1 opposes ! selector :eel tee? ne> _! out] po9ts4 ,:5 ! "t :eel rolls to ! bottom ( ! track1 h[ev]1 ! pawl is all[$ to drop to ! bottom ( ! too?4 ,"s ( ! tee? on ! selector :eel are =m$ s t !y w effectually engage ) ! pawl only :5 ! latt] is 9 normal position1 :ile o!rs w engage only :ile ! pawl is at ! bottom position2 ?us innum]able comb9ations c be made :i* w respond to c]ta9 comb9ations ( rapid impulses ) int]vals betwe54 ,! correct comb9ation ( impulses & int]vals /eps ! selector :eel cle> ar\nd s t a contact is made4 ,! selector :eels at all o!r /ations fail to rea* _! contact position because at "s po9t or po9ts 9 _! revolution ! pawls h slipp$ out1 all[+ ! selector :eels to return home4 ,! answ]-back is provid$ 9 ?is selector by means ( a few inductive turns ( ! bell circuit :i* are w\nd on ! selector relay4 ,! op]ation ( ! bell ?r\gh ^! turns induces an alt]nat+ curr5t 9 ! selector w9d+ :i* fl[s out on ! l9e & is he>d z a di/9ctive buzz+ noise by ! dispat*]4 ,illu/ration3 ,fig4 #dhj4 ,cumm+s-,wray ,dispat*]'s ,s5d] ,! ,cumm+s-,wray ,selector4 ,bo? ( ! selectors already describ$ are ( a type kn[n z ! individual-call selectors1 mean+ t only "o /ation at a "t c be call$4 ,if a plurality ( calls is desir$1 ! dispat*] calls "o /ation aft] ano!r4 ,! ?ird type ( selector 9 use today is ( a type kn[n z ! multiple-call1 9 :i* ! dispat*] c call simultane\sly z _m /ations z he desires4 ,! ,cumm+s-,wray selector & t ( ! ,kellogg ,swit*bo>d & ,supply ,company are ( ?is type & op]ate on ! pr9ciple ( syn*ron\s clocks4 ,:5 ! dispat*] wi%es to put ?r\gh a call1 he ?r[s ! keys ( all ! /ations t he desires & !n op]ates a />t+ key4 ,! bells at all ^! /ations are rung by "o op]ation4 ,! dispat*]'s s5d+ equipm5t ( ! ,cumm+s-,wray sy/em is %[n 9 ,fig4 #dhj1 & ! way/ation selector 9 ,fig4 #dha4 ,x is necess>y ) ?is sy/em = ! clocks at all /ations to be w\nd e eight days4 ,illu/ration3 ,fig4 #dha4 ,cumm+s-,wray ,selector ,9 ! dispat*]'s ma/] s5d] ! clock-"w me*anism op]ates a contact arm :i* %[s on ! face ( ! s5d] 9 ,fig4 #dhj4 ,!re is "o contact = e /ation on ! l9e4 ,! clock at ?is (fice & ! clocks at all ! way/ation (fices />t toge!r1 & x is by ?is means t ! /ations are signal$1 z w be describ$ lat]1 :5 ! detail$ op]ation ( ! circuits is tak5 up4 ,telephone ,equipm5t4 ,( no less importance ?an ! selective devices is ! telephone app>atus4 ,t :i* is "h illu/rat$ is ! product ( ! ,we/]n ,electric ,company1 to :om we are indebt$ = all ! illu/rations 9 ?is *apt]4 ,dispat*]'s ,transmitt]4 ,! dispat*]1 9 mo/ cases1 uses ! *e/ transmitt] simil> to t employ$ by swit*bo>d op]ators 9 e-day s]vice4 ,he is connect$ at all times to ! telephone circuit1 & = ?is reason equipm5t easy = him to we> is ess5tial4 ,9 v noisy locations he is equipp$ ) a d\ble head receiv]4 ,on acc\nt ( ! dispat*] be+ connect$ across ! l9e p]man5tly & ( 8 be+ requir$ to talk a l>ge "p ( ! "t1 !re is a sev]e dra9 on ! transmitt] batt]y4 ,= ?is reason /orage batt]ies are g5]ally us$4 ,illu/ration3 ,fig4 #dhb4 ,way/ation ,desk ,telephone ,way/ation ,telephones4 ,at ! way/ations v>i\s types ( telephone equipm5t may be us$4 ,p]haps ! mo/ common is ! famili> desk /& %[n 9 ,fig4 #dhb1 :i*1 = railroad s]vice1 is arrang$ ) a special hook-swit* lev] = use ) a head receiv]4 ,(t5 "s ( ! famili> sw++-arm telephone supports are us$1 9 connection ) head receiv]s1 b c]ta9 special types develop$ p>ticul>ly = railway use are advantage\s1 because 9 _m cases ! op]ator :o h&les tra9 ord]s is locat$ 9 a t[] :]e he mu/ also att5d to ! int]lock+ signals1 & = su* s]vice x is necess>y = him to be able to get away f ! telephone & back to x quickly4 ,! ,we/]n ,electric telephone arm develop$ = ?is use is %[n 9 ,fig4 #dhc4 ,9 ?is ! transmitt] & ! receiv] are s dispos$ z to con=m approximately to ! %ape ( ! op]ator's head4 ,:5 ! arm is ?r[n back out ( ! way x op5s ! transmitt] circuit by means ( a commutator 9 its base4 ,illu/ration3 ,fig4 #dhc4 ,telephone ,arm ,sid+ ,telephones4 ,two types ( sets are employ$ = sid+ purposes4 ,! fir/ is an ord9>y magneto wall in/rum5t1 :i* embodies ! special app>atus & circuit features employ$ 9 ! /&>d way/ation sets4 ,^! are us$ only :]e x is possible to locate !m indoors or 9 boo?s along ! l9e4 ,^! sets are p]man5tly connect$ to ! tra9 wire1 & s9ce ! *ances are small t m ?an "o ( !m w be 9 use at a "t1 !y are rung by ! dispat*]1 by means ( a regul> h& g5]ator1 :5 x is necess>y = him to signal a swit*+4 ,illu/ration3 ,fig4 #dhd4 ,wea!r-,pro( ,telephone ,set ,9 c]ta9 cases x is n feasible to locate ^! sid+ telephone sets indoors1 & to meet ^! conditions an iron wea!r-pro( set is employ$1 z %[n 9 ,figs4 #dhd & #dhe4 ,! app>atus 9 ?is set is treat$ ) a moi/ure-pro(+ comp\nd1 & ! cas+ itself is imp]vi\s to wea!r conditions4 ,illu/ration3 ,fig4 #dhe4 ,wea!r-,pro( ,telephone ,set ,portable ,tra9 ,sets4 ,portable telephone sets are be+ c>ri$ regul>ly on wreck+ tra9s & _! use is com+ into m & m g5]al acceptance on freight & pass5g] tra9s4 ,fig4 #dhf %[s "o ( ^! sets equipp$ ) a five-b> g5]ator = call+ ! dispat*]4 ,fig4 #dhg %[s a small set )\t g5]ator = conductors' & inspectors' use on l9es :]e ! dispat*] is at all times connect$ 9 ! circuit4 ,illu/ration3 ,fig4 #dhf4 ,portable ,telephone ,set ,illu/ration3 ,fig4 #dhg4 ,portable ,telephone ,set ,^! sets are connect$ to ! telephone circuit at any po9t on ! l9e by means ( a light portable pole arrang$ ) t]m9als at its out] extremity = hook+ ov] ! l9e wires1 & ) flexible conduct+ cords lead+ to ! portable set4 ,! use ( ^! sets among (ficials on _! private c>s1 among con/ruction & bridge gangs work+ on ! l9e1 & among telephone inspectors & repairm5 = report+ tr\ble1 is becom+ m & m g5]al4 ,we/]n ,electric ,circuits4 ,z already /at$1 a telephone tra9-dispat*+ circuit may be f #be to #cjj miles 9 l5g?1 & ^u ?is may be z _m /ations z c be h&l$ by "o dispat*]4 ,! l>ge/ kn[n numb] ( /ations ^u an exi/+ circuit ( ?is "* is #fe4 ,illu/ration3 ,fig4 #dhh4 ,dispat*]'s ,/ation--,we/]n ,electric ,sy/em ,dispat*]'s ,circuit ,arrangem5t4 ,! circuits ( ! dispat*]'s /ation 9 ! ,we/]n ,electric sy/em are %[n 9 ,fig4 #dhh1 ! op]ation ( :i* is briefly z foll[s3 ,:5 ! dispat*] wi%es to call any p>ticul> /ation1 he gives ! key correspond+ to t /ation a qu>t] turn4 ,?is s5ds out a s]ies ( rapid direct-curr5t impulses on ! telephone l9e ?r\gh ! contact ( a special telegraph relay :i* is op]at$ by ! key 9 a local circuit4 ,! telegraph relay is equipp$ ) sp>k-elim9at+ cond5s]s ar\nd its contacts & is ( heavy con/ruction ?r\gh\t 9 ord] to c>ry prop]ly ! s5d+ curr5t4 ,voltage4 ,! voltage ( ! s5d+ batt]y is dep5d5t on ! l5g? ( ! l9e & ! numb] ( /ations ^u x4 ,x ranges f #ajj to #cjj volts 9 mo/ cases4 ,:5 high] voltages are requir$ 9 ord] successfully to op]ate ! circuit1 x is g5]ally cu/om>y to in/all a telegraph repeat] circuit at ! c5t] ( ! l9e1 9 ord] to keep ! voltage )9 safe limits4 ,"o reason = limit+ ! voltage employ$ is t ! cond5s]s us$ 9 ! circuit w n /& mu* high] pot5tials )\t dang] ( burn+ out4 ,x is also possible to halve ! voltage by plac+ ! dispat*] 9 ! c5t] ( ! l9e1 f :i* position he may signal 9 two directions in/ead ( f "o end4 ,simultane\s ,talk+ & ,signal+4 ,ret>dation coils & cond5s]s w be notic$ 9 s]ies ) ! circuit ?r\gh :i* ! signal+ curr5t mu/ pass be=e go+ out on ! l9e4 ,^! are = ! purpose ( absorb+ ! noise :i* is caus$ by high-voltage batt]y1 ?us enabl+ ! dispat*] to talk & signal simultane\sly4 ,! #bej-ohm resi/ance connect$ across ! circuit ?r\gh "o back contact ( ! telegraph relay absorbs ! dis*>ge ( ! #f-micr(>ad cond5s]4 ,illu/ration3 ,fig4 #dhi4 ,selector ,set--,we/]n ,electric ,sy/em ,way/ation ,circuit4 ,! complete selector set = ! way/ations is %[n 9 ,fig4 #dhi1 & ! wir+ diagram ( its app>atus 9 ,fig4 #dij4 ,! fir/ impulse s5t out by ! key 9 ! dispat*]'s (fice is a long direct-curr5t impulse1 ! fir/ too? be+ ?ree or f\r times z wide z ! o!r tee?4 ,?is impulse op]ates bo? magnets ( ! selector & attracts _! armatures1 :i*1 9 turn1 cause two pawls to engage ) ! rat*et :eel1 :ile ! rema9+ quick impulses op]ate ! /epp+-up pawl & rotate ! :eel ! requisite numb] ( tee?4 ,ret>dation coils are plac$ 9 s]ies ) ! selector 9 ord] to *oke back any lightn+ dis*>ges :i* might come 9 ov] ! l9e4 ,! selector contact1 :5 op]at$1 closes a bell circuit1 & x w be not$ t bo? ! selector & ! bell are op]at$ f batt]y curr5t com+ ov] ! ma9 l9e ?r\gh v>iable resi/ances4 ,!re are1 ( c\rse1 a numb] ( selectors bridg$ across ! circuit1 & ! v>iable resi/ance at ea* /ation is s adju/$ z to give ea* approximately #aj milliamp]es1 :i* all[s a l>ge factor ( safety = l9e leakage 9 wet wea!r4 ,! drop across ! coils at #aj milliamp]es is #ch volts4 ,if ^! coils 7 n employ$1 x is cle> t ! selectors ne>] ! dispat*] w\ld get mo/ ( ! curr5t & ^? fur!r away v little4 ,illu/ration3 ,fig4 #dij4 ,selector ,set--,we/]n ,electric ,sy/em ,a "t-signal contact is also indicat$ on ! selector-circuit diagram ( ,fig4 #dij4 ,?is is common to all (fices & may be op]at$ by a special key 9 ! dispat*]'s (fice1 !reby enabl+ him to s5d out "t signals ov] ! telephone circuit4 ,illu/ration3 ,fig4 #dia4 ,gill ,dispat*]'s ,/ation ,gill ,circuits4 ,! circuit arrangem5t = ! dispat*]'s outfit ( ! ,gill sy/em is %[n 9 ,fig4 #dia4 ,?is is simil> to t ( ! ,we/]n ,electric sy/em j describ$4 ,! me?od ( op]ation also is simil>1 ! me*anical means ( accompli%+ ! selection be+ ! ma9 po9t ( diff]5ce4 ,9 ,fig4 #dib ! wir+ ( ! ,gill selector at a way/ation = local-batt]y s]vice is %[n4 ,! selector contact closes ! bell circuit 9 ! /ation & a few w9d+s ( ?is circuit are locat$ on ! selector magnets1 z %[n4 ,^! provide ! answ]-back by inductive means4 ,illu/ration3 ,fig4 #dib4 ,gill ,selector--,local ,batt]y ,fig4 #dic %[s ! wir+ ( ! way/ation1 c5tral-en]gy ,gill selector4 ,9 ?is case1 ! local batt]y = ! op]ation ( ! bell is omitt$ & ! bell is rung1 z is ! case ( ! ,we/]n ,electric selector1 by ! ma9 s5d+ batt]y 9 ! dispat*]'s (fice4 ,illu/ration3 ,fig4 #dic4 ,gill ,selector--,c5tral ,en]gy ,! s5d+ keys ( ^! two types ( circuits diff]1 9 t ) ! local-batt]y selector ! key contact is op5 aft] ! selector has op]at$1 & ! r++ ( ! bell mu/ be /opp$ by ! dispat*] press+ a button or call+ ano!r /ation4 ,ei!r ( ^! op]ations s5ds out a new curr5t impulse :i* releases ! selector & op5s its circuit4 ,) ! c5tral-en]gy selector1 h[ev]1 ! contacts ( ! s5d+ key at ! dispat*]'s (fice rema9 clos$ aft] op]ation = a def9ite l5g? ( "t4 ,?is is obvi\sly necess>y 9 ord] t batt]y may be kept on ! l9e = ! op]ation ( ! bell4 ,9 ?is case ! contacts rema9 clos$ dur+ a c]ta9 portion ( ! revolution ( ! key1 & ! bell /ops r++ :5 t portion ( ! revolution is complet$4 ,if1 h[ev]1 ! dispat*] desires to give any /ation a long] r+1 he may d s by keep+ ! key contacts clos$ ?r\gh an auxili>y /rap key z soon z he he>s ! answ]-back signal f ! call$ /ation4 ,cumm+s-,wray ,circuits4 ,! ,cumm+s-,wray sy/em1 z previ\sly /at$1 is ( ! multiple-call type1 op]at+ ) syn*ron\s clocks4 ,in/ead ( op]at+ "o key aft] ano!r 9 ord] to call a numb] ( /ations1 all ! keys are op]at$ at once & a />t+ key sets ! me*anism 9 motion :i* calls all ^! /ations ) "o op]ation4 ,fig4 #did %[s ! circuit arrangem5t ( ?is sy/em4 ,illu/ration3 ,fig4 #did4 ,cumm+s-,wray ,sy/em ,9 ord] to r+ "o or m /ations1 ! dispat*] presses ! correspond+ key or keys & !n op]ates ! />t+ key4 ,?is />t+ key ma9ta9s its contact = an appreciable l5g? ( "t to all[ ! clock me*anism to get "u way & get cle> ( ! releas+ magnet clut*4 ,clos+ ! />t+ key op]ates ! clock-releas+ magnet & also op]ates ! two telegraph-l9e relays4 ,^! s5d out an impulse ( batt]y on ! l9e op]at+ ! bridg$ #b1ejj-ohm l9e relays &1 9 turn1 ! selector releas+ magnets2 ?us1 all ! way/ation clocks />t 9 unison ) ! ma/] clock4 ,! second h& arbor ( ea* clock c>ries an arm1 :i* at ea* way/ation is set at a diff]5t angle ) ! normal position ?an t at any o!r /ation4 ,ea* ( ^! arms makes contact precisely at ! mom5t ! ma/]-clock arm is pass+ ov] ! contact correspond+ to t /ation4 ,if1 n[1 a giv5 /ation key is press$ 9 ! ma/] s5d]1 ! telegraph-l9e relays w aga9 op]ate :5 ! ma/]-clock arm rea*es t po9t1 s5d+ out ano!r impulse ( batt]y ov] ! l9e4 ,! selector contact at ! way/ation is clos$ at ?is mom5t2 !re=e1 ! clos+ ( ! relay contact op]ates ! r++ relay ?r\gh a local circuit1 z %[n4 ,! r++ relay is imm$iately lock$ ?r\gh its own contact1 ?us ma9ta9+ ! bell circuit clos$ until x is op5$ by ! key & ! r++ is /opp$4 ,z ! ma/]-clock arm passes ! la/ po9t on ! contact dial1 ! curr5t fl[s ?r\gh ! re/or+ relay op]at+ ! re/or+ magnet :i* releases all ! keys4 ,a pu% button is provid$ by means ( :i* ! keys may be manually releas$1 if desir$4 ,?is is us$ 9 case ! dispat*] presses a key by mi/ake4 ,ret>dation coils & v>iable resi/ances are provid$ at ! way/ation j z ) ! o!r selector sy/ems :i* h be5 describ$ & = ! same reasons4 ,! circuits ( ! op]ator's telephone equipm5t %[n 9 ,fig4 #die1 are also bridg$ across ! l9e4 ,?is app>atus is ( high imp$ance & ( a special design adapt$ to railroad s]vice4 ,!re may be any numb] ( telephones li/5+ 9 ^u a railroad tra9 wire at ! same "t1 & (t5 a dispat*] calls 9 five or six at once to give ord]s4 ,^! conditions h necessitat$ ! special circuit arrangem5t %[n 9 ,fig4 #die4 ,illu/ration3 ,fig4 #die4 ,telephone ,circuits ,! receiv]s us$ at ! way/ations are ( high imp$ance & are normally connect$1 ?r\gh ! hook swit*1 directly across ! l9e 9 s]ies ) a cond5s]4 ,:5 ! op]ator1 at a way/ation wi%es to talk1 h[ev]1 he presses ! key %[n4 ,?is puts ! receiv] across ! l9e 9 s]ies ) ! ret>dation coil & 9 p>allel ) ! second>y ( ! induction coil4 ,x closes ! transmitt] batt]y circuit at ! same "t ?r\gh ! prim>y ( ! induction coil4 ,! ret>dation coil is = ! purpose ( prev5t+ excessive side tone1 & x also increases ! imp$ance ( ! receiv] circuit1 :i* is a %unt on ! induction coil4 ,?is latt] coil1 h[ev]1 is ( a special design :i* p]mits j en\gh curr5t to fl[ ?r\gh ! receiv] to all[ ! dispat*] to int]rupt a way/ation op]ator :5 he is talk+4 ,! key us$ to close ! transmitt] batt]y is op]at$ by h& & is ( a non-lock+ type4 ,9 "s cases1 :]e ! op]ators are v busy1 a foot swit* is us$ 9 place ( ?is key4 ,! use ( su* a key or swit* 9 practical op]ation has be5 f\nd p]fectly satisfactory1 & x takes ! op]ators b a %ort "t to become us$ to x4 ,! circuits ( ! dispat*]'s (fice are simil>ly arrang$1 ,fig4 #die1 be+ design$ especially to facilitate _! op]ation4 ,9 o!r words1 z ! dispat*] is do+ mo/ ( ! "w on ! circuit1 8 receiv] is ( a l[-imp$ance type1 :i* gives him slightly bett] transmission ?an ! way/ations obta94 ,! key 9 8 transmitt] circuit is ( ! lock+ type1 s t he does n h to hold x 9 :ile talk+4 ,?is is = ! reason t ! dispat*] does mo/ ( ! talk+ on ?is circuit4 ,foot swit*es are also employ$ 9 "s cases by ! dispat*]s4 ,te/ ,bo>ds4 ,x is becom+ q a g5]al practice among ! railroads to in/all m ?an "o telephone circuit along _! rights-(-way4 ,9 _m cases 9 addition to ! tra9 wire1 a message circuit is also equipp$1 & q frequ5tly a block wire also op]at$ by telephone1 p>allels ^! two4 ,x is desirable on ^! circuits to be able to make simple te/s & also to be able to pat* "o circuit ) ano!r 9 cases ( em]g5cy4 ,illu/ration3 ,fig4 #dif4 ,te/ ,bo>d ,te/ bo>ds h be5 design$ = facilitat+ ?is "w4 ,^! consi/ ( simple plug & jack boxes1 ! g5]al appe>ance ( :i* is %[n 9 ,fig4 #dif4 ,! circuit arrangem5t ( "o ( ^! is %[n 9 ,fig4 #dig4 ,ea* wire comes into an individual jack z w be not$ on "o side ( ! bo>d1 & passes ?r\gh ! inside contact ( ?is jack1 out ?r\gh a simil> jack on ! opposite side4 ,! selector & telephone set at an (fice are tak5 (f ^! inside contacts ?r\gh a key1 z %[n4 ,! outside contacts ( ?is key are wir$ across two pairs ( cords4 ,n[1 assume ! tra9 wire comes 9 on jacks #a & #c1 & ! message wire on jacks #i & #aa4 ,9 case ( an accid5t to ! tra9 wire betwe5 two /ations1 x is desirable to pat* ?is connection ) a message wire 9 ord] to keep ! all-important tra9 wire work+4 ,! dispat*] in/ructs ! op]ator at ! la/ /ation :i* he c obta91 to ins]t plugs #a & #b 9 jacks #a & #aj1 & plugs #c & #d 9 jacks #c & #ab1 at ! same "t ?r[+ ! left-h& key4 ,!n1 obta9+ an op]ator beyond ! break by any available means1 he in/ructs him likewise to ins]t plugs #a & #b 9 jacks #i & #b1 & plugs #c & #d 9 jacks #aa & #d1 simil>ly ?r[+ ! left-h& key4 ,by trac+ ?is out1 x w be obs]v$ t ! tra9 wire is pat*$ ov] ! disabl$ section by means ( ! message circuit1 & t ! selector & ! telephone equipm5t are cut ov] on to ! pat*$ connections2 9 o!r words1 bridg$ across ! pat*+ cords4 ,illu/ration3 ,fig4 #dig4 ,circuits ( ,te/ ,bo>d ,x w also be se5 t ) ?is bo>d x is possible to op5 any circuit m]ely by plugg+ into a jack4 ,two wires c be %ort-circuit$ or a loop made by plugg+ two cords ( correspond+ colors into ! two jacks4 ,a gr\nd jack is provid$ = gr\nd+ any wire4 ,9 ?is way1 a v flexible arrangem5t ( circuits is obta9$1 & x is possible to make any ( ! simple te/s :i* are all t are usually requir$ on ?is type ( circuit4 ,block+ ,sets4 ,z 0 j m5tion$1 q frequ5tly 9 addition to tra9 wires & message circuits1 block wires are also op]at$ by telephone4 ,9 "s cases sep>ate telephone in/rum5ts are us$ = ! block+ s]vice1 b 9 o!rs ! same man h&les all ?ree circuits ov] ! same telephone4 ,! block wire is g5]ally a conv]t$ telegraph wire betwe5 /ations1 usually ( iron & usually gr\nd$4 ,x seldom ranges 9 l5g? ov] six miles4 ,illu/ration3 ,fig4 #dih4 ,block+ ,set ,:]e ! block wires are op]at$ z individual units ) _! own in/rum5ts1 x is unnecess>y to h any auxili>y app>atus to be us$ 9 connection ) !m4 ,:]e1 h[ev]1 !y are op]at$ z "p ( a sy/em & ! same telephone is us$ on ^! t is us$ on ! tra9 wire & message wire1 additional app>atus1 call$ a block+ set1 is requir$4 ,?is block+ set1 %[n 9 ,figs4 #dih & #dii1 0 develop$ especially = ?is s]vice by ! ,we/]n ,electric ,company4 ,z w be not$1 a repeat+ coil at ! top & a key on ! front ( ! set are wir$ 9 connection ) a pair ( tra9 wire cords4 ,?is repeat+ coil is = use 9 connect+ a gr\nd$ circuit to a metallic circuit1 z1 = in/ance1 connect+ a block wire to ! tra9 wire1 & is1 ( c\rse1 = ! purpose ( elim9at+ noise4 ,bel[ ! key are ?ree comb9$ jacks & signals4 ,"o block wire comes into ea* ( ^! & a private l9e may be br\ght into ! middle "o4 ,:5 ! next block r+s up1 a visual signal is display$ :i* op]ates a bell 9 ! (fice by means ( a local circuit4 ,! op]ator answ]s by plugg+ ! telephone cord ext5d+ f ! bottom ( ! set into ! prop] jack4 ,?is automatically re/ores ! signal & /ops ! bell4 ,illu/ration3 ,fig4 #dii4 ,block+ ,set ,bel[ ^! signals appe> f\r jacks4 ,"o is wir$ across ! tra9 wire2 "o across ! message wire2 & ! o!r two are bridg$ across ! two pairs ( pat*+ cords on ea* side ( ! set4 ,! op]ator answ]s a call on any circuit by plugg+ 8 telephone cord into ! prop] jack4 ,if a way/ation is n kept op5 9 ! ev5+1 or ! op]ator leaves x = any reason & locks up1 he c connect two blocks toge!r by means ( ! block-wire cords4 ,^! are arrang$ simply = connect+ two gr\nd$ circuits toge!r & s]ve to jo9 two adjac5t blocks1 !reby elim9at+ "o /ation4 ,a jack is wir$ across ^! cords1 s t ! way/ation op]ator c li/5 9 on ! connection if he s desires4 ,9 "s cases n only are ! telephone circuits br\ght into ! te/ bo>d1 b also two telegraph wires are loop$ ?r\gh ?is bo>d be=e go+ to ! peg swit*bo>d4 ,?is is becom+ q a frequ5t practice &1 9 times ( great em]g5cy1 enables pat*es to be made to ! telegraph wires z well z to ! telephone wires4 ,dispat*+ on ,electric ,railways4 ,z int]urban electric railways are becom+ m ext5d$1 & z _! traffic is becom+ heavi]1 !y approximate m closely to /eam me?ods ( op]ation4 ,x is n unusual = an electric railway to dispat* its c>s exactly z 9 ! case ( a /eam road4 ,!re is a t5d5cy1 h[ev]1 9 ?is class ( "w1 t[>d slightly diff]5t me?ods1 & ^! w be briefly outl9$4 ,on ^? electric railways :]e ! traffic is n especially heavy1 an ord9>y magneto telephone l9e is frequ5tly employ$ ) /&>d magneto in/rum5ts4 ,9 "s cases ! telephone sets are plac$ 9 wait+ rooms or boo?s along ! l9e ( ! road4 ,9 o!r cases x is n feasible to locate ! telephone indoors & !n iron wea!r-pro( sets1 su* z are %[n 9 ,figs4 #dhd & #dhe1 are m\nt$ directly on ! poles along ! l9e ( railway4 ,) a l9e ( ?is "* !re is usually "s c5tral po9t f :i* ord]s are issu$ & ! tra9m5 call ?is numb] :5 arriv+ at sid+s or :]ev] !y may ne$ to d s4 ,ano!r me?od ( in/all+ a telephone sy/em ^u electric railways is z foll[s3 ,in/ead ( in/rum5ts be+ m\nt$ 9 boo?s or on poles along ! l9e1 portable telephone sets are c>ri$ on ! c>s & jacks are locat$ at regul> int]vals along ! "r-(-way on ! poles4 ,! crew ( ! c> wi%+ to get 9 t\* ) ! c5tral (fice or ! dispat*]1 plugs into "o ( ^! jacks & uses ! portable telephone set4 ,at indoor /ations1 9 (fices or build+s belong+ to ! railroad1 ! regul> magneto sets may be employ$1 z 9 ! fir/ case outl9$4 ,on electric railway sy/ems :]e ! traffic is heavy1 ! tra9 or c> movem5ts may be h&l$ by a dispat*] j z on ! /eam railroad4 ,!re is usually "o diff]5ce1 h[ev]4 ,on a /eam road1 ! op]ators :o give ! tra9 crews _! ord]s & manipulate ! semaphore signals are locat$ at regul> int]vals 9 ! diff]5t way/ations4 ,no su* op]ators are usually f\nd on electric railways1 except1 p]haps1 at v important po9ts1 &1 !re=e1 x is necess>y = ! dispat*] to be able to signal c>s at any po9t & to get into communication ) ! crews ( ^! c>s4 ,he does ?is by means ( semaphores op]at$ by telephone selectors ov] ! telephone l9e4 ,! telephone circuit may be equipp$ ) any numb] ( selectors desir$1 & ! dispat*] c op]ate any p>ticul> "o )\t op]at+ any o!r "o on ! circuit4 ,ea* selector1 :5 op]at$1 closes a pair ( contacts4 ,?is completes a local circuit :i* ?r[s ! semaphore arm to ! dang] position1 at ! same "t giv+ ! dispat*] a di/9ctive buzz 9 8 e>1 :i* in=ms him t ! arm has actually mov$ to ?is position4 ,he c get ?is signal only by ! op]ation ( ! arm4 ,ea* semaphore is locat$ adjac5t to a telephone boo? 9 :i* is also plac$ ! re/or+ lev]1 by means ( :i* ! semaphore is set 9 ! cle> position by ! crew ( ! c> :i* has be5 signal$4 ,! wall-type telephone set is usually employ$ = ?is class ( s]vice1 b if desir$1 desk /&s or any ( ! v>i\s transmitt] arms may be us$4 ,x is necess>y = ! crew ( ! c> :i* fir/ approa*es a semaphore set at dang]1 to get out1 communicate ) ! dispat*]1 & re/ore ! signal to ! cle> position4 ,! dispat*] c n re/ore ! signal4 ,! signal is set only 9 ord] t ! tra9 crew may get into telephonic communication ) ! dispat*]1 & 9 ord] to d ?is1 x is necess>y = !m to g into ! boo? 9 any case4 ,footnote ,a3 ,we wi% p>ticul>ly to ackn[l$ge ! c\rtesy ( ! ,we/]n ,electric ,company 9 _! g5]\s assi/ance 9 ! prep>ation ( ?is *apt]4 ,,review ,,que/ions ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #aa--fh 99 99 99 99 99 #a4 ,:at are ! advantages ( a common-batt]y sy/em8 #b4 ,:5 is ! local batt]y to be pref]r$ to ! common-batt]y8 #c4 ,enum]ate ! diff]5t k9ds ( l9e signals4 #d4 ,make a diagram ( ! arrangem5t ( a direct l9e lamp signal4 #e4 ,:at is a direct l9e lamp ) balla/8 ,give sket*4 #f4 ,describe a l9e lamp ) relay4 #g4 ,:at is a pilot lamp & :at are its functions8 #h4 ,sket* ?ree diff]5t k9ds ( batt]ies appli$ to cord circuits4 #i4 ,:at is a sup]visory signal8 #aj4 ,make diagram ( a complete simple common-batt]y swit*bo>d circuit4 #aa4 ,:5 w ! sup]visory signal become op]ative8 #ab4 ,:at is ! c&le-p[] ( inc&esc5t lamps us$ = l9e & sup]visory signals8 #ac4 ,at :at voltages d !y op]ate8 #ad4 ,:at are visual signals8 #ae4 ,describe ! me*anical signal ( ! ,we/]n ,electric ,company4 #af4 ,give a %ort description ( ! g5]al assembly ( ! p>ts ( a simple common-batt]y swit*bo>d4 #ag4 ,:at is a transf] swit*bo>d8 #ah4 ,outl9e ! limitations ( a simple swit*bo>d4 #ai4 ,describe & sket* a plug-end$ transf] l9e4 #bj4 ,:y is ! plug-seat swit* n m widely adopt$ = use8 #ba4 ,make diagram ( an ord]-wire arrangem5t4 #bb4 ,:at are ! limitations ( ! transf] sy/em8 #bc4 ,:at are ! fundam5tal features ( ! multiple swit*bo>d8 #bd4 ,:at is a multiple jack8 #be4 ,:at is an answ]+ jack8 #bf4 ,make a diagram %[+ ! pr9ciple ( multiple swit*bo>ds4 #bg4 ,:at is ! busy signal8 #bh4 ,:at det]m9es ! size ( a multiple swit*bo>d8 #bi4 ,:at is ! use ( ! int]m$iate di/ribut+ frame8 #cj4 ,make diagram ( ! s]ies magneto multiple swit*bo>d & describe its op]ation4 #ca4 ,:at are ! defects ( ?is sy/em8 #cb4 ,give a diagram ( ! bran* t]m9al magneto multiple swit*bo>d4 #cc4 ,give a diagram & a %ort description ( ! ,mon>* magneto multiple swit*bo>d4 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #fi--acd 99 99 99 99 99 #a4 ,sket* & describe ! l9e circuit ( ! common-batt]y multiple swit*bo>d ( ! ,bell companies4 #b4 ,make a diagram ( ! cord circuit ( ! ,we/]n ,electric /&>d multiple common-batt]y swit*bo>d4 #c4 ,describe ! busy te/ 9 ?is sy/em4 #d4 ,:at is ! function ( ! ord]-wire circuits8 #e4 ,:at is jump] wire8 #f4 ,give a %ort description ( ! relay m\nt+ 9 ! /&>d ,no4 #a relay bo>d ( ! ,we/]n ,electric ,company4 #g4 ,:at is ! ultimate capacity ( ! ,no4 #a ,we/]n ,electric swit*bo>d8 #h4 ,:at is ! capacity ( ! ,no4 #aj ,we/]n ,electric swit*bo>d8 #i4 ,h[ does ?is swit*bo>d ,no4 #aj diff] f ,no4 #a8 #aj4 ,give a diagram ( ! two-wire l9e circuit ( ! ,kellogg ,company4 #aa4 ,:at is ! capacity ( ! cond5s] ( ! cord circuit 9 ! =ego+ sy/em8 #ab4 ,give a complete diagram ( ! ,kellogg two-wire bo>d4 #ac4 ,describe ! busy te/ 9 ?is sy/em4 #ad4 ,give diagram ( ! ,/romb]g-,c>lson multiple-bo>d circuit4 #ae4 ,:at is ! mo/ important piece ( app>atus 9 a multiple swit*bo>d8 #af4 ,:at is ! spac+ ( ! multiple jacks 9 ! ,no4 #a ,we/]n ,electric swit*bo>d8 #ag4 ,h[ d ! relays ( ! ,we/]n ,electric ,company diff] f ^? ( o!r companies8 #ah4 ,describe ! relay con/ruction ( ! ,mon>* ,telephone ,company4 #ai4 ,:at is meant by int]-(fice trunk+8 #bj4 ,:at is ! pres5t practice 9 ,am]ica z to ! capacity ( multiple ho>ds8 #ba4 ,:at is ! t5d5cy 9 ,europe reg>d+ ! capacity ( multiple bo>ds8 #bb4 ,discuss ! pref]5ces 9 ,am]ican practice4 #bc4 ,/ate ! diff]5t me?ods ( trunk+ betwe5 ex*anges4 #bd4 ,:5 are two-way trunks employ$8 #be4 ,make diagram ( ! ,we/]n ,electric int]-(fice connection sy/em4 #bf4 ,describe ! /&>d f\r-p>ty l9e trunk r++ key ( ! ,we/]n ,electric ,company4 #bg4 ,sket* & describe a keyless trunk4 #bh4 ,give diagram ( ! int]-(fice connection ( ! ,kellogg sy/em4 #bi4 ,h[ does ?is sy/em diff] f ! ,we/]n ,electric 9 reg>d to ! r++8 #cj4 ,:y are ! ,a & ,b swit*bo>ds 9 l>ge ex*anges entirely sep>at$8 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #ace--bbf 99 99 99 99 99 #a4 ,:at is ! g5]al object ( automatic telephone sy/ems8 #b4 ,:at are ! common argum5ts aga9/ ^! sy/ems & h[ are !y met8 #c4 ,give ! op]ations t ! call+ subscrib] has to g ?r\gh 9 any "o ( ! successful sy/ems4 #d4 ,dur+ call+ :at is happ5+ at ! c5tral (fice8 #e4 ,describe ! action ( ! ,/r[g] or ,automatic ,electric ,company select+ swit*4 #f4 ,:at is ! function ( a l9e swit*8 #g4 ,describe ! ,/r[g] s*eme ( trunk+ & illu/rate its action by diagram4 #h4 ,make a diagram ( ! sub-/ation app>atus & connections4 #i4 ,make a diagram ( ! l9e swit* unit4 #aj4 ,describe ! action ( ! v>i\s gu>d+ features necess>y to protect a busy l9e4 #aa4 ,make a simple diagram ( ! circuits ( ! fir/ selector4 #ab4 ,give ! functions & op]ations ( ! connector4 #ac4 ,give a diagram ( connect+ circuits4 #ad4 ,tell all y c reg>d+ ! batt]y supply to ! connect$ subscrib]4 #ae4 ,h[ are subscrib]s disconnect$ aft] !y are ?r\gh talk+8 #af4 ,describe a multi-(fice sy/em4 #ag4 ,give a diagram ( circuits ( ! trunk repeat]4 #ah4 ,make a complete diagram ( ! connections betwe5 a call+ & a call$ subscrib] 9 an automatic sy/em4 #ai4 ,:at is ! rot>y connector8 #bj4 ,describe ! sub-/ation equipm5t ( ! ,lorim] automatic sy/em4 #ba4 ,describe ! ,lorim] c5tral-(fice app>atus4 #bb4 ,give a description ( ! progress ( a call f its in/itution to ! f9al disconnection 9 ! ,lorim] sy/em4 #bc4 ,:at is ! automanual sy/em8 #bd4 ,give g5]al features ( ! op]ation 9 ! automanual sy/em4 #be4 ,describe ! automanual sy/em subscrib]s' app>atus4 #bf4 ,give a description ( ! automanual c5tral-(fice equipm5t4 ,,review ,,que/ions ,,on ,,subject ,,( ,,telephony ,,pages #bbg--bgj 99 99 99 99 99 #a4 ,:at k9ds ( curr5ts are employ$8 #b4 ,:at types ( p[] plants are us$8 #c4 ,describe ! s\rces ( curr5t suppli$ = ! op]ator's transmitt] curr5t & r++ curr5t4 #d4 ,make a diagram ( ! ,w>n] pole *ang]4 #e4 ,make a diagram ( pole *ang]s = h>monic r++4 #f4 ,:at is a multi-cyclic g5]ator set8 #g4 ,make a diagram ( gov]nor = h>monic r++ g5]ators4 #h4 ,describe ! v>i\s prim>y s\rces ( p[]4 #i4 ,make a diagram ( ! m]cury-arc-rectifi] circuits4 #aj4 ,:at provision aga9/ breakd[n is made8 #aa4 ,tell all y c ab\t ! /orage batt]y--its con/ruction & its op]ation4 #ab4 ,:at is a pilot cell8 #ac4 ,describe ! swit*es1 met]s1 & protective devices us$ on ! p[] swit*bo>d4 #ad4 ,give a diagram %[+ a typical example ( a common-batt]y manual swit*bo>d equipm5t & circuits4 #ae4 ,give ! ma9 po9ts conc]n+ ! con/ruction ( a c5tral-(fice build+4 #af4 ,:at provision %\ld be made = cable runways8 #ag4 ,make a sket* ( a small c5tral-(fice floor plan4 #ah4 ,describe ! ,we/]n ,electric ma9 & int]m$iate frames4 ,give diagrams4 #ai4 ,give pr9cipal po9ts reg>d+ small (fice t]m9al app>atus4 #bj4 ,give types ( l9e circuits4 #ba4 ,describe ! typical equipm5t ( a l>ge manual (fice4 ,give floor plans4 #bb4 ,give floor plan ( an automatic (fice4 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #bga--cbj 99 99 99 99 99 #a4 ,:at is a private-bran* ex*ange8 #b4 ,:at does ,p4 ,b4 ,x4 mean8 #c4 ,:at is ! function ( ! private-bran* ex*ange op]ator8 #d4 ,describe ! key type ( a small private-bran* ex*ange swit*bo>d4 #e4 ,describe ! diff]5t me?ods ( sup]vision ( private-bran* connections4 #f4 ,describe ! automatic equipm5t ( ! common-batt]y type 9 private-bran* ex*anges4 #g4 ,h[ is secrecy ( individual l9es obta9$ 9 a private-ex*ange equipm5t8 #h4 ,:at is an int]communicat+ sy/em8 #i4 ,sket* a magneto int]communicat+ sy/em4 #aj4 ,sket* & describe a plug type common-batt]y int]communicat+ sy/em4 #aa4 ,sket* & describe ! action ( ! pu% button 9 ! ,mon>* sy/em & 9 ! ,we/]n ,electric sy/em4 #ab4 ,sket* & describe ! ,mon>* int]communicat+ sy/em4 #ac4 ,:at is ! (fice ( ! junction box 9 ?is sy/em8 #ad4 ,:at is a long-di/ance message8 #ae4 ,:at is ! function ( ! repeat+ coil 9 ! long-di/ance l9e8 #af4 ,:i* is ! simple/ =m ( long-di/ance swit*8 #ag4 ,:at is a phantom circuit8 #ah4 ,"u :at control is ! r++ ( ! subscrib] 9 long-di/ance calls8 #ai4 ,:at is meant by ticket pass+8 #bj4 ,:at p>ticul> advantage has a common-batt]y set on long-di/ance l9es8 #ba4 ,give a typical load curve = telephone traffic4 #bb4 ,:y is traffic a /udy ( importance8 #bc4 ,/ate ! function ( ! int]m$iate di/ribut+ frame4 #bd4 ,/ate ! diff]5t me?ods ( traffic /udy4 #be4 ,:at is ! trunk+ factor8 #bf4 ,def9e trunk+ effici5cy4 #bg4 ,enum]ate "s ( ! elem5ts ^u :i* ! quality ( s]vice 9 a manual sy/em dep5ds4 #bh4 ,:at is team "w8 #bi4 ,h[ does ! co/ ( telephone s]vice v>y8 #cj4 ,:at two g5]al me?ods ( *>g+ = telephone s]vice are 9 use8 #ca4 ,describe a calculagraph & h[ is x us$8 #cb4 ,h[ are toll connections tim$ by ! ,mon>* ,telephone ,company8 #cc4 ,sket* & describe ! ,we/]n ,electric ,company l9e circuit & s]vice met]4 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #cba--ceh 99 99 99 99 99 #a4 ,describe a phantom circuit ) diagram4 #b4 ,expla9 h[ two phantoms may be jo9$ by a physical circuit4 #c4 ,:i* are ! bett]1 phantom or physical circuits1 & :y8 #d4 ,expla9 h[ ! simplex circuit diff]s f ! phantom telephone circuit4 #e4 ,:y are n telegraph wires z s]viceable = telephone "w z telephone wires are = telegraph "w8 #f4 ,give ! names ( ! diff]5t p>ts ( a railway composite set & expla9 me?od ( op]at+4 #g4 ,/ate ! causes ( ! introduction ( ! telephone into ! tra9 dispat*+ field & expla9 ! advantages x has ov] ! telegraph = ?is "w4 #h4 ,9 transmitt+ ord]s = tra9 dispat*+1 h[ are mi/akes avoid$8 #i4 ,describe ! ,we/]n ,electric selector & expla9 its use4 #aj4 ,9 :at way does ! ,gill selector diff] f ! ,we/]n ,electric8 #aa4 ,:at special feature does ! multiple coil selector possess8 #ab4 ,:at special arrangem5t is provid$ = ! tra9 dispat*] 9 noisy locations8 #ac4 ,h[ c a man on a wreck+ tra9 get connection ) ! tra9 dispat*]8 #ad4 ,:at is ! usual limit 9 l5g? ( a telephone tra9 dispat*+ circuit & :at is ! l>ge/ numb] ( /ations at pres5t exi/+ on su* a circuit8 #ae4 ,:at is ! voltage ( ! s5d+ batt]y = a tra9 dispat*]'s circuit & ^u :at is x dep5d5t8 #af4 ,= :at purpose is a repeat] circuit us$8 #ag4 ,h[ is ! noise caus$ by a high voltage batt]y absorb$ s t ! dispat*] may talk & signal simultane\sly8 #ah4 ,draw a diagram %[+ ! circuit arrangem5t = ! dispat*]'s outfit ( ! ,gill sy/em4 #ai4 ,expla9 fully ! purpose ( ! ret>dation coil 9 connection ) a way/ation set4 #bj4 ,9 case ( accid5t to a tra9 wire betwe5 two /ations1 h[ c ! connection be pat*$ if ! road is also equipp$ ) a message circuit 9 addition to ! tra9 wire8 #ba4 ,:y d "s railroads h block wires 9 addition to tra9 wires & message circuits8 #bb4 ,if a way/ation on a block wire is to be cut out = any l5g? ( "t1 by :at me?od c ! two adjac5t blocks be connect$1 elim9at+ ! /ation betwe58 #bc4 ,:at are "s ( ! me?ods us$ = dispat*+ on electric railways :]e ! traffic is n especially heavy8 #bd4 ,on an electric road 9 case a c> approa*es a semaphore set at dang]1 :at mu/ ! crew ( ! c> d8 ,,index ,! page numb]s ( ?is volume w be f\nd at ! bottom ( ! pages2 ! numb]s at ! top ref] only to ! section4 ,a ,automanual sy/em #bah automatic di/ribution ( calls #bbc automatic swit*+ equipm5t #bbb build+ up a connection #bbd *>act]i/ics ( #bah op]ation #bai op]ator's equipm5t #bbj sett+ up a connection #bbd spe$ 9 h&l+ calls #bbd subscrib]'s app>atus #bai ,automatic desk /& #aeh ,automatic ,electric ,company's telephone sy/em #adi automatic sub-(fices #bja connector #ahe function ( #ahe location ( #ahf op]ation ( #ahf fir/ selector op]ation #agi function ( l9e swit* #aeb l9e swit* #aec1 #afc bridge cut-(f #agc circuit op]ations #afg gu>d+ functions #agc l9e & trunk contacts #afd lock+ segm5t #agb ma/] swit* #aga relation (1 to connectors #agd /ructure ( #aff summ>y ( op]ation #agd trunk ratio #afe trunk selection #afe multi-(fice sy/em #aif p>ty l9es #bjb release aft] conv]sation #aif rot>y connector #bjb second selector op]ation #ahb select+ swit*es #aec1 #age release me*anism #agh side swit* #age subdivision ( subscrib]s' l9es #aeb subscrib]s' /ation app>atus #aeh op]ation #afj bell & transmitt] spr+s #afj gr\nd spr+s #afj impulse spr+s #afa release spr+s #afc r++ spr+s #afc sali5t po9ts #afc trunk+ #aed connector action #aeg fir/ selector action #aef l9e swit* action #aed second selector action #aef two-wire automatic sy/ems #bjc two-wire & ?ree-wire sy/ems #aeg und]ly+ feature ( trunk+ sy/em #aec ,automatic telephone sy/ems #ace argum5ts aga9/ #ace attitude ( public #ada complexity #acf exp5se #adj flexibility #adj subscrib]'s /ation equipm5t #adb automatic vs4 manual #adc comp>ative co/s #adb def9ition #ace me?ods ( op]ation #adc fundam5tal idea #adg gr\p+ ( subscrib]s #ade local & int]-(fice trunks #adh ,lorim] sy/em #add magnet vs4 p[]-driv5 swit*es #add ,automatic telephone sy/ems me?ods ( op]ation multiple vs4 trunk+ #ade outl9e ( action #adf ,/r[g] sy/em #adc te/+ #adh trunk+ betwe5 gr\ps #ade ,automatic wall set #aeh ,b ,block+ sets #cee ,busy te/ #dh busy-te/ faults #ej pot5tial ( te/ ?imbles #di pr9ciple #di ,c ,circuits #cba applications #cbb composite #cbf phantom #cba transmission ov] #cbd transpositions #cbc railway composite #cbg r++ #cbg simplex #cbd ,common-batt]y multiple swit*bo>d #fi assembly #ajf ,dean multiple bo>d #ic cord circuit #id l9e circuit #ic li/5+ key #id r++ keys #id te/ #id ,kellogg two-wire multiple bo>d #hd batt]y fe$ #hh busy te/ #ij complete cord & l9e circuit #hh cord circuit #hf l9e circuit #he summ>y ( op]ation #ia sup]visory signals #hg wir+ ( l9e circuit #ib multiple swit*bo>d app>atus #ig jacks #ii lamp jacks #ajj relays #aja ,/romb]g-,c>lson multiple bo>d #if cord circuit #if sup]visory signals #ig te/ #ig ,we/]n ,electric ,no4 #a relay bo>d #fi capacity range #hj cord circuit #ga functions ( di/ribut+ frames #gg l9e circuit #fi modifi$ relay w9d+s #gi op]ation #gb op]ator's circuit detail #ge ord]-wire circuits #gh pilot signals #gi relay m\nt+ #hj te/+--call$ l9e busy #ge te/+--call$ l9e idle #gd wir+ ( l9e circuit #gf ,we/]n ,electric ,no4 #aj bo>d #hj circuits #ha economy #hd op]ation #hc te/ #hc ,common-batt]y swit*bo>d #aa advantages ( op]ation #aa common batt]y vs4 magneto #ab cord circuit #bj batt]y supply #bj complete circuit #ba sup]visory signals #ba cycle ( op]ations #bc jacks #cj lamps #bd m\nt+ #be l9e signals #ad direct-l9e lamp #ad direct-l9e lamp ) balla/ #ae l9e lamp ) relay #ag pilot signals #ag me*anical signals #bg ,kellogg #bh ,mon>* #bh ,we/]n ,electric #bg relays #bh swit*bo>d assembly #ca ,composite circuits #cbf ,connector #ahe ,cord circuit #bj ,cord circuit batt]y supply #bj complete circuit #ba sup]visory signals #ba ,cord-rack connectors #ff ,cumm+s-,wray selector #cdb ,d ,dean multiple bo>d #ic ,dispat*]s' keys #cci ,dispat*+ on electric railways #cef ,g ,gill selector #cda ,h ,h\s+ c5tral-(fice equipm5t #bdi arrangem5t ( app>atus 9 small manual (fices #beb comb9$ ma9 & int]m$iate frames #bec floor plans = #beb types ( l9e circuits #bee automatic (fices #bfg typical automatic (fice #bgj c5tral-(fice build+ #bdi fire haz>d #bdi provision = cable runways #bea provision = employes #bea size ( build+ #bej /r5g? ( build+ #bej l>ge manual (fice #bef ,i ,int]communicat+ sy/ems #bhb common-batt]y sy/ems #bhc ,kellogg plug type #bhd ,kellogg pu%-button type #bhe ,mon>* sy/em #bhg ,we/]n ,electric sy/em #bhe def9ition #bhb limitations #bhb = private-bran* ex*anges #bij simple magneto sy/em #bhb ,j ,jacks #cj ,k ,kellogg me*anical signal #bh ,kellogg trunk circuits #abe ,kellogg two-wire multiple bo>d #hd ,keybo>d wir+ #fg ,l ,lamp m\nt+ #be ,lamps #bd ,l9e signals #ad direct-l9e lamp #ad direct-l9e lamp ) balla/ #ae l9e lamp ) relay #ag pilot signals #ag ,l9e swit* #afc ,long-di/ance swit*+ #bic def9itions #bic c5t]-*eck+ #big op]ators' ord]s #bid by call circuits #bid by telegraph #bid p>ticul> p>ty calls #bie swit*+ ?r\gh local bo>d #bic ticket pass+ #bif trunk+ #bie high-voltage toll trunks #bie ?r\gh r++ #bie two-numb] calls #bid use ( repeat+ coil #bic way/ations #big ,lorim] automatic sy/em #add1 #bje c5tral-(fice app>atus #bjh connective division #baj sectional app>atus #bji swit*es #bac int]connector #bad int]connector selector #bad prim>y connector #bac rot>y swit* #bac second>y connector #bad signal transmitt] controll] #bad op]ation #bae subscrib]'s /ation equipm5t #bjf ,m ,magneto multiple swit*bo>d #ec bran*-t]m9al multiple bo>d #eh arrangem5t ( app>atus #fa magnet w9d+s #fa op]ation #fj field ( utility #ec mod]n magneto multiple bo>d #fc assembly #ff cord circuit #fd te/ #fb ,magneto multiple swit*bo>d s]ies-multiple bo>d #ed defects #eg op]ation #ef ,measur$ s]vice #caj local s]vice #caf met] me?od #caf prepaym5t me?od #cah ticket me?od #caf rates #caj toll s]vice #caa long haul #caa %ort haul #caa tim+ toll connections #cab units ( *>g+ #caa ,me*anical signals #bg ,kellogg #bh ,mon>* #bh ,we/]n ,electric #bg ,m]cury-arc rectifi] circuits #bcg ,mon>* visual signal #bh ,multi-(fice ex*anges1 necessity = #aji ,multiple swit*bo>d #dc busy te/ #dh cord circuits #df diagram %[+ pr9ciple ( #dg d\ble connections #df field ( ea* op]ator #ea field ( utility #dc influ5ce ( traffic #eb l9e signals #de multiple feature #dc ,p ,phantom circuit #cba ,pilot signals #ag ,plug-seat swit* #ch ,pole *ang]s = h>monic r++ #bca ,p[] plants #bbg auxili>y signal+ curr5ts #bcc curr5ts employ$ #bbg alt]nat+ curr5t #bbg direct curr5t #bbg op]ator's transmitt] supply #bbh p[] plant circuit #bdh p[] swit*bo>d #bdf met]s #bdf protective devices #bdh swit*es #bdf prim>y s\rces #bcd *>g+ f direct-curr5t ma9s #bcd *>g+ dynamos #bce m]cury-arc rectifi]s #bcf rot>y conv]t]s #bcd provision aga9/ breakd[n #bcg capacity ( p[] units #bch duplicate *>g+ ma*9es #bch duplicate prim>y s\rces #bch duplicate r++ ma*9es #bch r++-curr5t supply #bbi magneto g5]ators #bbi pole *ang]s #bbi r++ dynamos #bcb /orage batt]y #bci initial *>ge #bda in/allation #bdj l[ cells #bdd op]ation #bdb ov]*>ge #bdc pilot cell #bdc regul> *>ge #bdd replac+ batt]ies #bde s$im5t #bde types #bbg common-batt]y sy/ems #bbh magneto sy/ems #bbh ,p[] swit*bo>d #bdf ,private-bran* ex*anges #bga ) automatic (fices #bgh secrecy #bgi batt]y supply #bgi circuits1 key-type bo>d #bgf def9itions #bga desirable features #bha functions ( ! private-bran* ex*ange op]ator #bgb m>k+ ( app>atus #bha private-bran* swit*bo>ds #bgc common-batt]y type #bgc cord type #bge key type #bge magneto type #bgc r++ curr5t #bhj sup]vision ( private-bran* connections #bgg ,r ,relays #bh ,rot>y connector #bjb ,s ,select+ swit*es #age ,selector #age ,simplex circuits #cbd ,/orage batt]y #bci ,/orage cell #bdj ,/romb]g-,c>lson multiple bo>d #if ,/r[g] automatic sy/em #adc ,subscrib]s' bo>d #bei-bfa ,swit*bo>d assembly #ca ,t ,table automanual sy/em "t data #bbe automatic sy/ems1 messages p] trunk 9 #cje call+ rates #cjb long-di/ance gr\ps1 messages p] trunk 9 #cje manual sy/em1 messages p] trunk 9 #cjd out-trunk+1 effect (1 on op]ator's capacity #cjc subscrib]s' wait+ "t #bbf ,telephone traffic #bih importance ( traffic /udy #cjj me?ods ( traffic /udy #cja obs]vation ( s]vice #cjh quality ( s]vice #cje accuracy & promptness #cjg answ]+ "t #cjf busy & don't answ] calls #cjg c\rtesy & =m #cjg disconnect+ "t #cjf enunciation #cjh team "w #cjh rates ( call+ #cjj repres5tative traffic data #cjb call+ rates #cjb op]ators' loads #cjb toll traffic #cjd trunk effici5cy #cjc trunk+ factor #cjc traffic v>iations #bih busy h\r ratio #bii unit ( traffic #bih ,telephone tra9 dispat*+ #ccc advantages #cce app>atus #cch ,cumm+s-,wray selector #cdb dispat*]'s transmitt] #cdc ,gill selector #cda portable tra9 sets #cde sid+ telephones #cde way/ation telephones #cdd ,we/]n ,electric selector #cch block+ sets #cee causes ( its introduction #ccd ,cumm+s-,wray circuits #cej on electric railways #cef ,gill circuits #cdi railroad conditions #ccg rapid gr[? #ccc te/ bo>ds #cec transmitt+ ord]s #ccg way/ation circuits #cdh ,we/]n ,electric circuits #cdg ,telephone tra9-dispat*+ circuit ,cumm+s-,wray #cej ,gill #cdi way/ation #cdh ,we/]n ,electric #cdg ,te/ bo>ds #cec ,transf] swit*bo>d #cd field ( usefulness #da h&l+ transf]s #ch limitations #dj plug-seat swit* #ch transf] l9es #ce jack-end$ trunk #ce plug-end$ trunk #cg ,trunk+ 9 multi-(fice sy/ems #aji classification #aab "o-way trunks #ajc two-way trunks #aab ,kellogg trunk circuits #abe necessity = ex*anges #aji ,we/]n ,electric trunk circuits #aaf ,w ,w>n] pole *ang] #bcj ,way/ation telephones #cdd ,we/]n ,electric me*anical signal #bg selector #cch trunk circuits #aaf ,transcrib]'s ,notes4 ,spell+ v>iants :]e x wasn't possible to det]m9e ! au?or's int5t 7 left z is4 ,^! include3 clockwork & clock-"w2 doorkeep] & door-keep]2 int]relation & int]-relation2 multicyclic & multi-cyclic2 r$esign & re-design1 along ) d]ivatives4 ,add$ clos+ d\ble quote 9 ,/e9metz entry 9 li/ ( au?orities3 ,!oretical ,elem5ts ( ,electrical ,eng9e]+4 ,*ang$ swit*-hook to swit* hook on page #hh3 ! subscrib]'s swit* hook4 ,page #ajg says !re is room = #cjj banks ( #ajj multiple jacks1 b !n says ?is all[s = #c1jjj multiple jacks 9 all1 r ?an #cj1jjj4 ,bas$ on ! figure1 #cjj banks %\ld be #cj banks1 :i* w\ld correct ! ari?metic4 ,h[ev]1 ,i did n *ange ?is4 ,*ang$ bi-pa?s to by-pa?s on page #ahe3 circuits or by-pa?s4 ,*ang$ app>>us to app>atus on page #bji3 ,! sectional app>atus4 ,*ang$ two numb] to two-numb] on page #cab3 ! two-numb] calls are ticket$4 ,on page #ccc1 a p>agraph beg9s ) ,x has be5 only )9 ! pa/ ?ree few4 ,p]haps ! au?or meant ,x has be5 only )9 ! pa/ ?ree ye>s or ,x has be5 only )9 ! pa/ few ye>s4 ,b s9ce ,i didn't "k1 ,i left is z is4 ,*ang$ !m a9 to ! ma9 on page #ccc3 on ! ma9 l9e4 ,*ang$ wea!rpro( to wea!r-pro( on page #ceg3 iron wea!r-pro( sets4 ,*ang$ int](fice to int]-(fice ?ree times on page #cfd1 to mat* ! spell+ 9 ! body ( ! docum5t3 meant by int]-(fice trunk+2 int]-(fice connection sy/em2 ( ! int]-(fice connection4 ,*ang$ break-d[n to breakd[n on page #cfg3 provision aga9/ breakd[n4 ,*ang$ way-/ation to way/ation twice on page #cgb3 ) a way/ation set2 & a way/ation on a block wire4 ,*ang$ way /ations to way/ations on page #cge1 9 ! entry = ,long-di/ance swit*+4 ,ea* page ( ! ,index repeat$ ?is text3 ,note4--,= page numb]s see foot ( pages4 ,!y 7 remov$4