,transcrib]'s ,note3 ,ref]5ces to page numb]s 9 table ( cont5ts & index remov$1 z well z ! numb]s !mselves4 ,illu/ration3 ,,alex&] ,,graham ,,bell ,! ,inv5tor ( ! ,telephone4 ,cyclop$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 ,au?ors & ,collaborators 99 99 99 99 99 ,,kemp/] ,b4 ,,mill]4 ,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$]ick ,,coll9s ,editor1 ,coll9s ,wireless ,bullet9 ,au?or ( ,wireless ,telegraphy1 ,its ,hi/ory1 ,!ory1 & ,practice 99 99 99 99 99 ,,francis ,b4 ,,crock]1 ,e4,m41 ,ph4,d4 ,head1 ,dep>tm5t ( ,electrical ,eng9e]+1 ,columbia ,univ]sity ,pa/-,presid5t1 ,am]ican ,in/itute ( ,electrical ,eng9e]s 99 99 99 99 99 ,,morton ,,ar5dt1 ,e4,e4 ,in/ructor 9 ,electrical ,eng9e]+1 ,columbia ,univ]sity1 ,new ,york 99 99 99 99 99 ,,edw>d ,b4 ,,waite ,head1 ,in/ruction ,dep>tm5t1 ,am]ican ,s*ool ( ,correspond5ce ,am]ican ,society ( ,me*anical ,eng9e]s ,we/]n ,society ( ,eng9e]s 99 99 99 99 99 ,,david ,p4 ,,moreton1 ,b4,s41 ,e4,e4 ,associate ,pr(essor ( ,electrical ,eng9e]+1 ,arm\r ,in/itute ( ,te*nology ,am]ican ,in/itute ( ,electrical ,eng9e]s1 99 99 99 99 99 ,,leigh ,s4 ,,kei?1 ,b4,s4 ,manag+ ,eng9e] ) ,mc,meen & ,mill]1 ,electrical ,eng9e]s & ,pat5t ,exp]ts ,*icago ,associate ,memb]1 ,am]ican ,in/itute ( ,electrical ,eng9e]s 99 99 99 99 99 ,,jessie ,m4 ,,%eph]d1 ,a4,b4 ,associate ,editor1 ,textbook ,dep>tm5t1 ,am]ican ,s*ool ( ,correspond5ce 99 99 99 99 99 ,,erne/ ,l4 ,,wallace1 ,b4,s4 ,assi/ant ,exam9]1 ,unit$ ,/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 ,telephone4 ,! ,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,sc1 ,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,sc1 ,,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 ,,mcmillan1 ,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]3 ,=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$]ick ,,coll9s ,editor1 ,coll9s ,wireless ,bullet94 ,au?or ( ,wireless ,telegraphy1 ,its ,hi/ory1 ,!ory & ,practice1 ,manual ( ,wireless ,telegraphy1 ,design & ,con/ruction ( ,induction ,coils1 etc4 99 99 99 99 99 ,,s*uyl] ,s4 ,,:eel]1 ,d4,sc4 ,presid5t1 ,crock]-,:eel] ,co42 ,pa/-,presid5t1 ,am]ican ,in/itute ( ,electrical ,eng9e]s4 ,jo9t ,au?or ( ,managem5t ( ,electrical ,ma*9]y4 99 99 99 99 99 ,,*>les ,,proteus ,,/e9metz ,consult+ ,eng9e]1 ) ! ,g5]al ,electric ,co42 ,pr(essor ( ,electrical ,eng9e]+1 ,union ,college4 ,au?or ( ,! ,!ory & ,calculation ( ,alt]nat+-,curr5t ,ph5om5a1 ,!oretical ,elem5ts ( ,electrical ,eng9e]+1 etc4 99 99 99 99 99 ,,george ,w4 ,,patt]son1 ,s4,b41 ,ph4,d4 ,head ( ,dep>tm5t ( ,electrical ,eng9e]+1 ,univ]sity ( ,mi*igan4 ,jo9t ,au?or ( ,electrical ,measurem5ts4 99 99 99 99 99 ,,william ,,mav]1 ,,jr4 ,ex-,electrician ,baltimore & ,ohio ,telegraph ,company2 ,memb] ( ! ,am]ican ,in/itute ( ,electrical ,eng9e]s4 ,au?or ( ,am]ican ,telegraphy & ,encyclop$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 ,a ,,typical ,,small ,,magneto ,,swit*bo>d ,,in/allation ,illu/ration3 ,a ,,typical ,,c5tral ,,(fice ,,= ,,rural ,,ex*ange ,l9e ,protectors on ,wall at ,left4 ,=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$gm5t is due to ! /aff ( au?ors & collaborators1 )\t ^: he>ty co-op]ation ?is "w w\ld h be5 impossible4 ,table ( ,cont5ts ,,volume ,i ,,fundam5tal ,,pr9ciples ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen,a ,ac\/ics--,*>act]i/ics ( ,s\nd--,l\dness--,pit*--,vibration ( ,diaphragms--,timbre--,human ,voice--,human ,e>--,spee*--,magneto ,telephones--,loose-,contact ,pr9ciple--,induction ,coils--,simple ,telephone ,circuit--,capacity--,telephone ,curr5ts--,audible & ,visible ,signals--,telephone ,l9es--,conductors--,inductance--,insula tion ,,sub/ation ,,equipm5t ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,transmitt]s--,v>iable ,resi/ance--,mat]ials--,s+le & ,multiple ,electrodes--,solid-,back ,transmitt]--,types ( ,transmitt]s--,electrodes--,pack+--,ac\/ icon ,transmitt]--,swit*bo>d ,transmitt]--,receiv]s--,types ( ,receiv]s--,op]ator's ,receiv]--,prim>y ,cells--,s]ies & ,multiple ,connections--,types ( ,prim>y ,cells--,magneto ,signal+ ,app>atus--,batt]y ,bell--,magneto ,bell--,magneto ,g5]ator--,armature--,automatic ,%unt--,pol>iz$ ,r+]--,hook ,swit*--,electromagnets--,imp$ance1 ,induction1 & ,repeat+ ,coils--,non-,inductive ,resi/ance ,devices--,diff]5tially-,w\nd ,unit--,cond5s]s--,mat]ials--,curr5t ,supply to ,transmitt]s--,local ,batt]y--,common ,batt]y--,diagrams ( ,common-,batt]y ,sy/ems--,telephone ,sets3 ,magneto1 ,s]ies & ,bridg+1 ,common-,batt]y ,,p>ty-,,l9e ,,sy/ems ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,non-,selective ,p>ty-,l9e ,sy/ems--,s]ies & ,bridg+--,signal ,code--,selective ,p>ty-,l9e ,sy/ems3 ,pol>ity1 ,h>monic1 ,/ep-by-,/ep1 & ,brok5-,l9e--,lock-,out ,p>ty-,l9e ,sy/ems3 ,poole1 ,/ep-by-,/ep1 & ,brok5-,l9e ,,protection ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,electrical ,haz>ds--,high ,pot5tials--,air-,gap ,arre/]--,dis*>ge across ,gaps--,types ( ,arre/]--,vacuum ,arre/]--,/rong ,curr5ts--,fuses--,sneak ,curr5ts--,l9e ,protection--,c5tral-,(fice & ,subscrib]s' ,/ation ,protectors--,city ,ex*ange ,requirem5ts--,electrolysis ,,manual ,,swit*bo>ds ,by ,k4 ,b4 ,mill] & ,s4 ,g4 ,mc,meen ,! ,telephone ,ex*ange--,subscrib]s'1 ,trunk1 & ,toll ,l9es--,di/ricts--,swit*bo>ds--,simple ,magneto ,swit*bo>d--,op]ation--,comm]cial ,types ( ,drops & ,jacks--,manual vs4 ,automatic ,re/oration--,swit*bo>d ,plugs & ,cords--,r++ & ,li/5+ ,keys--,op]ator's ,telephone ,equipm5t--,circuits ( ,complete ,swit*bo>d--,night-,al>m ,circuits--,gr\nd$ & ,metallic ,circuit ,l9e--,cord ,circuit--,swit*bo>d ,assembly ,,review ,,que/ions ,,index ,footnote ,a3 ,= pr(essional /&+ ( au?ors1 see li/ ( ,au?ors & ,collaborators at front ( volume4 ,illu/ration3 ,,old ,,bran*-,,t]m9al ,,multiple ,,bo>d1 ,,p>is1 ,,france ,,telephony ,,introduction ,! telephone 0 inv5t$ 9 #ahge by ,alex&] ,graham ,bell1 a resid5t ( ! ,unit$ ,/ates1 a native ( ,scotl&1 & by pr(ession a tea*] ( deaf mutes 9 ! art ( vocal spee*4 ,9 t ye>1 ,pr(essor ,bell 0 engag$ 9 ! exp]im5tal developm5t ( a sy/em ( multiplex telegraphy1 bas$ on ! use ( rapidly v>y+ curr5ts4 ,dur+ ^? exp]im5ts1 he obs]v$ an iron re$ to vibrate be=e an electromagnet z a result ( ano!r iron re$ vibrat+ be=e a di/ant electromagnet connect$ to ! ne>] "o by wires4 ,! telephone result$ f ?is obs]vation ) great promptness4 ,9 ! in/rum5t fir/ made1 s\nd vibrat$ a membrane diaphragm support+ a bit ( iron ne> an electromagnet2 a l9e jo9$ ?is simple device ( ?ree elem5ts to ano!r l x2 a batt]y 9 ! l9e magnetiz$ bo? electromagnet cores2 ! vibration ( ! iron 9 ! s5d+ device caus$ ! curr5t 9 ! l9e to undulate & to v>y ! magnetism ( ! receiv+ device4 ,! diaphragm ( ! latt] 0 vibrat$ 9 consequ5ce ( ! v>y+ pull ^u its bit ( iron1 & ^! vibrations reproduc$ ! s\nd t vibrat$ ! s5d+ diaphragm4 ,! fir/ public use ( ! electric telephone 0 at ! ,c5t5nial ,exposition 9 ,philadelphia 9 #ahgf4 ,x 0 !re te/$ by _m int]e/$ obs]v]s1 among !m ,sir ,william ,?omson1 lat] ,"l ,kelv91 ! em95t ,scot* au?ority on matt]s ( electrical communication4 ,x 0 he :o contribut$ s l>gely to ! success ( ! e>ly telegraph cable sy/em betwe5 ,engl& & ,am]ica4 ,two ( 8 comm5ts :i* are *>act]i/ic are z foll[s3 ,to-day ,i h se5 t :i* ye/]day ,i %\ld h deem$ impossible4 ,soon lov]s w :isp] _! secrets ov] an electric wire4 99 99 99 99 99 ,:o c b admire ! h>dihood ( inv5tion :i* devis$ su* slight means to realize ! ma!matical conception t if electricity is to convey all ! delicacies ( s\nd :i* di/+ui% articulate spee*1 ! /r5g? ( its curr5t mu/ v>y cont9u\sly z ne>ly z may be 9 simple proportion to ! velocity ( a p>ticle ( ! air engag$ 9 con/itut+ ! s\nd4 ,contr>y to usual me?ods ( improv+ a new art1 ! e>lie/ improvem5t ( ! telephone simplifi$ x4 ,! diaphragms became ?9 iron disks1 in/ead ( membranes c>ry+ iron2 ! electromagnet cores 7 made ( p]man5tly magnetiz$ /eel in/ead ( tempor>ily magnetiz$ s(t iron1 & ! batt]y 0 omitt$ f ! l9e4 ,! undulatory curr5t 9 a sy/em ( two su* telephones jo9$ by a l9e is produc$ 9 ! s5d+ telephone by ! vibration ( ! iron diaphragm4 ,! vibration ( ! diaphragm 9 ! receiv+ telephone is produc$ by ! undulatory curr5t4 ,s\nd is produc$ by ! vibration ( ! diaphragm ( ! receiv+ telephone4 ,su* a telephone is at once ! simple/ kn[n =m ( electric g5]ator or motor = alt]nat+ curr5ts4 ,x is capable ( translat+ motion into curr5t or curr5t into motion ?r\gh a wide range ( frequ5cies4 ,x is n kn[n t !re is any frequ5cy ( alt]nat+ curr5t :i* x is n capable ( produc+ & translat+4 ,x c produce & translate curr5ts ( great] complexity ?an any o!r exi/+ electrical ma*9e4 ,?\gh possess+ ^! admirable qualities z an electrical ma*9e1 ! simple electromagnetic telephone _h n ! ability to transmit spee* l\dly en\gh = all practical uses4 ,transmitt]s produc+ /rong] telephonic curr5ts 7 develop$ soon aft] ! fundam5tal inv5tion4 ,"s =ms ( ^! 7 inv5t$ by ,pr(essor ,bell himself4 ,o!r inv5tors contribut$ devices embody+ ! use ( c>bon z a resi/ance to be v>i$ by ! motions ( ! diaphragm4 ,?is g5]al =m ( transmitt+ telephone has prevail$ & at pres5t is ! /&>d type4 ,x is int]e/+ to note t ! e>lie/ inc&esc5t lamps1 z inv5t$ by ,mr4 ,edison1 _h a resi/ance mat]ial compos$ ( c>bon1 & t su* a lamp reta9$ its position z ! mo/ effici5t small electric illum9ant until ! rec5t introduction ( metal filam5t lamps4 ,x is possible t "s =m ( metal may be introduc$ z ! resi/ance m$ium = telephone transmitt]s1 & t su* a *ange z has tak5 place 9 inc&esc5t lamps may increase ! effici5cy ( telephone transmitt+ devices4 ,at ! "t ( ! inv5tion ( ! telephone1 !re 7 9 exi/5ce two di/9ct types ( telegraph1 work+ 9 regul> comm]cial s]vice4 ,9 ! m g5]al type1 _m telegraph /ations 7 connect$ to a l9e & :atev] 0 telegraph$ betwe5 two /ations c\ld be read by all ! /ations ( t l9e4 ,9 ! o!r & less g5]al type1 _m l9es1 ea* hav+ a s+le telegraph /ation1 7 c5t]$ 9 an (fice or ex*ange1 & at ! desire ( a us] 8 l9e c\ld be connect$ to ano!r & lat] disconnect$ f x4 ,bo? ( ^! types ( telegraph s]vice 7 imitat$ at once 9 telephone practice4 ,l9es c>ry+ _m telephones ea*1 7 e/abli%$ ) great rapidity4 ,telephones actually displac$ telegraphic app>atus 9 ! ex*ange me?od ( work+ 9 ,am]ica4 ,! fundam5tal pr9ciple on :i* telegraph or telephone ex*anges op]ate1 be+ t ( plac+ any l9e 9 communication ) any o!r 9 ! sy/em1 gave to ea* l9e an ultimate scope s great z to make ?is =m ( communication m popul> ?an any arrangem5t ( telephones on a s+le l9e4 ,beg9n+ 9 #ahgg1 telephone ex*anges 7 develop$ ) great rapidity 9 all ( ! l>g] communities ( ! ,unit$ ,/ates4 ,telegraph swit*+ devices 7 utiliz$ at ! outset or 7 modifi$ 9 su* m9or p>ticul>s z 7 necess>y to fit !m to ! new task4 ,9 its simple/ =m1 a telephone sy/em is1 ( c\rse1 a s+le l9e p]man5tly jo9+ two telephones4 ,9 its next simple/ =m1 x is a l9e p]man5tly jo9+ m ?an two telephones4 ,9 its mo/ useful =m1 x is a l9e jo9+ a telephone to "s means ( connect+ x at w to ano!r4 ,a telephone ex*ange c5tral (fice conta9s means = connect+ l9es at w 9 t useful way4 ,! lea/ complicat$ ma*9e = t purpose is a swit*bo>d to be op]at$ by h&1 hav+ "s way ( lett+ ! op]ator "k t a connection is wi%$ & a way ( mak+ x4 ,! cu/om>y way ( connect+ ! l9es always has be5 by means ( flexible conductors fitt$ ) plugs to be ins]t$ 9 sockets4 ,if ! swit*bo>d be small en\gh s t all ! l9es are )9 arm's rea* ( ! op]ator1 ! :ole process is individual1 & may be said to be at its be/ & simple/4 ,!re are b few communities1 h[ev]1 9 :i* ! numb] ( l9es to be s]v$ & calls to be answ]$ is small en\gh s t ! entire traffic ( ! ex*ange c be h&l$ by a s+le p]son4 ,an obvi\s way1 !re=e1 is to provide z _m op]ators 9 a c5tral (fice z may be requir$ by ! numb] ( calls to be answ]$1 & to t]m9ate be=e ea* ( ! op]ators en\gh ( ! l9es to br+ en\gh "w to keep t op]ator economically occupi$4 ,?is pres5ts ! additional problem1 h[ to connect a l9e t]m9at+ be=e "o op]ator to a l9e normally t]m9at+ be=e ano!r op]ator4 ,! obvi\s answ] is to provide l9es f ea* op]ator's place ( "w to ea* o!r op]ator's place1 connect+ a call+ l9e to "s "o ( ^! l9es :i* are local )9 ! c5tral (fice1 &1 9 turn1 connect+ t *os5 local l9e to ! l9e :i* is call$4 ,su* l9es betwe5 op]ators h come to be kn[n z trunk l9es1 because ( ! obvi\s analogy to trunk l9es ( railways betwe5 common c5t]s1 & su* a sy/em ( telephone l9es may be call$ a trunk+ sy/em4 ,v good s]vice has be5 giv5 & c be giv5 by su* an arrangem5t ( local trunks1 b ! gr[? 9 l9es & 9 traffic has develop$ 9 mo/ in/ances c]ta9 weaknesses :i* make x advisable to f9d spe$i]1 m accurate1 & m reliable means4 ,= ! s]v+ ( a l>ge traffic f a l>ge numb] ( l9es1 z is requir$ 9 practically e city ( ! _w1 a v great contribution to ! practical art 0 made by ! developm5t ( ! multiple swit*bo>d4 ,su* a swit*bo>d is m]ely su* a device z has be5 describ$ = ! simpl] cases1 ) ! fur!r ref9em5t t )9 rea* ( ea* op]ator 9 ! c5tral (fice appe>s e l9e :i* ent]s t (fice1 & ?is )\t reg>d to :at po9t 9 ! swit*bo>d ! l9es may t]m9ate = ! answ]+ ( calls4 ,9 o!r words1 :ile ea* op]ator answ]s a c]ta9 subord9ate gr\p ( ! total numb] ( l9es1 ea* op]ator may rea*1 = call+ purposes1 e l9e :i* ent]s t (fice4 ,x is probable t ! inv5tion & developm5t ( ! multiple swit*bo>d 0 ! fir/ great impetus t[>d ! wide-spread use ( telephone s]vice4 ,co9cid5t ) ! developm5t ( ! multiple swit*bo>d = manually op]at$1 c5tral-(fice me*anisms 0 ! beg9n+ ( ! developm5t ( automatic app>atus "u ! control ( ! call+ subscrib] = f9d+ & connect+ ) a call$ l9e4 ,x is int]e/+ to note ! g5]al tr5d ( ! e>ly developm5t ( automatic app>atus 9 comp>ison ) ! developm5t1 to t "t1 ( manual telephone app>atus4 ,:ile ! manual app>atus on ! "o h& attempt$ to meet its problem by provid+ local trunks betwe5 ! v>i\s op]ators ( a c5tral (fice1 & fail+ ( success 9 t1 f9ally develop$ a means :i* plac$ all ! l9es ( a c5tral (fice )9 connect+ rea* ( ea* op]ator1 automatic telephony1 beg9n+ at t po9t1 fail$ ( success 9 attempt+ to br+ ea* l9e 9 ! c5tral (fice )9 connect+ rea* ( ea* connect+ me*anism4 ,9 o!r t]ms1 ! fir/ automatic swit*+ equipm5t consi/$ ( a ma*9e = ea* l9e1 :i* ma*9e 0 s organiz$ z to be able to f9d & connect its call+ l9e ) any call$ l9e ( ! entire c5tral-(fice gr\p4 ,x may be said t an attempt to develop ?is plan 0 ! fundam5tal reason = ! repeat$ failure ( automatic app>atus to solve ! problem x attack$4 ,all t ! e>li] automatic sy/em did 0 to prove m or less successfully t automatic app>atus _h a "r to exi/1 & t to dem& ( ! subscrib] t he manipulate f 8 /ation a di/ant ma*9e to make ! connection )\t human aid 0 n fallaci\s4 ,:5 x _h be5 recogniz$ t ! entire multiple swit*bo>d idea c\ld n be c>ri$ into automatic telephony ) success1 ! fir/ dawn ( hope 9 t art may be said to h come4 ,success 9 automatic telephony did come by ! re-adoption ( ! trunk+ me?od4 ,z adopt$ = automatic telephony1 ! me?od contemplates t ! call+ l9e %all be ext5d$1 l9k by l9k1 until x f9ds itself l5g!n$ & direct$ s z to be able to seize ! call$ l9e 9 a v mu* small] multiple ?an ! total gr\p ( "o (fice ( ! ex*ange4 ,a simil> curi\s rev]sion has tak5 place 9 ! developm5t ( telephone l9es4 ,! e>lie/ telephone l9es 7 m]ely telegraph l9es equipp$ ) telephone in/rum5ts1 & ! e>lie/ telegraph l9es 7 plann$ by ,pr(essor ,morse to be insulat$ wires laid 9 ! e>?4 ,a lack ( skill 9 prep>+ ! wires = putt+ 9 ! e>? caus$ ^! e>ly und]gr\nd l9es to be failures4 ,at ! urg+ ( "o ( 8 associates1 ,pr(essor ,morse cons5t$ to place 8 e>lie/ telegraph l9es on poles 9 ! air4 ,ea* su* l9e orig9ally consi/$ ( two wires1 "o = ! go+ & "o = ! return+ curr5t1 z 0 !n consid]$ ! action4 ,^u its be+ discov]$ t a s+le wire1 us+ ! e>? z a return1 w\ld s]ve z a satisfactory telegraph l9e1 su* practice became univ]sal4 ,^u ! arrival ( ! telephone1 all l9es obvi\sly 7 built 9 ! same way1 & until =ce ( new] circum/ances compell$ x1 ! pres5t metallic circuit )\t an e>? connection did n come into g5]al use4 ,! extraord9>y gr[? ( ! numb] ( telephone l9es 9 a community & ! developm5t ( o!r me?ods ( electrical utilization1 z well z ! gr[? 9 ! k ( telephony itself1 ultimately =c$ ! wires und]gr\nd aga94 ,at ! same "t & = ! same causes1 a telephone l9e became "o ( two wires1 s t x becomes aga9 ! c\nt]p>t ( ! e>lie/ telegraph l9e ( ,pr(essor ,morse4 ,ano!r curi\s & int]e/+ example ( ?is rev]sion to type exi/s 9 ! simple telephone receiv]4 ,an e>ly improvem5t 9 telephone receiv]s aft] ,pr(essor ,bell's orig9al inv5tion 0 to provide ! necess>y magnetism ( ! receiv] core by mak+ x ( /eel & p]man5tly magnetiz+ x1 :]eas ,pr(essor ,bell's in/rum5t provid$ its magnetism by means ( direct curr5t fl[+ 9 ! l9e4 ,9 lat] days ! telephone receiv] has return$ almo/ to ! orig9al =m 9 :i* ,pr(essor ,bell produc$ x & ?is *ange has simplifi$ o!r elem5ts ( telephone-ex*ange app>atus 9 a v int]e/+ & gratify+ way4 ,by reason ( improvem5ts 9 me?ods ( l9e con/ruction & app>atus arrangem5t1 ! radius ( communication /eadily has increas$4 ,comm]cial spee* n[ is possible betwe5 po9ts sev]al ?\s& miles ap>t1 & !re is no !oretical reason :y communication might n be e/abli%$ betwe5 any two po9ts on ! e>?'s surface4 ,! practical reasons ( dem& & co/ may prev5t s great an accompli%m5t z talk+ half ar\nd ! e>?4 ,s f> z sci5ce is conc]n$ !re w\ld seem to be no reason :y ?is might n be done today1 by ! c>eful application ( :at already is kn[n4 ,9 ! ,unit$ ,/ates1 telephone s]vice f its beg9n+ has be5 suppli$ to us]s by private ent]prise4 ,9 o!r c\ntries1 x is suppli$ by means ( gov]nm5tally-own$ equipm5t4 ,9 g5]al1 x may be said t ! adequacy & ! am\nt1 z well z ! quality ( telephone s]vice1 is be/ 9 c\ntries :]e ! s]vice is provid$ by private ent]prise4 ,telephone sy/ems 9 ! ,unit$ ,/ates 7 "u ! control ( ! ,bell ,telephone ,company f ! inv5tion ( ! device 9 #ahgf until #ahic4 ,! fundam5tal telephone pat5t expir$ 9 #ahic4 ,?is op5$ ! telephone art to ! g5]al public1 because x no long] 0 necess>y to secure telephones solely f ! pat5t-hold+ company nor to pay royalty = ! "r to use !m1 if secur$ at all4 ,manufactur]s ( electrical app>atus g5]ally !n began to make & sell telephones & telephone app>atus1 & op]at+ companies1 also indep5d5t ( ! ,bell organization1 began to in/all & use telephones4 ,at ! end ( sev5te5 ye>s ( pat5t monopoly 9 ! ,unit$ ,/ates1 !re 7 9 op]ation a little ov] #bej1jjj telephones4 ,9 ! sev5te5 ye>s s9ce ! expiration ( ! fundam5tal pat5t1 indep5d5t telephone companies ?r\gh\t ! ,unit$ ,/ates h in/all$ & n[ h 9 daily successful use ov] #c1iaa1djj telephones4 ,9 o!r words1 s9ce its fir/ beg9n+s1 indep5d5t telephony has br\ght into cont9u\s daily use ne>ly sixte5 times z _m telephones z 7 br\ght into use 9 ! equal "t ( ! complete monopoly ( ! ,bell organization4 ,at ! beg9n+ ( #aiaj1 !re 7 9 s]vice by ! ,bell organization ab\t #c1fcc1ijj telephones4 ,^! ) ! #c1iaa1djj indep5d5t telephones1 make a total ( #g1ede1cjj1 or ab\t "o-twelf? z _m telephones z !re are inhabitants ( ! ,unit$ ,/ates4 ,! influ5ce ( ?is developm5t ^u ! lives ( ! p has be5 pr(\nd4 ,:e!r ! influ5ce has be5 :olly = good may n be s conclusively app>5t4 ,"l ,bacon has decl>$ t1 except+ only ! alphabet & ! art ( pr9t+1 ^? inv5tions abridg+ di/ance are ( ! greate/ s]vice to mank9d4 ,if ?is be true1 x may be said t ! inv5tion ( telephony des]ves high place among ! civiliz+ influ5ces4 ,!re is no indu/rial art 9 :i* ! advancem5t ( ! times has be5 foll[$ m closely by practical application ?an 9 telephony4 ,comm]cial spee* by telephone is possible by means ( curr5ts :i* s f> are practically unmeasurable4 ,9 o!r words1 x is possible to speak cle>ly & satisfactorily ov] a l9e by means ( curr5ts :i* _c be read1 ) c]ta9ty z to _! am\nt1 by any electrical measur+ device s f> kn[n4 ,9 ?is reg>d1 telephony is less well =tifi$ ?an are any ( ! arts utiliz+ electrical p[] 9 l>g] quantities4 ,! real wond] is t ) s little k ( :at takes place1 p>ticul>ly z to am\nt1 ^? work+ 9 ! art h be5 able to d z well z !y h4 ,:5 an exact k ( quantity is easily obta9able1 v /rik+ advances may be look$ =4 ,! /ud5t ( ^! phases ( physical sci5ce & indu/rial art w d well to comb9e ?ree processes3 /udy ( ! words ( o!rs2 p]sonal exp]im5tation2 & dige/ive ?\ght4 ,! la/ m5tion$ is ! process ( pr(\nde/ value4 ,on x f9ally dep5ds ma/]y4 ,x is n ( s mu* importance h[ soon ! concept %all f9ally be ga9$ z t x is ga9$4 ,a /atem5t by ano!r may seem lifeless & in]t & ! mean+ ( an obs]vation may be obscure4 ,dige/ive ?\ght is ! only assimilative process4 ,! :ole art ( telephony hangs on tak+ ?\ght ( ?+s4 ,judge ,r4,f4 ,taylor ( ,indiana said ( ,pr(essor ,bell1 ,x has be5 said t no man by tak+ ?\ght may add a cubit to 8 /ature1 yet "h is a man :o1 by tak+ ?\ght1 has add$ n cubits b miles to ! l5g?s ( m5's tongues & e>s4 ,9 obs]vations ( _m /ud5ts1 x is f\nd t ! notion ( ea* mu/ pass ?r\gh a c]ta9 p]iod ( incubation be=e 8 private & p]sonal k ( ,ohm's law is hat*$4 ,once hat*$1 h[ev]1 x is 84 ,by j su* a process mu/ come ea* pr9cipal addition to 8 /ock ( concepts4 ,! p]iods may v>y & practice 9 ! uses ( ! m9d may tra9 x 9 al]tness 9 its "w4 ,if "t is requir$1 "t %\ld be giv51 ! object always be+ to keep ?9k+ or re-read+ or re-try+ until ! ?\ght is :olly encompass$ & possess$4 ,,*apt] ,i ,,ac\/ics ,telephony is ! art ( reproduc+ at a di/ant po9t1 usually by ! ag5cy ( electricity1 s\nds produc$ at a s5d+ po9t4 ,9 ?is art ! elem5ts ( two g5]al divisions ( physical sci5ce are conc]n$1 s\nd & electricity4 ,s\nd is ! effect ( vibrations ( matt] ^u ! e>4 ,! vibrations may be ^? ( air or o!r matt]4 ,v>i\s =ms ( matt] transmit s\nd vibrations 9 v>y+ degrees1 at diff]5t specific spe$s1 & ) diff]5t effects ^u ! vibrations4 ,any =m ( matt] may s]ve z a transmitt+ m$ium = s\nd vibrations4 ,s\nd itself is an effect ( s\nd vibrations ^u ! e>4 ,propagation ( ,s\nd4 ,s9ce human be+s communicate ) ea* o!r by means ( spee* & he>+ ?r\gh ! air1 x is ) air t ! ac\/ics ( telephony pr9cipally is conc]n$4 ,9 air1 s\nd vibrations consi/ ( successive cond5sations & r>efactions t5d+ to proce$ outw>dly f ! s\rce 9 all directions4 ,! s\rce is ! c5t] ( a sph]e ( s\nd vibrations4 ,:atev] may be ! nature ( ! s\nds or ( ! m$ium transmitt+ !m1 !y consi/ ( waves emitt$ by ! s\rce & obs]v$ by ! e>4 ,a s\nd wave is "o complete cond5sation & r>efaction ( ! transmitt+ m$ium4 ,x is produc$ by "o complete vibration ( ! s\nd-produc+ ?+4 ,s\nd waves 9 air travel at a rate ( ab\t #a1jij feet p] second4 ,! rate ( propagation ( s\nd waves 9 o!r mat]ials v>ies ) ! d5sity ( ! mat]ial4 ,= example1 ! spe$ ( transmission is mu* great] 9 wat] ?an 9 air1 & is mu* less 9 highly r>efi$ air ?an 9 air at ord9>y d5sity4 ,! propagation ( s\nd waves 9 a vacuum may be said n to take place at all4 ,*>act]i/ics ( ,s\nd4 ,?ree qualities di/+ui% s\nd3 l\dness1 pit*1 & timbre4 ,l\dness4 ,l\dness dep5ds ^u ! viol5ce ( ! effect ^u ! e>2 s\nds may be alike 9 _! o!r qualities & diff] 9 l\dness1 ! l\d] s\nds be+ produc$ by ! /rong] vibrations ( ! air or o!r m$ium at ! e>4 ,o!r ?+s be+ equal1 ! l\d] s\nd is produc$ by ! s\rce radiat+ ! great] en]gy & s produc+ ! great] degree ( cond5sation & r>efaction ( ! m$ium4 ,pit*4 ,pit* dep5ds ^u ! frequ5cy at :i* ! s\nd waves /rike ! e>4 ,pit*es are ref]r$ to z high or l[ z ! frequ5cy ( waves rea*+ ! e> are great] or few]4 ,famili> l[ pit*es are ! left-h& /r+s ( a piano2 ! l>g] ones ( /r+$ in/rum5ts g5]ally2 bass voices2 & l>ge bells4 ,famili> high pit*es are "r-h& piano /r+s2 small] ones ( o!r /r+$ in/rum5ts2 soprano voices2 small bells2 & ! voices ( mo/ birds & insects4 ,doppl]'s ,pr9ciple3--,z pit* dep5ds ^u ! frequ5cy at :i* s\nd waves /rike ! e>1 an object may emit s\nd waves at a con/ant frequ5cy1 yet may produce diff]5t pit*es 9 e>s diff]5tly situat$4 ,su* a case is n usual1 b an example ( x w s]ve a useful purpose 9 fix+ c]ta9 facts z to pit*4 ,conceive two railroad tra9s to pass ea* o!r1 runn+ 9 opposite directions1 ! eng9e bells ( bo? tra9s r++4 ,pass5g]s on ea* tra9 w he> ! bell ( ! o!r1 fir/ z a ris+ pit*1 !n z a fall+ "o4 ,pass5g]s on ea* tra9 w he> ! bell ( _! own tra9 at a con/ant pit*4 ,! diff]5ce 9 ! obs]vations 9 su* a case is due to relative positions betwe5 ! e> & ! s\rce ( ! s\nd4 ,z to ! bell ( _! own tra91 ! pass5g]s are a fix$ di/ance f x1 :e!r ! tra9 moves or /&s2 z to ! bell ( ! o!r tra91 ! pass5g]s fir/ rapidly approa* x1 !n pass x1 !n rec$e f x4 ,! di/ances at :i* x is he>d v>y z ! secants ( a circle1 ! radius 9 ?is case be+ a l5g? :i* is ! close/ approa* ( ! e> to ! bell4 ,if ! bell h a con/ant intr9sic fundam5tal pit* ( #bjj waves p] second 7a wave-l5g? ( ab\t #e4e feet71 x fir/ w be he>d at a pit* ( ab\t #bjj waves p] second4 ,b ?is pit* rises rapidly1 z if ! bell 7 *ang+ its own pit*1 :i* bells d n d4 ,! ris+ pit* is he>d because ! e> is ru%+ d[n ! wave-tra91 e in/ant ne>] to ! s\rce4 ,at a spe$ ( #de miles an h\r1 ! pit* rises rapidly1 ab\t #ab vibrations p] second4 ,if ! rate ( approa* betwe5 ! e> & ! bell 7 con/ant1 ! pit* ( ! bell w\ld be he>d at #bab waves p] second4 ,b sudd5ly ! e> passes ! bell1 he>s ! pit* /op ris+ & beg9 to fall2 & ! tone drops #ab waves p] second z x _h ris54 ,su* a circumflex is an excell5t example ( ! be>+ ( wavel5g?s & frequ5cies ^u pit*4 ,vibration ( ,diaphragms3--,s\nd waves 9 air h ! p[] to move o!r diaphragms ?an t ( ! e>4 ,s\nd waves con/antly vibrate su* diaphragms z panes ( w9d[s & ! walls ( h\ses4 ,! record+ diaphragm ( a phonograph is a w9d[ pane be>+ a /ylus adapt$ to engrave a groove 9 a record blank4 ,9 ! cyl9d] =m ( record1 ! groove v>ies 9 dep? ) ! vibrations ( ! diaphragm4 ,9 ! disk type ( phonograph1 ! groove v>ies sidewise f its normal true spiral4 ,if ! disk record be du/$ ) talcum p[d]1 wip$1 & exam9$ ) a magnify+ glass1 ! wav+ spiral l9e may be se54 ,its v>iations are ! result ( ! bl[s /ruck ^u ! diaphragm by a tra9 ( s\nd waves4 ,9 reproduc+ a phonograph record1 increas+ ! spe$ ( ! record rotation causes ! pit* to rise1 because ! bl[s ^u ! air are increas$ 9 frequ5cy & ! wave-l5g?s %ort5$4 ,a transitory decrease 9 spe$ 9 record+ w cause a transitory rise 9 pit* :5 t record is reproduc$ at uni=m spe$4 ,timbre4 ,"* ( s\nd d5otes t diff]5ce ( effect produc$ ^u ! e> by s\nds o!rwise alike 9 pit* & l\dness4 ,?is *>act]i/ic is call$ timbre4 ,x is extraord9>ily useful 9 human affairs1 human voices be+ di/+ui%$ f ea* o!r by x1 & a great "p ( ! joy ( music ly+ 9 x4 ,a bell1 a /ret*$ /r+1 a re$1 or o!r s\nd-produc+ body1 emits a c]ta9 l[e/ possible tone :5 vibrat$4 ,?is is call$ its fundam5tal tone4 ,! pit*1 l\dness1 & timbre ( ?is tone dep5d ^u v>i\s controll+ causes4 ,usually ?is fundam5tal tone is accompani$ by a numb] ( o!rs ( high] pit*1 bl5d+ ) x to =m ! g5]al tone ( t object4 ,^! high] tones are call$ h>monics4 ,! ,g]mans call !m ov]tones4 ,!y are always ( a frequ5cy :i* is "s multiple ( ! fundam5tal frequ5cy4 ,t is1 ! rate ( vibration ( a h>monic is #b1 #c1 #d1 #e1 or "s o!r integral numb]1 times z great z ! fundam5tal itself4 ,a tone hav+ no h>monics is r>e 9 nature & is n an attractive "o4 ,! tones ( ! human voice are ri* 9 h>monics4 ,9 any tone hav+ a fundam5tal & h>monics 7multiples71 ! wave-tra9 consi/s ( a complex s]ies ( cond5sations & r>efactions ( ! air or o!r transmitt+ m$ium4 ,9 ! case ( m]e noises ! tra9 ( vibrations is irregul> & foll[s no def9ite ord]4 ,?is is ! diff]5ce betwe5 v[el s\nds & o!r musical tones on ! "o h& & all unmusical s\nds 7or noises7 on ! o!r4 ,human ,voice4 ,human be+s communicate ) ea* o!r 9 v>i\s ways4 ,! *ief me?od is by spee*4 ,voice is s\nd vibration produc$ by ! vocal cords1 ^! be+ two ligam5ts 9 ! l>ynx4 ,! vocal cords 9 man are actuat$ by ! air f ! lungs4 ,! size & t5sion ( ! vocal cords & ! volume & ! velocity ( ! air f ! lungs control ! tones ( ! voice4 ,! m tightly ! vocal cords be drawn1 o!r ?+s be+ equal1 ! high] w be ! pit* ( ! s\nd2 t is1 ! high] ! frequ5cy ( vibration produc$ by ! voice4 ,! pit*es ( ! human voice lie1 9 g5]al1 betwe5 ! frequ5cies ( #hg & #gfh p] second4 ,^! are ! extremes ( pit*1 & x is n to be und]/ood t any su* range ( pit* is utiliz$ 9 ord9>y spee*4 ,an av]age man speaks mo/ly betwe5 ! fundam5tal frequ5cies ( #he & #afj p] second4 ,_m female speak+ voices use fundam5tal frequ5cies betwe5 #aej & #cbj vibrations p] second4 ,x is obvi\s f :at has be5 said t 9 all cases ^! speak+ fundam5tals are accompani$ by _! multiples1 giv+ complexity to ! result+ wave-tra9s & "* to ! speak+ voice4 ,spee*-s\nds result f %ocks giv5 to ! air by ! organs ( spee*2 ^! organs are pr9cipally ! m\? cavity1 ! tongue1 & ! tee?4 ,! vocal cords are voice-organs2 t is1 man only truly speaks1 yet ! l[] animals h voice4 ,spee* may be :isp]$1 us+ no voice4 ,note ! di/9ction betwe5 spee* & voice1 & ! organs ( bo?4 ,! spee* ( adults has a mean pit* l[] ?an t ( *ildr52 ( adult males1 l[] ?an t ( females4 ,!re is no close analogue = ! voice-organ 9 artificial me*anism1 b ! use ( ! lips 9 play+ a bugle1 trumpet1 cornet1 or trombone is a fairly close "o4 ,"h ! lips1 9 contact ) ea* o!r1 are /ret*$ across "o end ( a tube 7! m\?piece7 :ile ! air is bl[n betwe5 ! lips by ! lungs4 ,a musical tone results2 if ! in/rum5t be a bugle or a trumpet ( fix$ tube l5g?1 ! pit* w be "s "o ( sev]al c]ta9 tones1 dep5d+ on ! t5sion on ! lips4 ,! l\dness dep5ds on ! =ce ( ! bla/ ( air2 ! "* dep5ds l>gely on ! bugle4 ,human ,e>4 ,! human e>1 ! organ ( he>+ 9 man1 is a complex me*anism ( ?ree g5]al p>ts1 relative to s\nd waves3 a wave-collect+ "p2 a wave-obs]v+ "p1 & a wave-int]pret+ "p4 ,! out] e> collects & reflects ! waves inw>dly to beat ^u ! tympanum1 or e> drum1 a membrane diaphragm4 ,! uses ( ! rolls or convolutions ( ! out] e> are n conclusively kn[n1 b x is obs]v$ t :5 !y are fill$ up ev5ly ) a wax or its equival5t1 ! s5se ( direction ( s\nd is impair$1 & usually ( l\dness also4 ,! diaphragm ( ! e> vibrates :5 /ruck by s\nd waves1 z does any o!r diaphragm4 ,by means ( bone & n]ve me*anism1 ! vibration ( ! diaphragm f9ally is made kn[n to ! bra9 & is int]pretable !re94 ,! human e> c appreciate & int]pret s\nd waves at frequ5cies f #cb to ab\t #cb1jjj vibrations p] second4 ,bel[ ! less]-numb]1 ! t5d5cy is to appreciate ! sep>ate vibrations z sep>ate s\nds4 ,above ! high] numb]1 ! vibrations are inaudible to ! human e>4 ,! mo/ acute p]ception ( s\nd diff]5ces lies at ab\t #c1jjj vibrations p] second4 ,x may be t ! range ( he>+ ( organisms o!r ?an man lies f> above ! range ) :i* human be+s are famili>4 ,"s tra9$ musicians are able to discrim9ate betwe5 two s\nds z diff]+ "o f ! o!r :5 ! diff]5ce 9 frequ5cy is less ?an "o-?\s&? ( ei!r numb]4 ,o!r e>s are unable to detect a diff]5ce 9 two s\nds :5 !y diff] by z mu* z "o full /ep ( ! *romatic scale4 ,:atev] faculty an individual may possess z to tone discrim9ation1 x c be improv$ by tra9+ & practice4 ,,*apt] ,,ii ,,electrical ,,reproduction ,,( ,,spee* ,! art ( telephony 9 its pres5t =m has = its problem s to relate two diaphragms & an electrical sy/em t "o diaphragm w respond to all ! fundam5tal & h>monic vibrations beat+ ^u x & cause ! o!r to vibrate 9 exact consonance1 produc+ j su* vibrations1 :i* beat ^u an e>4 ,! art does n d all ?is today2 x falls %ort ( x 9 e phase4 ,_m ( ! h>monics are lo/ 9 "o or ano!r /age ( ! process2 new h>monics are ins]t$ by ! op]ations ( ! sy/em itself & mu* ( ! volume orig9ally available fails to reappe>4 ,! art1 h[ev]1 has be5 able to *ange comm]cial & social affairs 9 a pr(\nd degree4 ,conv]sion f ,s\nd ,waves to ,vibration ( ,diaphragm4 ,h[ev] produc$1 by ! voice or o!rwise1 s\nds to be transmitt$ by telephone consi/ ( vibrations ( ! air4 ,^! vibrations1 ^u rea*+ a diaphragm1 cause x to move4 ,! greate/ amplitude ( motion ( a diaphragm is1 or is wi%$ to be1 at its c5t]1 & its edge ord9>ily is fix$4 ,! diaphragm ?us s]ves z a translat+ device1 *ang+ ! en]gy c>ri$ by ! molecules ( ! air into localiz$ oscillations ( ! matt] ( ! diaphragm4 ,! waves ( s\nd 9 ! air advance2 ! vibrations ( ! molecules are localiz$4 ,! ag5cy ( ! air z a m$ium = s\nd transmission %\ld be und]/ood to be "o 9 :i* its g5]al volume has no ne$ to move f place to place4 ,:at occurs is t ! vibrations ( ! s\nd-produc] cause alt]nate cond5sations & r>efactions ( ! air4 ,ea* molecule ( ! air conc]n$ m]ely oscillates ?r\gh a small amplitude1 produc+1 by jo9t action1 %ells ( waves1 ea* travel+ outw>d f ! s\nd-produc+ c5t] l rapidly gr[+ cov]+s ( a ball4 ,conv]sion f ,vibration to ,voice ,curr5ts4 ,fig4 #a illu/rates a simple ma*9e adapt$ to translate motion ( a diaphragm into an alt]nat+ electrical curr5t4 ,! device is m]ely "o =m ( magneto telephone *os5 to illu/rate ! po9t ( imm$iate conv]sion4 #a is a diaphragm adapt$ to vibrate 9 response to ! s\nds rea*+ x4 #b is a p]man5t magnet & #c is its armature4 ,! armature is 9 contact ) "o pole ( ! p]man5t magnet & ne>ly 9 contact ) ! o!r4 ,! ef=t ( ! armature to t\* ! pole x ne>ly t\*es places ! diaphragm "u t5sion4 ,! free arm ( ! magnet is surr\nd$ by a coil #d1 ^: ends ext5d to =m ! l9e4 ,illu/ration3 ,fig4 #a4 ,type ( ,magneto ,telephone ,:5 s\nd vibrates ! diaphragm1 x vibrates ! armature also1 increas+ & decreas+ ! di/ance f ! free pole ( ! magnet4 ,! l9es ( =ce ?read+ ! coil #d are v>i$ z ! gap betwe5 ! magnet & ! armature is v>i$4 ,! result ( v>y+ ! l9es ( =ce ?r\gh ! turns ( ! coil is to produce an electromotive =ce 9 !m1 & if a clos$ pa? is provid$ by ! l9e1 a curr5t w fl[4 ,?is curr5t is an alt]nat+ "o hav+ a frequ5cy ! same z ! s\nd caus+ x4 ,z 9 spee* ! frequ5cies v>y con/antly1 _m pit*es con/itut+ ev5 a s+le spok5 ^w1 s ! alt]nat+ voice curr5ts are ( great v>y+ complexity1 & e fundam5tal frequ5cy has its h>monics sup]pos$4 ,conv]sion f ,voice ,curr5ts to ,vibration4 ,! be/ k ( ! action ( su* a telephone z is %[n 9 ,fig4 #a leads to ! conclusion t a half-cycle ( alt]nat+ curr5t is produc$ by an inw>d /roke ( ! diaphragm & a second half-cycle ( alt]nat+ curr5t by ! succe$+ outw>d /roke1 ^! half-cycles fl[+ 9 opposite directions4 ,assume "o complete cycle ( curr5t to pass ?r\gh ! l9e & also ?r\gh ano!r su* device z 9 ,fig4 #a & t ! fir/ half-cycle is ( su* direction z to increase ! p]man5t magnetism ( ! core4 ,! ef=t ( ?is increase is to n>r[ ! gap betwe5 ! armature & pole piece4 ,! diaphragm w ?rob inw>d dur+ ! half-cycle ( curr5t4 ,! succe$+ half-cycle be+ ( opposite direction w t5d to oppose ! magnetism ( ! core4 ,9 practice1 ! fl[ ( oppos+ curr5t nev] w\ld be great en\gh :olly to nullify & rev]se ! magnetism ( ! core1 s t ! opposition results 9 a m]e decrease1 caus+ ! armature's gap to increase & ! diaphragm to respond by an outw>d bl[4 ,complete ,cycle ( ,conv]sion4 ,! cycle ( actions ?us is complete2 "o complete s\nd-wave 9 air has produc$ a cycle ( motion 9 a diaphragm1 a cycle ( curr5t 9 a l9e1 a cycle ( magnetic *ange 9 a core1 a cycle ( motion 9 ano!r diaphragm1 & a result+ wave ( s\nd4 ,x is to be obs]v$ t ! *a9 ( op]ation involves ! exp5diture ( en]gy only by ! speak]1 ! only function ( any ( ! p>ts be+ t ( translat+ ?is en]gy f "o =m to ano!r4 ,9 e /age ( ^! translations1 !re are losses2 ! devis+ ( means ( limit+ ^! losses z greatly z possible is a problem ( telephone eng9e]+4 ,illu/ration3 ,fig4 #b4 ,magneto ,telephones & ,l9e ,magneto ,telephones4 ,! device 9 ,fig4 #a is a practical magneto receiv] & transmitt]4 ,x is *os5 z be/ pictur+ ! idea to be propos$4 ,fig4 #b illu/rates a pair ( magneto telephones ( ! e>ly ,bell type2 #a-a are diaphragms2 #b-b are p]man5t magnets ) a free end ( ea* br\ght z ne> z possible1 )\t t\*+1 to ! diaphragm4 ,ea* magnet be>s on its end ne>e/ ! diaphragm a w9d+ ( f9e wire1 ! two ends ( ea* ( ^! w9d+s be+ jo9$ by means ( a two-wire l9e4 ,all t has be5 said conc]n+ ,fig4 #a is true also ( ! electrical & magnetic actions ( ! devices ( ,fig4 #b4 ,9 ! latt]1 ! flux :i* ?reads ! f9e wire w9d+ is di/urb$ by motions ( ! transmitt+ diaphragm4 ,?is di/urbance ( ! flux creates electromotive =ces 9 ^? w9d+s4 ,simil>ly1 a v>iation ( ! electromotive =ces 9 ! w9d+s v>ies ! pull ( ! p]man5t magnet ( ! receiv+ in/rum5t ^u its diaphragm4 ,illu/ration3 ,no4 #aj ,,s]ies ,,multiple ,,swit*bo>d ,mon>* ,telephone ,mfg4 ,co4 ,illu/ration3 ,fig4 #c4 ,magneto ,telephones )\t ,p]man5t ,magnets ,fig4 #c illu/rates a simil> arrangem5t1 b x is to be und]/ood t ! cores ab\t :i* ! w9d+s are c>ri$ 9 ?is case are ( s(t iron & n ( h>d magnetiz$ /eel4 ,! necess>y magnetism :i* con/antly enables ! cores to ex]t a pull ^u ! diaphragm is provid$ by ! batt]y :i* is ins]t$ s]ially 9 ! l9e4 ,su* an arrangem5t 9 action diff]s 9 no p>ticul> f t ( ,fig4 #b1 = ! reason t x matt]s n at all :e!r ! magnetism ( ! core be produc$ by electromagnetic or by p]man5tly magnetic conditions4 ,! arrangem5t ( ,fig4 #c is a fundam5tal c\nt]p>t ( ! orig9al telephone ( ,pr(essor ,bell1 & x is ( p>ticul> int]e/ 9 ! pres5t /age ( ! art = ! reason t a t5d5cy lately is %[n to rev]t to ! e>ly type1 ab&on+ ! use ( ! p]man5t magnet4 ,! modifications :i* h be5 made 9 ! orig9al magneto telephone1 practically z %[n 9 ,fig4 #b1 h be5 _m4 ,?irty-five ye>s' exp]im5tation ^u & daily use ( ! in/rum5t has result$ 9 its ref9em5t to a po9t :]e x is a mo/ successful receiv] & a mo/ unsuccessful transmitt]4 ,its use = ! latt] purpose may be said to be no?+4 ,z a receiv]1 x is n only :olly satisfactory = comm]cial use 9 its regul> function1 b x is1 9 addition1 "o ( ! mo/ s5sitive electrical detect+ devices kn[n to ! art4 ,loose ,contact ,pr9ciple4 ,e>ly exp]im5t]s ^u ,bell's device1 all us+ 9 _! fir/ "w ! arrangem5t utiliz+ curr5t f a batt]y 9 s]ies ) ! l9e1 notic$ t s\nd 0 giv5 out by di/urb+ loose contacts 9 ! l9e circuit4 ,?is obs]vation l$ to ! arrangem5t ( circuits 9 su* a way t "s imp]fect contacts c\ld be %ak5 by means ( ! diaphragm1 & ! resi/ance ( ! l9e circuit v>i$ 9 ?is mann]4 ,an e>ly & int]e/+ =m ( su* imp]fect contact transmitt] device consi/$ m]ely ( metal conductors laid loosely 9 contact4 ,a simple example is t ( ?ree wire nails1 ! ?ird ly+ across ! o!r two1 ! two loose contacts ?us =m$ be+ arrang$ 9 s]ies ) a batt]y1 ! l9e1 & ! receiv+ in/rum5t4 ,su* a device :5 slightly j>r$1 by ! voice or o!r means1 causes abrupt v>iation 9 ! resi/ance ( ! l9e1 & w transmit spee*4 ,e>ly ,conceptions4 ,! conception ( ! possibility & desirability ( transmitt+ spee* by electricity may h occurr$ to _m1 long prior to its accompli%m5t4 ,x is c]ta9 t "o p]son1 at lea/1 _h a cle> idea ( ! g5]al problem4 ,9 #ahed1 ,*>les ,b\rseul1 a ,fr5*man1 wrote3 ,i h ask$ myself1 = example1 if ! spok5 ^w itself c\ld n be transmitt$ by electricity2 9 a ^w1 if :at 0 spok5 9 ,vi5na might n be he>d 9 ,p>is8 ,! ?+ is practicable 9 ?is way3 ,illu/ration3 ,fig4 #d4 ,reis ,transmitt] ,suppose t a man speaks ne> a movable disk suffici5tly flexible to lose none ( ! vibrations ( ! voice2 t ?is disk alt]nately makes & breaks ! connection f a batt]y2 y may h at a di/ance ano!r disk :i* w simultane\sly execute ! same vibrations4 ,! idea s express$ is weak 9 only "o p>ticul>4 ,?is p>ticul> is %[n by ! words italiciz$ by ourselves4 ,x is impossible to transmit a complex s]ies ( waves by any simple s]ies ( makes & breaks4 ,philipp ,reis1 a ,g]man1 devis$ ! arrangem5t %[n 9 ,fig4 #d = ! transmission ( s\nd1 lett+ ! make & break ( ! contact betwe5 ! diaphragm #a & ! po9t #b int]rupt ! l9e circuit4 ,8 receiv] took sev]al =ms1 all electromagnetic4 ,8 success 0 limit$ to ! transmission ( musical s\nds1 & x is n believ$ t articulate spee* ev] 0 transmitt$ by su* an arrangem5t4 ,x mu/ be rememb]$ t ! art ( telegraphy1 p>ticul>ly 9 ,am]ica1 0 well e/abli%$ long be=e ! inv5tion ( ! telephone1 & t an arrangem5t ( keys1 relays1 & a batt]y1 z %[n 9 ,fig4 #e1 0 well kn[n to a great _m p]sons4 ,atta*+ ! armatures ( ! relays ( su* a l9e to diaphragms1 z 9 ,fig4 #f1 at any "t aft] #ahch1 w\ld h produc$ ! telephone4 ,! h>dihood ( inv5tion to conceive su* a *ange 0 ! quality requir$4 ,illu/ration3 ,fig4 #e4 ,typical ,telegraph ,l9e ,limitations ( ,magneto ,transmitt]4 ,= reasons n f9ally e/abli%$1 ! ability ( ! magneto telephone to produce l>ge curr5ts f l>ge s\nds is n equal to its ability to produce l>ge s\nds f l>ge curr5ts4 ,z a receiv+ device1 x is unexcell$1 & b slight improvem5t has be5 made s9ce its fir/ inv5tion4 ,x is inadequate z a transmitt]1 & z e>ly z #ahgf1 ,pr(essor ,bell exhibit$ o!r means ?an electromagnetic action = produc+ ! v>y+ curr5ts z a consequ5ce ( diaphragm motion4 ,mu* o!r inv5tive ef=t 0 address$ to ?is problem1 ! aim ( all be+ to s5d out m robu/ voice curr5ts4 ,illu/ration3 ,fig4 #f4 ,telegraph ,equipm5t ,conv]t$ into ,telephone ,equipm5t ,o!r ,me?ods ( ,produc+ ,voice ,curr5ts4 ,"s ( ^! means are ! v>iation ( resi/ance 9 ! pa? ( direct curr5t1 v>iation 9 ! pressure ( ! s\rce ( t curr5t1 & v>iation 9 ! electro/atic capacity ( "s "p ( ! circuit4 ,electro/atic ,telephone4 ,! latt] me?od is pr9cipally t ( ,dolbe> & ,edison4 ,dolbe>'s ?\ght is illu/rat$ 9 ,fig4 #g4 ,two conduct+ plates are br\ght close toge!r4 ,"o is free to vibrate z a diaphragm1 :ile ! o!r is fix$4 ,! elem5t #a 9 ,fig4 #g is m]ely a /ud to hold rigid ! plate x be>s aga9/4 ,ea* ( two in/rum5ts connect$ by a l9e conta9s su* a pair ( plates1 & a batt]y 9 ! l9e keeps !m *>g$ to its pot5tial4 ,! two diaphragms ( ea* in/rum5t are kept drawn t[>ds ea* o!r because _! unlike *>ges attract ea* o!r4 ,! vibration ( "o ( ! diaphragms *anges ! pot5tial ( ! o!r pair2 ! degree ( attraction ?us is v>i$1 s t vibration ( ! diaphragm & s\nd waves result4 ,examples ( ?is me?od ( telephone transmission are m famili> to lat] practice 9 ! =m ( cond5s] receiv]s4 ,a cond5s]1 9 usual pres5t practice1 be+ a pair ( closely adjac5t conductors ( consid]able surface insulat$ f ea* o!r1 a rapidly v>y+ curr5t actually may move "o or bo? ( ! conductors4 ,ord9>ily ^! are ( ?9 %eet metal 7foil7 int]leav$ ) an insulat+ mat]ial1 su* z pap] or mica4 ,voice curr5ts c vibrate ! metal %eets 9 a degree to cause ! cond5s] to speak4 ,^! cond5s] me?ods ( telephony h n become comm]cial4 ,illu/ration3 ,fig4 #g4 ,electro/atic ,telephone ,v>iation ( ,electrical ,pressure4 ,v>iation ( ! pressure ( ! s\rce is a conceivable way ( transmitt+ spee*4 ,to utilize x1 w\ld require t ! vibrations ( ! diaphragm cause ! electromotive =ce ( a batt]y or ma*9e to v>y 9 h>mony ) ! s\nd waves4 ,s f> z we are in=m$ ?is me?od nev] has come into practical use4 ,v>iation ( ,resi/ance4 ,v>iation ( resi/ance proportional to ! vibrations ( ! diaphragm is ! me?od :i* has produc$ ! pres5t prevail+ =m ( transmission4 ,pr(essor ,bell's ,c5t5nial exhibit conta9$ a wat]-resi/ance transmitt]4 ,dr4 ,eli%a ,gray also devis$ "o4 ,9 bo?1 ! diaphragm act$ to increase & dim9i% ! di/ance betwe5 two conductors imm]s$ 9 wat]1 l[]+ & rais+ ! resi/ance ( ! l9e4 ,x lat] 0 discov]$ by ,edison t c>bon possesses a peculi>ly great prop]ty ( v>y+ its resi/ance "u pressure4 ,pr(essor ,david ,e4 ,hughes discov]$ t two conduct+ bodies1 pref]ably ( r poor conductivity1 :5 laid toge!r s z to =m a loose contact betwe5 !m1 possess$1 9 rem>kable degree1 ! ability to v>y ! resi/ance ( ! pa? ?r\gh !m :5 subject to su* vibrations z w\ld alt] ! intimacy ( contact4 ,he ?us discov]$ & =mulat$ ! pr9ciples ( loose contact ^u :i* ! op]ation ( all mod]n transmitt]s re/s4 ,hughes' device 0 nam$ by him a microphone1 indicat+ a magnification ( s\nd or an ability to respond to & make audible m9ute s\nds4 ,x is %[n 9 ,fig4 #h4 ,firmly atta*$ to a bo>d are two c>bon blocks1 %[n 9 section 9 ! figure4 ,a rod ( c>bon ) cone-%ap$ ends is support$ loosely betwe5 ! two blocks1 conical depressions 9 ! blocks receiv+ ! ends ( ! rod4 ,a batt]y & magneto receiv] are connect$ 9 s]ies ) ! device4 ,"u c]ta9 conditions ( contact1 ! arrangem5t is extraord9>ily s5sitive to small s\nds & approa*es an ability indicat$ by its "n4 ,its practical usefulness has be5 n z a s]viceable spee* transmitt]1 b z a /imulus to ! devis+ ( transmitt]s us+ c>bon 9 o!r ways4 ,v>iation ( ! resi/ance ( metal conductors & ( contact betwe5 metals has s]v$ to transmit voice curr5ts1 b no mat]ial approa*es c>bon 9 ?is prop]ty4 ,illu/ration3 ,fig4 #h4 ,hughes' ,microphone ,c>bon4 ,adaptability4 ,! application ( c>bon to use 9 transmitt]s has tak5 _m =ms4 ,!y may be classifi$ z ^? hav+ a s+le contact & ^? hav+ a plurality ( contacts2 9 all cases1 ! intimacy ( contact is v>i$ by ! diaphragm excursions4 ,an example ( ! s+le-contact type is ! ,blake transmitt]1 long famili> 9 ,am]ica4 ,an example ( ! multiple-contact type is ! loose-c>bon type univ]sal n[4 ,o!r types popul> at o!r times & 9 p>ticul> places use solid rods or blocks ( c>bon hav+ _m po9ts ( contact1 ?\gh n 9 a p[d]$ or granul> =m4 ,fig4 #i %[s an example ( ea* ( ! g5]al =ms ( transmitt]s4 ,! use ( granul> c>bon z a transmitt] mat]ial has ext5d$ greatly ! radius ( spee*1 & has be5 a pr9cipal contribut+ cause = ! great spread ( ! telephone indu/ry4 ,illu/ration3 ,fig4 #i4 ,g5]al ,types ( ,transmitt]s ,sup]iority4 ,! sup]iority ( c>bon ov] o!r resi/ance-v>y+ mat]ials = transmitt]s is well recogniz$1 b ! reason = x is n well kn[n4 ,v>i\s !ories h be5 propos$ to expla9 :y1 = example1 ! resi/ance ( a mass ( c>bon granules v>ies ) ! vibrations or compressions to :i* !y are subject$4 ,f\r pr9cipal !ories respectively allege3 ,fir/1 t *ange 9 pressure actually *anges ! specific resi/ance ( c>bon4 ,second1 t ^u ! surface ( c>bon bodies exi/s "s gas 9 "s =m ( atta*m5t or comb9ation1 v>iations ( pressure caus+ v>iations ( resi/ance m]ely by r$uc+ ! ?ickness ( ?is int]v5+ gas4 ,?ird1 t ! *ange ( resi/ance is caus$ by v>iations 9 ! l5g? ( electrical arcs betwe5 ! p>ticles4 ,f\r?1 t *ange ( pressure *anges ! area ( contact1 z is true ( solids g5]ally4 ,"o may take 8 *oice4 ,a solid c>bon block or rod is n f\nd to decrease its resi/ance by be+ subject$ to pressure4 ,! gas !ory lacks exp]im5tal pro( also4 ,! exi/5ce ( arcs betwe5 ! granules nev] has be5 se5 or o!rwise obs]v$ "u normal work+ conditions ( a transmitt]2 :5 arcs surely are exp]im5tally e/abli%$ betwe5 ! granules ! usefulness ( ! transmitt] ceases4 ,! f9al !ory1 t *ange ( pressure *anges area ( surface contact1 does n expla9 :y o!r conductors ?an c>bon are n good mat]ials = transmitt]s4 ,?is1 x may be notic$1 is j :at ! !ories set out to make cle>4 ,!re are _m :o feel t m exp]im5tal data is requir$ be=e a conclusive & satisfactory !ory c be set up4 ,!re is ne$ ( "o1 = a prop] !ory (t5 po9ts ! way = effective advance 9 practice4 ,c>bon & magneto transmitt]s diff] :olly 9 _! me?ods ( action4 ,! magneto transmitt] produces curr5t2 ! c>bon transmitt] controls curr5t4 ,! =m] is an alt]nat+-curr5t g5]ator2 ! latt] is a rheo/at4 ,! magneto transmitt] produces alt]nat+ curr5t )\t input ( any electricity at all2 ! c>bon transmitt] m]ely controls a direct curr5t1 suppli$ by an ext]nal s\rce1 & v>ies its am\nt )\t *ang+ its direction4 ,! c>bon transmitt]1 h[ev]1 may be associat$ ) o!r devices 9 a circuit 9 su* a way z to trans=m direct curr5ts into alt]nat+ ones1 or x may be us$ m]ely to *ange con/ant direct curr5ts into undulat+ ones1 :i* nev] rev]se direction1 z alt]nat+ curr5ts always d4 ,^! di/9ctions are important4 ,illu/ration3 ,fig4 #aj4 ,batt]y 9 ,l9e ,circuit ,limitations4 ,a c>bon transmitt] be+ m]ely a resi/ance-v>y+ device1 its usefulness dep5ds on h[ mu* its resi/ance c v>y 9 response to motions ( air molecules4 ,a granul>-c>bon transmitt] may v>y betwe5 resi/ances ( #e to #ej ohms :ile transmitt+ a p>ticul> tone1 hav+ ! l[] resi/ance :5 its diaphragm is driv5 inw>d4 ,conceive ?is transmitt] to be 9 a l9e z %[n 9 ,fig4 #aj1 ! l9e1 di/ant receiv]1 & batt]y toge!r hav+ a resi/ance ( #a1jjj ohms4 ,! m9imum resi/ance !n is #a1jje ohms & ! maximum #a1jej ohms4 ,! v>iation is limit$ to ab\t #d4e p] c5t4 ,! great] ! resi/ance ( ! l9e & o!r elem5ts ?an ! transmitt]1 ! less relative *ange ! transmitt] c produce1 & ! less l\dly ! di/ant receiv] c speak4 ,illu/ration3 ,fig #aa4 ,batt]y 9 ,local ,circuit ,induction ,coil4 ,mr4 ,edison realiz$ ?is limitation to ! use ( ! c>bon transmitt] direct 9 ! l9e1 & contribut$ ! means ( remov+ x4 ,8 me?od is to introduce an induction coil betwe5 ! l9e & ! transmitt]1 its function be+ to translate ! v>iation ( ! direct curr5t controll$ by ! transmitt] into true alt]nat+ curr5ts4 ,an induction coil is m]ely a trans=m]1 & = ! use "u discussion consi/s ( two insulat$ wires w\nd ar\nd an iron core4 ,*ange 9 ! curr5t c>ri$ by "o ( ! w9d+s produces a curr5t 9 ! o!r4 ,if direct curr5t be fl[+ 9 "o ( ! w9d+s1 & rema9s con/ant1 no curr5t :atev] is produc$ 9 ! o!r4 ,x is important to note t x is *ange1 & *ange only1 :i* produces t alt]nat+ curr5t4 ,fig4 #aa %[s an induction coil relat$ to a c>bon transmitt]1 a batt]y1 & a receiv]4 ,fig4 #ab %[s exactly ! same arrangem5t1 us+ conv5tional signs4 ,! w9d+ ( ! induction coil :i* is 9 s]ies ) ! transmitt] & ! batt]y is call$ ! prim>y w9d+2 ! o!r is call$ ! second>y w9d+4 ,9 ! arrangem5t ( ,figs4 #aa & #ab ! batt]y has no metallic connection ) ! l9e1 s t x is call$ a local batt]y4 ,! circuit conta9+ ! batt]y1 transmitt]1 & prim>y w9d+ ( ! induction coil is call$ ! local circuit4 ,let u obs]ve :at is ! advantage ( ?is arrangem5t ov] ! case ( ,fig4 #aj4 ,us+ ! same values ( resi/ance 9 ! transmitt] & l9e1 assume ! local circuit ap>t f ! transmitt] to h a fix$ resi/ance ( #e ohms4 ,! limits ( v>iations 9 ! local circuit1 !re=e1 are #aj & #ee ohms1 ?us mak+ ! maximum #e4e times ! m9imum1 or an increase ( #dej p] c5t z aga9/ #d4e p] c5t 9 ! case ( ,fig4 #aj4 ,! *anges1 !re=e1 are #ajj times z great4 ,illu/ration3 ,fig4 #ab4 ,conv5tional ,diagram ( ,talk+ ,circuit ,! relation betwe5 ! w9d+s ( ! induction coil 9 ?is practice are su* t ! second>y w9d+ conta9s _m m turns ?an ! prim>y w9d+4 ,*anges 9 ! circuit ( ! prim>y w9d+ produce pot5tials 9 ! second>y w9d+ correspond+ly high] ?an ! pot5tials produc+ !m4 ,^! second>y pot5tials dep5d ^u ! ratio ( turns 9 ! two w9d+s & !re=e1 )9 close limits1 may be *os5 z wi%$4 ,high pot5tials 9 ! second>y w9d+ are admirably adapt$ to transmit curr5ts 9 a high-resi/ance l9e1 = exactly ! same reason t long-di/ance p[] transmission meets ) b "o-qu>t] ( "o k9d ( loss :5 ! s5d+ pot5tial is d\bl$1 "o-hundr$? ( t loss :5 x is rais$ t5fold1 & simil>ly4 ,! induction coil1 !re=e1 s]ves ! d\ble purpose ( a /ep-up trans=m] to limit l9e losses & a device = va/ly increas+ ! range ( *ange 9 ! transmitt] circuit4 ,fig4 #ac is (f]$ to rem9d ! /ud5t ( ! action ( an induction coil or trans=m] 9 ^: prim>y circuit a direct curr5t is increas$ & decreas$4 ,an increase ( curr5t 9 ! local w9d+ produces an impulse ( opposite direction 9 ! turns ( ! second>y w9d+2 a decrease ( curr5t 9 ! local w9d+ produces an impulse ( ! same direction 9 ! turns ( ! second>y w9d+4 ,! key ( ,fig4 #ac be+ clos$1 curr5t fl[s upw>d 9 ! prim>y w9d+ z drawn 9 ! figure1 induc+ a d[nw>d impulse ( curr5t 9 ! second>y w9d+ & its circuit z not$ at ! "r ( ! figure4 ,on ! key be+ op5$1 curr5t ceases 9 ! prim>y circuit1 induc+ an upw>d impulse ( curr5t 9 ! second>y w9d+ & circuit z %[n4 ,dur+ o!r ?an in/ants ( op5+ & clos+ 7*ang+7 ! local circuit1 no curr5t :atev] fl[s 9 ! second>y circuit4 ,illu/ration3 ,fig4 #ac4 ,induction-,coil ,action ,x is by ^! means t telephone transmitt]s draw direct curr5t f prim>y batt]ies & s5d high-pot5tial alt]nat+ curr5ts ov] l9es2 ! same process produces :at 9 ,!rapeutics are call$ ,f>adic curr5ts1 & enables also a simple vibrat+ contact-mak] to produce alt]nat+ curr5ts = op]at+ pol>iz$ r+]s ( telephone sets4 ,detrim5tal ,effects ( ,capacity4 ,electro/atic capacity plays an important "p 9 ! transmission ( spee*4 ,its pres5ce betwe5 ! wires ( a l9e & betwe5 !m & ! e>? causes "o ( ! losses f :i* long-di/ance telephony suff]s4 ,its pres5ce 9 cond5s]s assi/s 9 ! solution ( _m circuit & app>atus problems4 ,a cond5s] is a device compos$ ( two or m conductors insulat$ f ea* o!r by a m$ium call$ ! dielectric4 ,a pair ( metal plates sep>at$ by glass1 a pair ( wires sep>at$ by air1 or a pair ( %eets ( foil sep>at$ by pap] or mica may con/itute a cond5s]4 ,! use ( cond5s]s z pieces ( app>atus & ! problems pres5t$ by electro/atic capacity 9 l9es are discuss$ 9 o!r *apt]s4 ,measurem5ts ( ,telephone ,curr5ts4 ,x has be5 recogniz$ 9 all bran*es ( eng9e]+ t a def9ite advance is possible only :5 quantitative data exi/s4 ,! lack ( reliable means ( measur+ telephone curr5ts has be5 a pr9cipal cause ( ! difficulty 9 solv+ _m ( its problems4 ,x is only 9 v rec5t times t accurate & reliable means h be5 work$ out = measur+ ! small curr5ts :i* fl[ 9 telephone l9es4 ,^! ways are ( two g5]al k9ds3 by !rmal & by electromagnetic means4 ,!rmal ,me?od4 ,! !rmal me?ods simply measure1 9 "s way1 ! am\nt ( heat :i* is produc$ by a receiv$ telephone curr5t4 ,:5 ?is curr5t is all[$ to pass ?r\gh a conductor ! effect ( ! heat g5]at$ 9 t conductor1 is obs]v$ 9 "o ( ?ree ways3 by ! expansion ( ! conductor1 by its *ange 9 resi/ance1 or by ! production ( an electromotive =ce 9 a !rmo-electric c\ple heat$ by ! conductor4 ,any "o ( ^! ?ree ways c be us$ to get "s idea ( ! am\nt ( curr5t :i* is receiv$4 ,none ( !m gives an accurate k ( ! =ms ( ! waves :i* cause ! reproduction ( spee* 9 ! telephone receiv]4 ,illu/ration3 ,fig4 #ad4 ,oscillogram ( ,telephone ,curr5ts ,electromagnetic ,me?od4 ,an electromagnetic device adapt$ to tell some?+ ( ! magnitude ( ! telephone curr5t & also some?+ ( its =m1 i4e41 some?+ ( its v>i\s increases & decreases & also ( its *anges 9 direction is ! oscillograph4 ,an oscillograph is compos$ ( a magnetic field =m$ by direct curr5ts or by a p]man5t magnet1 a turn ( wire "u me*anical t5sion 9 t field1 & a mirror borne by ! turn ( wire1 adapt$ to reflect a beam ( light to a photographic film or to a rotat+ mirror4 ,:5 a curr5t is to be measur$ by ! oscillograph1 x is pass$ ?r\gh ! turn ( wire 9 ! magnetic field4 ,:ile no curr5t is pass+1 ! wire does n move 9 ! magnetic field & its mirror reflects a /ation>y beam ( light4 ,a photographic film mov$ 9 a direction normal to ! axis ( ! turn ( wire w h drawn ^u x a /raight l9e by ! beam ( light4 ,if ! beam ( light1 h[ev]1 is mov$ by a curr5t1 f side to side at "r angles to ?is axis1 x w draw a wavy l9e on ! photographic film & ?is wavy l9e w picture ! alt]nations ( t curr5t & ! oscillations ( ! molecules ( air :i* c>ri$ ! orig9at+ s\nd4 ,fig4 #ad is a photograph ( n9e diff]5t v[el s\nds :i* h caus$ ! oscillograph to take _! pictures4 ,!y are copies ( records made by ,mr4 ,bela ,gati1 assi/$ by ,mr4 ,tolnai4 ,! measur+ in/rum5t consi/$ ( an oscillograph ( ! type describ$1 ! transmitt] be+ ( ! c>bon type actuat$ by a #b-volt batt]y4 ,! prim>y curr5t 0 trans=m$ by an induction coil ( ! ord9>y type & ! trans=m$ curr5t 0 s5t ?r\gh a non-inductive resi/ance ( #c1jjj ohms4 ,no cond5s]s 7 plac$ 9 ! circuit4 ,x w be se5 t ! integral values ( ! curves1 />t+ f z]o1 are v>iable4 ,! positive & ! negative portions ( ! curves are n equal1 s t ! solution ( ! individual h>monic motion is difficult & labori\s4 ,^! photographs po9t out sev]al facts v cle>ly4 ,"o is t ! alt]nations ( curr5ts 9 ! telephone l9e1 l ! motions ( ! molecules ( air ( ! orig9al s\nd1 are highly complex & are n1 z musical tones are1 regul> recurr5ces ( equal vibrations4 ,!y %[ also t any v[el s\nd may be consid]$ to be a regul> recurr5ce ( c]ta9 gr\ps ( vibrations ( diff]5t amplitudes & ( diff]5t frequ5cies4 ,,*apt] ,,iii ,,electrical ,,signals ,electric calls or signals are ( two k9ds3 audible & visible4 ,illu/ration3 ,fig4 #ae4 ,telegraph ,s\nd] & ,key ,illu/ration3 ,fig4 #af4 ,vibrat+ ,bell ,audible ,signals4 ,telegraph ,s\nd]4 ,! e>lie/ electric signal 0 an audible "o1 be+ ! telegraph s\nd]1 or ! ,morse regi/] consid]$ ap>t f its regi/]+ function4 ,ea* telegraph s\nd] s]ves z an audible electric signal & is capable ( signify+ m ?an t ! call is be+ made4 ,su* a signal is op]at$ by ! mak+ & break+ ( curr5t f a batt]y4 ,an arrangem5t ( ?is k9d is %[n 9 ,fig4 #ae1 9 :i* pressure ^u ! key causes ! curr5t f ! batt]y to en]gize ! s\nd] & give "o %>p audible rap ( ! lev] ^u ! /rik+ po/4 ,vibrat+ ,bell4 ,! vibrat+ bell1 s widely us$ z a door bell1 is a device consequ5t to ! telegraph4 ,its action is to give a s]ies ( bl[s on its gong :5 its key or pu% button closes ! batt]y circuit4 ,at ! risk ( describ+ a trite ?\gh n trivial ?+1 x may be said t :5 ! contact #a ( ,fig4 #af is clos$1 curr5t f ! batt]y en]gizes ! armature #b1 caus+ ! latt] to /rike a bl[ on ! gong & to break ! l9e circuit z well1 by op5+ ! contact back ( ! armature4 ,s de-en]giz$1 ! armature falls back & ! cycle is repeat$ until ! button contact is releas$4 ,a comp>ison ( ?is action ) t ( ! pol>iz$ r+] 7to be describ$ lat]7 w be f\nd ( int]e/4 ,illu/ration3 ,fig4 #ag4 ,elem5tal ,magneto-,g5]ator ,magneto-,bell4 ,! magneto-bell came into wide use ) ! spread ( telephone s]vice4 ,its two fundam5tal p>ts are an alt]nat+-curr5t g5]ator & a pol>iz$ bell-r++ device4 ,ea* _h its c\nt]p>t long be=e ! inv5tion ( ! telephone1 ?\gh made famili> by ! latt]4 ,! alt]nat+-curr5t g5]ator ( ! magneto-bell consi/s ( a rotatable armature compos$ ( a coil ( insulat$ wire & usually a core ( s(t iron1 its rotation tak+ place 9 a magnetic field4 ,?is field is usually provid$ by a p]man5t magnet1 h5ce ! "n magneto-g5]ator4 ,! puri/ 9 t]ms may well say1 h[ev]1 t e =m :atev] ( ! dynamo-electric g5]ator is a magneto-g5]ator1 z magnetism is "o l9k 9 e su* conv]sion ( me*anical p[] into electricity4 ,! t]ms magneto-electric1 magneto-g5]ator1 etc41 involv+ ! t]m magneto1 h come to imply ! pres5ce ( p]man5tly magnetiz$ /eel z an elem5t ( ! con/ruction4 ,9 its e>ly =m1 ! magneto-g5]ator consi/$ ( ! arrangem5t %[n 9 ,fig4 #ag1 :]e9 a p]man5t magnet c rotate on an axis be=e an electromagnet hav+ s(t iron cores & a w9d+4 ,rev]sals ( magnetism produce curr5t 9 alt]nately rev]s+ half-cycles1 "o complete rotation ( ! magnet produc+ "o su* cycle4 ,obvi\sly ! result w\ld be ! same if ! magnet 7 /ation>y & ! coils %\ld rotate1 :i* is ! con/ruction ( m mod]n devices4 ,! turn+ ( ! crank ( a magneto-bell rotates ! armature 9 ! magnetic field by "s =m ( ge>+ at a rate usually ( ! ord] ( tw5ty turns p] second1 produc+ an alt]nat+ curr5t ( t frequ5cy4 ,?is curr5t is caus$ by an effective electromotive =ce :i* may be z great z #ajj volts1 produc$ imm$iately by ! en]gy ( ! us]4 ,9 an equipm5t us+ a magneto-telephone z bo? receiv] & transmitt] & a magneto-bell z its signal-s5d+ ma*9e1 z 0 usual 9 #ahgg1 x is int]e/+ to note t ! entire motive p[] = signals & spee* transmission 0 suppli$ by ! muscul> tissues ( ! us]--a case ( work+ "o's passage4 ,illu/ration3 ,fig4 #ah4 ,ext5sion ( a ,p]man5t ,magnet ,! alt]nat+ curr5t f ! g5]ator is receiv$ & conv]t$ into s\nd by means ( ! pol>iz$ r+]1 a device :i* is int]e/+ z dep5d+ ^u sev]al ( ! electrical1 me*anical1 & magnetic actions :i* are ! f\ndations ( telephone eng9e]+4 ,illu/ration3 ,fig4 #ai4 ,ext5sion ( a ,p]man5t ,magnet ,:y ! r+] r+s may be ga!r$ f a /udy ( ,figs4 #ah to #ba4 ,a p]man5t magnet w imp>t tempor>y magnetism to pieces ( iron ne> x4 ,9 ,fig4 #ah two pieces ( iron are s en]giz$4 ,! ends ( ^! pieces :i* are ne>e/ to ! p]man5t magnet #a are ( ! opposite pol>ity to ! end !y approa*1 ! free ends be+ ( opposite pol>ity4 ,9 ! figure1 ^! free ends are m>k$ ,n1 mean+ !y are ( a pol>ity to po9t nor? if free to po9t at all4 ,engli%-speak+ p]sons call ?is nor? pol>ity4 ,simil>ly1 z 9 ,fig4 #ai1 any arrangem5t ( iron ne> a p]man5t magnet always w h free poles ( ! same pol>ity z ! end ( ! p]man5t magnet ne>e/ !m4 ,a p]man5t magnet s relat$ to iron =ms "p ( a pol>iz$ r+]4 ,s does an electromagnet compos$ ( w9d+s & iron cores4 ,fig4 #bj rem9ds u ( ! law ( electromagnets4 ,if curr5t fl[s f ! plus t[>ds ! m9us side1 ) ! w9d+s z drawn1 pol>ities w be induc$ z m>k$4 ,illu/ration3 ,fig4 #bj4 ,electromagnet ,illu/ration3 ,fig4 #ba4 ,pol>iz$ ,r+] ,if1 n[1 su* an electromagnet1 a p]man5t magnet1 & a pivot$ armature be relat$ to a pair ( gongs z %[n 9 ,fig4 #ba1 a pol>iz$ r+] results4 ,x %\ld be not$ t a p]man5t magnet has bo? its poles pres5t$ 7?\gh "o ( ! poles is n actually atta*$7 to two p>ts ( ! iron ( ! electro-magnet4 ,! result is t ! ends ( ! armature are ( s\? pol>ity & ^? ( ! core are ( nor? pol>ity4 ,all ! m>k+s ( ,fig4 #ba relate to ! pol>ity produc$ by ! p]man5t magnet4 ,if1 n[1 a curr5t fl[ 9 ! r+] w9d+ f plus to m9us1 obvi\sly ! "r-h& pole w be additively magnetiz$1 ! curr5t t5d+ to produce nor? magnetism !re2 also ! left-h& pole w be subtractively magnetiz$1 ! curr5t t5d+ to produce s\? magnetism !re4 ,if ! curr5t be ( a c]ta9 /r5g?1 relative to ! c]ta9 r+] "u /udy1 magnetism 9 ! left pole w be neutraliz$ & t 9 ! "r pole d\bl$4 ,h5ce ! armature w be attract$ m by ! "r pole ?an by ! left & w /rike ! "r-h& gong4 ,a rev]sal ( curr5t produces an opposite action1 ! left-h& gong be+ /ruck4 ,! curr5t ceas+1 ! armature rema9s :]e la/ ?r[n4 ,illu/ration3 ,,op]ator',s ,,equipm5t ,clem5t ,automanual ,sy/em4 ,x is important to note t ! /r5g? ( action dep5ds ^u ! /r5g? ( ! curr5t up to a c]ta9 po9t only4 ,t dep5ds ^u ! /r5g? ( ! p]man5t magnet4 ,:5ev] ! curr5t is great en\gh j to neutralize ! normal magnetism ( "o pole & to d\ble t ( ! o!r1 no increase 9 curr5t w cause ! device to r+ any l\d]4 ,?is makes obvi\s ! importance ( a prop] p]man5t magnetism & displays ! fallacy ( "s ef=t to increase ! output ( v>i\s devices dep5d+ ^u ^! pr9ciples4 ,?is discussion ( magneto-electric signal+ is introduc$ "h because ( a belief 9 its be+ fundam5tal4 ,*apt] ,,viii treats ( su* a signal+ 9 fur!r detail4 ,telephone ,receiv]4 ,! telephone receiv] itself s]ves a useful purpose z an audible signal4 ,an int]rupt$ or alt]nat+ curr5t ( prop] frequ5cy & am\nt w produce 9 x a musical tone :i* c be he>d ?r\gh\t a l>ge room4 ,?is fact enables a telephone c5tral (fice to signal a subscrib] :o has left 8 receiv] (f ! swit* hook1 s t normal conditions may be re/or$4 ,visible ,signals4 ,electromagnetic ,signal4 ,practical visual signals are ( two g5]al k9ds3 electromagnetic devices = mov+ a t>get or po9t]1 & inc&esc5t lamps4 ,! e>lie/ & mo/ widely us$ visible signal 9 telephone practice 0 ! annunciator1 hav+ a %utt] adapt$ to fall :5 ! magnet is en]giz$4 ,fig4 #bb is su* a signal4 ,%utt] #a is held by ! cat* #b f dropp+ to ! "r by its own gravity4 ,! "n gravity-drop is ?us obvi\s4 ,curr5t en]giz+ ! core attracts ! armature #c1 lifts ! cat* #b1 & ! %utt] falls4 ,a simple modification ( ! gravity-drop produces ! visible signal %[n 9 ,fig4 #bc4 ,en]giz+ ! core lifts a t>get s z to r5d] x visible ?r\gh an op5+ 9 ! plate #a4 ,a contra/ ( color betwe5 ! plate & ! t>get height5s ! effect4 ,illu/ration3 ,fig4 #bb4 ,gravity-,drop ,! gravity-drop is pr9cipally adapt$ to ! magneto-bell sy/em ( signal+1 :]e an alt]nat+ curr5t is s5t ov] ! l9e to a c5tral (fice by ! op]ation ( a bell crank at ! subscrib]'s /ation1 ?is curr5t1 la/+ only z long z ! crank is turn$1 en]gizes ! drop1 :i* may be re/or$ by h& or o!rwise & w rema9 lat*$4 ,! visible signal is bett] adapt$ to l9es 9 :i* ! signal+ is done by means ( direct curr5t1 z1 = example1 9 sy/ems :]e ! removal ( ! receiv] f ! hook at ! subscrib]'s /ation closes ! l9e circuit1 caus+ curr5t to fl[ ?r\gh ! w9d+ ( ! visible signal & s display+ x until ! receiv] has be5 hung ^u ! hook or ! circuit op5$ by "s op]ation at ! c5tral (fice4 ,visible signals ( ! magnetic type ( ,fig4 #bc h be5 widely us$ 9 connection ) common-batt]y sy/ems1 bo? = l9e signals & = sup]visory purposes1 indicat+ ! /ate & ! progress ( ! connection & conv]sation4 ,illu/ration3 ,fig4 #bc4 ,electromagnetic ,visible ,signal ,illu/ration3 ,fig4 #bd4 ,lamp ,signal & ,l5s ,electric-,lamp ,signal4 ,inc&esc5t electric lamps appe>$ 9 telephony z a consid]able elem5t ab\t #ahij4 ,!y are bett] ?an ei!r =m ( me*anical visible signals because ( ?ree pr9cipal qualities3 simplicity & ease ( re/or+ !m to normal z comp>$ ) drops2 _! compactness2 & _! great] prom95ce :5 display$4 ,( ! latt] quality1 "o may say t !y are m insi/5t1 z !y give out light in/ead ( reflect+ x1 z d all o!r visible signals4 ,9 its be/ =m1 ! lamp signal is m\nt$ beh9d a hemisph]ical l5s1 ei!r slightly cl\d$ or cut 9 facets4 ,?is l5s s]ves to di/ribute ! rays ( light f ! lamp1 ) ! result t ! signal may be se5 f a wide angle ) ! axis ( ! l5s1 z %[n 9 ,fig4 #bd4 ,?is is ( p>ticul> advantage 9 connection ) manual-swit*bo>d connect+ cords1 z x enables ! signals to be m\nt$ close to & ev5 among ! cords1 _! great visible prom95ce :5 %9+ sav+ !m f be+ hidd54 ,! influ5ce ( ! lamp signal 0 "o ( ! pot5t ones 9 ! developm5t ( ! type ( multiple swit*bo>d :i* is n[ univ]sal z ! me*anism ( l>ge manual ex*anges4 ,! fir/ l>ge trial ( su* an equipm5t 0 9 #ahif 9 ,worce/]1 ,mass4 ,no l>ge & successful multiple swit*bo>d ) any o!r type ( signal has be5 built s9ce t "t4 ,any electric signal has upp] & l[] limits ( curr5t betwe5 :i* x is to be actuat$4 ,x mu/ receive curr5t en\gh to op]ate b n en\gh to become damag$ by ov]heat+4 ,! magnetic types ( visible signals h a wid] range betwe5 ^! limits ?an h lamp signals4 ,if curr5t 9 a lamp is too little1 its filam5t ei!r w n gl[ at all or m]ely at a dull r$1 insuffici5t = a prop] signal4 ,if ! curr5t is too great1 ! filam5t is heat$ beyond its /r5g? & p>ts at ! weake/ place4 ,?is range betwe5 curr5t limits 9 magnetic visible signals is great en\gh to enable !m to be us$ direct 9 telephone l9es1 ! op]at+ curr5t ?r\gh ! l9e & signal 9 s]ies ) a fix$ voltage at ! c5tral (fice be+ n h>mfully great :5 ! entire l9e resi/ance is %unt$ out at or ne> ! c5tral (fice4 ,! increase ( curr5t may be z great z t5 times )\t damage to ! w9d+ ( su* a signal4 ,9 lamps1 ! safe m>g9 is mu* less4 ,! curr5t :i* j gives a suffici5t light+ ( ! signal may be ab\t d\bl$ ) safety to ! filam5t ( ! lamp4 ,consequ5tly x is n feasible to place ! lamp directly 9 s]ies ) long expos$ l9es4 ,a %ort circuit ( su* a l9e ne> ! c5tral (fice w burn x out4 ,illu/ration3 ,fig4 #be4 ,lamp ,signal ,controll$ by ,relay ,! qualities ( electromagnets & lamps 9 ^! respects are us$ to advantage by ! lamp signal arrangem5t %[n 9 ,fig4 #be4 ,a relay is 9 s]ies ) ! l9e & provides a l>ge range ( s5sibility4 ,x is able to c>ry any curr5t ! c5tral-(fice curr5t s\rce c pass ?r\gh x4 ,! local circuit ( ! relay includes ! lamp4 ,en]giz+ ! relay lights ! lamp1 & ! rev]se2 ! lamp is ?us isolat$ f dang] & receives ! curr5t be/ adapt$ to its ne$s4 ,all l9es are n long & :5 enclos$ 9 cable or 9 well-insulat$ int]ior wire1 may be only remotely 9 dang] ( be+ %ort-circuit$4 ,su* conditions exi/ 9 private-bran* ex*anges1 :i* are gr\ps ( telephones1 usually local to limit$ premises1 connect$ to a swit*bo>d on ^? premises4 ,su* a situation p]mits ! omission ( ! l9e relay1 ! lamp be+ directly 9 ! l9e4 ,fig4 #bf %[s ! extreme simplicity ( ! arrangem5t1 conta9+ no mov+ p>ts or co/ly elem5ts4 ,lamps = su* s]vice h improv$ greatly s9ce ! dem& began to gr[4 ,! small bulk p]mitt$ by ! ne$ ( compactness1 ! high filam5t resi/ance requir$ = simplicity ( ! g5]al p[] s*eme ( ! sy/em1 & ! ne$ ( consid]able /urd9ess 9 ! complet$ ?+ h made ! task a h>d "o4 ,! practical result1 h[ev]1 is a signal lamp :i* is highly satisfactory4 ,illu/ration3 ,fig4 #bf4 ,lamp ,signal ,directly 9 ,l9e ,illu/ration3 ,fig4 #bg4 ,lamp ,signal & ,balla/ ,! nature ( c>bon & c]ta9 e>?s be+ t _! conductivity rises ) ! temp]ature & t ( metals be+ t _! conductivity falls ) ! temp]ature1 has enabl$ ! ,n]n/ lamp to be successful4 ,! same relation ( prop]ties has enabl$ inc&esc5t-lamp signals to be connect$ direct to l9es )\t relays1 b comp5sat$ aga9/ too great a curr5t by caus+ ! resi/ance 9 s]ies ) ! lamp to be increas$ inv]sely z ! resi/ance ( ! filam5t4 ,employm5t ( a balla/ resi/ance 9 ?is way is ref]r$ to 9 ,*apt] ,,xi4 ,9 ,fig4 #bg is %[n its relation to a signal lamp directly 9 ! l9e4 #a is ! c>bon-filam5t lamp2 #b is ! balla/4 ,! latt]'s conductor is f9e iron wire 9 a vacuum4 ,! resi/ance ( ! lamp falls z t ( ! balla/ rises4 ,)9 c]ta9 limits1 ^! *anges balance ea* o!r1 wid5+ ! range ( all[able *ange 9 ! total resi/ance ( ! l9e4 ,,*apt] ,,iv ,,telephone ,,l9es ,! l9e is a pa? ov] :i* ! telephone curr5t passes f telephone to telephone4 ,! t]m telephone l9e circuit is equival5t4 ,l9e & l9e circuit mean slightly diff]5t ?+s to "s p]sons1 l9e mean+ ! out-(-doors portion ( ! l9e & l9e circuit mean+ ! indoor portion1 compos$ ( app>atus & associat$ wir+4 ,su* %ades ( mean+ are inevitable & s]ve useful purposes4 ,! op5+ def9ition h]e( is accurate4 ,a telephone l9e consi/s ( two conductors4 ,"o ( ^! conductors may be ! e>?2 ! o!r always is "s conduct+ mat]ial o!r ?an ! e>?--almo/ univ]sally x is ( metal & 9 ! =m ( a wire4 ,a l9e us+ "o wire & ! e>? z its pair ( conductors has sev]al defects1 to be discuss$ lat] h]e94 ,bo? conductors ( a l9e may be wires1 ! e>? s]v+ z no "p ( ! circuit1 & ?is is ! be/ practice4 ,a l9e compos$ ( "o wire & ! e>? is call$ a gr\nd$ l9e2 a l9e compos$ ( two wires n ne$+ ! e>? z a conductor is call$ a metallic circuit4 ,9 ! e>lie/ telephone practice1 all l9es 7 gr\nd$ ones4 ,! wires 7 ( iron1 support$ by poles & insulat$ f !m by glass1 e>!nw>e1 or rubb] insulators4 ,= c]ta9 uses1 su* l9es /ill repres5t good practice4 ,= telegraph s]vice1 !y repres5t ! pres5t /&>d practice4 ,copp] is a bett] conductor ?an iron1 does n ru/1 & :5 drawn into wire 9 su* a way z to h a suffici5t t5sile /r5g? to support itself is ! be/ available conductor = telephone l9es4 ,only "o metal surpasses x 9 any quality = ! purpose3 silv] is a bett] conductor by #a or #b p] c5t4 ,copp] is bett] ?an silv] 9 /r5g? & price4 ,9 ! op5 c\ntry1 telephone l9es consi/ ( b>e wires ( copp]1 ( iron1 ( /eel1 or ( copp]-cov]$ /eel support$ on insulators borne by poles4 ,if ! wires on ! poles be _m1 cross-arms c>ry f\r to t5 wires ea* & ! insulators are m\nt$ on p9s 9 ! cross-arms4 ,if ! wires on ! poles be few1 ! insulators are m\nt$ on brackets nail$ to ! poles4 ,wires s c>ri$ are call$ op5 wires4 ,9 t[ns & cities :]e _m wires are to be c>ri$ along ! same r\te1 ! wires are r$uc$ 9 size1 insulat$ by a cov]+ ov] ea*1 & assembl$ into a gr\p4 ,su* a bundle ( insulat$ wires is call$ a cable4 ,x may be drawn into a duct 9 ! e>? & be call$ an und]gr\nd cable2 x may be laid on ! bottom ( ! sea or o!r wat] & be call$ a subm>9e cable2 or x may be susp5d$ on poles & be call$ an arial cable4 ,9 ! mo/ g5]al practice ea* wire is insulat$ f all o!rs by a wrapp+ ( pap] ribbon1 :i* cov]+ is only adequate :5 v dry4 ,cables =m$ ( pap]-insulat$ wires1 !re=e1 are cov]$ by a seamless1 cont9u\s lead %ea?1 no "p ( ! pap] insulation ( ! wires be+ expos$ to ! atmosph]e dur+ ! cable's entire life 9 s]vice4 ,telephone cables = c]ta9 uses are =m$ ( wires insulat$ ) su* mat]ials z s(t rubb]1 gutta-p]*a1 & cotton or jute saturat$ ) m9]al comp\nds4 ,:5 insulat$ ) rubb] or gutta-p]*a1 no cont9u\s lead %ea? is ess5tial = insulation1 z ^? mat]ials1 if cont9u\s ^u ! wire1 insulate ev5 :5 ! cable is imm]s$ 9 wat]4 ,%ea?s & o!r armors c assi/ 9 protect+ ^! insulat+ mat]ials f me*anical injury1 & (t5 are us$ = t purpose4 ,! uses to :i* su* cables are suitable 9 telephony are n _m1 z w be %[n4 ,a wire support$ on poles requires t x be l>ge en\gh to support its own weight4 ,! small] ! wire1 ! weak] x is1 & ) poles a giv5 di/ance ap>t1 ! /r5g? ( ! wire mu/ be above a c]ta9 m9imum4 ,9 regions :]e freez+ occurs1 wires 9 ! op5 air c collect ice 9 w9t] & ev]y:]e op5 wires are subject to w9d pressure2 = ^! reasons additional /r5g? is requir$4 ,speak+ g5]ally1 ! practical & economical spac+ ( poles requires t wires1 to be /rong en\gh to meet ! above conditions1 %all h a diamet] n less ?an 4#jh in*1 if ( h>d-drawn copp]1 & 4#jfd in*1 if ( iron or /eel4 ,! honor ( develop+ ways ( draw+ copp] wire ) suffici5t t5sile /r5g? = op5-air uses belongs to ,mr4 ,?omas ,b4 ,doolittle ( ,massa*usetts4 ,l9es ^: l5g?s are limit$ to a few miles d n require a conductivity z great z t ( copp] wire ( 4#jh-;in* diamet]4 ,a wire ( t size weighs approximately #ajj p\nds p] mile4 ,less ?an #ajj p\nds ( copp] p] mile ( wire w n give /r5g? en\gh = use on poles2 b z little z #aj p\nds p] mile ( wire gives ! necess>y conductivity = ! l9es ( ! ?\s&s ( telephone /ations 9 t[ns & cities4 ,op5 wires1 be+ expos$ to ! elem5ts1 suff] damage f /orms2 _! insulation is injur$ by contact ) trees2 !y may make contact ) electric p[] circuits1 p]haps injur+ app>atus1 !mselves1 & p]sons2 !y endang] life & prop]ty by ! possibility ( fall+2 !y & _! cross-arm supports are less sightly ?an a m compact arrangem5t4 ,gr\p+ small wires ( telephone l9es into cables has1 !re=e1 ! advantage ( all[+ less copp] to be us$1 ( r$uc+ ! space requir$1 ( improv+ appe>ance1 & ( increas+ safety4 ,on ! o!r h&1 ?is same gr\p+ introduces negative advantages z well z ! =ego+ positive ones4 ,x is n possible to talk z f> or z well ov] a l9e 9 an ord9>y cable z ov] a l9e ( two op5 wires4 ,long-di/ance telephone circuits1 !re=e1 h n yet be5 plac$ 9 cables = l5g?s great] ?an #bjj or #cjj miles1 & special treatm5t ( cable circuits is requir$ to talk ?r\gh !m = ev5 #ajj miles4 ,"o may talk #b1jjj miles ov] op5 wires4 ,! reasons = ! sup]iority ( ! op5 wires h to d ) position r ?an mat]ial4 ,obvi\sly x is possible to insulate & bury any wire :i* c be c>ri$ 9 ! air4 ,! diff]5ces 9 ! prop]ties ( l9es ^: wires are diff]5tly situat$ ) ref]5ce to ea* o!r & surr\nd+ ?+s are int]e/+ & important4 ,a telephone l9e compos$ ( two conductors always possesses f\r pr9cipal prop]ties 9 "s am\nt3 7#a7 conductivity ( ! conductors2 7#b7 electro/atic capacity betwe5 ! conductors2 7#c7 inductance ( ! circuit2 7#d7 insulation ( ea* conductor f o!r ?+s4 ,conductivity ( ,conductors4 ,! conductivity ( a wire dep5ds ^u its mat]ial1 its cross-section1 its l5g?1 & its temp]ature4 ,conductivity ( a copp] wire1 = example1 increases 9 direct ratio to its weight1 9 inv]se ratio to its l5g?1 & its conductivity falls z ! temp]ature rises4 ,resi/ance is ! reciprocal ( conductivity & ! prop]ties1 conductivity & resi/ance1 are m (t5 express$ 9 t]ms ( resi/ance4 ,! unit ( ! latt] is ! ohm2 ( ! =m] ! mho4 ,a conductor hav+ a resi/ance ( #ajj ohms has a conductivity ( 4#ja mho4 ,! exact correlative t]ms are resi/ance & conductance1 resi/ivity & conductivity4 ,! use ( ! t]ms z 9 ! =ego+ is 9 accordance ) colloquial practice4 ,curr5t 9 a circuit hav+ resi/ance only1 v>ies inv]sely z ! resi/ance4 ,electromotive =ce be+ a cause1 & resi/ance a /ate1 curr5t is ! result4 ,! =mula ( ?is relation1 ,ohm's law1 is ,c ,e_/,r ,c be+ ! curr5t :i* results f ,e1 ! electromotive =ce1 act+ ^u ,r1 ! resi/ance4 ,! units are3 ( curr5t1 ! amp]e2 ( electromotive =ce1 ! volt2 ( resi/ance1 ! ohm4 ,z ! conductivity or resi/ance ( a l9e is ! prop]ty ( controll+ importance 9 telegraphy1 a simil> relation 0 expect$ 9 e>ly telephony4 ,z ! curr5t 9 ! telephone l9e v>ies rapidly1 c]ta9 o!r prop]ties ( ! l9e assume an importance !y d n h 9 telegraphy 9 any su* degree4 ,! importance t ^! prop]ties assume is1 t if !y did n act & ! resi/ance ( ! conductors alone limit$ spee*1 transmission w\ld be possible direct f ,europe to ,am]ica ov] a pair ( wires weigh+ #bjj p\nds p] mile ( wire1 :i* is less ?an half ! weight ( ! wire ( ! be/ long-di/ance l& l9es n[ 9 s]vice4 ,! di/ance f ,europe to ,am]ica is ab\t twice z great z ! pres5t comm]cial radius by l& l9es ( #dce-p\nd wire4 ,9 o!r words1 good spee* is possible ?r\gh a m]e resi/ance tw5ty times great] ?an ! resi/ance ( ! longe/ actual op5-wire l9e x is possible to talk ?r\gh4 ,! talk+ ratio betwe5 a m]e resi/ance & ! resi/ance ( a regul> telephone cable is /ill great]4 ,electro/atic ,capacity4 ,x is ! possession ( electro/atic capacity :i* enables ! cond5s]1 ( :i* ! ,leyd5 j> is a good example1 to be useful 9 a telephone l9e4 ,! simple/ =m ( a cond5s] is illu/rat$ 9 ,fig4 #bh1 9 :i* two conduct+ surfaces are sep>at$ by an insulat+ mat]ial4 ,! l>g] ! surfaces1 ! clos] !y are toge!r2 & ! high] ! specific inductive capacity ( ! insulator1 ! great] ! capacity ( ! device4 ,an insulator us$ 9 ?is relation to two conduct+ surfaces is call$ ! dielectric4 ,illu/ration3 ,fig4 #bh4 ,simple ,cond5s] ,illu/ration3 ,fig4 #bi4 ,cond5s] ,symbols ,two conv5tional signs are us$ to illu/rate cond5s]s1 ! upp] "o ( ,fig4 #bi gr[+ out ( ! orig9al cond5s] ( two metal plates1 ! l[] "o sugge/+ ! ?\ght ( int]leav$ conductors ( t9 foil1 z = _m ye>s 0 ! practice 9 cond5s] con/ruction4 ,) relation to ?is prop]ty1 a telephone l9e is j z truly a cond5s] z is any o!r arrangem5t ( conductors & insulators4 ,assume su* a l9e to be op5 at ! di/ant end & its wires to be well insulat$ f ea* o!r & ! e>?4 ,telegraphy ?r\gh su* a l9e by ord9>y means w\ld be impossible4 ,all t ! batt]y or o!r s\rce c\ld d w\ld be to cause curr5t to fl[ into ! l9e = an inf9itesimal "t1 rais+ ! wires to its pot5tial1 aft] :i* no curr5t w\ld fl[4 ,b1 by virtue ( electro/atic capacity1 ! condition is mu* z %[n 9 ,fig4 #cj4 ,! cond5s]s :i* t figure %[s bridg$ across ! l9e f wire to wire are int5d$ m]ely to fix 9 ! m9d t !re is a pa? = ! transf] ( electrical en]gy f wire to wire4 ,illu/ration3 ,fig4 #cj4 ,l9e ) ,%unt ,capacity ,a simple te/ w enable two ( ! results ( a %ort-circuit+ capacity to be appreciat$4 ,conceive a v %ort l9e ( two wires to connect two local batt]y telephones4 ,su* a l9e possesses negligible resi/ance1 inductance1 & %unt capacity4 ,its insulation is practically inf9ite4 ,let cond5s]s be bridg$ across ! l9e1 "o by "o1 :ile conv]sation goes on4 ,! li/5+ obs]v] w notice t ! s\nds rea*+ 8 e> /eadily gr[ less l\d z ! capacity across ! l9e increases4 ,! speak+ obs]v] w notice t ! s\nds he he>s ?r\gh ! receiv] 9 s]ies ) ! l9e /eadily gr[ l\d] z ! capacity across ! l9e increases4 ,fig4 #ca illu/rates ! te/4 ,! speak]'s obs]vation 9 ?is te/ %[s t increas+ ! capacity across ! l9e increas$ ! am\nt ( curr5t ent]+ x4 ,! he>]'s obs]vation 9 ?is te/ %[s t increas+ ! capacity across ! l9e decreas$ ! am\nt ( en]gy turn$ into s\nd at 8 receiv]4 ,illu/ration3 ,fig4 #ca4 ,te/ ( ,l9e ) ,v>y+ ,%unt ,capacity ,! unit ( electro/atic capacity is ! f>ad4 ,z ?is unit is inconv5i5tly l>ge1 = practical applications ! unit micr(>ad--million? ( a f>ad--is employ$4 ,if quantities are kn[n 9 micr(>ads & are to be us$ 9 calculations 9 :i* ! values ( ! capacity require to be f>ads1 c>e %\ld be tak5 to introduce ! prop] corrective factor4 ,! electro/atic capacity betwe5 ! conductors ( a telephone l9e dep5ds ^u _! surface area1 _! l5g?1 _! position1 & ! nature ( ! mat]ials sep>at+ !m f ea* o!r & f o!r ?+s4 ,= in/ance1 9 an op5 wire l9e ( two wires1 ! electro/atic capacity dep5ds ^u ! diamet] ( ! wires1 ^u ! l5g? ( ! l9e1 ^u _! di/ance ap>t1 ^u _! di/ance above ! e>?1 & ^u ! specific inductive capacity ( ! air4 ,air be+ s common an insulat+ m$ium1 x is tak5 z a conv5i5t mat]ial ^: specific inductive capacity may be us$ z a basis ( ref]5ce4 ,!re=e1 ! specific inductive capacity ( air is tak5 z unity4 ,all solid matt] has high] specific inductive capacity ?an air4 ,! electro/atic capacity ( two op5 wires 4#afe in* diamet]1 #a ft4 ap>t1 & #cj ft4 above ! e>?1 is ( ! ord] ( 4#jji micr(>ads p] mile4 ,?is quantity w\ld be high] if ! wires 7 clos] toge!r2 or ne>] ! e>?2 or if !y 7 surr\nd$ by a gas o!r ?an ! air or hydrog52 or if ! wires 7 insulat$ n by a gas b by any solid cov]+4 ,z ano!r example1 a l9e compos$ ( two wires ( a diamet] ( 4#jcf in*1 if wrapp$ ) pap] & twi/$ into a pair z a "p ( a telephone-cable1 has a mutual electro/atic capacity ( approximately 4#jh micr(>ads p] mile1 ?is quantity be+ great] if ! cable be m tightly compress$4 ,! use ( pap] z an insulator = wires 9 telephone cables is due to its l[ specific inductive capacity4 ,?is is because ! insulation ( ! wires is s l>gely dry air4 ,rubb] & simil> insulat+ mat]ials give capacities z great z twice t ( dry pap]4 ,! cond5s] or o!r capacity acts z an effective b>ri] to ! /eady fl[ ( direct curr5ts4 ,apply+ a fix$ pot5tial causes a m]e ru% ( curr5t to *>ge its surface to a def9ite degree1 dep5d5t ^u ! p>ticul> conditions4 ,! cond5s] does n act z su* a b>ri] to alt]nat+ curr5ts1 = x is possible to talk ?r\gh a cond5s] by means ( ! alt]nat+ voice curr5ts ( telephony1 or to pass ?r\gh x alt]nat+ curr5ts ( mu* l[] frequ5cy4 ,a cond5s] is us$ 9 s]ies ) a pol>iz$ r+] = ! purpose ( lett+ ?r\gh alt]nat+ curr5t = r++ ! bell1 & ( prev5t+ ! fl[ ( direct curr5t4 ,! degree to :i* ! cond5s] all[s alt]nat+ curr5ts to pass :ile /opp+ direct curr5ts1 dep5ds on ! capacity ( ! cond5s] & on ! frequ5cies ( alt]nat+ curr5t4 ,! l>g] ! cond5s] capacity or ! high] ! frequ5cy ( ! alt]nations1 ! great] w be ! curr5t pass+ ?r\gh ! circuit4 ,! degree to :i* ! curr5t is oppos$ by ! capacity is ! reactance ( t capacity = t frequ5cy4 ,! =mula is ,capacity reactance #a _/,comega :]e9 ,c is ! capacity 9 f>ads & omega is #bpin1 or twice #c4adaf times ! frequ5cy4 ,all ! =ego+ leads to ! g5]alization t ! high] ! frequ5cy1 ! less ! opposition ( a capacity to an alt]nat+ curr5t4 ,if ! frequ5cy be z]o1 ! reactance is inf9ite1 i4e41 ! circuit is op5 to direct curr5t4 ,if ! frequ5cy be inf9ite1 ! reactance is z]o1 i4e41 ! circuit is z if ! cond5s] 7 replac$ by a solid conductor ( no resi/ance4 ,comp>e ?is /atem5t ) ! correlative g5]alization :i* foll[s ! next ?\ght ^u inductance4 ,inductance ( ! ,circuit4 ,inductance is ! prop]ty ( a circuit by :i* *ange ( curr5t 9 x t5ds to produce 9 itself & o!r conductors an electromotive =ce o!r ?an t :i* causes ! curr5t4 ,its unit is ! h5ry4 ,! inductance ( a circuit is "o h5ry :5 a *ange ( "o amp]e p] second produces an electromotive =ce ( "o volt4 ,induction betwe5 circuits occurs because ! circuits possess inductance2 x is call$ mutual induction4 ,induction )9 a circuit occurs because ! circuit possesses inductance2 x is call$ self-induction4 ,l5z' law says3 ,9 all cases ( electromagnetic induction1 ! induc$ curr5ts h su* a direction t _! reaction t5ds to /op ! motion :i* produc$ !m4 ,illu/ration3 ,fig4 #cb4 ,spiral ( ,wire ,illu/ration3 ,fig4 #cc4 ,spiral ( ,wire ,ar\nd ,iron ,core ,all conductors possess inductance1 b /raight wires us$ 9 l9es h negligible inductance 9 mo/ actual cases4 ,all wires :i* are w\nd into coils1 su* z electromagnets1 possess inductance 9 a greatly increas$ degree4 ,a wire w\nd into a spiral1 z indicat$ 9 ,fig4 #cb1 possesses mu* great] inductance ?an :5 drawn out /raight4 ,if iron be ins]t$ into ! spiral1 z %[n 9 ,fig4 #cc1 ! inductance is /ill fur!r increas$4 ,x is = ! purpose ( elim9at+ inductance t resi/ance coils are w\nd ) d\ble wires1 s t curr5t pass+ ?r\gh su* coils turns 9 "o direction half ! way & 9 ! o!r direction ! o!r half4 ,a simple te/ w enable ! results ( a s]ies inductance 9 a l9e to be appreciat$4 ,conceive a v %ort l9e ( two wires to connect two local batt]y telephones4 ,su* a l9e possesses negligible resi/ance1 inductance1 & %unt capacity4 ,its insulation is practically inf9ite4 ,let inductive coils su* z electromagnets be ins]t$ s]ially 9 ! wires ( ! l9e "o by "o1 :ile conv]sation goes on4 ,! li/5+ obs]v] w notice t ! s\nds rea*+ 8 e> /eadily gr[ fa9t z ! inductance 9 ! l9e increases & ! speak+ obs]v] w notice ! same ?+ ?r\gh ! receiv] 9 s]ies ) ! l9e4 ,bo? obs]vations 9 ?is te/ %[ t ! am\nt ( curr5t ent]+ & em]g+ f ! l9e decreas$ z ! inductance increas$4 ,comp>e ?is ) ! te/ ) bridg$ capacity & ! load+ ( l9es describ$ lat] h]e91 obs]v+ ! curi\s b5eficial result :5 bo? hurtful prop]ties are pres5t 9 a l9e4 ,! te/ is illu/rat$ 9 ,fig4 #cd4 ,! degree 9 :i* any curr5t is oppos$ by inductance is t]m$ ! reactance ( t inductance4 ,its =mula is ,inductive reactance ,lomega :]e9 ,l is ! inductance 9 h5rys & omega is #bpin1 or twice #c4adaf times ! frequ5cy4 ,to di/+ui% ! two k9ds ( reactance1 t due to ! capacity is call$ capacity reactance & t due to inductance is call$ inductive reactance4 ,all ! =ego+ leads to ! g5]alization t ! high] ! frequ5cy1 ! great] ! opposition ( an inductance to an alt]nat+ curr5t4 ,if ! frequ5cy be z]o1 ! reactance is z]o1 i4e41 ! circuit conducts direct curr5t z m]e resi/ance4 ,if ! frequ5cy be inf9ite1 ! reactance is inf9ite1 i4e41 ! circuit is op5 to ! alt]nat+ curr5t & t curr5t _c pass ?r\gh x4 ,comp>e ?is ) ! correlative g5]alization foll[+ ! prec$+ ?\ght ^u capacity4 ,illu/ration3 ,fig4 #cd4 ,te/ ( ,l9e ) ,v>y+ ,s]ial ,inductance ,capacity & inductance dep5d only on /ates ( matt]4 ,_! reactances dep5d on /ates ( matt] & actions ( en]gy4 ,9 circuits hav+ bo? resi/ance & capacity or resi/ance & inductance1 bo? prop]ties affect ! passage ( curr5t4 ,! jo9t reaction is express$ 9 ohms & is call$ imp$ance4 ,its value is ! squ>e root ( ! sum ( ! squ>es ( ! resi/ance & reactance1 or1 ,z be+ imp$ance1 ------------------------- _/ #a ,z _/ ,r#b ---------------- _/ ,c#bomega#b & -------------------------- ,z _/ ,r#b ,l#bomega#b _/ ! symbols mean+ z be=e4 ,9 words1 ^! =mulas mean t1 kn[+ ! frequ5cy ( ! curr5t & ! capacity ( a cond5s]1 or ! frequ5cy ( ! curr5t & ! inductance ( a circuit 7a l9e or piece ( app>atus71 & 9 ei!r case ! resi/ance ( ! circuit1 "o may le>n ! imp$ance by calculation4 ,insulation ( ,conductors4 ,! f\r? prop]ty ( telephone l9es1 insulation ( ! conductors1 usually is express$ 9 ohms z an insulation resi/ance4 ,9 practice1 ?is prop]ty ne$s to be intr9sically high1 & usually is measur$ by millions ( ohms resi/ance f ! wire ( a l9e to its mate or to ! e>?4 ,x is a conv5i5ce to employ a l>ge unit4 ,a million ohms1 !re=e1 is call$ a megohm4 ,9 telephone cables1 an insulation resi/ance ( #ejj megohms p] mile at #fj ,fahr5heit is ! usual specification4 ,s high an insulation resi/ance 9 a pap]-insulat$ conductor is only atta9$ by apply+ ! lead %ea? to ! cable :5 its core is made practically anhydr\s & kept s dur+ ! splic+ & t]m9at+ ( ! cable4 ,insulation resi/ance v>ies inv]sely z ! l5g? ( ! conductor4 ,if a piece ( cable #ebh feet long has an insulation resi/ance ( #f1gej megohms1 a mile 7t5 times z mu*7 ( su* cable1 w h an insulation resi/ance ( #fge megohms1 or "o-t5? z great4 ,inductance vs4 ,capacity4 ,! mutual capacity ( a telephone l9e is great] z its wires are clos] toge!r4 ,! self-induction ( a telephone l9e is small] z its wires are clos] toge!r4 ,! electromotive =ce induc$ by ! capacity ( a l9e leads ! impress$ electromotive =ce by #ij degrees4 ,! inductive electromotive =ce lags #ij degrees beh9d ! impress$ electromotive =ce4 ,& s1 9 g5]al1 ! natures ( ^! two prop]ties are opposite4 ,9 a cable1 ! wires are s close toge!r t _! induction is negligible1 :ile _! capacity is s great z to limit comm]cial transmission ?r\gh a cable hav+ 4#jf micr(>ads p] mile capacity & #id ohms loop resi/ance p] mile1 to a di/ance ( ab\t #cj miles4 ,9 ! case ( op5 wires spac$ #ab in*es ap>t1 ! limit ( comm]cial transmission is great]1 n only because ! wires are l>g]1 b because ! capacity is l[] & ! inductance high]4 ,table ,i %[s-! practical limit+ conv]sation di/ance ov] uni=m l9es ) pres5t /&>d telephone app>atus4 ,,table ,i ,limit+ ,transmission ,di/ances ---------------------------------------- ----------- ,,size ,,& ,,gauge ,,( ,,wire ,,limit+ ,,di/ance ---------------------------------------- ----------- ,no4 #h ,b4 ,w4 ,g4 copp] #ijj miles #aj ,b4 ,w4 ,g4 copp] #gjj miles #aj ,b4 ,s4 copp] #djj miles #ab ,n4 ,b4 ,s4 copp] #djj miles #ab ,b4 ,s4 copp] #bdj miles #ad ,n4 ,b4 ,s4 copp] #bdj miles #h ,b4 ,w4 ,g4 iron #ace miles #aj ,b4 ,w4 ,g4 iron #abj miles #ab ,b4 ,w4 ,g4 iron #ij miles #af ,b4 ,s4 cable1 copp] #dj miles #ai ,b4 ,s4 cable1 copp] #cj miles #bb ,b4 ,s4 cable1 copp] #bj miles ---------------------------------------- ----------- ,9 #ahic1 ,oliv] ,heaviside propos$ t ! inductance ( telephone l9es be increas$ above ! am\nt natural = ! int]-axial spac+1 ) a view to c\nt]act+ ! hurtful effects ( ! capacity4 ,8 mean+ 0 t ! increas$ inductance--a h>mful quality 9 a circuit n hav+ also a h>mfully great capacity--w\ld act oppositely to ! capacity1 & if prop]ly *os5 & appli$1 %\ld decrease or elim9ate di/ortion by mak+ ! l9e's effect on fundam5tals & h>monics m ne>ly uni=m1 & z well %\ld r$uce ! att5uation by neutraliz+ ! action ( ! capacity 9 dissipat+ en]gy4 ,!re are two ways 9 :i* inductance might be introduc$ into a telephone l9e4 ,z ! capacity ^: effects are to be neutraliz$ is di/ribut$ uni=mly ?r\gh\t ! l9e1 ! c\nt]act+ inductance mu/ also be di/ribut$ ?r\gh\t ! l9e4 ,m]e increase ( di/ance betwe5 two wires ( ! l9e v happily acts bo? to increase ! inductance & to l[] ! capacity2 unhappily = practical results1 ! increase ( sep>ation to br+ ! qualities into useful neutraliz+ relation is beyond practical limits4 ,! wires w\ld ne$ to be s f> above ! e>? & s f> ap>t z to make ! arrangem5t comm]cially impossible4 ,practical results h be5 secur$ 9 increas+ ! di/ribut$ inductance by wrapp+ f9e iron wire ov] ea* conductor ( ! l9e4 ,su* a treatm5t increases ! inductance & improves transmission4 ,! mo/ m>k$ success has come z a result ( ! /udies ( ,pr(essor ,mi*ael ,idvorsky ,pup94 ,he ins]ts inductances 9 s]ies ) ! wires ( ! l9e1 s adapt+ !m to ! con/ants ( ! circuit t att5uation & di/ortion are dim9i%$ 9 a gratify+ degree4 ,?is me?od ( c\nt]act+ ! effects ( a di/ribut$ capacity by ! ins]tion ( localiz$ inductance requires n only t ! requisite total am\nt ( inductance be kn[n1 b t ! prop] subdivision & spac+ ( ! local portions ( t inductance be kn[n4 ,pr(essor ,pup9's me?od is describ$ 9 a pap] entitl$ ,wave ,transmission ,ov] ,non-uni=m ,cables & ,long-,di/ance ,air ,l9es1 read by him at a meet+ ( ! ,am]ican ,in/itute ( ,electrical ,eng9e]s 9 ,philadelphia1 ,may #ai1 #aijj4 ,,note4 ,unit$ ,/ates ,lett]s ,pat5t 7 issu$ to ,pr(essor ,pup9 on ,june #ai1 #aijj1 ^u 8 practical me?od ( r$uc+ att5uation ( electrical waves4 ,a pap] ^u ,propagation ( ,long ,electric ,waves 0 read by ,pr(essor ,pup9 be=e ! ,am]ican ,in/itute ( ,electrical ,eng9e]s on ,m>* #bb1 #ahii1 & appe>s 9 ,vol4 #ae ( ! ,transactions ( t society4 ,! /ud5t w f9d ^! docum5ts useful 9 8 /udies on ! subject4 ,he is ref]r$ also to ,electrical ,pap]s & ,electromagnetic ,!ory ( ,oliv] ,heaviside4 ,pr(essor ,pup9 lik5s ! transmission ( electric waves ov] long-di/ance circuits to ! transmission ( me*anical waves ov] a /r+4 ,conceive an ord9>y light /r+ to be fix$ at "o end & %ak5 by ! h& at ! o!r2 waves w pass ov] ! /r+ f ! %ak5 to ! fix$ end4 ,c]ta9 reflections w occur f ! fix$ end4 ,! am\nt ( en]gy :i* c be s5t 9 ?is case f ! %ak5 to ! fix$ po9t is small1 b if ! /r+ be load$ by atta*+ bullets to x1 uni=mly ?r\gh\t its l5g?1 x n[ may transmit mu* m en]gy to ! fix$ end4 ,illu/ration3 ,,ma9 ,,entrance ,,& ,,public ,,(fice1 ,,san ,,francisco ,,home ,,telephone ,,company ,contract ,dep>tm5t on ,left4 ,acc\nt+ ,dep>tm5t on ,"r4 ,! addition ( inductance to a telephone l9e is analog\s to ! addition ( bullets to ! /r+1 s t a telephone l9e is said to be load$ :5 inductances are ins]t$ 9 x1 & ! inductances !mselves are kn[n z load+ coils4 ,fig4 #ce %[s ! g5]al relation ( ,pup9 load+ coils to ! capacity ( ! l9e4 ,! cond5s]s ( ! figure are m]ely conv5tionals to repres5t ! cond5s] :i* ! l9e itself =ms4 ,! inductances ( ! figure are ! actual load+ coils4 ,illu/ration3 ,fig4 #ce4 ,load$ ,l9e ,! load+ ( op5 wires is n z successful 9 practice z is t ( cables4 ,! fundam5tal reason lies 9 ! fact t two ( ! prop]ties ( op5 wires--insulation & capacity--v>y ) atmosph]ic *ange4 ,! ins]t$ inductance rema9+ con/ant1 its b5efits may become detrim5ts :5 ! o!r two con/ants *ange4 ,! load+ ( cable circuits is n subject to ^! defects4 ,su* load+ improves transmission2 saves copp]2 p]mits ! use ( long] und]gr\nd cables ?an are usable :5 n load$2 l[]s ma9t5ance co/s by plac+ int]urban cables und]gr\nd2 & p]mits subm>9e telephone cables to jo9 places n o!rwise able to speak ) ea* o!r4 ,und]gr\nd long-di/ance l9es n[ jo9 or are jo9+ ,bo/on & ,new ,york1 ,philadelphia & ,new ,york1 ,milwaukee & ,*icago4 ,engl& & ,france are connect$ by a load$ subm>9e cable4 ,!re is no !oretical reason :y ,europe & ,am]ica %\ld n speak to ea* o!r4 ,! /ud5t wi%+ to det]m9e = himself :at are ! effects ( ! prop]ties ( l9es ^u op5 or cable circuits w f9d mo/ ( ! subject 9 ! foll[+ equation4 ,x tells ! value ( a 9 t]ms ( ! f\r prop]ties1 a be+ ! att5uation con/ant ( ! l9e4 ,t is1 ! l>g] a is1 ! m ! voice curr5t is r$uc$ 9 pass+ ov] ! l9e4 ,! equation is ---------------------------------------- ------------------------------- _/ ---------------------------------------- ------- a _/ _/7,r#b,l#bomega#b77,s#b;,c#bomega#b 7,,rs-,,lcomega#b _/ _/ ,! quantities are ,r ,resi/ance 9 ohms ,l ,inductance 9 h5rys ,c ,mutual 7%unt7 capacity 9 f>ads omega #bpin #f4bhcb times ! frequ5cy ,s ,%unt leakage 9 mhos ,! quantity ,s is a measure ( ! comb9$ direct-curr5t conductance 7reciprocal ( insulation resi/ance7 & ! app>5t conductance due to dielectric hy/]esis4 ,,note4 ,an excell5t pap]1 assi/+ su* /udy1 & ( imm$iate practical value z help+ ! und]/&+ ( cables & _! reasons1 is t ( ,mr4 ,frank ,b4 ,jewett1 pres5t$ at ! ,?\s& ,isl&s ,conv5tion ( ! ,am]ican ,in/itute ( ,electrical ,eng9e]s1 ,july #a1 #aiji4 ,*apt] #dc treats cables 9 fur!r detail4 ,!y =m a mo/ important "p ( telephone wire-plant practice1 & _! uses are becom+ wid] & m valuable4 ,possible ,ways ( ,improv+ ,transmission4 ,practical ways ( improv+ telephone transmission are ( two k9ds3 to improve ! l9es & to improve ! app>atus4 ,! =ego+ %[s :at are ! qualities ( l9es & ! ways !y require to be treat$4 ,app>atus treatm5t1 9 ! pres5t /ate ( ! art1 is address$ l>gely to ! r$uction ( losses4 ,!oretical consid]ations seem to %[1 h[ev]1 t great advance 9 app>atus effectiv5ess /ill is possible4 ,m p[]ful transmitt]s--& m fai?ful ones--m s5sitive & accurate receiv]s1 & m effici5t translat+ devices surely are possible4 ,discov]y may ne$ to int]v5e1 to enable inv5tion to re/imulate4 ,9 bo? telegraphy & telephony1 ! long] ! l9e ! weak] ! curr5t :i* is receiv$ at ! di/ant end4 ,9 bo? telegraphy & telephony1 !re is a l5g? ( l9e ) a giv5 k9d & size ( wire & me?od ( con/ruction ov] :i* x is j possible to s5d intelligible spee* or intelligible signals4 ,a repeat]1 9 telegraphy1 is a device 9 ! =m ( a relay :i* is adapt$ to receive ^! highly att5uat$ signal impulses & to re-transmit !m ) fre% p[] ov] a new l5g? ( l9e4 ,an arrangem5t ( two su* relays makes x possible to telegraph bo? ways ov] a pair ( l9es unit$ by su* a repeat]4 ,x is practically possible to jo9 up sev]al su* l9ks ( l9es to repeat+ devices &1 if ne$ be1 ev5 subm>9e cables c be jo9$ to l& l9es )9 practical limits4 ,if x 7 necess>y1 x probably w\ld be possible to telegraph ar\nd ! _w 9 ?is way4 ,if x 7 possible to imitate ! telegraph repeat] 9 telephony1 att5uat$ voice curr5ts might be caus$ to actuate x s z to s5d on ^? voice curr5ts ) r5ew$ p[] ov] a l5g? ( l9e1 section by section4 ,su* a device has be5 s\ght = _m ye>s1 & x once 0 quot$ 9 ! public press t a rew>d ( "o million doll>s _h be5 (f]$ by ,*>les ,j4 ,glidd5 = a successful device ( t k9d4 ,! records ( ! pat5t (fices ( ! _w %[ :at ef=t has be5 made 9 t direction & _m m devices h be5 inv5t$ ?an h be5 pat5t$ 9 all ! c\ntries toge!r4 ,l "s o!r problems 9 telephony1 ?is "o seems simpl] at fir/ sight ?an x proves to be aft] m exhau/ive /udy4 ,x is possible = any amateur to produce at once a repeat+ device :i* w relay telephone circuits 9 "o direction4 ,x is requir$1 h[ev]1 t 9 practice ! voice curr5ts be relay$ 9 bo? directions1 & fur!r1 t ! relay actually augm5t ! en]gy :i* passes ?r\gh x2 t is1 t x w s5d on a m p[]ful curr5t ?an x receives4 ,mo/ ( ! devices s f> inv5t$ fail 9 "o or ! o!r ( ^! p>ticul>s4 ,sev]al ways h be5 %[n ( assembl+ repeat+ devices :i* w talk bo? ways1 b n _m assembl+ repeat+ devices h be5 %[n t w talk bo? ways & augm5t 9 bo? directions4 ,illu/ration3 ,fig4 #cf4 ,%reeve ,repeat] & ,circuit ,practical repeat]s h be5 produc$1 h[ev]1 & at lea/ "o type is 9 daily successful use4 ,x is n conclusively %[n ev5 ( x t x augm5ts 9 ! same degree all ( ! voice waves :i* rea* x1 or ev5 t x augm5ts "s ( !m at all4 ,its action1 h[ev]1 is di/9ctly an improvem5t 9 comm]cial practice4 ,x is ! inv5tion ( ,mr4 ,h]b]t ,e4 ,%reeve & is %[n 9 ,fig4 #ci4 ,prim>ily x consi/s ( a telephone receiv]1 ( a p>ticul> type devis$ by ,gundla*1 associat$ ) a granul> c>bon transmitt] button4 ,x is fur!r associat$ ) an arrangem5t ( induction coils or repeat+ coils1 ! object ( ^! be+ to accompli% ! two-way action1 t is1 ( speak+ 9 bo? directions & ( prev5t+ reactive int]f]5ce betwe5 ! receiv+ & transmitt+ elem5ts4 ,! batt]y #a en]gizes ! field ( ! receiv+ elem5t2 ! receiv$ l9e curr5t v>ies t field2 ! result+ motion v>ies ! resi/ance ( ! c>bon button & trans=ms curr5t f batt]y #b into a new alt]nat+ l9e curr5t4 ,by reactive int]f]5ce is meant action :]eby ! transmitt] elem5t1 9 emitt+ a wave1 affects its own controll+ receiv] elem5t1 ?us sett+ up an action simil> to t :i* occurs :5 ! receiv] ( a telephone is held close to its transmitt] & humm+ or s++ ensues4 ,no repeat] is successful unless x is free f ?is reactive int]f]5ce4 ,illu/ration3 ,fig4 #cg4 ,m]cury-,arc ,telephone ,relay ,en\gh has be5 accompli%$ by practical te/s ( ! ,%reeve device & o!rs l x to %[ t ! se>* = a me?od ( relay+ telephone voice curr5ts is n look+ = a pot ( gold at ! end ( ! ra9b[4 ,! mo/ rem>kable tru? e/abli%$ by ! success ( repeat]s ( ! ,%reeve type is t a device embody+ s l>ge in]tia ( mov+ p>ts c succe$ at all4 ,if ?is mean any?+1 x is t a device 9 :i* in]tia is absolutely elim9at$ might d v mu* bett]4 ,_m ( ! me?ods already propos$ by inv5tors attack ! problem 9 ?is way & "o ( ! mo/ rec5t & mo/ promis+ ways is t ( ,mr4 ,j4,b4 ,taylor1 ! circuit ( ^: telephone-relay pat5t is %[n 9 ,fig4 #cg4 ,9 x1 #a is an electromagnet en]giz$ by voice curr5ts2 its v>y+ field v>ies an arc betwe5 ! electrodes #b-b & #c 9 a vacuum tube4 ,^! fluctuations are trans=m$ into l9e curr5ts by ! coil #d4 ,,*apt] ,v ,,transmitt]s ,v>iable ,resi/ance4 ,z already po9t$ out 9 ,*apt] ,,ii1 ! v>iable-resi/ance me?od ( produc+ curr5t waves1 correspond+ to s\nd waves = telephonic transmission1 is ! "o t l5ds itself mo/ readily to practical purposes4 ,practically all telephone transmitt]s ( today employ ?is v>iable-resi/ance pr9ciple4 ,! reason = ! adoption ( ?is me?od in/ead ( ! o!r possible ones is t ! devices act+ on ?is pr9ciple are capable1 ) great simplicity ( con/ruction1 ( produc+ mu* m p[]ful results ?an ! o!rs4 ,_! simplicity is su* z to make !m capable ( be+ manufactur$ at l[ co/ & ( be+ us$ successfully by unskill$ p]sons4 ,mat]ials4 ,( all ! mat]ials available = ! v>iable-resi/ance elem5t 9 telephone transmitt]s1 c>bon is by f> ! mo/ suitable1 & its use is well nigh univ]sal4 ,sometimes "o ( ! r>] metals1 su* z plat9um or gold1 is to be f\nd 9 comm]cial transmitt]s z "p ( ! resi/ance-v>y+ device1 b1 ev5 :5 ?is is s1 x is always us$ 9 comb9ation ) c>bon 9 "s =m or o!r4 ,mo/ ( ! transmitt]s 9 use1 h[ev]1 dep5d solely ^u c>bon z ! conductive mat]ial ( ! v>iable-resi/ance elem5t4 ,arrangem5t ( ,electrodes4 ,foll[+ ! pr9ciples po9t$ out by ,hughes1 ! transmitt]s ( today always employ z _! v>iable-resi/ance elem5ts "o or m loose contacts betwe5 "o or m pairs ( electrodes1 :i* electrodes1 z j /at$1 are usually ( c>bon4 ,always ! arrangem5t is su* t ! s\nd waves w v>y ! intimacy ( contact betwe5 ! electrodes &1 !re=e1 ! resi/ance ( ! pa? ?r\gh ! electrodes4 ,a multitude ( arrangem5ts h be5 propos$ & tri$4 ,sometimes a s+le pair ( electrodes has be5 employ$ hav+ a s+le po9t ( loose contact betwe5 !m4 ,^! may be t]m$ s+le-contact transmitt]s4 ,sometimes ! v>iable-resi/ance elem5t has includ$ a great] numb] ( electrodes arrang$ 9 multiple1 or 9 s]ies1 or 9 s]ies-multiple1 & ^! h be5 t]m$ multiple-electrode transmitt]s1 signify+ a plurality ( electrodes4 ,a lat] developm5t1 an outgr[? ( ! multiple-electrode transmitt]1 makes use ( a pair ( pr9cipal electrodes1 betwe5 :i* is includ$ a mass ( f9ely divid$ c>bon 9 ! =m ( granules or small sph]es or pellets4 ,^!1 reg>dless ( ! exact =m ( ! c>bon p>ticles1 are call$ granul>-c>bon transmitt]s4 ,illu/ration3 ,fig4 #ch4 ,blake ,transmitt] ,s+le ,electrode4 ,blake4 ,! mo/ notable example ( ! s+le-contact transmitt] is ! once famili> ,blake in/rum5t4 ,at "o "t ?is =m$ a "p ( ! /&>d equipm5t ( almo/ e telephone 9 ! ,unit$ ,/ates1 & x 0 also l>gely us$ abroad4 ,probably no transmitt] has ev] exce$$ x 9 cle>ness ( articulation1 b x 0 decid$ly defici5t 9 p[] 9 comp>ison ) ! mod]n transmitt]s4 ,9 ?is in/rum5t1 :i* is %[n 9 ,fig4 #ch1 ! v>iable-resi/ance contact 0 t betwe5 a c>bon & a plat9um electrode4 ,! diaphragm #a 0 ( %eet iron m\nt$1 z usual 9 lat] transmitt]s1 9 a s(t rubb] gasket #b4 ,! :ole diaphragm 0 m\nt$ 9 a ca/-iron r+ #c1 support$ on ! inside ( ! box conta9+ ! entire in/rum5t4 ,! front electrode #d 0 m\nt$ on a light spr+ #e1 ! upp] end ( :i* 0 support$ by a movable b> or lev] #f1 flexibly support$ on a spr+ #g secur$ to ! ca/+ :i* support$ ! diaphragm4 ,! t5sion ( ?is spr+ #e 0 su* z to cause ! plat9um po9t to press lightly away f ! c5t] ( ! diaphragm4 ,! re> electrode 0 ( c>bon 9 ! =m ( a small block #i1 secur$ 9 a heavy brass button #aj4 ,! entire re> electrode /ructure 0 support$ on a heavi] spr+ #aa c>ri$ on ! same lev] z ! spr+ #e4 ,! t5sion ( ?is latt] spr+ 0 su* z to press aga9/ ! front electrode &1 by its great] /r5g?1 press ?is aga9/ ! c5t] ( ! diaphragm4 ,! adju/m5t ( ! in/rum5t 0 secur$ by means ( ! screw #ab1 c>ri$ 9 a lug ext5d+ re>w>dly f ! diaphragm support+ ca/+1 ?is screw1 by its position1 det]m9+ ! /r5g? ) :i* ! re> electrode press$ aga9/ ! front electrode & t aga9/ ! diaphragm4 ,?is in/rum5t 0 ord9>ily m\nt$ 9 a wood5 box toge!r ) ! induction coil1 :i* is %[n 9 ! upp] portion ( ! figure4 ,! ,blake transmitt] has pass$ almo/ entirely out ( use 9 ?is c\ntry1 be+ sup]s$$ by ! v>i\s =ms ( granul> in/rum5ts1 :i*1 :ile mu* m p[]ful1 are n p]haps capable ( produc+ q su* cle> & di/9ct articulation4 ,! great tr\ble ) ! s+le-contact transmitt]s1 su* z ! ,blake1 0 t x 0 impossible to pass en\gh curr5t ?r\gh ! s+le po9t ( contact to secure ! desir$ p[] ( transmission )\t ov]heat+ ! contact4 ,if too mu* curr5t is s5t ?r\gh su* transmitt]s1 an undue am\nt ( heat is g5]at$ at ! po9t ( contact & a vibration is set up :i* causes a peculi> humm+ or squeal+ s\nd :i* int]f]es ) ! transmission ( o!r s\nds4 ,multiple ,electrode4 ,to rem$y ?is difficulty ! s-call$ multiple-electrode transmitt] 0 br\ght out4 ,?is took a v great numb] ( =ms1 ( :i* ! "o %[n 9 ,fig4 #ci is typical4 ,! diaphragm %[n at #a1 9 ?is p>ticul> =m1 0 made ( ?9 p9e wood4 ,on ! re> side ( ?is1 susp5d$ f a rod #c c>ri$ 9 a bracket #d1 7 a numb] ( c>bon rods or p5dants #e1 loosely re/+ aga9/ a rod #b1 c>ri$ on a bracket #f also m\nt$ on ! re> ( ! diaphragm4 ,! pivotal rod #c & ! rod #b1 aga9/ :i* ! p5dants re/$1 7 sometimes1 l ! p5dant rods1 made ( c>bon & sometimes ( metal1 su* z brass4 ,:5 ! diaphragm vibrat$1 ! intimacy ( contact betwe5 ! p5dant rod #e & ! rod #b 0 alt]$1 & ?us ! resi/ance ( ! pa? ?r\gh all ( ! p5dant rods 9 multiple 0 *ang$4 ,illu/ration3 ,fig4 #ci4 ,multiple-,electrode ,transmitt] ,a multitude ( =ms ( su* transmitt]s came into use 9 ! e>ly eighties1 & :ile !y 9 "s measure rem$i$ ! difficulty enc\nt]$ ) ! ,blake transmitt]1 i4e41 ( n be+ able to c>ry a suffici5tly l>ge curr5t1 !y 7 all subject to ! effects ( extreme s5sitiv5ess1 & w\ld rattle or break :5 call$ ^u to transmit s\nds ( m ?an ord9>y l\dness4 ,fur!rmore1 ! pres5ce ( su* l>ge masses ( mat]ial1 :i* x 0 necess>y to ?r[ into vibration by ! s\nd waves1 0 di/9ctly aga9/ ?is =m ( transmitt]4 ,! in]tia ( ! mov+ p>ts 0 s great t cle>ness ( articulation 0 int]f]$ )4 ,granul> ,c>bon4 ,! idea ( employ+ a mass ( granul> c>bon1 support$ betwe5 two electrodes1 "o ( :i* vibrat$ ) ! s\nd waves & ! o!r 0 /ation>y1 0 propos$ by ,h5ry ,hunn+s 9 ! e>ly eighties4 ,:ile ?is idea =ms ! basis ( all mod]n telephone transmitt]s1 yet x did n prev5t ! almo/ univ]sal adoption ( ! s+le-contact =m ( in/rum5t dur+ ! next decade4 ,we/]n ,electric ,solid-,back ,transmitt]4 ,9 ! e>ly n9eties1 h[ev]1 ! granul>-c>bon transmitt] came into its own ) ! adv5t & wide adoption ( ! transmitt] design$ by ,an?ony ,c4 ,:ite1 kn[n z ! ,:ite1 or solid-back1 transmitt]4 ,?is has = _m ye>s be5 ! /&>d in/rum5t ( ! ,bell companies op]at+ ?r\gh\t ! ,unit$ ,/ates1 & has f\nd l>ge use abroad4 ,a horizontal cross-section ( ?is in/rum5t is %[n 9 ,fig4 #dj1 & a re> view ( ! work+ p>ts 9 ,fig4 #da4 ,! work+ p>ts are all m\nt$ on ! front ca/+ #a4 ,?is is support$ 9 a cup #b1 9 turn support$ on ! lug #c1 :i* is pivot$ on ! transmitt] arm or o!r support4 ,! front & re> electrodes ( ?is in/rum5t are =m$ ( ?9 c>bon disks %[n 9 solid black4 ,! re> electrode1 ! l>g] "o ( ^! disks1 is securely atta*$ by sold] to ! face ( a brass disk hav+ a re>w>dly project+ screw-?read$ %ank1 :i* s]ves to hold x & ! re> electrode 9 place 9 ! bottom ( a heavy brass cup #d4 ,! front electrode is m\nt$ on ! re> face ( a /ud4 ,clamp$ aga9/ ! head ( ?is /ud1 by a screw-?read$ clamp+ r+ #g1 is a mica wa%]1 or disk #f4 ,! c5t] portion ( ?is mica wa%] is !re=e rigid ) respect to ! front electrode & p>takes ( its movem5ts4 ,! out] edge ( ?is mica wa%] is simil>ly clamp$ aga9/ ! front edge ( ! cup #d1 a screw-?read$ r+ #i s]v+ to hold ! edge ( ! mica rigidly aga9/ ! front ( ! cup4 ,! out] edge ( ?is wa%] is1 !re=e1 rigid ) respect to ! re> electrode1 :i* is fix$4 ,:atev] relative movem5t !re is betwe5 ! two electrodes mu/1 !re=e1 be p]mitt$ by ! flex+ ( ! mica wa%]4 ,?is mica wa%] n only s]ves to ma9ta9 ! electrodes 9 _! normal relative positions1 b also s]ves to close ! *amb] :i* conta9s ! electrodes1 &1 !re=e1 to prev5t ! granul> c>bon1 ) :i* ! space betwe5 ! electrodes is fill$1 f fall+ out4 ,illu/ration3 ,fig4 #dj4 ,:ite ,solid-,back ,transmitt] ,! cup #d1 conta9+ ! electrode *amb]1 is rigidly fa/5$ ) respect to ! body ( ! transmitt] by a re>w>dly project+ %ank held 9 a bridge piece #h :i* is secur$ at its ends to ! front block4 ,! ne$$ rigidity ( ! re> electrode is ?us obta9$ & ?is is probably ! reason = call+ ! in/rum5t ! solid-back4 ,! front electrode1 on ! o!r h&1 is fa/5$ to ! c5t] ( ! diaphragm by means ( a %ank on ! /ud1 :i* passes ?r\gh a hole 9 ! diaphragm & is clamp$ !reto by two small nuts4 ,aga9/ ! re> face ( ! diaphragm ( ?is transmitt] !re re/ two damp+ spr+s4 ,^! are n %[n 9 ,fig4 #dj b are 9 ,fig4 #da4 ,!y are secur$ at "o end to ! re> flange ( ! front ca/+ #a1 & be> ) _! o!r or free ends aga9/ ! re> face ( ! diaphragm4 ,! damp+ spr+s are prev5t$ f com+ into actual contact ) ! diaphragm by small insulat+ pads4 ,! purpose ( ! damp+ spr+s is to r$uce ! s5sitiv5ess ( ! diaphragm to extrane\s s\nds4 ,z a result1 ! ,:ite transmitt] does n pick up all ( ! s\nds 9 its vic9ity z readily z d ! m s5sitive transmitt]s1 & ?us ! transmission is n int]f]$ ) by extrane\s noises4 ,on ! o!r h&1 ! provision ( ^! heavy damp+ spr+s makes x necess>y t ?is transmitt] %all be spok5 into directly by ! us]4 ,illu/ration3 ,fig4 #da4 ,:ite ,solid-,back ,transmitt] ,! action ( ?is transmitt] is z foll[s3 ,s\nd waves are conc5trat$ aga9/ ! c5t] ( ! diaphragm by ! m\?-piece1 :i* is ( ! famili> =m4 ,^! waves imp+e aga9/ ! diaphragm1 caus+ x to vibrate1 & ?is1 9 turn1 produces simil> vibrations 9 ! front electrode4 ,! vibrations ( ! front electrode are p]mitt$ by ! ela/icity ( ! mica wa%] #f4 ,! re> electrode is1 h[ev]1 held /ation>y )9 ! heavy *amb]$ block #d & :i* 9 turn is held immovable by its rigid m\nt+4 ,z a result1 ! front electrode approa*es & rec$es f ! re> electrode1 ?us compress+ & decompress+ ! mass ( granul> c>bon betwe5 !m4 ,z a result1 ! intimacy ( contact betwe5 ! electrode plates & ! granules & also betwe5 ! granules !mselves is alt]$1 & ! resi/ance ( ! pa? f "o electrode to ! o!r ?r\gh ! mass ( granules is v>i$4 ,new ,we/]n ,electric ,transmitt]4 ,! ,:ite transmitt] 0 ! prototype ( a l>ge numb] ( o!rs embody+ ! same features ( hav+ ! re> electrode m\nt$ 9 a /ation>y cup or *amb] & ! front electrode movable ) ! diaphragm1 a wa%] ( mica or o!r flexible insulat+ mat]ial s]v+ to close ! front ( ! electrode *amb] & at ! same "t to p]mit ! necess>y vibration ( ! front electrode ) ! diaphragm4 ,illu/ration3 ,fig4 #db4 ,new ,we/]n ,electric ,transmitt] ,"o ( ^! transmitt]s1 embody+ ^! same features b ) modifi$ details1 is %[n 9 ,fig4 #db1 ?is be+ ! new transmitt] manufactur$ by ! ,we/]n ,electric ,company4 ,9 ?is ! bridge ( ! orig9al ,:ite transmitt] is disp5s$ )1 ! electrode *amb] be+ support$ by a press$ metal cup #a1 :i* supports ! *amb] z a :ole4 ,! electrode cup1 in/ead ( be+ made ( a solid block z 9 ! ,:ite in/rum5t1 is compos$ ( two portions1 a cyl9drical or tubul> portion #b & a back #c4 ,! cyl9drical portion is ext]nally screw-?read$ s z to engage an int]nal screw ?read 9 a flang$ op5+ 9 ! c5t] ( ! cup #a4 ,by ?is means ! electrode *amb] is held 9 place 9 ! cup #a1 & by ! same means ! mica wa%] #d is clamp$ betwe5 ! flange 9 ?is op5+ & ! tubul> portion #b ( ! electrode *amb]4 ,! front electrode is c>ri$1 z 9 ! ,:ite transmitt]1 on ! mica wa%] & is rigidly atta*$ to ! c5t] ( ! diaphragm s z to p>take ( ! movem5t !re(4 ,x w be se51 !re=e1 t ?is is ess5tially a ,:ite transmitt]1 b ) a modifi$ m\nt+ = ! electrode *amb]4 ,a feature 9 ?is transmitt] t is n f\nd 9 ! ,:ite transmitt] is t bo? ! front & ! re> electrodes1 9 fact1 ! entire work+ portions ( ! transmitt]1 are insulat$ f ! expos$ metal p>ts ( ! in/rum5t4 ,?is is accompli%$ by insulat+ ! diaphragm & ! support+ cup #a f ! transmitt] front4 ,! t]m9al #e on ! cup #a =ms ! electrical connection = ! re> electrode1 :ile ! t]m9al #f1 :i* is m\nt$ on b insulat$ f ! cup #a & is connect$ ) ! front electrode by a ?9 flexible connect+ /rip1 =ms ! electrical connection = ! front electrode4 ,kellogg ,transmitt]4 ,! transmitt] ( ! ,kellogg ,swit*bo>d & ,supply ,company1 orig9ally develop$ by ,mr4 ,w4,w4 ,dean & modifi$ by 8 successors 9 ! ,kellogg ,company1 is %[n 9 ,fig4 #dc4 ,9 ?is1 ! electrode *amb]1 in/ead ( be+ m\nt$ 9 a /ation>y & rigid position1 z 9 ! case ( ! ,:ite in/rum5t1 is m\nt$ on1 &1 9 fact1 =ms a "p ( ! diaphragm4 ,! electrode :i* is associat$ ) ! mica wa%] in/ead ( mov+ ) ! diaphragm1 z 9 ! ,:ite in/rum5t1 is rigidly connect$ to a bridge s z to be z free z possible f all vibrations4 ,ref]r+ to ,fig4 #dc1 :i* is a horizontal cross-section ( ! in/rum5t1 #a indicates ! diaphragm4 ,?is is ( alum9um & x has 9 its c5t] a =w>dly deflect$ portion =m+ a *amb] = ! electrodes4 ,! front electrode #b ( c>bon is back$ by a disk ( brass & rigidly secur$ 9 ! front ( ?is *amb]1 z cle>ly indicat$4 ,! re> electrode #c1 also ( c>bon1 is back$ by a disk ( brass1 & is clamp$ aga9/ ! c5tral portion ( a mica disk by means ( ! enl>g$ head ( /ud #f4 ,a nut #g1 engag+ ! end ( a screw-?read$ %ank f ! back ( ! re> electrode1 s]ves to b9d ^! two p>ts toge!r securely1 clamp+ ! mica wa%] betwe5 !m4 ,! out] edge ( ! mica wa%] is clamp$ to ! ma9 diaphragm #a by an alum9um r+ & rivets1 z cle>ly indicat$4 ,x is se51 !re=e1 t ! diaphragm itself conta9s ! electrode *amb] z an integral "p !re(4 ,! entire /ructure ( ! diaphragm1 ! front & back electrodes1 & ! granul> c>bon )9 are p]man5tly assembl$ 9 ! factory & _c be dissociat$ )\t de/roy+ "s ( ! p>ts4 ,! re> electrode is held rigidly 9 place by ! bridge #e & ! /ud #f1 ?is /ud pass+ ?r\gh a block #i m\nt$ on ! bridge b insulat$ f x4 ,! /ud #f is clamp$ 9 ! block #i by means ( ! set screw #h1 s z to hold ! re> electrode 9 prop] position aft] ?is position has be5 det]m9$4 ,illu/ration3 ,fig4 #dc4 ,kellogg ,transmitt] ,9 ?is transmitt]1 z 9 ! transmitt] %[n 9 ,fig4 #db1 all ( ! work+ p>ts are insulat$ f ! expos$ metal cas+4 ,! diaphragm is insulat$ f ! front ( ! in/rum5t by means ( a wa%] #d ( impregnat$ clo?1 z indicat$4 ,! re> electrode is insulat$ f ! o!r portions ( ! in/rum5t by means ( ! mica wa%] & by means ( ! insulation betwe5 ! block #i & ! bridge #e4 ,! t]m9al = ! re> electrode is m\nt$ on ! block #i1 :ile ! t]m9al = ! front electrode1 %[n at #aj1 is m\nt$ on1 b insulat$ f1 ! bridge4 ,?is t]m9al #aj is connect$ ) ! diaphragm & !re=e ) ! front electrode by means ( a ?91 flexible metallic connection4 ,?is transmitt] is provid$ ) damp+ spr+s simil> to ^? ( ! ,:ite in/rum5t4 ,x is claim$ by advocates ( ?is type ( in/rum5t t1 9 addition to ! ord9>y action due to ! compression & decompression ( ! granul> c>bon betwe5 ! electrodes1 !re exi/s ano!r action due to ! agitation ( ! granules z ! *amb] is caus$ to vibrate by ! s\nd waves4 ,9 o!r words1 9 addition to ! ord9>y action1 :i* may be t]m$ ! pi/on action betwe5 ! electrodes1 x is claim$ t ! g5]al %ak+-up effect ( ! granules :5 ! *amb] vibrates produces an add$ effect4 ,c]ta9 x is1 h[ev]1 t transmitt]s ( ?is g5]al type are v effici5t & h prov5 _! capability ( giv+ satisfactory s]vice ?r\gh long p]iods ( "t4 ,ano!r int]e/+ feature ( ?is in/rum5t z x is n[ manufactur$ is ! use ( a transmitt] front t is /ruck up f %eet metal r ?an ! employm5t ( a ca/+ z has ord9>ily be5 ! practice4 ,! =mation ( ! support+ lug = ! transmitt] f ! %eet metal :i* =ms ! re> cas+ or %ell ( ! in/rum5t is also an int]e/+ feature4 ,automatic ,electric ,company ,transmitt]4 ,! transmitt] ( ! ,automatic ,electric ,company1 ( ,*icago1 %[n 9 ,fig4 #dd1 is ( ! same g5]al type z ! "o j discuss$1 9 t ! electrode *amb] is m\nt$ on & vibrates ) ! diaphragm in/ead ( be+ rigidly support$ on ! bridge z 9 ! case ( ! ,:ite or solid-back type ( in/rum5t4 ,9 ?is in/rum5t ! transmitt] front #a is /ruck up f %eet metal & conta9s a re>w>dly project+ flange1 c>ry+ an int]nal screw ?read4 ,a heavy inn] cup #b1 toge!r ) ! diaphragm #c1 =m an enclosure conta9+ ! electrode *amb]4 ,! diaphragm is1 9 ?is case1 p]man5tly secur$ at its edge to ! p]iph]y ( ! inn] cup #b by a b& ( metal #d s =m$ z to embrace ! edges ( bo? ! cup & ! diaphragm & p]man5tly lock !m toge!r4 ,?is inn] *amb] is held 9 place 9 ! transmitt] front #a by means ( a lock r+ #e ext]nally screw-?read$ to engage ! int]nal screw-?read on ! flange on ! front4 ,! electrode *amb] prop] is made 9 ! =m ( a cup1 rigidly secur$ to ! diaphragm s z to move !re)1 z cle>ly indicat$4 ,! re> electrode is m\nt$ on a screw-?read$ /ud c>ri$ 9 a block :i* is fitt$ to a close c5tral op5+ 9 ! cup #b4 ,?is transmitt] does n make use ( a mica wa%] or diaphragm1 b employs a felt wa%] :i* surr\nds ! %ank ( ! re> electrode & s]ves to close & seal ! c>bon conta9+ cup4 ,by ?is means ! granul> c>bon is reta9$ 9 ! *amb] & ! necess>y flexibility or fre$om ( motion is p]mitt$ betwe5 ! front & ! re> electrodes4 ,z 9 ! ,kellogg & ! lat] ,bell in/rum5ts1 ! entire work+ p>ts ( ?is transmitt] are insulat$ f ! metal conta9+ case1 ! inn] *amb]1 =m$ by ! cup #b & ! diaphragm #c1 be+ insulat$ f ! transmitt] front & its lock+ r+ by means ( insulat+ wa%]s1 z %[n4 ,fig4 #dd4 ,automatic ,electric ,company ,transmitt] ,mon>* ,transmitt]4 ,! transmitt] ( ! ,mon>* ,telephone ,manufactur+ ,company1 %[n 9 ,fig4 #de1 diff]s f bo? ! /ation>y-cup & ! vibrat+-cup types1 al?\gh x has ! *>act]i/ics ( bo?4 ,x might be said t x diff]s f ea* ( ^! two types ( transmitt]s 9 t x has ! *>act]i/ics ( bo?4 ,?is transmitt]1 x w be se51 has two flexible mica wa%]s betwe5 ! electrodes & ! walls ( ! electrode cup4 ,! front & ! back electrodes are atta*$ to ! diaphragm & ! bridge1 respectively1 by a me?od simil> to t employ$ 9 ! solid-back transmitt]s1 :ile ! c>bon *amb] itself is free to vibrate ) ! diaphragm z is *>act]i/ic ( ! ,kellogg transmitt]4 ,illu/ration3 ,fig4 #de4 ,mon>* ,transmitt] ,an alum9um diaphragm is employ$1 ! circumf]5tial edge ( :i* is =w>dly deflect$ to =m a seat4 ,! edge ( ! diaphragm re/s aga9/ & is sep>at$ f ! brass front by means ( a "o-piece gasket ( specially treat$ l954 ,?is =ms an insulator :i* is n affect$ by heat or moi/ure4 ,z 9 ! transmitt]s previ\sly describ$1 ! electrodes are firmly sold]$ to brass disks :i* h solid /uds ext5d+ f _! c5t]s4 ,9 ! case ( bo? ! front & ! re> electrodes1 a mica disk is plac$ ov] ! support+ /ud & held 9 place by a brass hub :i* has a base ( ! same size z ! electrode4 ,! c>bon-*amb] wall consi/s ( a brass r+ to :i* are fa/5$ ! mica disks ( ! front & ! back electrodes by means ( brass coll>s clamp$ ov] ! edge ( ! mica & ar\nd ! rim ( ! brass r+ =m+ ! *amb]4 ,illu/ration3 ,,ma9 ,,(fice ,,build+1 ,,b]keley1 ,,cali=nia ,conta9+ ,automatic ,equipm5t1 ,=m+ ,"p ( ,l>g] ,sy/em ,op]at+ 9 ,san ,francisco & ,vic9ity4 ,bay ,cities ,home ,telephone ,company4 ,electrodes4 ,! electrode plates ( ne>ly all mod]n transmitt]s are ( specially treat$ c>bon4 ,^! are fir/ copp]-plat$ & sold]$ to _! brass support+ disks4 ,aft] ?is !y are turn$ & gr\nd s z to be truly circul> 9 =m & to pres5t absolutely flat faces t[>d ea* o!r4 ,^! faces are !n highly poli%$ & ! utmo/ ef=t is made to keep !m absolutely clean4 ,great pa9s are tak5 to remove f ! pores ( ! c>bon1 z well z f ! surface1 all ( ! acids or o!r *emicals t may h ent]$ !m dur+ ! process ( electroplat+ !m or ( sold]+ !m to ! brass support+ disk4 ,t ! two electrodes1 :5 m\nt$ 9 a transmitt]1 %\ld be p>allel ) ea* o!r1 is an item ( great importance z w be po9t$ out lat]4 ,9 a few cases1 z previ\sly /at$1 gold or plat9um has be5 sub/itut$ = ! c>bon electrodes 9 transmitt]s4 ,^! are capable ( giv+ good results :5 us$ 9 connection ) ! prop] =m ( granul> c>bon1 b1 on ! :ole1 ! t5d5cy has be5 to ab&on all =ms ( electrode mat]ial except c>bon1 & its use is n[ well nigh univ]sal4 ,prep>ation ( ,c>bon4 ,! granul> c>bon is prep>$ f c>efully select$ an?racite coal1 :i* is specially treat$ by roa/+ or re-c>boniz+ & is !n cru%$ to approximately ! prop] f95ess4 ,! cru%$ c>bon is !n scre5$ ) extreme c>e to elim9ate all du/ & to reta9 only granules ( uni=m size4 ,pack+4 ,9 ! e>li] =ms ( granul>-c>bon transmitt]s a great deal ( tr\ble 0 exp]i5c$ due to ! s-call$ pack+ ( ! in/rum5t4 ,?is1 z ! t]m indicates1 0 a tr\ble due to ! t5d5cy ( ! c>bon granules to settle into a compact mass & ?us n respond to ! v>iable pressure4 ,?is 0 sometimes due to ! pres5ce ( moi/ure 9 ! electrode *amb]2 sometimes to ! employm5t ( granules ( v>y+ sizes1 s t !y w\ld f9ally arrange !mselves "u ! vibration ( ! diaphragm into a fairly compact mass2 or sometimes1 & m frequ5tly1 to ! granules 9 "s way w$g+ ! two electrodes ap>t & hold+ !m at a great] di/ance f ea* o!r ?an _! normal di/ance4 ,! tr\ble due to moi/ure has be5 entirely elim9at$ by s seal+ ! granule *amb]s z to prev5t ! entrance ( moi/ure4 ,! tr\ble due to ! lack ( uni=mity 9 size ( ! granules has be5 entirely elim9at$ by mak+ !m all ( "o size & by mak+ !m ( suffici5t h>dness s t !y w\ld n break up into granules ( small] size4 ,! tr\ble due to ! settl+ ( ! granules & w$g+ ! electrodes ap>t has be5 practically elim9at$ 9 well-design$ in/rum5ts1 by great me*anical nicety 9 manufacture4 ,almo/ any transmitt] may be pack$ by draw+ ! diaphragm =w>d s z to widely sep>ate ! electrodes4 ,?is all[s ! granules to settle to a l[] level ?an !y normally occupy & :5 ! diaphragm is releas$ & attempts to resume its normal position x is prev5t$ f do+ s by ! mass ( granules betwe54 ,transmitt]s ( ! e>ly types c\ld be pack$ by plac+ ! lips aga9/ ! m\?piece & draw+ 9 ! brea?4 ,! slots n[ provid$ at ! base ( /&>d m\?pieces effectually prev5t ?is4 ,9 g5]al x may be said t ! pack+ difficulty has be5 almo/ entirely elim9at$1 n by ! employm5t ( rem$ial devices1 su* z ^? (t5 propos$ = /irr+ up ! c>bon1 b by prev5t+ ! tr\ble by ! design & manufacture ( ! in/rum5ts 9 su* =ms t !y w n be subject to ! evil4 ,c>ry+ ,capacity4 ,obvi\sly1 ! p[] ( a transmitt] is dep5d5t on ! am\nt ( curr5t t x may c>ry1 z well z on ! am\nt ( v>iation t x may make 9 ! resi/ance ( ! pa? ?r\gh x4 ,granul> c>bon transmitt]s are capable ( c>ry+ mu* heavi] curr5t ?an ! old ,blake or o!r s+le or multiple electrode types4 ,if =c$ to c>ry too mu* curr5t1 h[ev]1 ! same fry+ or sizzl+ s\nd is noticeable z 9 ! e>li] types4 ,?is is due to ! heat+ ( ! electrodes & to small arcs t occur betwe5 ! electrodes & ! granules4 ,"o way to increase ! curr5t-c>ry+ capacity ( a transmitt] is to increase ! area ( its electrodes1 b a limit is soon rea*$ 9 ?is direction ow+ to ! increas$ in]tia ( ! mov+ electrode1 :i* necess>ily comes ) its l>g] size4 ,! c>ry+ capacity ( transmitt]s may also be increas$ by provid+ special means = c>ry+ away ! heat g5]at$ 9 ! v>iable-resi/ance m$ium4 ,sev]al s*emes h be5 propos$ = ?is4 ,"o is to employ unusually heavy metal = ! electrode *amb]1 & ?is practice is be/ exemplifi$ 9 ! ,:ite solid-back in/rum5t4 ,x has also be5 propos$ by o!rs to wat]-jacket ! electrode *amb]1 & also to keep x cool by plac+ x 9 close proximity to ! relatively cool jo9ts ( a !rmopile4 ,nei!r ( ^! two latt] s*emes seems to be w>rant$ 9 ord9>y comm]cial practice4 ,s5sitiv5ess4 ,9 all ! transmitt]s s f> discuss$ damp+ spr+s ( "o =m or ano!r h be5 employ$ to r$uce ! s5sitiv5ess ( ! in/rum5t4 ,= ord9>y comm]cial use too great a degree ( s5sitiv5ess is a fault1 z has already be5 po9t$ out4 ,!re are1 h[ev]1 c]ta9 adaptations ( ! telephone transmitt] :i* make a maximum degree ( s5sitiv5ess desirable4 ,"o ( ^! adaptations is f\nd 9 ! telephone equipm5ts = assi/+ p>tially deaf p to he>4 ,9 ^! ! transmitt] is c>ri$ on "s portion ( ! body ( ! deaf p]son1 ! receiv] is /rapp$ or o!rwise held at 8 e>1 & a batt]y = furni%+ ! curr5t is c>ri$ 9 8 pocket4 ,x is n feasible1 = ?is sort ( use1 t ! s\nd :i* ?is transmitt] is to reproduce %all always occur imm$iately 9 front ( ! transmitt]4 ,x m (t5 occurs at a di/ance ( sev]al feet4 ,= ?is reason ! transmitt] is made z s5sitive z possible1 & yet is s con/ruct$ t x w n be caus$ to produce too l\d or unduly h>% s\nds 9 response to a l\d s\nd tak+ place imm$iately 9 front ( x4 ,ano!r adaptation ( su* highly s5sitive transmitt]s is f\nd 9 ! special int]communicat+ telephone sy/ems = use betwe5 ! v>i\s dep>tm5ts or desks 9 bus9ess (fices4 ,9 ^! x is desirable t ! transmitt] %all be able to respond adequately to s\nds occurr+ any:]e 9 a small-siz$ room1 = in/ance4 ,ac\/icon ,transmitt]4 ,9 ,fig4 #df is %[n a transmitt] adapt$ = su* use4 ,?is has be5 t]m$ by its mak]s ! ac\/icon transmitt]4 ,l all ! transmitt]s previ\sly discuss$1 ?is is ( ! v>iable-resi/ance type1 b x diff]s f !m all 9 t x has no damp+ spr+s2 9 t c>bon balls are sub/itut$ = c>bon granules2 & 9 t ! diaphragm itself s]ves z ! front electrode4 ,?is transmitt] consi/s ( a cup #a1 into :i* is set a cyl9drical block #b1 9 "o face ( :i* are a numb] ( hemisph]ical recesses4 ,! diaphragm #c is made ( ?9 c>bon & is s plac$ 9 ! transmitt] z to cov] ! op5+s ( ! recesses 9 ! c>bon block1 & lie close en\gh to ! c>bon block1 )\t engag+ x1 to prev5t ! c>bon p>ticles f fall+ out4 ,! diaphragm ?us s]ves z ! front electrode & ! c>bon block z ! re> electrode4 ,! recesses 9 ! c>bon block are ab\t two-?irds fill$ ) small c>bon balls1 :i* are ab\t ! size ( f9e s&4 ,! front piece #d ( ! transmitt] is ( %eet metal & s]ves to hold ! diaphragm 9 place4 ,to admit ! s\nd waves x is provid$ ) a circul> op5+ opposite to & ab\t ! size ( ! re> electrode block4 ,on ?is front piece are m\nt$ ! two t]m9als ( ! transmitt]1 connect$ respectively to ! two electrodes1 t]m9al #e be+ insulat$ f ! front piece & connect$ by a ?9 metal /rip ) ! diaphragm1 :ile t]m9al #f is m\nt$ directly on ! front piece & connect$ ?r\gh ! cup #a ) ! c>bon block #b1 or back electrode ( ! transmitt]4 ,illu/ration3 ,fig #df4 ,ac\/icon ,transmitt] ,:5 ?is transmitt] is us$ 9 connection ) outfits = ! deaf1 x is plac$ 9 a h>d rubb] conta9+ case1 consi/+ ( a holl[ cyl9drical piece #g1 :i* has fa/5$ to x a cov] #h4 ,?is cov] has a circul> r[ ( op5+s or holes ne> its out] edge1 z %[n at #i1 ?r\gh :i* ! s\nd waves may pass to ! *amb] )91 & !nce f9d _! way ?r\gh ! r\nd hole 9 ! c5t] ( ! front plate #d to ! diaphragm #c4 ,x is probable also t ! front face ( ! cov] #h ( ! out] case vibrates1 & 9 ?is way also causes s\nd waves to imp+e aga9/ ! diaphragm4 ,?is arrangem5t provides a l>ge receiv+ surface = ! s\nd waves1 b1 ow+ to ! fact t ! op5+s 9 ! conta9+ case are n opposite ! op5+ 9 ! transmitt] prop]1 ! s\nd waves d n imp+e directly aga9/ ! diaphragm4 ,?is peculi> arrangem5t is probably ! result ( an endeavor to prev5t ! transmitt] f be+ too /rongly actuat$ by viol5t s\nds close to x4 ,in/rum5ts ( ?is k9d are v s5sitive & "u prop] conditions are readily responsive to words spok5 9 an ord9>y tone t5 feet away4 ,illu/ration3 ,fig4 #dg4 ,swit*bo>d ,transmitt] ,swit*bo>d ,transmitt]4 ,ano!r special adaptation ( ! telephone transmitt] is t = use ( telephone op]ators at c5tral-(fice swit*bo>ds4 ,! requirem5ts 9 ?is case are su* t ! op]ator mu/ always be able to speak into ! transmitt] :ile seat$ be=e ! swit*bo>d1 & yet all[ bo? ( h] h&s to be free = use4 ,?is 0 =m]ly accompli%$ by susp5d+ an ord9>y granul>-c>bon transmitt] 9 front ( ! op]ator1 b a lat] developm5t has result$ 9 ! adoption ( ! s-call$ brea/ transmitt]1 %[n 9 ,fig4 #dg4 ,?is is m]ely an ord9>y granul>-c>bon transmitt] m\nt$ on a plate :i* is /rapp$ on ! brea/ ( ! op]ator1 ! transmitt] be+ provid$ ) a long curv$ m\?piece :i* projects 9 su* a mann] z to lie j 9 front ( ! op]ator's lips4 ,?is device has ! advantage ( automatically foll[+ ! op]ator 9 h] movem5ts4 ,! brea/ transmitt] %[n 9 ,fig4 #dg1 is t ( ! ,dean ,electric ,company4 ,illu/ration3 ,fig4 #dh4 ,transmitt] ,symbols ,conv5tional ,diagram4 ,!re are sev]al common ways ( illu/rat+ transmitt]s 9 diagrams ( circuits 9 :i* !y are employ$4 ,! ?ree mo/ common ways are %[n 9 ,fig4 #dh4 ,! "o at ! left is suppos$ to be a side view ( an ord9>y in/rum5t1 ! "o 9 ! c5t] a front view1 & ! "o at ! "r to be m]ely a sugge/ive arrangem5t ( ! diaphragm & ! re> electrode4 ,! "o at ! "r is be/ & p]haps mo/ common2 ! c5t] "o is ! poore/ & lea/ us$4 ,,*apt] ,,vi ,,receiv]s ,! telephone receiv] is ! device :i* translates ! en]gy ( ! voice curr5ts into ! en]gy ( correspond+ s\nd waves4 ,all telephone receiv]s today are ( ! electromagnetic type1 ! voice curr5ts caus+ a v>y+ magnetic pull on an armature or diaphragm1 :i* 9 turn produces ! s\nd waves correspond+ to ! undulations ( ! voice curr5ts4 ,e>ly ,receiv]s4 ,! e>ly =ms ( telephone receiv]s 7 ( ! s+le-pole type2 t is1 ! type :]e9 b "o pole ( ! electromagnet 0 pres5t$ to ! diaphragm4 ,! s+le-pole receiv] t =m$ ! companion piece to ! old ,blake transmitt] & t 0 ! /&>d ( ! ,bell companies = _m ye>s1 is %[n 9 ,fig4 #di4 ,:ile ?is has almo/ completely pass$ out ( use1 x may be pr(itably /udi$ 9 ord] t a comp>ison may be made betwe5 c]ta9 features ( its con/ruction & ^? ( ! lat] =ms ( receiv]s4 ,! coil ( ?is receiv] 0 w\nd on a r\nd iron core #b1 flatt5$ at "o end to af=d means = atta*+ ! p]man5t magnet4 ,! p]man5t magnet 0 ( lam9at$ con/ruction1 consi/+ ( f\r h>d /eel b>s #a1 ext5d+ ne>ly ! entire l5g? ( ! receiv] %ell4 ,^! /eel b>s 7 all magnetiz$ sep>ately & plac$ ) l poles toge!r s z to =m a s+le b> magnet4 ,!y 7 laid toge!r 9 pairs s z to include betwe5 ! pairs ! flatt5$ end ( ! pole piece #b at "o end & ! flatt5$ portion ( ! tail piece #c at ! o!r end4 ,?is :ole magnet /ructure1 includ+ ! core1 ! tail piece1 & ! p]man5tly magnetiz$ /eel b>s1 0 clamp$ toge!r by screws z %[n4 ,! conta9+ %ell 0 ( h>d rubb] consi/+ ( ?ree pieces1 ! b>rel #d1 ! e>-piece #e1 & ! tail cap #f4 ,! b>rel & ! e> piece engag$ ea* o!r by means ( a screw ?read & s]v$ to clamp ! diaphragm betwe5 !m4 ,! comp\nd b> magnet 0 held 9 place )9 ! %ell by means ( a screw #g pass+ ?r\gh ! h>d rubb] tail cap #f & into ! tail block #c ( ! magnet4 ,ext]nal b9d+ po/s m\nt$ on ! tail cap1 z %[n1 7 connect$ by heavy lead+-9 wires to ! t]m9als ( ! electromagnet4 ,a casual consid]ation ( ! magnetic circuit ( ?is in/rum5t w %[ t x 0 ineffici5t1 s9ce ! return pa? = ! l9es ( =ce set up by ! b> magnet 0 necess>ily ?r\gh a v long air pa?4 ,not)/&+ ?is1 ^! receiv]s 7 capable ( giv+ excell5t articulation & 7 ( m>vel\s delicacy ( action4 ,a v grave fault 0 t ! magnet 0 support$ 9 ! %ell at ! end f>!/ remov$ f ! diaphragm4 ,z a result x 0 difficult to ma9ta9 a p]man5t adju/m5t betwe5 ! pole piece & ! diaphragm4 ,"o reason = ?is 0 t h>d rubb] & /eel contract & exp& "u *anges ( temp]ature at v diff]5t rates1 & !re=e ! di/ance betwe5 ! pole piece & ! diaphragm *ang$ ) *anges ( temp]ature4 ,ano!r grave defect1 br\ght ab\t by ?is ty+ toge!r ( ! p]man5t magnet & ! %ell :i* support$ ! diaphragm at ! end f>!/ f ! diaphragm1 0 t any me*anical %ocks 7 ?us giv5 a good *ance to alt] ! adju/m5t4 ,illu/ration3 ,fig4 #di4 ,s+le-,pole ,receiv] ,mod]n ,receiv]s4 ,receiv]s ( today diff] f ?is old s+le-pole receiv] 9 two radical respects4 ,9 ! fir/ place1 ! mod]n receiv] is ( ! bi-pol> type1 consi/+ ess5tially ( a horse%oe magnet pres5t+ bo? ( its poles to ! diaphragm4 ,9 ! second place1 ! mod]n practice is to ei!r support all ( ! work+ p>ts ( ! receiv]1 i4e41 ! magnet1 ! coils1 & ! diaphragm1 by an inn] metallic frame entirely indep5d5t ( ! %ell2 or1 if ! %ell is us$ z a "p ( ! /ructure1 to rigidly fa/5 ! sev]al p>ts close to ! diaphragm r ?an at ! end f>!/ remov$ f ! diaphragm4 ,we/]n ,electric ,receiv]4 ,! /&>d bi-pol> receiv] ( ! ,we/]n ,electric ,company1 9 use by practically all ( ! ,bell op]at+ companies ?r\gh\t ?is c\ntry & 9 l>ge use abroad1 is %[n 9 ,fig4 #ej4 ,9 ?is ! %ell is ( ?ree pieces1 consi/+ ( ! b>rel #a1 ! e> cap #b1 & ! tail cap #c4 ,! tail cap & ! b>rel are p]man5tly fa/5$ toge!r to =m sub/antially a s+le piece4 ,two p]man5tly magnetiz$ b> magnets #d-d are employ$1 ^! be+ clamp$ toge!r at _! upp] ends1 z %[n1 s z to include ! s(t iron block #e betwe5 !m4 ,! nor? pole ( "o ( ^! magnets is clamp$ to ! s\? pole ( ! o!r1 s t 9 reality a horse%oe magnet is =m$4 ,at _! l[] ends1 ^! two p]man5t magnets are clamp$ aga9/ ! s(t iron pole pieces #f-f1 a ?read$ block #g also be+ clamp$ rigidly betwe5 ^! pole pieces at ?is po9t4 ,on ! ends ( ! pole pieces ! bobb9s are w\nd4 ,! :ole magnet /ructure is secur$ )9 ! %ell #a by means ( a screw ?read on ! block #g :i* engages a correspond+ int]nal screw ?read 9 ! %ell #a4 ,z a result ( ?is con/ruction ! :ole magnet /ructure is b\nd rigidly to ! %ell /ructure at a po9t close to ! diaphragm1 comp>atively speak+1 & z a result ( ?is close c\pl+1 ! relation betwe5 ! diaphragm & ! pole piece is v mu* m rigid & sub/antial ?an 9 ! case :]e ! magnet /ructure & ! %ell 7 secur$ toge!r at ! end f>!/ remov$ f ! diaphragm4 ,illu/ration3 ,fig4 #ej4 ,we/]n ,electric ,receiv] ,al?\gh ?is receiv] %[n 9 ,fig4 #ej is ! /&>d 9 use by ! ,bell companies ?r\gh\t ?is c\ntry1 its numb]s runn+ well into ! millions1 x _c be said to be a /rictly mod]n receiv]1 because ( at lea/ "o r antiquat$ feature4 ,! b9d+ po/s1 by :i* ! circuit conductors are l$ to ! coils ( ?is in/rum5t1 are m\nt$ on ! outside ( ! receiv] %ell1 z indicat$1 & are ?us subject to dang] ( me*anical injury & !y are also expos$ to ! t\* ( ! us]1 s t he may1 9 case ( ! wires be+ *>g$ to an abnormal pot5tial1 receive a %ock4 ,probably a m s]i\s feature ?an ei!r "o ( ^! is t ! t]m9als ( ! flexible cords :i* atta* to ^! b9d+ po/s are atta*$ outside ( ! receiv] %ell1 & are !re=e expos$ to ! we> & te> ( use1 r ?an be+ protect$ z !y %\ld be )9 ! %ell4 ,not)/&+ ?is undesirable feature1 ?is receiv] is a v effici5t "o & is excell5tly con/ruct$4 ,illu/ration3 ,fig4 #ea4 ,kellogg ,receiv] ,kellogg ,receiv]4 ,9 ,fig4 #ea is %[n a bi-pol> receiv] ) int]nal or conceal$ b9d+ po/s4 ,?is p>ticul> receiv] is typical ( a l>ge numb] ( simil> k9ds & is manufactur$ by ! ,kellogg ,swit*bo>d & ,supply ,company4 ,two /raight p]man5tly magnetiz$ b> magnets #a-a are clamp$ toge!r at _! opposite ends s z to =m a horse%oe magnet4 ,at ! end opposite ! diaphragm ^! b>s clamp betwe5 !m a cyl9drical piece ( iron #b1 s z to complete ! magnetic circuit at ! end4 ,at ! end ne>e/ ! diaphragm !y clamp betwe5 !m ! ends ( ! s(t iron pole pieces #c-c1 & also a block ( composite metal #d hav+ a l>ge circul> flange #d' :i* s]ves z a means = support+ ! magnet /ructure )9 ! %ell4 ,! screws by means ( :i* ! disk #d' is clamp$ to ! %\ld]$ seat 9 ! %ell d n ent] ! %ell directly1 b r ent] screw-?read$ brass blocks :i* are m\ld$ into ! /ructure ( ! %ell4 ,x is se5 f ?is con/ruction t ! diaphragm & ! pole pieces & ! magnet /ructure itself are all rigidly secur$ toge!r ?r\gh ! m$ium ( ! %ell at a po9t z close z possible to ! diaphragm4 ,betwe5 ! magnets #a-a !re is clamp$ an insulat+ block #e1 to :i* are fa/5$ ! t]m9al plates #f1 "o on ea* side ( ! receiv]4 ,^! t]m9al plates are ?or\ghly insulat$ f ! magnets !mselves & f all o!r metallic p>ts by means ( %eets ( fib]1 z indicat$ by ! heavy black l9es4 ,on ^! plates #f are c>ri$ ! b9d+ po/s = ! receiv] cord t]m9als4 ,a long tongue ext5ds f ea* ( ! plates #f ?r\gh a hole 9 ! disk #d'1 into ! coil *amb] ( ! receiv]1 at :i* po9t ! t]m9al ( ! magnet w9d+ is secur$ to x4 ,?is tongue is insulat$ f ! disk #d'1 :]e x passes ?r\gh x1 by means ( insulat+ bu%+1 z %[n4 ,! o!r t]m9al ( ! magnet coils is br\ght out to ! o!r plate #f by means ( a simil> tongue on ! o!r side4 ,9 ord] t ! receiv] t]m9als prop] may n be subject$ to any /ra9 9 case ! receiv] is dropp$ & its weight caught on ! receiv] cord1 a /ra9 loop is =m$ z a cont9uation ( ! braid$ cov]+ ( ! receiv] cord1 & ?is is ti$ to ! p]man5t magnet /ructure1 z %[n4 ,by mak+ ?is /ra9 loop %ort1 x is obvi\s t :atev] pull ! cord receives w n be tak5 by ! cord conductors lead+ to ! b9d+ po/s or by ! b9d+ po/s or ! cord t]m9als !mselves4 ,a numb] ( o!r manufactur]s h gone ev5 a /ep fur!r ?an ?is 9 secur+ p]man5cy ( adju/m5t betwe5 ! receiv] diaphragm & pole pieces4 ,!y h done ?is by n dep5d+ at all on ! h>d rubb] %ell z a "p ( ! /ructure1 b by enclos+ ! magnet coil 9 a cup ( metal ^u :i* ! diaphragm is m\nt$1 s t ! p]man5cy ( relation betwe5 ! diaphragm & ! pole pieces is dep5d5t only ^u ! metallic /ructure & n at all ^u ! less durable %ell4 ,direct-,curr5t ,receiv]4 ,until ab\t ! middle ( ! ye> #aiji1 x 0 ! univ]sal practice to employ p]man5t magnets = giv+ ! initial pol>ization to ! magnet cores ( telephone receiv]s4 ,?is is /ill done1 & necess>ily s1 9 receiv]s employ$ 9 connection ) magneto telephones4 ,9 common-batt]y sy/ems1 h[ev]1 :]e ! direct transmitt] curr5t is f$ f ! c5tral (fice to ! local /ations1 x has be5 f\nd t ?is curr5t :i* mu/ fl[ at any rate ?r\gh ! l9e may be made to s]ve ! additional purpose ( en]giz+ ! receiv] magnets s z to give !m ! necess>y initial pol>ity4 ,a type ( receiv] has come into wide use z a result1 :i* is commonly call$ ! direct-curr5t receiv]1 d]iv+ its "n f ! fact t x employs ! direct curr5t t is fl[+ 9 ! common-batt]y l9e to magnetize ! receiv] cores4 ,! ,automatic ,electric ,company1 ( ,*icago1 0 probably ! fir/ company to adopt ?is =m ( receiv] z its /&>d type4 ,_! receiv] is %[n 9 cross-section 9 ,fig4 #eb1 & a photograph ( ! same in/rum5t p>tially disassembl$ is giv5 9 ,fig4 #ec4 ,! mo/ noticeable ?+ ab\t ! con/ruction ( ?is receiv] is ! abs5ce ( p]man5t magnets4 ,! entire work+ p>ts are conta9$ )9 ! brass cup #a1 :i* s]ves n only z a conta9] = ! magnet1 b also z a seat = ! diaphragm4 ,?is receiv] is !re=e illu/rative ( ! type m5tion$ above1 :]e9 ! relation betwe5 ! diaphragm & ! pole pieces is n dep5d5t ^u any connection ?r\gh ! %ell4 ,illu/ration3 ,fig4 #eb4 ,automatic ,electric ,company ,direct-,curr5t ,receiv] ,illu/ration3 ,fig4 #ec4 ,automatic ,electric ,company ,direct-,curr5t ,receiv] ,! coil ( ?is in/rum5t consi/s ( a s+le cyl9drical spool #b1 m\nt$ on a cyl9drical core4 ,?is bobb9 lies )9 a s(t iron-pun*+ #c1 ! =m ( :i* is mo/ cle>ly %[n 9 ,fig4 #ec1 & ?is pun*+ af=ds a return pa? to ! diaphragm = ! l9es ( =ce set up 9 ! magnet core4 ,obvi\sly a magnetiz+ curr5t pass+ ?r\gh ! w9d+ ( ! coil w cause ! end ( ! core t[>d ! diaphragm to be pol>iz$1 say positively1 :ile ! end ( ! enclos+ %ell w be pol>iz$ 9 ! o!r pol>ity1 negatively4 ,bo? poles ( ! magnet are !re=e pres5t$ to ! diaphragm & ! only air gap 9 ! magnetic circuit is t betwe5 ! diaphragm & ^! poles4 ,! magnetic circuit is !re=e "o ( great effici5cy1 s9ce x consi/s almo/ entirely ( iron1 ! only air gap be+ t across :i* ! attraction ( ! diaphragm is to take place4 ,! action ( ?is receiv] w be und]/ood :5 x is /at$ t 9 common-batt]y practice1 z w be %[n 9 lat] *apt]s1 a /eady curr5t fl[s ov] ! l9e = en]giz+ ! transmitt]4 ,on ?is curr5t is sup]pos$ ! incom+ voice curr5ts f a di/ant /ation4 ,! /eady curr5t fl[+ 9 ! l9e w1 9 ! case ( ?is receiv]1 pass ?r\gh ! magnet w9d+ & e/abli% a normal magnetic field 9 ! same way z if a p]man5t magnet 7 employ$4 ,! sup]pos$ incom+ voice curr5ts w !n be able to v>y ?is magnetic field 9 exactly ! same way z 9 ! ord9>y receiv]4 ,an a/oni%+ feature ( ?is rec5t developm5t ( ! s-call$ direct-curr5t receiv] is t x did n come into use until aft] ab\t tw5ty ye>s ( common-batt]y practice4 ,!re is no?+ new 9 ! pr9ciples involv$1 z all ( !m 7 already und]/ood & "s ( !m 7 employ$ by ,bell 9 8 orig9al telephone2 9 fact1 ! idea _h be5 advanc$ "t & aga91 & ?r[n aside z n be+ wor? consid]ation4 ,?is is an illu/ration ( a frequ5t occurr5ce 9 ! developm5t ( almo/ any rapidly gr[+ art4 ,ideas t are disc>d$ z wor?less 9 ! e>ly /ages ( ! art are f9ally pick$ up & made use (4 ,! reason = ?is is t 9 "s cases ! ideas come 9 advance ( ! art1 or !y are propos$ be=e ! art is ready to use !m4 ,9 o!r cases ! idea z orig9ally propos$ lack$ "s small b ess5tial detail1 or1 z is m (t5 ! case1 ! exp]im5t] 9 ! e>ly days did n h suffici5t skill or k to make x fit ! requirem5ts z he saw !m4 ,mon>* ,receiv]4 ,! receiv] ( ! ,automatic ,electric ,company j discuss$ employs b a s+le electromagnet by :i* ! initial magnetization ( ! cores & also ! v>iable magnetization necess>y = spee* reproduction is secur$4 ,! problem ( ! direct-curr5t receiv] has be5 attack$ 9 ano!r way by ,erne/ ,e4 ,yaxley1 ( ! ,mon>* ,telephone ,manufactur+ ,company1 ) ! result %[n 9 ,fig4 #ed4 ,! con/ruction 9 ?is case is n unlike t ( an ord9>y p]man5t-magnet receiv]1 except t 9 ! place ( ! p]man5t magnets two s(t iron cores #a-a are employ$4 ,on ^! are w\nd two long bobb9s ( insulat$ wire s t ! direct curr5t fl[+ ov] ! telephone l9e w pass ?r\gh ^! & magnetize ! cores to ! same degree & = ! same purpose z 9 ! case ( p]man5t magnets4 ,^! s(t iron magnet cores #a-a cont9ue to a po9t ne> ! coil *amb]1 :]e !y jo9 ! two s(t iron pole pieces #b-b1 ^u :i* ! ord9>y voice-curr5t coils are w\nd4 ,! two long coils #d-d1 :i* may be t]m$ ! direct-curr5t coils1 are ( some:at l[] resi/ance ?an ! two voice-curr5t coils #c-c4 ,!y are1 h[ev]1 by virtue ( _! great] numb] ( turns & ! great] am\nt ( iron t is includ$ 9 _! cores1 ( mu* high] imp$ance ?an ! voice-curr5t coils #c-c4 ,^! two sets ( coils #d-d & #c-c are connect$ 9 multiple4 ,z a result ( _! l[] ohmic resi/ance ! coils #d-d w take a great] am\nt ( ! /eady curr5t :i* comes ov] ! l9e1 & !re=e ! great] proportion ( ! /eady curr5t w be employ$ 9 magnetiz+ ! b> magnets4 ,on acc\nt ( _! high] imp$ance to alt]nat+ curr5ts1 h[ev]1 ne>ly all ( ! voice curr5ts :i* are sup]pos$ on ! /eady curr5ts1 fl[+ 9 ! l9e w pass ?r\gh ! voice-curr5t coils #c-c1 &1 be+ ne> ! diaphragm1 ^! curr5ts w s v>y ! /eady magnetism 9 ! cores #b-b z to produce ! necess>y vibration ( ! diaphragm4 ,illu/ration3 ,fig4 #ed4 ,mon>* ,direct-,curr5t ,receiv] ,?is receiv]1 l ! "o ( ! ,automatic ,electric ,company1 does n rely on ! %ell 9 any respect to ma9ta9 ! p]man5cy ( relation betwe5 ! pole pieces & ! diaphragm4 ,! cup #e1 :i* is ( press$ brass1 conta9s ! voice-curr5t coils & also acts z a seat = ! diaphragm4 ,! entire work+ p>ts ( ?is receiv] may be remov$ by m]ely unscrew+ ! e> piece f ! h>d rubb] %ell1 ?us p]mitt+ ! :ole works to be )drawn 9 an obvi\s mann]4 ,dean ,receiv]4 ,( su* decid$ novelty z to be almo/ revolution>y 9 "* is ! receiv] rec5tly put on ! m>ket by ! ,dean ,electric ,company & %[n 9 ,fig4 #ee4 ,?is receiv] is ( ! direct-curr5t type & employs b a s+le cyl9drical bobb9 ( wire4 ,! core ( ?is bobb9 & ! return pa? = ! magnetic l9es ( =ce set up 9 x are compos$ ( s(t iron pun*+s ( sub/antially ,e %ape4 ,^! pun*+s are laid toge!r s z to =m a lam9at$ s(t-iron field1 ! limbs ( :i* are ab\t squ>e 9 cross-section4 ,! coil is w\nd on ! c5t] portion ( ?is ,e z a core1 ! core be+1 z /at$1 approximately squ>e 9 cross-section4 ,! g5]al =m ( magnetic circuit 9 ?is in/rum5t is !re=e simil> to t ( ! ,automatic ,electric ,company's receiv]1 %[n 9 ,figs4 #eb & #ec1 b ! core is lam9at$ in/ead ( be+ solid z 9 t in/rum5t4 ,illu/ration3 ,fig4 #ee4 ,dean ,/eel ,%ell ,receiv] ,! mo/ unusual feature ( ?is ,dean receiv] is t ! use ( h>d rubb] or composition does n ent] into ! =mation ( ! %ell1 b in/ead a %ell compos$ entirely ( /eel /amp+s has be5 sub/itut$ !re=4 ,! ma9 portion ( ?is %ell is ! b>rel #a4 ,great skill has evid5tly be5 ex]cis$ 9 ! =m+ ( ?is by ! cold-drawn process1 x pres5t+ nei!r seams nor welds4 ,! e> piece #b is also =m$ ( /eel ( ab\t ! same gauge z ! b>rel #a4 ,in/ead ( screw-?read+ ! /eel p>ts1 s t !y w\ld directly engage ea* o!r1 ! +5i\s device has be5 employ$ ( swag+ a brass r+ #c 9 ! b>rel portion & a simil> brass r+ #d 9 ! e> cap portion1 ^! two be+ slott$ & key$1 z %[n at #h1 s z to prev5t _! turn+ 9 _! respective seats4 ,! r+ #c is provid$ ) an ext]nal screw ?read & ! r+ #d ) an int]nal screw ?read1 s t ! receiv] cap is screw$ on to ! b>rel 9 ! same way z 9 ! ord9>y rubb] %ell4 ,by ! employm5t ( ^! brass screw-?read$ r+s1 ! ru/+ toge!r ( ! p>ts s t !y c\ld n be sep>at$ :5 requir$--a difficulty h]et(ore enc\nt]$ 9 /eel con/ruction ( simil> p>ts--has be5 rem$i$4 ,illu/ration3 ,fig4 #ef4 ,work+ ,p>ts ( ,dean ,receiv] ,! entire work+ p>ts ( ?is receiv] are conta9$ )9 ! cup #e1 ! edge ( :i* is flang$ outw>dly to af=d a seat = ! diaphragm4 ,! diaphragm is lock$ 9 place on ! %ell by a screw-?read$ r+ #f1 z is cle>ly indicat$4 ,a r+ #g ( insulat+ mat]ial is seat$ )9 ! enl>g$ portion ( ! b>rel #a1 & aga9/ ?is ! flange ( ! cup #e re/s & is held 9 place by ! cap #b :5 x is screw$ home4 ,! work+ p>ts ( ?is receiv] p>tially disassembl$ are %[n 9 ,fig4 #ef1 :i* gives a cle> idea ( "s ( ! features n cle>ly illu/rat$ 9 ,fig4 #ee4 ,x _c be d5i$ t "o ( ! pr9cipal items ( ma9t5ance ( subscrib]s' /ation equipm5t has be5 due to ! breakage ( receiv] %ells4 ,! us]s frequ5tly all[ _! receiv] to fall & /rike heavily aga9/ ! wall or floor1 ?us n only subject+ ! cords to great /ra91 b sometimes crack+ or entirely break+ ! receiv] %ell4 ,! innovation ?us propos$ by ! ,dean ,company ( mak+ ! entire receiv] %ell ( /eel is ( great int]e/4 ,! %ell1 z w be se51 is entirely insulat$ f ! circuit ( ! receiv] s t no contact exi/s by :i* a us] c\ld receive a %ock4 ,! %ell is enamel$ inside & out ) a heavy black insulat+ enamel bak$ on1 & said to be ( great durability4 ,h[ ?is enamel w we> rema9s to be se54 ,! insulation ( ! int]ior portions ( ! receiv] is fur!r gu>d$ by provid+ a l9+ ( fib] )9 ! %ell at all po9ts :]e x seems possible t a cross c\ld occur betwe5 "s ( ! work+ p>ts & ! metal ( ! %ell4 ,?is type ( receiv] has n be5 on ! m>ket long en\gh to draw def9ite conclusions1 bas$ on exp]i5ce 9 use1 z to :at its p]man5t p]=mance w be4 ,?us f> 9 ?is *apt] only ^? receiv]s :i* are commonly call$ h& receiv]s h be5 discuss$4 ,^! are ! receiv]s t are ord9>ily employ$ by ! g5]al public4 ,illu/ration3 ,fig4 #eg4 ,op]ator's ,receiv] ,op]ator's ,receiv]4 ,at ! c5tral (fice 9 telephone ex*anges ! op]ators are provid$ ) receiv]s 9 ord] t !y may communicate ) ! subscrib]s or ) o!r op]ators4 ,9 ord] t !y may h bo? ( _! h&s free to set up & take d[n ! connections & to p]=m all ( ! swit*+ op]ations requir$1 a special =m ( receiv] is employ$ = ?is purpose1 :i* is worn z a "p ( a head-ge> & is commonly t]m$ a head receiv]4 ,^! are necess>ily ( v light con/ruction1 9 ord] n to be burd5some to ! op]ators1 & obvi\sly !y mu/ be effici5t4 ,!y are ord9>ily held 9 place at ! e> by a metallic head b& fitt+ ov] ! head ( ! op]ator4 ,illu/ration3 ,,grant ,,av5ue ,,(fice ,,( ,,home ,,telephone ,,company1 ,,san ,,francisco1 ,,cal4 ,a ,type ( ,c5tral-,(fice ,build+s 9 ,d[n-,t[n ,di/ricts ( ,l>ge ,cities4 ,su* a receiv] is %[n 9 cross-section 9 ,fig4 #eg1 & completely assembl$ ) its head b& 9 ,fig4 #eh4 ,ref]r+ to ,fig4 #eg ! %ell #a ( ! receiv] is ( alum9um & ! magnets are =m$ ( /eel r+s #b1 cross-magnetiz$ s z to pres5t a nor? pole on "o side ( ! r+ & a s\? pole on ! o!r4 ,! two ,l-%ap$ pole pieces #c are secur$ by screws to ! poles ( ^! r+ magnets1 & ^! pole pieces c>ry ! magnet coils1 z is cle>ly indicat$4 ,^! poles are pres5t$ to a s(t iron diaphragm 9 exactly ! same way z 9 ! l>g] h& receiv]s1 ! diaphragm be+ clamp$ 9 place by a h>d rubb] e> piece1 z %[n4 ,! head b&s are frequ5tly ( /eel cov]$ ) lea!r4 ,!y h assum$ num]\s =ms1 b ! g5]al =m %[n 9 ,fig4 #eh is ! "o commonly adopt$4 ,illu/ration3 ,fig4 #eh4 ,op]ator's ,receiv] & ,cord ,illu/ration3 ,fig4 #ei4 ,receiv] ,symbols ,conv5tional ,symbols4 ,! usual diagrammatic symbols = h& & head receiv]s are %[n 9 ,fig4 #ei4 ,!y are self-explanatory4 ,! symbol at ! left 9 ?is figure1 %[+ ! g5]al outl9e ( ! receiv]1 is ! "o mo/ commonly us$ :]e any sort ( a receiv] is to be indicat$ 9 a circuit diagram1 b :]e x becomes desirable to indicate 9 ! diagram ! actual connections ) ! coil or coils ( ! receiv]1 ! symbol %[n at ! "r is to be pref]r$1 & obvi\sly x may be modifi$ z to numb] ( w9d+s & =m ( core z desir$4 ,,*apt] ,,vii ,,prim>y ,,cells ,galvani1 an ,italian physician1 discov]$1 9 #aghf1 t a curr5t ( electricity c\ld be produc$ by *emical action4 ,9 #ahjj1 ,volta1 a physici/1 also an ,italian1 ?rew fur!r light on ,galvani's discov]y & produc$ :at we "k z ! voltaic1 or galvanic1 cell4 ,9 honor ( ^! two discov]]s we h ! words volt1 galvanic1 & ! v>i\s words & t]ms d]iv$ !refrom4 ,simple ,voltaic ,cell4 ,a v simple voltaic cell may be made by plac+ two plates1 "o ( copp] & "o ( z9c1 9 a glass vessel p>tly fill$ ) dilute sulphuric acid1 z %[n 9 ,fig4 #fj4 ,:5 ! two plates are n connect$ by a wire or o!r conductor1 exp]im5t %[s t ! copp] plate be>s a positive *>ge ) respect to ! z9c plate1 & ! z9c plate be>s a negative *>ge ) respect to ! copp]4 ,:5 ! two plates are connect$ by a wire1 a curr5t fl[s f ! copp] to ! z9c plate ?r\gh ! metallic pa? ( ! wire1 j z is to be expect$ :5 any conductor ( relatively high electrical pot5tial is jo9$ to "o ( relatively l[ electrical pot5tial4 ,ord9>ily1 :5 "o *>g$ body is connect$ to ano!r ( diff]5t pot5tial1 ! result+ curr5t is ( b mom5t>y duration1 due to ! r$i/ribution ( ! *>ges & consequ5t equalization ( pot5tial4 ,9 ! case ( ! simple cell1 h[ev]1 ! curr5t is cont9u\s1 %[+ t "s action is ma9ta9+ ! *>ges on ! two plates & !re=e ma9ta9+ ! diff]5ce ( pot5tial betwe5 !m4 ,! en]gy ( ?is curr5t is d]iv$ f ! *emical action ( ! acid on ! z9c4 ,! cell is 9 reality a sort ( a z9c-burn+ furnace4 ,9 ! action ( ! cell1 :5 ! two plates are jo9$ by a wire1 x may be notic$ t ! z9c plate is consum$ & t bubbles ( hydrog5 gas are =m$ on ! surface ( ! copp] plate4 ,!ory4 ,j :y or h[ *emical action 9 a voltaic cell results 9 ! production ( a negative *>ge on ! consum$ plate is n kn[n4 ,mod]n !ory has x t :5 an acid is dilut$ 9 wat] ! molecules ( ! acid are split up or dissociat$ into two oppositely *>g$ atoms1 or gr\ps ( atoms1 "o be>+ a positive *>ge & ! o!r a negative *>ge ( electricity4 ,su* *>g$ atoms or gr\ps ( atoms are call$ ions4 ,?is sep>ation ( ! molecules ( a *emical comp\nd into positively & negatively *>g$ ions is call$ dissociation4 ,?us1 9 ! simple cell "u consid]ation ! sulphuric acid1 by dissociation1 splits up into hydrog5 ions be>+ positive *>ges1 & ,,s#d ions be>+ negative *>ges4 ,! solution z a :ole is neutral 9 pot5tial1 hav+ an equal numb] ( equal & opposite *>ges4 ,illu/ration3 ,fig4 #fj4 ,simple ,voltaic ,cell ,x is kn[n t :5 a metal is be+ dissolv$ by an acid1 ea* atom ( ! metal :i* is torn (f by ! solution leaves ! metal z a positively *>g$ ion4 ,! c>ry+ away ( positive *>ges f a hi!rto neutral body leaves t body ) a negative *>ge4 ,h5ce ! z9c1 or consum$ plate1 becomes negatively *>g$4 ,9 ! *emical attack ( ! sulphuric acid on ! z9c1 ! positive hydrog5 ions are lib]at$1 due to ! aff9ity ( ! negative ,,s#d ions = ! positive z9c ions1 ?is result+ 9 ! =mation ( z9c sulphate 9 ! solution4 ,n[ ! solution itself becomes positively *>g$1 due to ! positive *>ges leav+ ! z9c plate ) ! z9c ions1 & ! free positively *>g$ hydrog5 ions lib]at$ 9 ! solution z j describ$ are repell$ to ! copp] plate1 c>ry+ _! positive *>ges !reto4 ,h5ce ! copp] plate1 or ! unconsum$ plate1 becomes positively *>g$ & also coat$ ) hydrog5 bubbles4 ,! plates or electrodes ( a voltaic cell ne$ n consi/ ( z9c & copp]1 nor ne$ ! fluid1 call$ ! electrolyte1 be ( sulphuric acid2 any two dissimil> elem5ts imm]s$ 9 an electrolyte t attacks "o ( !m m readily ?an ! o!r w =m a voltaic cell4 ,9 e su* cell x w be f\nd t "o ( ! plates is consum$1 & t on ! o!r plate "s elem5t is deposit$1 ?is elem5t be+ sometimes a gas & sometimes a solid4 ,! plate :i* is consum$ is always ! negative plate1 & ! "o on :i* ! elem5t is deposit$ is always ! positive1 ! curr5t ?r\gh ! connect+ wire always be+1 !re=e1 f ! unconsum$ to ! consum$ plate4 ,?us1 9 ! simple copp]-z9c cell j consid]$1 ! z9c is consum$1 ! elem5t hydrog5 is deposit$ on ! copp]1 & ! curr5t fl[ ?r\gh ! ext]nal circuit is f ! copp] to ! z9c4 ,! positive *>ges1 leav+ ! z9c1 or consum$1 plate1 & pass+ ?r\gh ! electrolyte to ! copp]1 or unconsum$1 plate1 con/itute 9 effect a curr5t ( electricity fl[+ )9 ! electrolyte4 ,! curr5t )9 ! cell passes1 !re=e1 f ! z9c plate to ! copp] plate4 ,! z9c is1 !re=e1 said to be positive ) respect to ! copp]4 ,diff]5ce ( ,pot5tial4 ,! am\nt ( electromotive =ce1 t is g5]at$ betwe5 two dissimil> elem5ts imm]s$ 9 an electrolyte is diff]5t = diff]5t pairs ( elem5ts & = diff]5t electrolytes4 ,= a giv5 electrolyte ea* elem5t be>s a c]ta9 relation to ano!r2 i4e41 !y are ei!r electro-positive or electro-negative relative to ea* o!r4 ,9 ! foll[+ li/ a gr\p ( elem5ts are arrang$ ) respect to ! pot5tials :i* !y assume ) respect to ea* o!r ) dilute sulphuric acid z ! electrolyte4 ,! mo/ electro-positive elem5ts are at ! top & ! mo/ electro-negative at ! bottom4 ,sodium ,lead ,copp] ,magnesium ,iron ,silv] ,z9c ,nickel ,gold ,cadmium ,bismu? ,plat9um ,t9 ,antimony -,graphite 7,c>bon7 ,any two elem5ts select$ f ?is li/ & imm]s$ 9 dilute sulphuric acid w =m a voltaic cell1 ! am\nt ( diff]5ce ( pot5tial1 or electromotive =ce1 dep5d+ on ! di/ance ap>t 9 ?is s]ies ( ! two elem5ts *os54 ,! curr5t )9 ! cell w always fl[ f ! "o ne>e/ ! top ( ! li/ to ! "o ne>e/ ! bottom1 i4e41 f ! mo/ electro-positive to ! mo/ electro-negative2 &1 !re=e1 ! curr5t 9 ! wire jo9+ ! two plates w fl[ f ! "o l[e/ d[n 9 ! li/ to ! "o highe/ up4 ,f ?is s]ies x is easy to see :y z9c & copp]1 & also z9c & c>bon1 are (t5 *os5 z elem5ts ( voltaic cells4 ,!y are widely sep>at$ 9 ! s]ies & comp>atively *eap4 ,?is s]ies may n be tak5 z correct = all electrolytes1 = diff]5t electrolytes alt] some:at ! ord] ( ! elem5ts 9 ! s]ies4 ,?us1 if two plates1 "o ( iron & ! o!r ( copp]1 are imm]s$ 9 dilute sulphuric acid1 a curr5t is set up :i* proce$s ?r\gh ! liquid f ! iron to ! copp]2 b1 if ! plates aft] be+ c>efully wa%$ are plac$ 9 a solution ( potassium sulphide1 a curr5t is produc$ 9 ! opposite direction4 ,! copp] is n[ ! positive elem5t4 ,table ,,ii %[s ! electrical deportm5t ( ! pr9cipal metals 9 ?ree diff]5t liquids4 ,x is arrang$ l ! prec$+ "o1 ea* metal be+ electro-positive to any "o l[] 9 ! li/4 ,,table ,,ii ,behavior ( ,metals 9 ,diff]5t ,electrolytes ---------------------------------------- ----------------- ,,cau/ic ,,pota% ,,hydro*loric ,,acid ,,potassium ,,sulphide ---------------------------------------- ----------------- ,z9c ,z9c ,z9c ,t9 ,cadmium ,copp] ,cadmium ,t9 ,cadmium ,antimony ,lead ,t9 ,lead ,iron ,silv] ,bismu? ,copp] ,antimony ,iron ,bismu? ,lead ,copp] ,nickel ,bismu? ,nickel ,silv] ,nickel - ,silv] - ,antimony - ,iron ---------------------------------------- ----------------- ,x is important to rememb] t 9 all cells1 no matt] :at elem5ts or :at electrolyte are us$1 ! electrode :i* is consum$ is ! "o t becomes negatively *>g$ & its t]m9al1 !re=e1 becomes ! negative t]m9al or pole1 :ile ! electrode :i* is n consum$ is ! "o t becomes positively *>g$1 & its t]m9al is1 !re=e1 ! positive t]m9al or pole ( ! cell4 ,h[ev]1 because ! curr5t 9 ! electrolyte fl[s f ! consum$ plate to ! unconsum$ plate1 ! consum$ plate is call$ ! positive plate & ! unconsum$1 ! negative4 ,?is is likely to become confus+1 b if "o rememb]s t ! active plate is ! positive plate1 because x s5ds =? positive ions 9 ! electrolyte1 &1 !re=e1 itself becomes negatively *>g$1 "o w h ! prop] basis always to det]m9e ! direction ( ! curr5t fl[1 :i* is ! important ?+4 ,pol>ization4 ,if ! simple cell already describ$ h its t]m9als connect$ by a wire = "s "t1 x w be f\nd t ! curr5t rapidly weak5s until x ceases to be manife/4 ,?is weak5+ results f two causes3 fir/1 ! hydrog5 gas :i* is lib]at$ 9 ! action ( ! cell is deposit$ 9 a lay] on ! copp] plate1 !reby cov]+ ! plate & r$uc+ ! area ( contact ) ! liquid4 ,?is increases ! int]nal resi/ance ( ! cell1 s9ce hydrog5 is a non-conductor4 ,second1 ! plate s cov]$ becomes 9 effect a hydrog5 electrode1 & hydrog5 /&s high z an electro-positive elem5t4 ,!re is1 !re=e1 actual r$uction 9 ! electromotive =ce ( ! cell1 z well z an increase 9 int]nal resi/ance4 ,?is ph5om5on is kn[n z pol>ization1 & 9 comm]cial cells means mu/ be tak5 to prev5t su* action z f> z possible4 ,! means by :i* pol>ization ( cells is prev5t$ or r$uc$ 9 practice may be divid$ into ?ree g5]al classes3 ,fir/--me*anical means4 ,if ! hydrog5 bubbles be simply bru%$ away f ! surface ( ! electrode ! resi/ance & ! c\nt] pol>ity :i* !y cause w be dim9i%$4 ,! same result may be secur$ if air be bl[n into ! solution ?r\gh a tube1 or if ! liquid be kept agitat$4 ,if ! surface ( ! electrode be r\gh5$ or cov]$ ) po9ts1 ! bubbles collect m freely at ! po9ts & are m quickly c>ri$ away to ! surface ( ! liquid4 ,^! means are1 h[ev]1 h>dly practical except 9 cells = laboratory use4 ,second--*emical means4 ,if a highly oxidiz+ sub/ance be add$ to ! electrolyte1 x w de/roy ! hydrog5 bubbles by comb9+ ) !m :ile !y are 9 a nasc5t /ate1 & ?is w prev5t ! increase 9 int]nal resi/ance & ! oppos+ electromotive =ce4 ,su* sub/ances are bi*romate ( pota%1 nitric acid1 & *lor9e1 & are l>gely us$4 ,?ird--electro-*emical means4 ,d\ble cells1 arrang$ to sep>ate ! elem5ts & liquids by means ( por\s p>titions or by gravity1 may be s arrang$ t solid copp] is lib]at$ in/ead ( hydrog5 at a po9t :]e ! curr5t leaves ! liquid1 !reby entirely obviat+ pol>ization4 ,?is me?od also is l>gely us$4 ,local ,action4 ,:5 a simple cell /&s idle1 i4e41 ) its circuit op51 small hydrog5 bubbles may be notic$ ris+ f ! z9c electrode in/ead ( f copp]1 z is ! case :]e ! circuit is clos$4 ,?is is due to impurities 9 ! z9c plate1 su* z p>ticles ( iron1 t91 ars5ic1 c>bon1 etc4 ,ea* ( ^! p>ticles acts ) ! surr\nd+ z9c j z might be expect$ ( any pair ( dissimil> elem5ts oppos$ to ea* o!r 9 an electrolyte2 9 o!r words1 !y con/itute small voltaic cells4 ,local curr5ts1 !re=e1 are g5]at$1 circulat+ betwe5 ! two adjac5t metals1 &1 z a result1 ! z9c plate & ! electrolyte are ne$lessly wa/$ & ! g5]al condition ( ! cell is impair$4 ,?is is call$ local action4 ,amalgamat$ ,z9cs4 ,local action might be prev5t$ by ! use ( *emically pure z9c1 b ?is1 on acc\nt ( its exp5se1 _c be employ$ comm]cially4 ,local action1 h[ev]1 may be ov]come to a great ext5t by amalgamat+ ! z9c1 i4e41 coat+ x ) m]cury4 ,! iron p>ticles or o!r impurities d n dissolve 9 ! m]cury1 z does ! z9c1 b !y float to ! surface1 :5ce ! hydrog5 bubbles :i* may =m spe$ily c>ry !m (f1 &1 9 o!r cases1 ! impurities fall to ! bottom ( ! cell4 ,z ! z9c 9 ! pa/y amalgam dissolves 9 ! acid1 ! film ( m]cury unites ) fre% z9c1 & s always pres5ts a cle>1 bright1 homog5e\s surface to ! action ( ! electrolyte4 ,! process ( amalgamat+ ! z9c may be p]=m$ by dipp+ x 9 a solution compos$ ( ,nitric ,acid #a lb4 ,muriatic ,acid #b lbs4 ,m]cury #h oz4 ,! acids %\ld be fir/ mix$ & !n ! m]cury sl[ly add$ until dissolv$4 ,clean ! z9c ) lye & !n dip x 9 ! solution = a second or two4 ,r9se 9 clean wat] & rub ) a bru%4 ,ano!r me?od ( amalgamat+ z9cs is to clean !m by dipp+ !m 9 dilute sulphuric acid & !n 9 m]cury1 all[+ ! surplus to dra9 (f4 ,comm]cial z9cs1 = use 9 voltaic cells z n[ manufactur$1 usually h ab\t #d p] c5t ( m]cury add$ to ! molt5 z9c be=e ca/+ into ! =m ( plates or rods4 ,s]ies & ,multiple ,connections4 ,:5 a numb] ( voltaic cells are jo9$ 9 s]ies1 ! positive pole ( "o be+ connect$ to ! negative pole ( ! next "o1 & s on ?r\gh\t ! s]ies1 ! electromotive =ces ( all ! cells are add$1 & ! electromotive =ce ( ! gr\p1 !re=e1 becomes ! sum ( ! electromotive =ces ( ! compon5t cells4 ,! curr5ts ?r\gh all ! cells 9 ?is case w be equal to t ( "o cell4 ,if ! cells be jo9$ 9 multiple1 ! positive poles all be+ connect$ by "o wire & ! negative poles by ano!r1 !n ! curr5ts ( all ! cells w be add$ :ile ! electromotive =ce ( ! comb9ation rema9s ! same z t ( a s+le cell1 assum+ all ! cells to be alike 9 electromotive =ce4 ,obvi\sly comb9ations ( ^! two arrangem5ts may be made1 z by =m+ /r+s ( cells connect$ 9 s]ies1 & connect+ ! /r+s 9 multiple or p>allel4 ,! t]m batt]y is frequ5tly appli$ to a s+le voltaic cell1 b ?is t]m is m prop]ly us$ to designate a plurality ( cells jo9$ toge!r 9 s]ies1 or 9 multiple1 or 9 s]ies multiple s z to comb9e _! actions 9 caus+ curr5t to fl[ ?r\gh an ext]nal circuit4 ,we may !re=e ref] to a batt]y ( s _m cells4 ,x has1 h[ev]1 become common1 ?\gh te*nically improp]1 to ref] to a s+le cell z a batt]y1 s t ! t]m batt]y1 z indicat+ necess>ily m ?an "o cell1 has l>gely lo/ its significance4 ,cells may be ( two types1 prim>y & second>y4 ,prim>y cells are ^? consi/+ ( electrodes ( dissimil> elem5ts :i*1 :5 plac$ 9 an electrolyte1 become imm$iately ready = action4 ,second>y cells1 commonly call$ /orage cells & accumulators1 consi/ always ( two in]t plates ( metal1 or metallic oxide1 imm]s$ 9 an electrolyte :i* is incapable ( act+ on ei!r ( !m until a curr5t has fir/ be5 pass$ ?r\gh ! electrolyte f "o plate to ! o!r4 ,on ! passage ( a curr5t 9 ?is way1 ! decomposition ( ! electrolyte is effect$ & ! composition ( ! plates is s *ang$ t "o ( !m becomes electro-positive & ! o!r electro-negative4 ,! cell is !n1 :5 ! *>g+ curr5t ceases1 capable ( act+ z a voltaic cell4 ,?is *apt] is devot$ to ! prim>y cell or batt]y alone4 ,types ( ,prim>y ,cells4 ,prim>y cells may be divid$ into two g5]al classes3 fir/1 ^? adapt$ to furni% con/ant curr5t2 & second1 ^? adapt$ to furni% only int]mitt5t curr5ts4 ,! diff]5ce betwe5 cells 9 ?is respect re/s l>gely 9 ! means employ$ = prev5t+ or less5+ pol>ization4 ,obvi\sly 9 a cell 9 :i* pol>ization is entirely prev5t$ ! curr5t may be all[$ to fl[ con/antly until ! cell is completely exhau/$2 t is1 until ! z9c is all eat5 up or until ! hydrog5 is exhau/$ f ! electrolyte or bo?4 ,on ! o!r h& "s cells are s con/itut$ t pol>ization takes place fa/] ?an ! means int5d$ to prev5t x c act4 ,9 o!r words1 ! pol>ization gradually ga9s on ! prev5tive means & s gradually r$uces ! curr5t by increas+ ! resi/ance ( ! cell & l[]+ its electromotive =ce4 ,9 cells ( ?is k9d1 h[ev]1 ! arrangem5t is su* t if ! cell is all[$ to re/1 t is1 if ! ext]nal circuit is op5$1 ! depol>iz+ ag5cy w gradually act to remove ! hydrog5 f ! unattack$ electrode & ?us place ! cell 9 good condition = use aga94 ,( ^! two types ( prim>y cells ! int]mitt5t-curr5t cell is ( f> great] use 9 telephony ?an ! con/ant-curr5t cell4 ,?is is because ! use ( prim>y batt]ies 9 telephony is1 9 ! great majority ( cases1 int]mitt5t1 & = t reason a cell :i* w give a /rong curr5t = a few m9utes & :i* aft] su* use w rega9 practically all ( its initial /r5g? & be ready = use aga91 is m desirable ?an "o :i* w give a weak] curr5t cont9u\sly ?r\gh\t a long p]iod ( "t4 ,s9ce ! cells :i* are adapt$ to give con/ant curr5t are commonly us$ 9 connection ) circuits t are cont9u\sly clos$1 !y are call$ clos$-circuit cells4 ,! o!r cells1 :i* are bett] adapt$ = int]mitt5t curr5t1 are commonly us$ on circuits :i* /& op5 mo/ ( ! "t & are clos$ only occasionally :5 _! curr5t is desir$4 ,= ?is reason ^! are t]m$ op5-circuit cells4 ,op5-,circuit ,cells4 ,le,clanch ,cell3--,by f> ! mo/ important prim>y cell = telephone "w is ! s-call$ ,le,clanch cell4 ,?is assumes a l>ge v>iety ( =ms1 b always employs z9c z ! negatively *>g$ elem5t1 c>bon z ! positively *>g$ elem5t1 & a solution ( sal ammoniac z ! electrolyte4 ,?is cell employs a *emical me?od ( tak+ c>e ( pol>ization1 ! depol>iz+ ag5t be+ p]oxide ( manganese1 :i* is closely associat$ ) ! c>bon elem5t4 ,! orig9al =m ( ! ,le,clanch cell1 a =m 9 :i* x 0 v l>gely us$ up to )9 a %ort "t ago1 is %[n 9 ,fig4 #fa4 ,9 ?is ! c>bon elem5t is plac$ )9 a cyl9drical j> ( por\s clay1 ! walls ( ?is j> be+ ( su* consi/5cy z to all[ moi/ure sl[ly to p]meate ?r\gh x4 ,)9 ?is por\s cup1 z x is call$1 a plate or disk ( c>bon is plac$1 & ar\nd ?is ! depol>iz+ ag5t1 consi/+ ( black oxide ( manganese4 ,?is is usually mix$ )1 brok5 c>bon1 s z to increase ! effective area ( ! c>bon elem5t 9 contact ) ! depol>iz+ ag5t1 & also to r$uce ! total int]nal resi/ance ( ! cell4 ,! z9c electrode usually consi/$ m]ely 9 a rod ( z9c1 z %[n1 ) a suitable t]m9al at its upp] end4 ,illu/ration3 ,fig4 #fa4 ,le,clanch ,cell ,! *emical action tak+ place )9 ! ,le,clanch cell is1 briefly1 z foll[s3 ,sal ammoniac is *emically kn[n z *loride ( ammonium & is a comb9ation ( *lor9e & ammonia4 ,9 ! action :i* is assum$ to accompany ! passage ( curr5t 9 ?is cell1 ! sal ammoniac is decompos$1 ! *lor9e leav+ ! ammonia to unite ) an atom ( ! z9c plate1 =m+ *loride ( z9c & sett+ free ammonia & hydrog54 ,! ammonia is imm$iately dissolv$ 9 ! wat] ( ! cell1 & ! hydrog5 ent]s ! por\s cup & w\ld spe$ily pol>ize ! cell by adh]+ to ! c>bon plate b = ! fact t x enc\nt]s ! p]oxide ( manganese4 ,?is mat]ial is exce$+ly ri* 9 oxyg5 & x !re=e readily gives up a "p ( its oxyg51 :i* =ms wat] by comb9ation ) ! already lib]at$ hydrog5 & leaves :at is t]m$ a sesquioxide ( manganese4 ,?is absorption or comb9ation ( ! hydrog5 prev5ts imm$iate pol>ization1 b hydrog5 is evolv$ dur+ ! op]ation ( ! cell m rapidly ?an x c comb9e )typo 0 'w?' ! oxyg5 ( ! manganese1 !reby lead+ to pol>ization m rapidly ?an ! depol>iz] c prev5t x :5 ! cell is heavily work$4 ,:51 h[ev]1 ! cell is left ) its ext]nal circuit op5 = a "t1 depol>ization ensues by ! gradual comb9ation ( ! hydrog5 ) ! oxyg5 ( ! p]oxide ( manganese1 & z a result ! cell recup]ates & 9 a %ort "t atta9s its normal electromotive =ce4 ,! electromotive =ce ( ?is cell :5 new is ab\t #a4dg volts4 ,! int]nal resi/ance ( ! cell ( ! type %[n 9 ,fig4 #fa is approximately #a ohm1 ord9>ily less r ?an m4 ,a m rec5t =m ( ,le,clanch cell is %[n 9 cross-section 9 ,fig4 #fb4 ,?is uses practically ! same mat]ials & has ! same *emical action z ! old disk ,le,clanch cell %[n 9 ,fig4 #fa4 ,x disp5ses1 h[ev]1 ) ! por\s cup & in/ead employs a c>bon electrode1 :i* 9 itself =ms a cup = ! depol>iz+ ag5t4 ,illu/ration3 ,fig4 #fb4 ,c>bon ,cyl9d] ,le,clanch ,cell ,! c>bon electrode is 9 ! =m ( a corrugat$ holl[ cyl9d] :i* engages by means ( an int]nal screw ?read a correspond+ screw ?read on ! out] side ( ! c>bon cov]4 ,)9 ?is cyl9d] is conta9$ a mixture ( brok5 c>bon & p]oxide ( manganese4 ,! z9c electrode is 9 ! =m ( a holl[ cyl9d] almo/ surr\nd+ ! c>bon electrode & sep>at$ !refrom by means ( heavy rubb] b&s /ret*$ ar\nd ! c>bon4 ,! rod1 =m+ ! t]m9al ( ! z9c1 passes ?r\gh a porcela9 bu%+ on ! cov] plate to obviate %ort circuits4 ,?is type ( cell has an electromotive =ce ( ab\t #a4ee volts & recup]ates v quickly aft] sev]e use4 ,x also has consid]ably l[] int]nal resi/ance ?an ! type ( ,le,clanch cell employ+ a por\s cup1 &1 !re=e1 is capable ( g5]at+ a consid]ably l>g] curr5t4 ,cells ( ?is g5]al type h assum$ a v>iety ( =ms4 ,9 "s ! c>bon electrode1 toge!r ) ! brok5 c>bon & p]oxide ( manganese1 7 pack$ into a canvas bag :i* 0 susp5d$ 9 ! electrolyte & usually surr\nd$ by ! z9c electrode4 ,9 o!r =ms ! c>bon electrode has m\ld$ ) x ! manganese depol>iz]4 ,9 ord] to prev5t ! salts )9 ! cell f creep+ ov] ! edge ( ! conta9+ glass j> & also ov] ! upp] portion ( ! c>bon electrode1 x is common practice to imm]se ! upp] end ( ! c>bon elem5t & also ! upp] edge ( ! glass j> 9 hot p>aff94 ,9 sett+ up ! ,le,clanch cell1 place n m ?an f\r ounces ( :ite sal ammoniac 9 ! j>1 fill ! j> "o-?ird full ( wat]1 & /ir until ! sal ammoniac is all dissolv$4 ,!n put ! c>bon & z9c elem5ts 9 place4 ,a little wat] p\r$ 9 ! v5t hole ( ! por\s j> or c>bon cyl9d] w t5d to ha/5 ! action4 ,an excess ( sal ammoniac %\ld n be us$1 z a saturat$ solution t5ds to deposit cry/als on ! z9c2 on ! o!r h&1 ! solution %\ld n be all[$ to become too weak1 z 9 t case ! *loride ( z9c w =m on ! z9c4 ,bo? ( ^! causes mat]ially increase ! resi/ance ( ! cell4 ,a great advantage ( ! ,le,clanch cell is t :5 n 9 use !re is b little mat]ial wa/e4 ,x conta9s no highly corrosive *emicals4 ,su* cells require little att5tion1 & ! addition ( wat] n[ & !n to replace ! loss due to evaporation is ab\t all t is requir$ until ! elem5ts become exhau/$4 ,!y give a relatively high electromotive =ce & h a mod]ately l[ int]nal resi/ance1 s t !y are capable ( giv+ r l>ge curr5ts = %ort int]vals ( "t4 ,if prop]ly made1 !y recup]ate quickly aft] pol>ization due to heavy use4 ,dry ,cell4 ,all ! =ms ( cells s f> consid]$ may be q prop]ly t]m$ wet cells because ( ! fact t a free liquid electrolyte is us$4 ,?is t]m is employ$ 9 contradi/9ction to ! lat] develop$ cell1 commonly t]m$ ! dry cell4 ,?is t]m dry cell is 9 "s respects a misnom]1 s9ce x is n dry & if x 7 dry x w\ld n "w4 ,x is ess5tial to ! op]ation ( ^! cells t !y %all be moi/ )91 & :5 su* moi/ure is dissipat$ ! cell is no long] usable1 z !re is no fur!r useful *emical action4 ,! dry cells are all ( ! ,le,clanch type1 ! liquid electrolyte ( t type be+ replac$ by a semi-solid sub/ance t is capable ( reta9+ moi/ure = a consid]able p]iod4 ,z 9 ! ord9>y wet ,le,clanch cell1 ! electrodes are ( c>bon & z9c1 ! z9c elem5t be+ 9 ! =m ( a cyl9drical cup & =m+ ! reta9+ vessel ( ! cell1 :ile ! c>bon elem5t is 9 ! =m ( a rod or plate & occupies a c5tral position ) reg>d to ! z9c1 be+ held out ( contact ) ! z9c1 h[ev]1 at all po9ts4 ,a cross-section ( an excell5t =m ( dry cell is %[n 9 ,fig4 #fc4 ,! out] cas+ is ( z9c1 =m$ 9 ! %ape ( a cyl9drical cup1 & s]ves n only z ! reta9+ vessel1 b z ! negatively *>g$ electrode4 ,! out] surface ( ! z9c is completely cov]$ on its sides & bottom ) heavy pa/ebo>d s z to insulate x f bodies ) :i* x may come 9 contact1 & p>ticul>ly f ! z9c cups ( o!r cells us$ 9 ! same batt]y4 ,! positively *>g$ electrode is a c>bon rod corrugat$ longitud9ally1 z %[n1 9 ord] to obta9 great] surface4 ,?is rod is held 9 ! c5t] ( ! z9c cup out ( contact !re)1 & ! int]v5+ space is fill$ ) a mixture ( p]oxide ( manganese1 p[d]$ c>bon1 & sal ammoniac4 ,sev]al ?icknesses ( blott+ pap] con/itute a l9+ = ! inn] portion ( ! z9c electrode & s]ve to prev5t ! manganese mixture f com+ directly into contact !re)4 ,! cell is seal$ ) pit*1 :i* is plac$ on a lay] ( s& & sawdu/ mix$ 9 ab\t equal p>ts4 ,illu/ration3 ,fig4 #fc4 ,dry ,cell ,! electrolyte 9 su* cells v>ies l>gely z to quantities & proportions ( ! mat]ials employ$ 9 v>i\s types ( cells1 & also v>ies 9 ! me?od 9 :i* ! elem5ts are introduc$ into ! conta9]4 ,! foll[+ li/ & approximate proportions ( mat]ial w s]ve z a fair example ( ! fill+ mixture 9 well-kn[n types ( cells4 ,manganese dioxide #de p] c5t ,c>bon or graphite1 or bo? #de p] c5t ,sal ammoniac #g p] c5t ,z9c *loride #c p] c5t ,wat] is add$ to ! above & a suffici5t am\nt ( mixture is tak5 = ea* cell to fill ! z9c cup ab\t sev5-eigh?s full :5 ! c>bon is 9 place4 ,! mo/ suitable quantity ( wat] dep5ds ^u ! orig9al dryness & f95ess ( mat]ial & ^u ! quality ( ! pap] l9+4 ,9 "s =ms ( dry batt]ies1 />* or o!r pa/e is add$ to improve ! contact ( ! electrolyte ) ! z9c & promote a m ev5 di/ribution ( action ?r\gh\t ! electrolyte4 ,m]cury1 too1 is (t5 add$ to effect amalgamation ( ! z9c4 ,z 9 ! ord9>y wet type ( ,le,clanch cell1 ! purpose ( ! manganese is to act z a depol>iz]2 ! c>bon or graphite be+ add$ to give conductivity to ! manganese & to =m a l>ge electrode surface4 ,x is important t ! sal ammoniac1 :i* is ! active ag5t ( ! cell1 %\ld be free f lumps 9 ord] to mix prop]ly ) ! manganese & c>bon4 ,a small local action takes place 9 ! dry cell1 caus$ by ! dissimil> metals necess>ily employ$ 9 sold]+ up ! z9c cup & 9 sold]+ ! t]m9al rod ( z9c to ! z9c cup prop]4 ,?is action1 h[ev]1 is slight 9 ! bett] grades ( cells4 ,z a result ( ?is1 & also ( ! gradual dry+ out ( ! moi/ure )9 ! cell1 ^! cells gradually det]iorate ev5 :5 n 9 use--?is is commonly call$ %elf-we>4 ,%elf-we> is mu* m s]i\s 9 ! v small sizes ( dry cells ?an 9 ! l>g] ones4 ,dry cells are made 9 a l>ge numb] ( %apes & sizes4 ,! mo/ useful =m1 h[ev]1 is ! ord9>y cyl9drical type4 ,^! are made 9 sizes v>y+ f "o & "o-half in*es high & ?ree-qu>t]s in* 9 diamet] to eight in*es high & ?ree & ?ree-qu>t]s in*es 9 diamet]4 ,! mo/ us$ & /&>d size ( dry cell is ( cyl9drical =m six in*es high & two & ?ree-qu>t]s in*es 9 diamet]4 ,! dry cell :5 new & 9 good condition has an op5-circuit voltage ( f #a4e to #a4f volts4 ,p]haps #a4ee repres5ts ! usual av]age4 ,a cell ( ! two & ?ree-qu>t]s by six-in* size w give ?r\gh\t its useful life probably ?irty amp]e h\rs z a maximum1 b ?is v>ies greatly ) ! condition ( use & ! make ( cell4 ,its effective voltage dur+ its useful life av]ages ab\t "o volt1 & if dur+ ?is life x gives a total dis*>ge ( ?irty amp]e h\rs1 ! fair en]gy rat+ ( ! cell w be ?irty watt-h\rs4 ,?is may n be tak5 z an accurate figure1 h[ev]1 z ! watt-h\r capacity ( a cell dep5ds v l>gely1 n only on ! make ( ! cell1 b on ! rate ( its dis*>ge4 ,an exam9ation ( ,fig4 #fc %[s t ! dry cell has all ( ! ess5tial elem5ts ( ! ,le,clanch cell4 ,! mat]ials ( :i* ! electrodes are made are ! same & ! por\s cup ( ! disk ,le,clanch cell is repres5t$ 9 ! dry cell by ! blott+-pap] cyl9d]1 :i* sep>ates ! z9c f ! c>bon electrode4 ,! positively *>g$ electrode mu/ n be consid]$ z m]ely ! c>bon plate or rod alone1 b r ! c>bon rod ) its surr\nd+ mixture ( p]oxide ( manganese & brok5 c>bon4 ,su* be+ ! case1 x is obvi\s t ! sep>ation betwe5 ! electrodes is v small1 :ile ! surface pres5t$ by bo? electrodes is v l>ge4 ,z a result1 ! int]nal resi/ance ( ! cell is small & ! curr5t :i* x w give on a %ort circuit is correspond+ly l>ge4 ,a good cell ( ! two & ?ree-qu>t]s by six-in* size w give eighte5 or tw5ty amp]es on %ort-circuit1 :5 new4 ,z ! action ( ! cell proce$s1 z9c *loride & ammonia are =m$1 & !re be+ insuffici5t wat] to dissolve ! ammonia1 !re results ! =mation ( d\ble *lorides ( z9c & ammonium4 ,^! d\ble *lorides are less soluble ?an ! *lorides & f9ally occupy ! pores ( ! pap] l9+ betwe5 ! electrolyte & ! z9c & greatly increase ! int]nal resi/ance ( ! cell4 ,?is increase ( resi/ance is fur!r contribut$ to by ! gradual dry+ out ( ! cell z its age increases4 ,)9 ! la/ few ye>s dry batt]ies h be5 s p]fect$ me*anically1 *emically1 & electrically t !y h f> great] outputs & bett] recup]ative p[] ?an any ( ! o!r types ( ,le,clanch batt]ies1 :ile 9 po9t ( conv5i5ce & economy1 result+ f _! small size & non-breakable1 non-spillable features & l[ co/1 !y leave no room = comp>ison4 ,clos$-,circuit ,cells4 ,gravity-,cell3--,com+ n[ to ! consid]ation ( clos$-circuit or con/ant-curr5t cells1 ! mo/ important is ! well-kn[n gravity1 or blue-/one1 cell1 devis$ by ,daniell4 ,x is l>gely us$ 9 telegraphy1 & (t5 9 telephony 9 su* cases z require a con/antly fl[+ curr5t ( small quantity4 ,su* a cell is %[n 9 ,fig4 #fd4 ,! elem5ts ( ! gravity cell are electrodes ( copp] & z9c4 ,! solution 9 :i* ! copp] plate is imm]s$ is prim>ily a solution ( copp] sulphate1 commonly kn[n z blue-/one1 9 wat]4 ,! z9c plate aft] ! cell is 9 action is imm]s$ 9 a solution ( sulphate ( z9c :i* is =m$ ar\nd x4 ,! glass j> is usually cyl9drical1 ! /&>d sizes be+ #e in*es diamet] & #g in*es deep2 & also #f in*es diamet] & #h in*es deep4 ,! copp] electrode is ( %eet copp] ( ! =m %[n1 & x is p>tly cov]$ ) cry/als ( blue-/one or copp] sulphate4 ,frequ5tly1 9 lat] =ms ( cells1 ! copp] electrode consi/s m]ely ( a /raight1 ?ick1 rectangul> b> ( copp] laid horizontally1 directly on top ( ! blue-/one cry/als4 ,9 all cases a rubb]-insulat$ wire is atta*$ by rivet+ to ! copp] electrode1 & passes up ?r\gh ! electrolyte to =m ! positive t]m9al4 ,illu/ration3 ,fig4 #fd4 ,gravity ,cell ,! z9c is1 z a rule1 ( cr[foot =m1 z %[n1 :5ce ?is cell d]ives ! commonly appli$ "n ( cr[foot cell4 ,?is is ess5tially a two-fluid cell1 = 9 its action z9c sulphate is =m$1 & ?is be+ light] ?an copp] sulphate rises to ! top ( ! j> & surr\nds ! z9c4 ,gravity1 !re=e1 s]ves to keep ! two fluids sep>ate4 ,illu/ration3 ,,int]ior ,,( ,,w>eh\se ,,= ,,telephone ,,con/ruction ,,mat]ial ,9 ! action ( ! cell1 :5 ! ext]nal circuit is clos$1 sulphuric acid is =m$ :i* attacks ! z9c to =m sulphate ( z9c & to lib]ate hydrog51 :i* foll[s its t5d5cy to atta* itself to ! copp] plate4 ,b 9 s do+ ! hydrog5 necess>ily passes ?r\gh ! solution ( sulphate ( copp] surr\nd+ ! copp] plate4 ,! hydrog5 imm$iately comb9es ) ! ,,s#d radical1 =m+ !re) sulphuric acid1 & lib]at+ metallic copp]4 ,?is sulphuric acid1 be+ light] ?an ! copp] sulphate1 rises to ! surface ( ! z9c & attacks ! z9c1 ?us =m+ m sulphate ( z9c4 ,! metallic copp] s =m$ is deposit$ on ! copp] plate1 !reby keep+ ! surface bright & clean4 ,s9ce hydrog5 is ?us div]t$ f ! copp] plate1 pol>ization does n ensue4 ,! z9c sulphate be+ colorless1 :ile ! copp] sulphate is ( a d>k blue color1 ! sep>at+ l9e ( ! two liquids is easily di/+ui%able4 ,?is l9e is call$ ! blue l9e & c>e %\ld be tak5 t x does n rea* ! z9c & cause a deposit ( copp] to be plac$ !reon4 ,z has be5 /at$1 ^! two liquids d n mix readily1 b !y w ev5tually m+le unless ! action ( ! cell is suffici5t to use up ! copp] sulphate z spe$ily z x is dissolv$4 ,?us x w be se5 t :ile ! cell is free f pol>ization & local action1 !re is1 nev]!less1 a det]iorat+ effect if ! cell is all[$ to rema9 long on op5 circuit4 ,!re=e1 x %\ld be us$ :5 a con/ant curr5t is requir$4 ,prev5tion ( ,creep+3--,mu* tr\ble has be5 exp]i5c$ 9 gravity cells due to ! creep+ ( ! salts ov] ! edge ( ! j>4 ,frequ5tly ! upp] edges ( ! j>s are coat$ by dipp+ 9 hot p>aff9 wax 9 ! hope ( prev5t+ ?is4 ,sometimes oil is p\r$ on top ( ! fluid 9 ! j> to prev5t ! creep+ ( ! salts & ! evaporation ( ! electrolyte4 ,! foll[+ acc\nt ( exp]im5ts p]=m$ by ,mr4 ,william ,reid1 ( ,*icago1 ?r[s light on ! relative advantages ( ^! & o!r me?ods ( prev5t+ creep+4 ,! exp]im5t 0 made ) gravity cells hav+ #e-;in* by #g-;in* glass j>s4 ,f\r cells 7 made up & op]at$ 9 a r dry1 w>m place1 al?\gh p]haps "u no m sev]e local conditions ?an w\ld be f\nd 9 mo/ telephone ex*anges4 ,cell ,no4 #a 0 a pla9 cell z ord9>ily us$4 ,cell ,no4 #b _h ! top ( ! rim ( ! j> treat$ ) p>aff9 wax by dipp+ ! rim to ab\t "o in* 9 dep? 9 melt$ p>aff9 wax4 ,cell ,no4 #c _h melt$ p>aff9 wax p\r$ ov] ! surface ( ! liquid =m+ a seal ab\t #c_/af in* 9 ?ickness4 ,aft] cool+1 a few small holes 7 bor$ ?r\gh ! seal to let gases escape4 ,cell ,no4 #d _h a lay] ( heavy p>aff9 oil ne>ly #a_/b in* 9 ?ickness 7ab\t #f oz4 be+ us$7 on top ( ! solutions4 ,^! cells 7 all run on a load ( 4#bb to 4#bi amp]es = #ae-a_/b h\rs p] day = ?irty days1 aft] :i* ! foll[+ results 7 not$3 7a7 ,! pla9 cell1 or cell ,no4 #a1 _h to h #bf ounces ( wat] add$ to x to replace t :i* _h evaporat$4 ,! creep+ ( z9c sulphate salts 0 v bad4 7b7 ,! wax$ rim cell1 or cell ,no4 #b1 evaporat$ #bf ounces ( wat] & ! creep+ ( z9c sulphate salts 0 n prev5t$ by ! wax$ rim4 ,! wax prov$ ( no value4 7c7 ,! wax seal$ cell1 or cell ,no4 #c1 %[$ practically no evaporation & only v slight creep+ ( z9c sulphate salts4 ,! creep+ ( salts t took place 0 only ar\nd spots :]e ! edges ( ! seal 7 loose f ! j>4 7d7 ,! p>aff9 oil seal$ cell1 or cell ,no4 #d1 %[$ no evaporation & no creep+ ( salts4 ,x 0 conclud$ by ,mr4 ,reid f ! above exp]im5ts t ! wax appli$ to ! rim ( ! j> is totally ineffective & has no m]its4 ,! wax seal loos5s ar\nd ! edges & does n totally prev5t creep+ ( ! z9c sulphate salts1 al?\gh ne>ly s4 ,! wax-seal$ j> mu/ h holes drill$ 9 x to all[ ! gases to escape4 ,! me?od is h>dly comm]cial1 z x is difficult to make a neat appe>+ cell1 besides mak+ x almo/ impossible to manipulate its cont5ts4 ,a coat ( p>aff9 oil approximately #a_/b in* 9 ?ickness 7ab\t #f ounces7 gives p]fect protection aga9/ evaporation & creep+ ( ! z9c sulphate salts4 ,! cell1 hav+ ! p>aff9-oil seal1 _h a v neat1 clean appe>ance z comp>$ ) cells ,no4 #a & ,no4 #b4 ,x 0 f\nd t ! z9c c\ld be drawn out ?r\gh ! oil1 clean$1 & replac$ ) no appreciable effect on voltage or curr5t4 ,sett+ ,up3--,9 sett+ up ! batt]y ! copp] electrode is fir/ unfold$ to =m a cross & plac$ 9 ! bottom ( ! j>4 ,en\gh copp] sulphate1 or blue-/one cry/als1 is !n dropp$ into ! j> to almo/ cov] ! copp]4 ,! z9c cr[foot is !n hung 9 place1 occupy+ a position ab\t #d in*es above ! top ( ! copp]4 ,cle> wat] is !n p\r$ 9 suffici5t to fill ! j> )9 ab\t an in* ( ! top4 ,if x is n requir$ to use ! cell at once1 x may be plac$ on %ort circuit = a "t & all[$ to =m its own z9c sulphate4 ,! cell may1 h[ev]1 be made imm$iately available = use by draw+ ab\t "o-half p9t ( a solution ( z9c sulphate f a cell already 9 use & p\r+ x into ! j>1 or1 :5 ?is is n conv5i5t1 by putt+ into ! liquid f\r or five ounces ( pulv]iz$ sulphate ( z9c1 or by add+ ab\t t5 drops ( sulphuric acid4 ,:5 ! cell is 9 prop] work+ condition1 "o-half in* 9 ?ickness ( heavy p>aff9 oil ( good quality may be add$4 ,if ! blue l9e gets too l[1 & if !re is 9 ! bottom ( ! cell a suffici5t quantity ( sulphate ( copp]1 x may be rais$ by draw+ (f a portion ( ! z9c sulphate ) a batt]y syr+e & replac+ ?is ) wat]4 ,if ! blue l9e gets too high1 x may be l[]$ by %ort-circuit+ ! cell = a "t1 or by ! addition ( m sulphate ( z9c solution f ano!r batt]y4 ,if ! copp] sulphate becomes exhau/$1 x %\ld be repl5i%$ by dropp+ 9 m cry/als4 ,c>e %\ld be tak5 9 cold wea!r to ma9ta9 ! temp]ature ( ! batt]y above #fe or #gj ,fahr5heit4 ,if bel[ ?is temp]ature1 ! int]nal resi/ance ( a cell increases v rapidly1 s mu* s t ev5 at #ej ,fahr5heit ! action becomes v mu* impair$4 ,?is foll[s f ! facts t ! resi/ance ( a liquid decreases z its temp]ature rises1 & t *emical action is mu* sl[] at l[] temp]atures4 ,! gravity cell has a practically con/ant voltage ( #a4jh volts4 ,its int]nal resi/ance is comp>atively high1 seldom fall+ bel[ #a ohm & (t5 ris+ to #f ohms4 ,at be/1 !re=e1 x is only capable ( produc+ ab\t #a amp]e4 ,! gravity cell is p]haps ! mo/ common type ( cell :]e9 depol>ization is affect$ by electro-*emical means4 ,full] ,cell3--,a =m ( cell t is adapt$ to v heavy op5-circuit "w & also clos$-circuit "w :]e heavi] curr5ts are requir$ ?an c be suppli$ by ! gravity batt]y is ! ,full]4 ,9 ?is ! electrodes are ( z9c & c>bon1 respectively1 ! z9c usually be+ 9 ! =m ( a heavy cone & plac$ )9 a por\s cup4 ,! electrolyte ( ! ,full] cell is kn[n z electropoion fluid1 & consi/s ( a mixture ( sodium or potassium bi*romate1 sulphuric acid1 & wat]4 ,! v>i\s p>ts ( ! /&>d ,full] cell1 z once l>gely employ$ by ! v>i\s ,bell op]at+ companies1 are %[n 9 ,fig4 #fe4 ,9 ?is ! j> 0 made ( fl9t glass1 cyl9drical 9 =m1 six in*es 9 diamet] & eight in*es deep4 ,x is important t a good grade ( glass be us$ = ! j> 9 ?is cell1 because1 on acc\nt ( ! nature ( ! electrolyte1 breakage is disa/r\s 9 ! effects x may produce on adjac5t prop]ty4 ,! c>bon plate is rectangul> 9 =m1 ab\t f\r in*es wide1 eight & ?ree-qu>t]s in*es long1 & "o-qu>t] in* ?ick4 ,! metal t]m9al at ! top ( ! c>bon block is ( bronze1 bo? x & ! lock nuts & bolts be+ nickel-plat$ to m9imize corrosion4 ,! upp] end ( ! c>bon block is soak$ 9 p>aff9 s hot z to drive all ( ! moi/ure out ( ! p>aff9 & out ( ! pores ( ! block itself4 ,! z9c1 z is not$ f ! cut1 is 9 ! =m ( a truncat$ cone4 ,x is ab\t two & "o-eigh? in*es 9 diamet] at ! base & two & "o-half in*es high4 ,ca/ into ! z9c is a s(t copp] wire ab\t ,no4 #ab ,b4 ,s4 gauge4 ,?is wire ext5ds above ! top ( ! j> s z to =m a conv5i5t t]m9al = ! cell4 ,! por\s cup is cyl9drical 9 =m1 ab\t ?ree in*es 9 diamet] & sev5 in*es deep4 ,! wood5 cov] is ( kiln-dri$ :ite wood ?or\ghly coat$ ) two coats ( asphalt pa9t4 ,x is provid$ ) a slot = ! c>bon & a hole = ! copp] wire ext5d+ to ! z9c4 ,! electrolyte = ?is cell is made z foll[s3 ,sodium bi*romate #f oz4 ,sulphuric acid #ag oz4 ,s(t wat] #ef oz4 ,?is solution is mix$ by dissolv+ ! bi*romate ( sodium 9 ! wat] & !n add+ sl[ly ! sulphuric acid4 ,potassium bi*romate may be sub/itut$ = ! sodium bi*romate4 ,9 sett+ up ?is cell1 ! amalgamat$ z9c is plac$ )9 ! por\s cup1 9 ! bottom ( :i* are ab\t two teaspoonfuls ( m]cury1 ! latt] s]v+ to keep ! z9c well amalgamat$4 ,! por\s cup is !n plac$ 9 ! glass j> & a suffici5t quantity ( ! electrolyte is plac$ 9 ! out] j> to come )9 ab\t "o & "o-half in*es ( ! top ( ! por\s cup4 ,ab\t two teaspoonfuls ( salt are !n plac$ 9 ! por\s cup & suffici5t s(t wat] add$ to br+ ! level ( ! liquid )9 ! por\s cup ev5 ) ! level ( ! electrolyte 9 ! j> surr\nd+ ! cup4 ,! c>bon is !n plac$ ?r\gh ! slot 9 ! cov]1 & ! wire f ! z9c is pass$ ?r\gh ! hole 9 ! cov] provid$ = x1 & ! cov] is all[$ to fall 9 place4 ,! cell is n[ ready = imm$iate use4 ,! action ( ?is cell is z foll[s3 ,! sulphuric acid attacks ! z9c & =ms z9c sulphate1 lib]at+ hydrog54 ,! hydrog5 attempts to pass to ! c>bon plate z usual1 b 9 s do+ x meets ) ! oxyg5 ( ! *romic acid & =ms wat] !re)4 ,! rema9d] ( ! *romic acid comb9es ) ! sulphuric acid to =m *romium sulphate4 ,illu/ration3 ,fig #fe4 ,full] ,cell ,! m]cury plac$ 9 ! bottom ( ! por\s cup ) ! z9c keeps ! z9c 9 a /ate ( p]petual amalgamation4 ,?is x does by capill>y action1 z ! m]cury spreads ov] ! entire surface ( ! z9c4 ,! initial amalgamation1 :ile n absolutely ess5tial1 helps 9 a measure ?is capill>y action4 ,9 ano!r well-kn[n type ( ! ,full] batt]y ! c>bon is a holl[ cyl9d]1 surr\nd+ ! por\s cup4 ,9 ?is type ! z9c usually took ! =m ( a long b> hav+ a cross-%ap$ section1 ! l5g? ( ?is b> be+ suffici5t to ext5d ! entire dep? ( ! por\s cup4 ,?is type ( cell has ! advantage ( a some:at l[] int]nal resi/ance ?an ! /&>d =m j describ$4 ,%\ld ! electrolyte become sup]saturat$ by virtue ( ! batt]y be+ neglect$ or too heavily ov]work$1 a set ( second>y reactions w occur 9 ! cell1 result+ 9 ! =mation ( ! yell[ cry/als ^u ! c>bon4 ,?is s]i\sly affects ! e4m4f4 ( ! cell & also its int]nal resi/ance4 ,%\ld ?is occur1 "s ( ! solution %\ld be )drawn & dilute sulphuric acid ins]t$ 9 its place & ! cry/als :i* h =m$ on ! c>bon %\ld be c>efully wa%$ (f4 ,%\ld ! solution lose its orange t9t & turn blue1 x indicates t m bi*romate ( pota% or bi*romate ( sodium is ne$$4 ,?is cell gives an electromotive =ce ( #b4a volts & a v l>ge curr5t :5 x is 9 good condition1 s9ce its int]nal resi/ance is l[4 ,! ,full] cell 0 once l>gely us$ = supply+ curr5t to telephone transmitt]s at subscrib]s' /ations1 :]e v heavy s]vice 0 dem&$1 b ! adv5t ( ! s-call$ common-batt]y sy/ems1 9 "s cases1 & ( ! high-resi/ance transmitt]1 9 o!r cases1 has caus$ a great less5+ 9 its use4 ,?is is =tunate z ! cell is a dirty "o to h&le & is exp5sive to ma9ta94 ,! ,full] cell /ill w>rants att5tion1 h[ev]1 z an available s\rce ( curr5t1 :i* may be f\nd useful 9 c]ta9 cases ( em]g5cy "w1 & 9 supply+ special b tempor>y ne$s = heavi] curr5t ?an ! ,le,clanch or gravity cell c furni%4 ,lal&e ,cell3--,a type ( cell1 specially adapt$ to con/ant-curr5t "w1 & sometimes us$ z a c5tral s\rce ( curr5t 9 v small common-batt]y ex*anges is ! s-call$ copp] oxide1 or ,lal&e cell1 ( :i* ! ,edison & ! ,gordon are types4 ,9 all ( ^! ! negatively *>g$ elem5t is ( z9c1 ! positively *>g$ elem5t a mass ( copp] oxide1 & ! electrolyte a solution ( cau/ic pota% 9 wat]4 ,9 ! ,edison cell ! copp] oxide is 9 ! =m ( a compress$ slab :i* ) its connect+ copp] support =ms ! electrode4 ,9 ! ,gordon & o!r cells ( ?is type ! copp] oxide is conta9$ loosely 9 a p]=at$ cyl9d] ( %eet copp]4 ,! copp] oxide s]ves n only z an electrode1 b also z a depol>iz+ ag5t1 ! lib]at$ hydrog5 9 ! electrolyte unit+ ) ! oxyg5 ( ! copp] oxide to =m wat]1 & leav+ free metallic copp]4 ,on op5 circuit ! elem5ts are n attack$1 !re=e !re is no wa/e ( mat]ial :ile ! cell is n 9 use4 ,?is important feature1 & ! fact t ! int]nal resi/ance is l[1 make ?is cell well adapt$ = all =ms ( heavy op5-circuit "w4 ,! fact t !re is no pol>iz+ action )9 ! cell makes x fur!r adaptable to heavy clos$-circuit s]vice4 ,^! cells are int5d$ to be s proportion$ t all ( _! p>ts become exhau/$ at once s t :5 ! cell fails1 complete r5ewals are necess>y4 ,!re=e1 !re is nev] a "q z to :i* ( ! elem5ts %\ld be r5ew$4 ,aft] ! elem5ts & solution are 9 place ab\t "o-f\r? ( an in* ( heavy p>aff9 oil is p\r$ ^u ! surface ( ! solution 9 ord] to prev5t evaporation4 ,?is cell requires little att5tion & w ma9ta9 a con/ant e4m4f4 ( ab\t two-?irds ( a volt until completely exhau/$4 ,x is non-freezable at all ord9>y temp]atures4 ,its l[ voltage is its pr9cipal disadvantage4 ,/&>d ,cell4 ,*loride ( ,silv] ,cell3--,! *loride ( silv] cell is l>gely us$ z a /&>d = te/+ purposes4 ,its compactness & portability & its fre$om f local action make x p>ticul>ly adaptable to use 9 portable te/+ outfits :]e con/ant electromotive =ce & v small curr5ts are requir$4 ,illu/ration3 ,fig4 #ff4 ,*loride ( ,silv] ,cell ,a cross-section ( "o =m ( ! cell is %[n 9 ,fig4 #ff4 ,its elem5ts are a rod ( *emically-pure z9c & a rod ( *loride ( silv] imm]s$ 9 a wat] solution ( sal ammoniac4 ,z ord9>ily con/ruct$1 ! glass j> or tube is usually ab\t #b-a_/b in*es long by #a in* 9 diamet]4 ,aft] ! solution is p\r$ 9 & ! elem5ts are 9 place ! glass tube is h]metically seal$ ) a plug ( p>aff9 wax4 ,! e4m4f4 ( a cell ( ?is type is #a4jc volts & ! ext]nal resi/ance v>ies ) ! age ( ! cell1 be+ ab\t #d ohms at fir/4 ,c>e %\ld be tak5 n to %ort-circuit ^! cells1 or use !m 9 any b high-resi/ance circuits1 z !y h b little en]gy & become quickly exhau/$ if compell$ to "w 9 l[-resi/ance circuits4 ,conv5tional ,symbol4 ,! conv5tional symbol = a cell1 ei!r ( ! prim>y or ! second>y type1 consi/s ( a long ?9 l9e & a %ort heavy l9e side by side & p>allel4 ,a batt]y is repres5t$ by a numb] ( pairs ( su* l9es1 z 9 ,fig4 #fg4 ,! two l9es ( ea* pair are suppos$ to repres5t ! two electrodes ( a cell4 ,:]e any significance is to be plac$ on ! pol>ity ( ! cell or batt]y ! long ?9 l9e is suppos$ to repres5t ! positively *>g$ plate & ! %ort ?ick l9e ! negatively *>g$ plate4 ,! numb] ( pairs may indicate ! numb] ( cells 9 ! batt]y4 ,frequ5tly1 h[ev]1 a few pairs ( su* l9es are employ$ m]ely = ! purpose ( indicat+ a batt]y )\t reg>d to its pol>ity or its numb] ( cells4 ,illu/ration3 ,fig4 #fg4 ,batt]y ,symbols ,9 ,fig4 #fg ! repres5tation at ,a is t ( a batt]y ( a numb] ( cells connect$ 9 p>allel2 t at ,b ( a batt]y ) ! cells connect$ 9 s]ies2 & t at ,c ( a batt]y ) "o ( its poles gr\nd$4 ,,*apt] ,,viii ,,magneto ,,signal+ ,,app>atus ,me?od ( ,signal+4 ,! ord9>y app>atus1 by :i* spee* is receiv$ telephonically1 is n capable ( mak+ suffici5tly l\d s\nds to attract ! att5tion ( p at a di/ance f ! in/rum5t4 ,= ?is reason x is necess>y to employ auxili>y app>atus = ! purpose ( signal+ betwe5 /ations4 ,9 c5tral (fices :]e an att5dant is always on h&1 ! s5se ( sight is usually appeal$ to by ! use ( signals :i* give a visual indication1 b 9 ! case ( telephone in/rum5ts = use by ! public1 ! s5se ( he>+ is appeal$ to by employ+ an audible r ?an a visual signal4 ,batt]y ,bell4 ,! ord9>y vibrat+ or batt]y bell1 su* z is employ$ = door bells1 is sometimes1 ?\gh n (t51 employ$ 9 telephony4 ,x d]ives its curr5t f prim>y batt]ies or f any direct-curr5t s\rce4 ,! reason :y !y are n employ$ to a great] ext5t 9 telephony is t telephone signals usually h to be s5t ov] l9es ( consid]able l5g? & ! voltage t w\ld be requir$ to furni% curr5t to op]ate su* bells ov] su* l5g?s ( l9e is high] ?an w\ld ord9>ily be f\nd 9 ! batt]ies commonly employ$ 9 telephone "w4 ,besides ?is ! make-&-break contacts on :i* !1 ord9>y batt]y bell dep5ds = its op]ation are an objectionable feature f ! /&po9t ( ma9t5ance4 ,magneto ,bell4 ,=tunately1 h[ev]1 !re has be5 develop$ a simpl] type ( electric bell1 :i* op]ates on small] curr5ts1 & :i* requires no make-&-break contacts :atev]4 ,?is simpl] =m ( bell is commonly kn[n z ! pol>iz$1 or magneto1 bell or r+]4 ,x requires = its op]ation1 9 its ord9>y =m1 an alt]nat+ curr5t1 ?\gh 9 its modifi$ =ms x may be us$ ) pulsat+ curr5ts1 t is1 ) p]iodically recurr+ impulses ( curr5t always 9 ! same direction4 ,magneto ,g5]ator4 ,9 ! e>ly days ( telephony !re 0 ne>ly always associat$ ) ea* pol>iz$ bell a magneto g5]ator = furni%+ ! prop] k9d ( curr5t to r+ su* bells4 ,ea* telephone 0 !re=e equipp$1 9 addition to ! transmitt] & receiv]1 ) a signal-receiv+ device 9 ! =m ( a pol>iz$ bell1 & ) a curr5t g5]ator by :i* ! us] 0 enabl$ to develop 8 own curr5ts ( suitable k9d & voltage = r++ ! bells ( o!r /ations4 ,consid]+ ! signal+ app>atus ( ! telephones alone1 !re=e1 ea* telephone 0 equipp$ ) a p[] plant = g5]at+ curr5ts us$ by t /ation 9 signal+ o!r /ations1 ! prime mov] be+ ! muscles ( ! us] appli$ to ! turn+ ( a crank on ! side ( ! in/rum5t2 & also ) a curr5t-consum+ device 9 ! =m ( a pol>iz$ electromagnetic bell adapt$ to receive ! curr5ts g5]at$ at o!r /ations & to conv]t a portion ( _! en]gy into audible signals4 ,! magneto g5]ator is ab\t ! simple/ type ( dynamo-electric ma*9e1 & x dep5ds ^u ! same pr9ciples ( op]ation z ! mu* l>g] g5]ators1 employ$ 9 electric-light+ & /reet-railway p[] plants1 = in/ance4 ,in/ead ( develop+ ! necess>y magnetic field by means ( electromagnets1 z 9 ! case ( ! ord9>y dynamo1 ! field ( ! magneto g5]ator is develop$ by p]man5t magnets1 usually ( ! horse%oe =m4 ,h5ce ! "n magneto4 ,illu/ration3 ,fig4 #fh4 ,pr9ciples ( ,magneto ,g5]ator ,9 ord] to conc5trate ! magnetic field )9 ! space 9 :i* ! armature revolves1 pole pieces ( iron are s arrang$ 9 connection ) ! poles ( ! p]man5t magnet z to af=d a sub/antially cyl9drical space 9 :i* ! armature conductors may revolve & ?r\gh :i* practically all ! magnetic l9es ( =ce set up by ! p]man5t magnets w pass4 ,9 ,fig4 #fh !re is %[n1 diagrammatically1 a horse%oe magnet ) su* a pair ( pole pieces1 betwe5 :i* a loop ( wire is adapt$ to rotate4 ,! magnet #a is ( h>d5$ /eel & p]man5tly magnetiz$4 ,! pole pieces are %[n at #b & #c1 ea* be+ ( s(t iron adapt$ to make good magnetic contact on its flat side ) ! inn] flat surface ( ! b> magnet1 & be+ bor$ out s z to =m a cyl9drical recess betwe5 !m z indicat$4 ,! direction ( ! magnetic l9es ( =ce set up by ! b> magnet ?r\gh ! int]pol> space is indicat$ by ! long horizontal arr[s1 ?is fl[ be+ f ! nor? pole 7,n7 to ! s\? pole 7,s7 ( ! magnet4 ,at #d !re is %[n a loop ( wire suppos$ to revolve 9 ! magnetic field ( =ce on ! axis #e-e4 ,!ory4 ,9 ord] to und]/& h[ curr5ts w be g5]at$ 9 ?is loop ( wire #d1 x is only necess>y to rememb] t if a conductor is s mov$ z to cut across magnetic l9es ( =ce1 an electromotive =ce w be set up 9 ! conductor :i* w t5d to make ! curr5t fl[ ?r\gh x4 ,! magnitude ( ! electromotive =ce w dep5d on ! rate at :i* ! conductor cuts ?r\gh ! l9es ( =ce1 or1 9 o!r words1 on ! numb] ( l9es ( =ce t are cut ?r\gh by ! conductor 9 a giv5 unit ( "t4 ,aga91 ! direction ( ! electromotive =ce dep5ds on ! direction ( ! cutt+1 s t if ! conductor be mov$ 9 "o direction across ! l9es ( =ce1 ! electromotive =ce & ! curr5t w be 9 "o direction2 :ile if x moves 9 ! opposite direction across ! l9es ( =ce1 ! electromotive =ce & ! curr5t w be 9 ! rev]se direction4 ,x is1 evid5t t z ! loop ( wire #d revolves 9 ! field ( =ce ab\t ! axis #e-e1 ! portions ( ! conductor p>allel to ! axis w cut ?r\gh ! l9es ( =ce1 fir/ 9 "o direction & !n 9 ! o!r1 ?us produc+ electromotive =ces !re91 fir/ 9 "o direction & !n 9 ! o!r4 ,ref]r+ n[ to ,fig4 #fh1 & suppos+ t ! loop #d is revolv+ 9 ! direction ( ! curv$ arr[ %[n betwe5 ! upp] edges ( ! pole pieces1 x w be evid5t t j z ! loop /&s 9 ! v]tical position1 its horizontal memb]s w be mov+ 9 a horizontal direction1 p>allel ) ! l9es ( =ce &1 !re=e1 n cutt+ !m at all4 ,! electromotive =ce & ! curr5t w1 !re=e1 be z]o at ?is "t4 ,z ! loop advances t[>d ! position %[n 9 dott$ l9es1 ! upp] portion ( ! loop t is p>allel ) ! axis w beg9 to cut d[nw>dly ?r\gh ! l9es ( =ce1 & likewise ! l[] portion ( ! loop t is p>allel ) ! axis w beg9 to cut upw>dly ?r\gh ! l9es ( =ce4 ,?is w cause electromotive =ces 9 opposite directions to be g5]at$ 9 ^! portions ( ! loop1 & ^! w t5d to aid ea* o!r 9 caus+ a curr5t to circulate 9 ! loop 9 ! direction %[n by ! arr[s associat$ ) ! dott$ repres5tation ( ! loop4 ,x is evid5t t z ! motion ( ! loop progresses1 ! rate ( cutt+ ! l9es ( =ce w increase & w be a maximum :5 ! loop rea*es a horizontal position1 or at t "t ! two portions ( ! loop t are p>allel ) ! axis w be travel+ at "r angles to ! l9es ( =ce4 ,at ?is po9t1 !re=e1 ! electromotive =ce & ! curr5t w be a maximum4 ,f ?is po9t until ! loop aga9 assumes a v]tical position1 ! cutt+ ( ! l9es ( =ce w /ill be 9 ! same direction1 b at a con/antly decreas+ rate1 until1 f9ally1 :5 ! loop is v]tical ! movem5t ( ! p>ts ( ! loop t are p>allel ) ! axis w be 9 ! direction ( ! l9es ( =ce &1 !re=e1 no cutt+ w take place4 ,at ?is po9t1 !re=e1 ! electromotive =ce & ! curr5t 9 ! loop aga9 w be z]o4 ,we h se51 !re=e1 t 9 ?is half revolution ( ! loop f ! "t :5 x 0 9 a v]tical position to a "t :5 x 0 aga9 9 a v]tical position b upside d[n1 ! electromotive =ce v>i$ f z]o to a maximum & back to z]o1 & ! curr5t did ! same4 ,x is easy to see t1 z ! loop moves ?r\gh ! next half revolution1 an exactly simil> rise & fall ( electromotive =ce & curr5t w take place2 b ?is w be 9 ! opposite direction1 s9ce t portion ( ! loop :i* 0 go+ d[n ?r\gh ! l9es ( =ce is n[ go+ up1 & ! portion :i* 0 previ\sly go+ up is n[ go+ d[n4 ,! law conc]n+ ! g5]ation ( electromotive =ce & curr5t 9 a conductor t is cutt+ ?r\gh l9es ( magnetic =ce1 may be /at$ 9 ano!r way1 :5 ! conductor is b5t into ! =m ( a loop1 z 9 ! case "u consid]ation3 ,?us1 if ! numb] ( l9es ( =ce :i* pass ?r\gh a conduct+ loop be v>i$1 electromotive =ces w be g5]at$ 9 ! loop4 ,?is w be true :e!r ! numb] ( l9es pass+ ?r\gh ! loop be v>i$ by mov+ ! loop )9 ! field ( =ce or by v>y+ ! field ( =ce itself4 ,9 any case1 if ! numb] ( l9es ( =ce be increas$1 ! curr5t w fl[ 9 "o way1 & if x be dim9i%$ ! curr5t w fl[ 9 ! o!r way4 ,! am\nt ( ! curr5t w dep5d1 o!r ?+s be+ equal1 on ! rate at :i* ! l9es ( =ce ?r\gh ! loop are be+ v>i$1 reg>dless ( ! me?od by :i* ! v>iation is made to take place4 ,"o revolution ( ! loop1 !re=e1 results 9 a complete cycle ( alt]nat+ curr5t consi/+ ( "o positive foll[$ by "o negative impulse4 ,! diagram ( ,fig4 #fh is m]ely int5d$ to illu/rate ! pr9ciple involv$4 ,9 ! practical con/ruction ( magneto g5]ators m ?an "o b> magnet is us$1 &1 9 addition1 ! conductors 9 ! armature are s arrang$ z to include a great _m loops ( wire4 ,fur!rmore1 ! conductors 9 ! armature are w\nd ar\nd an iron core s t ! pa? ?r\gh ! armature loops or turns1 may pres5t su* l[ reluctance to ! passage ( l9es ( =ce z to greatly increase ! numb] ( su* l9es & also to cause practically all ( !m to g ?r\gh ! loops 9 ! armature conductor4 ,armature4 ,! iron ^u :i* ! armature conductors are w\nd is call$ ! core4 ,! core ( an ord9>y armature is %[n 9 ,fig4 #fi4 ,?is is usually made ( s(t gray ca/ iron1 turn$ s z to =m be>+ surfaces at #a & #b1 ^u :i* ! entire armature may rotate1 & also turn$ s t ! surfaces #c w be truly cyl9drical ) respect to ! axis ?r\gh ! c5t] ( ! %aft4 ,! armature conductors are put on by w9d+ ! space betwe5 ! two p>allel faces #d z full ( insulat$ wire z space w admit4 ,"o end ( ! armature w9d+ is sold]$ to ! p9 #e &1 !re=e1 makes contact ) ! frame ( ! g5]ator1 :ile ! o!r end ( ! w9d+ is sold]$ to ! p9 #f1 :i* engages ! /ud #g1 c>ri$ 9 an insulat+ bu%+ 9 a longitud9al hole 9 ! end ( ! armature %aft4 ,x is ?us se5 t ! frame ( ! ma*9e w =m "o t]m9al ( ! armature w9d+1 :ile ! insulat$ /ud #g w =m ! o!r t]m9al4 ,illu/ration3 ,fig4 #fi4 ,g5]ator ,armature ,ano!r =m ( armature l>gely employ$ 9 rec5t magneto g5]ators is illu/rat$ 9 ,fig4 #gj4 ,9 ?is ! %aft on :i* ! armature revolves does n =m an integral "p ( ! armature core b consi/s ( two cyl9drical /uds #b & #c project+ f ! c5t]s ( disks #d & #e1 :i* are screw$ to ! ends ( ! core #a4 ,?is ,h type ( armature core1 z x is call$1 :ile conta9+ some:at m p>ts ?an ! simpl] type %[n 9 ,fig4 #fi1 possesses di/9ct advantages 9 ! matt] ( w9d+4 ,by virtue ( its simpl] =m ( w9d+ space1 x is easi] to insulate & easi] to w9d1 & fur!rmore1 s9ce ! %aft does n run ?r\gh ! w9d+ space1 x is capable ( hold+ a consid]ably great] numb] ( turns ( wire4 ,! ends ( ! armature w9d+ are connect$1 "o directly to ! frame & ! o!r to an insulat$ p91 z is %[n 9 ! illu/ration4 ,illu/ration3 ,fig4 #gj4 ,g5]ator ,armature ,illu/ration3 ,fig4 #ga4 ,g5]ator ,field & ,armature ,! me?od commonly employ$ ( associat+ ! pole pieces ) ea* o!r & ) ! p]man5t magnets is %[n 9 ,fig4 #ga4 ,x is v important t ! space 9 :i* ! armature revolves %all be truly cyl9drical1 & t ! be>+s = ! armature %all be s align$ z to make ! axis ( rotation ( ! armature co9cide ) ! axis ( ! cyl9drical surface ( ! pole pieces4 ,a rigid /ructure is1 !re=e1 requir$ & ?is is frequ5tly secur$1 z %[n 9 ,fig4 #ga1 by jo9+ ! two pole pieces #a & #b toge!r by means ( heavy brass rods #c & #d1 ! rods be+ %\ld]$ & _! r$uc$ ends pass$ ?r\gh holes 9 flanges ext5d+ f ! pole pieces1 & rivet$4 ,! be>+ plates 9 :i* ! armature is j\rnal$ are !n secur$ to ! ends ( ^! pole pieces1 z w be %[n 9 subsequ5t illu/rations4 ,?is assures prop] rigidity betwe5 ! pole pieces & also betwe5 ! pole pieces & ! armature be>+s4 ,! reason :y ?is degree ( rigidity is requir$ is t x is necess>y to "w ) v small air gaps betwe5 ! armature core & its pole pieces & unless ^! g5]ators are me*anically well made !y are likely to alt] _! adju/m5t & ?us all[ ! armature faces to scrape or rub aga9/ ! pole pieces4 ,9 ,fig4 #ga "o ( ! p]man5t horse%oe magnets is %[n1 its ends re/+ 9 grooves on ! out] faces ( ! pole pieces & usually clamp$ !reto by means ( heavy iron ma*9e screws4 ,) ?is /ructure 9 m9d1 ! !ory ( ! magneto g5]ator develop$ 9 connection ) ,fig4 #fh may be c>ri$ a little fur!r4 ,:5 ! armature lies 9 ! position %[n at ! left ( ,fig4 #ga1 s t ! c5t] position ( ! core is horizontal1 a good pa? is af=d$ = ! l9es ( =ce pass+ f "o pole to ! o!r4 ,practically all ( ^! l9es w pass ?r\gh ! iron ( ! core r ?an ?r\gh ! air1 &1 !re=e1 practically all ( !m w pass ?r\gh ! convolutions ( ! armature w9d+4 ,:5 ! armature has advanc$1 say #de degrees1 9 its rotation 9 ! direction ( ! curv$ arr[1 ! l[] "r-h& portion ( ! armature flange w /ill lie opposite ! l[] face ( ! "r-h& pole piece & ! upp] left-h& portion ( ! armature flange w /ill lie opposite ! upp] face ( ! left-h& pole piece4 ,z a result !re w /ill be a good pa? = ! l9es ( =ce ?r\gh ! iron ( ! core & comp>atively little *ange 9 ! numb] ( l9es pass+ ?r\gh ! armature w9d+4 ,z ! corn]s ( ! armature flange pass away f ! corn]s ( ! pole pieces1 h[ev]1 !re is a sudd5 *ange 9 condition :i* may be be/ und]/ood by ref]5ce to ! "r-h& portion ( ,fig4 #ga4 ,! l9es ( =ce n[ no long] f9d pa? ?r\gh ! c5t] portion ( ! armature core--t ly+ at "r angles to _! direction ( fl[4 ,two o!r pa?s are at ?is "t provid$ ?r\gh ! n[ horizontal armature flanges :i* s]ve almo/ to connect ! two pole pieces4 ,! l9es ( =ce are ?us %unt$ out ( ! pa? ?r\gh ! armature coils & !re is a sudd5 decrease f a l>ge numb] ( l9es ?r\gh ! turns ( ! w9d+ to almo/ none4 ,z ! armature cont9ues 9 its rotation ! two pa?s ?r\gh ! flanges are brok51 & ! pa? ?r\gh ! c5t] ( ! armature core &1 !re=e1 ?r\gh ! coils !mselves1 is re/abli%$4 ,z a result ( ?is consid]ation x w be se5 t 9 actual practice ! *ange 9 ! numb] ( l9es pass+ ?r\gh ! armature w9d+ is n ( ! gradual nature t w\ld be indicat$ by a consid]ation ( ,fig4 #fh alone1 b r1 is abrupt1 z ! corn]s ( ! armature flanges leave ! corn]s ( ! pole pieces4 ,?is abrupt *ange produces a sudd5 rise 9 electromotive =ce j at ^! po9ts 9 ! rotation1 &1 !re=e1 ! electromotive =ce & ! curr5t curves ( ^! magneto g5]ators is n usually ( ! smoo? s9e-wave type b r ( a =m resembl+ ! s9e wave ) di/9ct humps add$ to ea* half cycle4 ,illu/ration3 ,fig4 #gb4 ,g5]ator ) ,magnets ,remov$ ,z is to be expect$ f any two-pole alt]nat+ g5]ator1 !re is "o cycle ( curr5t = ea* revolution ( ! armature4 ,"u ord9>y conditions a p]son is able to turn ! g5]ator h&le at ! rate ( ab\t two hundr$ revolutions a m9ute1 & z ! ratio ( ge>+ is ab\t five to "o1 ?is results 9 ab\t "o ?\s& revolutions p] m9ute ( ! g5]ator1 &1 !re=e1 9 a curr5t ( ab\t "o ?\s& cycles p] m9ute1 ?is v>y+ widely accord+ to ! p]son :o is do+ ! turn+4 ,illu/ration3 ,,h[>d ,,(fice ,,( ,,home ,,telephone ,,company1 ,,san ,,francisco ,an ,all-,concrete ,build+ ,s]v+ ! ,di/rict ,s\? ( ,m>ket ,/reet4 ,! end plates :i* support ! be>+s = ! armature are usually ext5d$ upw>dly1 z %[n 9 ,fig4 #gb1 s z to af=d be>+s = ! crank %aft4 ,! crank %aft c>ries a l>ge spur ge> :i* me%es ) a p9ion 9 ! end ( ! armature %aft1 s t ! us] may cause ! armature to revolve rapidly4 ,! con/ruction %[n 9 ,fig4 #gb is typical ( t ( a mod]n magneto g5]ator1 x be+ und]/ood t ! p]man5t magnets are remov$ = cle>ness ( illu/ration4 ,fig4 #gc is a view ( a completely assembl$ g5]ator su* z is us$ = s]vice requir+ a comp>atively heavy output4 ,o!r types ( g5]ators hav+ two1 ?ree1 or f\r p]man5t magnets in/ead ( five1 z %[n 9 ?is figure1 are also /&>d4 ,illu/ration3 ,fig4 #gc4 ,five-,b> ,g5]ator ,ref]r+ aga9 to ,fig4 #fi1 x w be rememb]$ t "o end ( ! armature w9d+ %[n diagrammatically 9 t figure1 is t]m9at$ 9 ! p9 #e1 :ile ! o!r t]m9ates 9 ! p9 #g4 ,:5 ! armature is assembl$ 9 ! frame ( ! g5]ator x is evid5t t ! frame itself is 9 metallic connection ) "o end ( ! armature w9d+1 s9ce ! p9 #e is 9 metallic contact ) ! armature ca/+ & ?is is 9 contact ) ! frame ( ! g5]ator ?r\gh ! be>+s4 ,! frame ( ! ma*9e is1 !re=e1 "o t]m9al ( ! g5]ator4 ,:5 ! g5]ator is assembl$ a spr+ ( "o =m or ano!r always re/s aga9/ ! t]m9al p9 #g ( ! armature s z to =m a t]m9al = ! armature w9d+ ( su* a nature z to p]mit ! armature to rotate freely4 ,su* spr+1 !re=e1 =ms ! o!r t]m9al ( ! g5]ator4 ,automatic ,%unt4 ,"u ne>ly all conditions ( practice x is desirable to h ! g5]ator automatically p]=m "s swit*+ function :5 x is op]at$4 ,z an example1 :5 ! g5]ator is connect$ s t its armature is 9 s]ies 9 a telephone l9e1 x is q obvi\s t ! pres5ce ( ! resi/ance & ! imp$ance ( ! armature w9d+ w\ld be objectionable if left 9 ! circuit ?r\gh :i* ! voice curr5ts _h to pass4 ,= ?is reason1 :at is t]m$ an automatic %unt is employ$ on g5]ators design$ = s]ies "w2 ?is %unt is s arrang$ t x w automatically %unt or %ort-circuit ! armature w9d+ :5 x is at re/ & also break ?is %unt :5 ! g5]ator is op]at$1 s z to all[ ! curr5t to pass to l9e4 ,illu/ration3 ,fig #gd4 ,g5]ator ,%unt ,swit* ,a simple & mu*-us$ arrangem5t = ?is purpose is %[n 9 ,fig4 #gd1 :]e #a is ! armature2 #b is a wire lead+ f ! frame ( ! g5]ator & =m+ "o t]m9al ( ! g5]ator circuit2 & #c is a wire =m+ ! o!r t]m9al ( ! g5]ator circuit1 ?is wire be+ atta*$ to ! spr+ #d1 :i* re/s aga9/ ! c5t] p9 ( ! armature s z to make contact ) ! opposite end ( ! armature w9d+ to t :i* is connect$ ) ! frame4 ,! circuit ?r\gh ! armature may be trac$ f ! t]m9al wire #b ?r\gh ! frame2 !nce ?r\gh ! be>+s to ! armature #a & ?r\gh ! p9 to ! "r-h& side ( ! armature w9d+4 ,cont9u+ ! circuit ?r\gh ! w9d+ itself1 x passes to ! c5t] p9 project+ f ! left-h& end ( ! armature %aft2 !nce to ! spr+ #d :i* re/s aga9/ ?is p92 & !nce to ! t]m9al wire #c4 ,normally1 ?is pa? is %unt$ by :at is practically a %ort circuit1 :i* may be trac$ f ! t]m9al #b ?r\gh ! frame ( ! g5]ator to ! crank %aft #e2 !nce to ! upp] end ( ! spr+ #d & out by ! t]m9al wire #c4 ,?is is ! condition :i* ord9>ily exi/s & :i* results 9 ! removal ( ! resi/ance & ! imp$ance on ! armature w9d+ f any circuit 9 :i* ! g5]ator is plac$1 z long z ! g5]ator is n op]at$4 ,an arrangem5t is provid$1 h[ev]1 :]eby ! crank %aft #e w be )drawn automatically f engag+ ) ! upp] end ( ! spr+ #d1 ?us break+ ! %unt ar\nd ! armature circuit1 :5ev] ! g5]ator crank is turn$4 ,9 ord] to accompli% ?is ! crank %aft #e is capable ( p>tial rotation & ( slight longitud9al movem5t )9 ! hub ( ! l>ge ge> :eel4 ,a spr+ #g usually presses ! crank %aft t[>d ! left & into engagem5t ) ! spr+ #d4 ,a p9 #h c>ri$ by ! crank %aft1 re/s 9 a ,v-%ap$ not* 9 ! end ( ! hub #f & z a result1 :5 ! crank is turn$ ! p9 rides on ! surface ( ?is not* be=e ! l>ge ge> :eel />ts to turn1 & ?us moves ! crank %aft #e to ! "r & breaks ! contact betwe5 x & ! spr+ #d4 ,?us1 z long z ! g5]ator is be+ op]at$1 its armature is connect$ 9 ! circuit ( ! l9e1 b z soon z x becomes idle ! armature is automatically %ort-circuit$4 ,su* devices z ?is are t]m$ automatic %unts4 ,9 /ill o!r cases x is desirable to h ! g5]ator circuit normally op5 s t x w n affect 9 any way ! electrical *>act]i/ics ( ! l9e :ile ! l9e is be+ us$ = talk+4 ,9 ?is case ! arrangem5t is made s t ! g5]ator w automatically be plac$ 9 prop] circuit relation ) ! l9e :5 x is op]at$4 ,illu/ration3 ,fig4 #ge4 ,g5]ator ,cut-9 ,swit* ,a common arrangem5t = do+ ?is is %[n 9 ,fig4 #ge1 :]e9 ! spr+ #a normally re/s aga9/ ! contact p9 ( ! armature & =ms "o t]m9al ( ! armature circuit4 ,! spr+ #b is adapt$ to =m ! o!r t]m9al ( ! armature circuit b x is normally insulat$ f ev]y?+4 ,! circuit ( ! g5]ator is1 !re=e1 op5 betwe5 ! spr+ #b & ! %aft #c1 b z soon z ! g5]ator is op]at$ ! crank %aft is bodily mov$ to ! left by means ( ! ,v-%ap$ not* 9 ! driv+ coll> #d & is ?us made to engage ! spr+ #b4 ,! circuit ( ! g5]ator is !n complet$ f ! spr+ #a ?r\gh ! armature p9 to ! armature w9d+2 !nce to ! frame ( ! ma*9e & ?r\gh %aft #c to ! spr+ #b4 ,su* devices z ?is are l>gely us$ 9 connection ) s-call$ bridg+ telephones 9 :i* ! g5]ators & bells are adapt$ to be connect$ 9 multiple across ! l9e4 ,a bett] arrangem5t = accompli%+ ! automatic swit*+ on ! "p ( ! g5]ator is to make no use ( ! crank %aft z a "p ( ! conduct+ pa? z is ! case 9 bo? ,figs4 #gd & #ge1 b to make ! crank %aft1 by its longitud9al movem5t1 imp>t ! necess>y motion to a swit* spr+ :i*1 9 turn1 is made to engage or dis5gage a correspond+ contact spr+4 ,an arrangem5t ( ?is k9d t is 9 common use is %[n 9 ,fig4 #gf4 ,?is ne$s no fur!r explanation ?an to say t ! crank %aft is provid$ on its end ) an insulat+ /ud #a1 aga9/ :i* a swit*+ spr+ #b be>s4 ,?is spr+ normally re/s aga9/ ano!r swit* spr+ #c1 b :5 ! g5]ator crank %aft moves to ! "r ^u ! turn+ ( ! crank1 ! spr+ #b dis5gages spr+ #c & engages spr+ #d1 ?us complet+ ! circuit ( ! g5]ator armature4 ,x is se5 t ?is op]ation accompli%es ! break+ ( "o circuit & ! mak+ ( ano!r1 a function t w be ref]r$ to lat] on 9 ?is "w4 ,illu/ration3 ,fig4 #gf4 ,g5]ator ,cut-9 ,swit* ,pulsat+ ,curr5t4 ,sometimes x is desirable to h a g5]ator capable ( develop+ a pulsat+ curr5t in/ead ( an alt]nat+ curr5t2 t is1 a curr5t :i* w consi/ ( impulses all 9 "o direction r ?an ( impulses alt]nat+ 9 direction4 ,x is obvi\s t ?is may be accompli%$ if ! circuit ( ! g5]ator be brok5 dur+ ea* half revolution s t its circuit is complet$ only :5 curr5t is be+ g5]at$ 9 "o direction4 ,su* an arrangem5t is indicat$ diagrammatically 9 ,fig4 #gg4 ,in/ead ( hav+ "o t]m9al ( ! armature w9d+ br\ght out ?r\gh ! frame ( ! g5]ator z is ord9>ily done1 bo? t]m9als are br\ght out to a commut+ device c>ri$ on ! end ( ! armature %aft4 ,?us1 "o end ( ! loop repres5t+ ! armature w9d+ is %[n connect$ directly to ! armature p9 #a1 aga9/ :i* be>s a spr+ #b1 9 ! usual mann]4 ,! o!r end ( ! armature w9d+ is c>ri$ directly to a disk #c1 m\nt$ on b insulat$ f ! %aft & revolv+ !re)4 ,"o-half ( ! circumf]5tial surface ( ?is disk is ( insulat+ mat]ial #d & a spr+ #e re/s aga9/ ?is disk & be>s alt]nately ^u ! conduct+ portion #c or ! insulat+ portion #d1 accord+ to ! position ( ! armature 9 its revolution4 ,x is obvi\s t :5 ! g5]ator armature is 9 ! position %[n ! circuit ?r\gh x is f ! spr+ #b to ! p9 #a2 !nce to "o t]m9al ( ! armature loop2 !nce ?r\gh ! loop & back to ! disk #c & out by ! spr+ #e4 ,if1 h[ev]1 ! armature 7 turn$ slightly1 ! spr+ #e w\ld re/ on ! insulat+ portion #d & ! circuit w\ld be brok54 ,illu/ration3 ,fig4 #gg4 ,pulsat+-,curr5t ,commutator ,illu/ration3 ,fig4 #gh4 ,g5]ator ,symbols ,x is obvi\s t if ! bru% #e is s dispos$ z to make contact ) ! disk #c only dur+ t portion ( ! revolution :ile positive curr5t is be+ g5]at$1 ! g5]ator w produce positive pulsations ( curr5t1 all ! negative ones be+ cut out4 ,if1 on ! o!r h&1 ! spr+ #e may be made to be> on ! opposite side ( ! disk1 !n x is evid5t t ! positive impulses w\ld all be cut out & ! g5]ator w\ld develop only negative impulses4 ,su* a g5]ator is t]m$ a direct-curr5t g5]ator or a pulsat+-curr5t g5]ator4 ,! symbols = magneto or h& g5]ators usually embody a simplifi$ side view1 %[+ ! crank & ! ge>s on "o side & ! %unt+ or o!r swit*+ device on ! o!r4 ,?us 9 ,fig4 #gh are %[n ?ree su* symbols1 diff]+ f ea* o!r only 9 ! details ( ! swit*+ device4 ,! "o at ! left %[s ! simple %unt1 adapt$ to %ort-circuit ! g5]ator at all times save :5 x is 9 op]ation4 ,! "o 9 ! c5t] %[s ! cut-91 ( :i* ano!r =m is describ$ 9 connection ) ,fig4 #ge2 :ile ! symbol at ! "r ( ,fig4 #gh is ( ! make-&-break device1 discuss$ 9 connection ) ,fig4 #gf4 ,9 su* diagrammatic repres5tations ( g5]ators x is usual to some:at exagg]ate ! size ( ! swit*+ spr+s1 9 ord] to make cle> _! action 9 respect to ! circuit connections 9 :i* ! g5]ator is us$4 ,pol>iz$ ,r+]4 ,! pol>iz$ bell or r+] is1 z has be5 /at$1 ! device :i* is adapt$ to respond to ! curr5ts s5t out by ! magneto g5]ator4 ,9 ord] t ! alt]nately opposite curr5ts may cause ! armature to move alt]nately 9 opposite directions1 ^! bells are pol>iz$1 i4e41 giv5 a def9ite magnetic set1 s to speak2 s ! effect ( ! curr5ts 9 ! coils is n to create magnetism 9 normally neutral iron1 b r to alt] ! magnetism 9 iron already magnetiz$4 ,we/]n ,electric ,r+]4 ,a typical =m ( pol>iz$ bell is %[n 9 ,fig4 #gi1 ?is be+ ! /&>d bell or r+] ( ! ,we/]n ,electric ,company4 ,! two electromagnets are m\nt$ side by side1 z %[n1 by atta*+ _! cores to a yoke piece #a ( s(t iron4 ,?is yoke piece also c>ries ! /&>ds #b ^u :i* ! gongs are m\nt$4 ,! me?od ( m\nt+ is su* t ! /&>ds may be adju/$ slightly s z to br+ ! gongs clos] to or f>!r f1 ! tapp]4 ,! s(t iron yoke piece #a also c>ries two brass po/s #c :i*1 9 turn1 c>ry ano!r yoke #d ( brass4 ,9 ?is yoke #d is pivot$1 by means ( trunnion screws1 ! armature #e1 ?is ext5d+ on ea* side ( ! pivot s t its ends lie opposite ! free poles ( ! electromagnets4 ,f ! c5t] ( ! armature projects ! tapp] rod c>ry+ ! ball or /rik] :i* plays betwe5 ! two gongs4 ,9 ord] t ! armature & cores may be normally pol>iz$1 a p]man5t magnet #f is secur$ to ! c5t] ( ! yoke piece #a4 ,?is b5ds ar\nd back ( ! electromagnets & comes into close proximity to ! armature #e4 ,by ?is means "o end ( ea* ( ! electromagnet cores is giv5 "o pol>ity--say nor?--:ile ! armature is giv5 ! o!r pol>ity--say s\?4 ,! two coils ( ! electromagnet are connect$ toge!r 9 s]ies 9 su* a way t curr5t 9 a giv5 direction w act to produce a nor? pole 9 "o ( ! free poles & a s\? pole 9 ! o!r4 ,if x be assum$ t ! p]man5t magnet ma9ta9s ! armature normally ( s\? pol>ity & t ! curr5t ?r\gh ! coils is ( su* direction z to make ! left-h& core nor? & ! "r-h& core s\?1 !n x is evid5t t ! left-h& end ( ! armature w be attract$ & ! "r-h& end repell$4 ,?is w ?r[ ! tapp] rod to ! "r & s\nd ! "r-h& bell4 ,a rev]sal 9 curr5t w obvi\sly produce ! opposite effect & cause ! tapp] to /rike ! left-h& bell4 ,an important feature 9 pol>iz$ bells is ! adju/m5t betwe5 ! armature & ! pole pieces4 ,?is is secur$ 9 ! ,we/]n ,electric bell by means ( ! nuts #g1 by :i* ! yoke #d is secur$ to ! /&>ds #c4 ,by mov+ ^! nuts up or d[n on ! /&>ds ! armature may be br\ght clos] to or f>!r f ! poles1 & ! device af=ds ready means = clamp+ ! p>ts into any position to :i* !y may h be5 adju/$4 ,illu/ration3 ,fig4 #gi4 ,pol>iz$ ,bell ,kellogg ,r+]4 ,ano!r typical r+] is t ( ! ,kellogg ,swit*bo>d & ,supply ,company1 %[n 9 ,fig4 #hj4 ,?is diff]s f t ( ! ,we/]n ,electric ,company ma9ly 9 ! details by :i* ! armature adju/m5t is obta9$4 ,! armature support+ yoke #a is atta*$ directly to ! cores ( ! magnets1 no support+ side rods be+ employ$4 ,in/ead ( provid+ means :]eby ! armature may be adju/$ t[>d or f ! poles1 ! rev]se practice is employ$1 t is1 ( mak+ ! poles !mselves ext5sible4 ,?is is done by means ( ! iron screws #b :i* =m ext5sions ( ! cores & :i* may be made to approa* or rec$e f ! armature by turn+ !m 9 su* direction z to screw !m 9 or out ( ! core ends4 ,illu/ration3 ,fig4 #hj4 ,pol>iz$ ,bell ,illu/ration3 ,fig4 #ha4 ,bias$ ,bell ,bias$ ,bell4 ,! pulsat+-curr5t g5]ator has already be5 discuss$ & its pr9ciple ( op]ation po9t$ out 9 connection ) ,fig4 #gg4 ,! companion piece to ?is g5]ator is ! s-call$ bias$ r+]4 ,?is is really no?+ b a common alt]nat+-curr5t pol>iz$ r+] ) a light spr+ s arrang$ z to hold ! armature normally 9 "o ( its extreme positions s t ! tapp] w re/ aga9/ "o ( ! gongs4 ,su* a r+] is %[n 9 ,fig4 #ha & ne$s no fur!r explanation4 ,x is obvi\s t if a curr5t fl[s 9 ! coils ( su* a r+] 9 a direction t5d+ to move ! tapp] t[>d ! left1 !n no s\nd w result because ! tapp] is already mov$ z f> z x c be 9 t direction4 ,if1 h[ev]1 curr5ts 9 ! opposite direction are caus$ to fl[ ?r\gh ! w9d+s1 !n ! electromagnetic attraction on ! armature w ov]come ! pull ( ! spr+ & ! tapp] w move ov] & /rike ! "r-h& gong4 ,a cessation ( ! curr5t w all[ ! spr+ to ex]t itself & ?r[ ! tapp] back into engagem5t ) ! left-h& gong4 ,a s]ies ( su* pulsations 9 ! prop] direction w1 !re=e1 cause ! tapp] to play betwe5 ! two gongs & r+ ! bell z usual4 ,a s]ies ( curr5ts 9 a wrong direction w1 h[ev]1 produce no effect4 ,conv5tional ,symbols4 ,9 ,fig4 #hb are %[n six conv5tional symbols ( pol>iz$ bells4 ,! ?ree at ! top1 consi/+ m]ely ( two circles repres5t+ ! magnets 9 plan view1 are p]haps to be pref]r$ z !y are well /&>diz$1 easy to draw1 & r sugge/ive4 ,! ?ree at ! bottom1 %[+ ! r+] z a :ole 9 side elevation1 are some:at m specific1 b are objectionable 9 t !y take m space & are n s easily drawn4 ,illu/ration3 ,fig4 #hb4 ,r+] ,symbols ,symbols ,a or ,b may be us$ = designat+ any ord9>y pol>iz$ r+]4 ,symbols ,c & ,d are int]*angeably us$ to indicate a bias$ r+]4 ,if ! bell is design$ to op]ate only on positive impulses1 !n ! plus sign is plac$ opposite ! symbol1 :ile a m9us sign s plac$ indicates t ! bell is to be op]at$ only by negative impulses4 ,"s specific types ( r+]s are design$ to op]ate only on a giv5 frequ5cy ( curr5t4 ,t is1 !y are s design$ z to be responsive to curr5ts hav+ a frequ5cy ( sixty cycles p] second1 = in/ance1 & to be unresponsive to curr5ts ( any o!r frequ5cy4 ,ei!r symbols ,e or ,f may be us$ to designate su* r+]s1 & if x is desir$ to indicate ! p>ticul> frequ5cy ( ! r+] ?is is done by add+ ! prop] num]al foll[$ by a %ort rev]s$ curve sign indicat+ frequ5cy4 ,?us #ej w\ld indicate a frequ5cy ( fifty cycles p] second4 ,,*apt] ,,ix ,,! ,,hook ,,swit* ,purpose4 ,9 complete telephone in/rum5ts1 compris+ bo? talk+ & signal+ app>atus1 x is obvi\sly desirable t ! two sets ( app>atus1 = talk+ & signal+ respectively1 %all n be connect$ ) ! l9e at ! same "t4 ,a c]ta9 swit*+ device is1 !re=e1 necess>y 9 ord] t ! signal+ app>atus alone may be left op]atively connect$ ) ! l9e :ile ! in/rum5t is n be+ us$ 9 ! transmission ( spee*1 & 9 ord] t ! signal+ app>atus may be cut out :5 ! talk+ app>atus is br\ght into play4 ,9 in/rum5ts employ+ batt]ies = ! supply ( transmitt] curr5t1 ano!r swit*+ function is ! clos+ ( ! batt]y circuit ?r\gh ! transmitt] & ! induction coil :5 ! in/rum5t is 9 use = talk+1 s9ce to leave ! batt]y circuit clos$ all ! "t w\ld be an obvi\s wa/e ( batt]y en]gy4 ,9 ! e>ly =ms ( telephones ^! swit*+ op]ations 7 p]=m$ by a manually op]at$ swit*1 ! position ( :i* ! us] 0 oblig$ to *ange be=e & aft] ea* use ( ! telephone4 ,! objection to ?is 0 n s mu* 9 ! manual labor impos$ on ! us] z 9 ! tax on 8 memory4 ,x 0 f\nd to be practically a necessity to make ?is swit*+ function automatic1 pr9cipally because ( ! liability ( ! us] to =get to move ! swit* to ! prop] position aft] us+ ! telephone1 result+ n only 9 ! rapid wa/e ( ! batt]y elem5ts b also 9 ! inop]ative condition ( ! signal-receiv+ bell4 ,! solution ( ?is problem1 a vex+ "o at fir/1 0 f\nd 9 ! s-call$ automatic hook swit* or swit* hook1 by :i* ! circuits ( ! in/rum5t 7 made automatically to assume _! prop] conditions by ! m]e act1 on ! "p ( ! us]1 ( remov+ ! receiv] f1 or plac+ x ^u1 a conv5i5tly arrang$ hook or =k project+ f ! side ( ! telephone cas+4 ,automatic ,op]ation4 ,x may be tak5 z a fundam5tal pr9ciple 9 ! design ( any piece ( telephone app>atus t is to be g5]ally us$ by ! public1 t ! necess>y acts :i* a p]son mu/ p]=m 9 ord] to use ! device mu/1 z f> z possible1 foll[ z a natural result f "s o!r act :i* x is p]fectly obvi\s to ! us] t he mu/ p]=m4 ,s 9 ! case ( ! swit* hook1 ! us] ( a telephone kn[s t he mu/ take ! receiv] f its normal support & hold x to 8 e>2 & likewise1 :5 he is ?r\gh ) x1 t he mu/ dispose ( x by hang+ x ^u a support obvi\sly provid$ = t purpose4 ,9 its usual =m a =k$ hook is provid$ = support+ ! receiv] 9 a conv5i5t place4 ,?is hook is at ! free end ( a pivot$ lev]1 :i* is normally press$ upw>d by a spr+ :5 ! receiv] is n support$ on x4 ,:51 h[ev]1 ! receiv] is support$ on x1 ! lev] is depress$ by its weight4 ,! motion ( ! lev] is me*anically imp>t$ to ! memb]s ( ! swit* prop]1 ! contacts ( :i* are usually enclos$ s z to be out ( rea* ( ! us]4 ,?is swit* is s arrang$ t :5 ! hook is depress$ ! circuits are held 9 su* condition t ! talk+ app>atus w be cut out1 ! batt]y circuit op5$1 & ! signal+ app>atus connect$ ) ! l9e4 ,on ! o!r h&1 :5 ! hook is 9 its rais$ position1 ! signal+ app>atus is cut out1 ! talk+ app>atus swit*$ into prop] work+ relation ) ! l9e1 & ! batt]y circuit clos$ ?r\gh ! transmitt]4 ,9 ! s-call$ common-batt]y telephones1 :]e no magneto g5]ator or local batt]y is includ$ 9 ! equipm5t at ! subscrib]'s /ation1 ! m]e rais+ ( ! hook s]ves ano!r important function4 ,x acts1 n only to complete ! circuit ?r\gh ! sub/ation talk+ app>atus1 b1 by virtue ( ! closure ( ! l9e circuit1 p]mits a curr5t to fl[ ov] ! l9e f ! c5tral-(fice batt]y :i* en]gizes a signal associat$ ) ! l9e at ! c5tral (fice4 ,?is use ( ! hook swit* 9 ! case ( ! common-batt]y telephone is a good illu/ration ( ! pr9ciple j laid d[n z to mak+ all ! functions :i* ! subscrib] has to p]=m dep5d1 z f> z possible1 on acts :i* 8 common s5se alone tells him he mu/ d4 ,?us1 9 ! common-batt]y telephone ! subscrib] has only to place ! receiv] at 8 e> & ask = :at he wants4 ,?is op]ation automatically displays a signal at ! c5tral (fice & he does no?+ fur!r until ! op]ator inquires = ! numb] t he wants4 ,he has !n no?+ to d b wait until ! call$-= p>ty responds1 & aft] ! conv]sation 8 own p]sonal conv5i5ce dem&s t he %all dispose ( ! receiv] 9 "s way1 s he hangs x up on ! mo/ conv5i5t object1 ! hook swit*1 & !reby n only places ! app>atus at 8 telephone 9 prop] condition to receive ano!r call1 b also conveys to ! c5tral (fice ! signal = disconnection4 ,likewise 9 ! case ( telephones op]at+ 9 connection ) automatic ex*anges1 ! hook swit* p]=ms a numb] ( functions automatically1 ( :i* ! subscrib] has no conception2 & :ile1 9 automatic telephones1 !re are m acts requir$ ( ! us] ?an 9 ! manual1 yet a /udy ( ^! acts w %[ t !y all foll[ 9 a way naturally sugge/$ to ! us]1 s t he ne$ h b ! b>e/ fundam5tal k 9 ord] to prop]ly make use ( ! in/rum5t4 ,9 all cases1 9 prop]ly design$ app>atus1 ! arrangem5t is su* t ! failure ( ! subscrib] to d a c]ta9 requir$ act w d no damage to ! app>atus or to ! sy/em1 &1 !re=e1 w inconv5i5ce only himself4 ,design4 ,! hook swit* is 9 reality a two-position swit*1 & :ile at pres5t x is a simple affair1 yet its developm5t to its high /ate ( p]fection has be5 sl[1 & its imp]fections 9 ! pa/ h be5 ! cause ( mu* annoyance4 ,sev]al important po9ts mu/ be borne 9 m9d 9 ! design ( ! hook swit*4 ,! spr+ provid$ to lift ! hook mu/ be suffici5tly /rong to accompli% ?is purpose & yet mu/ n be /rong en\gh to prev5t ! weight ( ! receiv] f mov+ ! swit* to its o!r position4 ,! movem5t ( ?is spr+ mu/ be some:at limit$ 9 ord] t x w n break :5 us$ a great _m times1 & also x mu/ be ( su* mat]ial & %ape t x w n lose its ela/icity ) use4 ,! %ape & mat]ial ( ! re/or+ spr+ are1 ( c\rse1 det]m9$ to a consid]able ext5t by ! l5g? ( ! lev] arm :i* acts on ! spr+1 & on ! space :i* is available = ! spr+4 ,! v>i\s contacts by :i* ! circuit *anges are br\ght ab\t ^u ! movem5t ( ! hook-swit* lev] usually take ! =m ( spr+s ( ,g]man silv] or phosphor-bronze1 h>d roll$ s z to h ! necess>y resili5cy1 & ^! are usually tipp$ ) plat9um at ! po9ts ( contact s z to assure ! necess>y "* ( surface at ! po9ts :]e ! electric circuits are made or brok54 ,a slight slid+ movem5t betwe5 ea* pair ( contacts z !y are br\ght toge!r is consid]$ desirable1 9 t x t5ds to rub (f any dirt t may h accumulat$1 yet ?is slid+ movem5t %\ld n be great1 z ! surfaces w !n cut ea* o!r &1 !re=e1 r$uce ! life ( ! swit*4 ,contact ,mat]ial4 ,on acc\nt ( ! high co/ ( plat9um1 mu* exp]im5tal "w has be5 done to f9d a sub/itute metal suitable = ! contact po9ts 9 hook swit*es & simil> uses 9 ! manufacture ( telephone app>atus4 ,plat9um is unque/ionably ! be/ kn[n mat]ial1 on acc\nt ( its non-corrosive & heat-resi/+ qualities4 ,h>d silv] is ! next be/ & is f\nd 9 "s fir/-class app>atus4 ,! v>i\s *eap alloys int5d$ z sub/itutes = plat9um or silv] 9 contact po9ts may be dismiss$ z wor?less1 s f> z ! writ]s' some:at ext5sive inve/igations h %[n4 ,9 ! m rec5t =ms ( hook swit*es1 ! swit* lev] itself does n =m a "p ( ! electrical circuit1 b s]ves m]ely z ! means by :i* ! spr+s t are conc]n$ 9 ! swit*+ functions are mov$ into _! alt]nate coop]ative relations4 ,"o advantage 9 ?us insulat+ ! swit* lev] f ! curr5t-c>ry+ portions ( ! app>atus & circuits is t1 s9ce x necess>ily projects f ! box or cab9et1 x is ?us liable to come 9 contact ) ! p]son ( ! us]4 ,by insulat+ x1 all liability ( ! us] receiv+ %ocks by contact ) x is elim9at$4 ,wall ,telephone ,hooks4 ,kellogg4 ,a typical =m ( hook swit*1 z employ$ 9 ! ord9>y wall telephone sets1 is %[n 9 ,fig4 #hc1 ?is be+ ! /&>d hook ( ! ,kellogg ,swit*bo>d & ,supply ,company4 ,9 ?is ! lev] #a is pivot$ at ! po9t #c 9 a bracket #e t =ms ! base ( all ! work+ p>ts & ! means ( secur+ ! entire hook swit* to ! box or framework ( ! telephone4 ,?is swit* lev] is normally press$ upw>d by a spr+ #b1 m\nt$ on ! bracket #e1 & engag+ ! "u side ( ! hook lev] at ! po9t #d4 ,atta*$ to ! lev] arm #a is an insulat$ p9 #f4 ,! contact spr+s by :i* ! v>i\s electrical circuits are made & brok5 are %[n at #g1 #h1 #i1 #aj1 & #aa1 ^! be+ m\nt$ 9 "o gr\p ) insulat$ bu%+s betwe5 !m2 ! entire gr\p is secur$ by ma*9e screws to a lug project+ horizontally f ! bracket #e4 ,! c5t] spr+ #i is provid$ ) a =k$ ext5sion :i* embraces ! p9 #f on ! hook lev]4 ,x is obvi\s t an up-&-d[n motion ( ! hook lev] w move ! long spr+ #i 9 su* mann] z to cause electrical contact ei!r betwe5 x & ! two upp] spr+s #g & #h1 or betwe5 x & ! two l[] spr+s #aj & #aa4 ,! hook is %[n 9 its rais$ position1 :i* is ! position requir$ = talk+4 ,:5 l[]$ ! two spr+s #g & #h are dis5gag$ f ! long spr+ #i & f ea* o!r1 & ! ?ree spr+s #i1 #aj1 & #aa are br\ght into electrical engagem5t1 ?us e/abli%+ ! necess>y signal+ conditions4 ,illu/ration3 ,fig4 #hc4 ,long ,lev] ,hook ,swit* ,! "r-h& ends ( ! contact spr+s are %[n project+ beyond ! insulat+ supports4 ,?is is = ! purpose ( facilitat+ mak+ electrical jo9ts betwe5 ^! spr+s & ! v>i\s wires :i* lead f !m4 ,^! project+ ends are commonly ref]r$ to z e>s1 & are usually provid$ ) holes or not*es into :i* ! connect+ wire is fa/5$ by sold]+4 ,we/]n ,electric4 ,fig4 #hd %[s ! type ( hook swit* q ext5sively employ$ by ! ,we/]n ,electric ,company 9 wall telephone sets :]e ! space is some:at limit$ & a compact arrangem5t is desir$4 ,x w readily be se5 t ! pr9ciple on :i* ?is hook swit* op]ates is simil> to t employ$ 9 ,fig4 #hc1 al?\gh ! me*anical arrangem5t ( ! p>ts diff]s radically4 ,! hook lev] #a is pivot$ at #c on a bracket #b1 :i* s]ves to support all ! o!r p>ts ( ! swit*4 ,! contact spr+s are %[n at #d1 #e1 & #f1 & ?is latt] spr+ #f is s design$ z to make x s]ve z an actuat+ spr+ = ! hook4 ,?is is accompli%$ by hav+ ! curv$ end ( ?is spr+ press aga9/ ! lug #g ( ! hook & ?us t5d to raise ! hook :5 x is reliev$ ( ! weight ( ! receiv]4 ,! two %ort] spr+s #h & #i h no electrical function b m]ely s]ve z supports aga9/ :i* ! spr+s #d & #e may re/1 :5 ! receiv] is on ! hook1 ^! spr+s #d & #e be+ giv5 a light normal t5sion t[>d ! /op spr+s #h & #i4 ,x is obvi\s t 9 ! p>ticul> arrangem5t ( ! spr+s 9 ?is swit* no contacts are clos$ :5 ! receiv] is on ! hook4 ,illu/ration3 ,fig4 #hd4 ,%ort ,lev] ,hook ,swit* ,conc]n+ ?is latt] feature1 x w be not$ t ! p>ticul> =m ( ,kellogg hook swit*1 %[n 9 ,fig4 #hc1 makes two contacts & breaks two :5 x is rais$4 ,simil>ly ! ,we/]n ,electric ,company's makes two contacts b does n break any :5 rais$4 ,f su* consid]ations x is cu/om>y to speak ( a hook su* z t %[n 9 ,fig4 #hc z hav+ two make & two break contacts1 & su* a hook z t %[n 9 ,fig4 #hd z hav+ two make contacts4 ,x w be se5 f ei!r ( ^! swit*es t ! modification ( ! spr+ arrangem5t1 s z to make !m include a v>y+ numb] ( make-&-break contacts1 is a simple matt]1 & swit*es ( almo/ any type are readily modifi$ 9 ?is respect4 ,illu/ration3 ,fig4 #he4 ,removable ,lev] ,hook ,swit* ,dean4 ,9 ,fig4 #he is %[n a decid$ly unique hook swit* = wall telephone sets :i* =ms ! /&>d equipm5t ( ! ,dean ,electric ,company4 ,! hook lev] #a is pivot$ at #b1 an auxili>y lev] #c also be+ pivot$ at ! same po9t4 ,! auxili>y lev] #c c>ries at its re> end a slott$ lug #d1 :i* engages ! long contact spr+ #e1 & s]ves to move x up & d[n s z to engage & dis5gage ! spr+ #f1 ^! two spr+s be+ m\nt$ on a base lug ext5d+ f ! base plate #g1 ^u :i* ! entire hook-swit* me*anism is m\nt$4 ,! curv$ spr+ #h1 also m\nt$ on ?is same base1 engages ! auxili>y lev] #c at ! po9t #i & normally s]ves to press ?is up s z to ma9ta9 ! contact spr+s #e 9 engagem5t ) contact spr+ #f4 ,! swit* spr+s are mov$ entirely by ! auxili>y lev] #c1 b 9 ord] t ?is lev] #c may be mov$ z requir$ by ! hook lev] #a1 ?is lev] is provid$ ) a not*$ lug #aj on its l[] side1 :i* not* is engag$ by a =w>dly project+ lug #aa t is integral ) ! auxili>y lev] #c4 ,! swit* lev] may be bodily remov$ f ! rema9+ p>ts ( ! hook swit* by depress+ ! lug #aa ) ! f+]1 s t x dis5gages ! not* 9 lug #aj1 & !n draw+ ! hook lev] out ( engagem5t ) ! pivot /ud #b1 z %[n 9 ! l[] portion ( ! figure4 ,x w be not$ t ! pivotal end ( ! hook lev] is made ) a slot in/ead ( a hole z is ! cu/om>y practice4 ,! advantage ( be+ able to remove ! hook swit* bodily f ! o!r portions arises ma9ly 9 connection ) ! %ipm5t or transportation ( in/rum5ts4 ,! project+ hooks cause ! in/rum5ts to take up m room & ?us make l>g] pack+ boxes necess>y ?an w\ld o!rwise be us$4 ,moreov]1 9 h&l+ ! telephones 9 /ore h\ses or transport+ !m to ! places :]e !y are to be us$1 ! project+ hook swit* is p>ticul>ly liable to become damag$4 ,x is = conv5i5ce "u su* conditions t ! ,dean hook swit* is made s t ! swit* lev] may be remov$ bodily & plac$1 = in/ance1 inside ! telephone box = transportation4 ,desk-,/& ,hooks4 ,! problem ( hook-swit* design = portable desk telephones1 :ile pres5t+ ! same g5]al *>act]i/ics1 diff]s 9 ! details ( con/ruction on acc\nt ( ! necess>ily re/rict$ space available = ! swit* contacts 9 ! desk telephone4 ,illu/ration3 ,,we/ ,,(fice ,,( ,,home ,,telephone ,,company1 ,,san ,,francisco ,s]v+ ! ,g5]al ,we/]n ,bus9ess & ,resid5ce ,di/ricts4 ,we/]n ,electric4 ,9 ,fig4 #hf is %[n an excell5t example ( hook-swit* design z appli$ to ! requirem5ts ( ! ord9>y portable desk set4 ,?is figure is a cross-sectional view ( ! base & /&>d ( a famili> type ( desk telephone4 ,! base itself is ( /amp$ metal con/ruction1 z indicat$1 & ! /&>d :i* supports ! transmitt] & ! swit* hook = ! receiv] is compos$ ( a black enamel$ or nickel-plat$ brass tube #a1 atta*$ to ! base by a screw-?read$ jo9t1 z %[n4 ,! swit* lev] #b is pivot$ at #c 9 a brass plug #d1 clos+ ! upp] end ( ! tube =m+ ! /&>d4 ,?is brass plug supports also ! transmitt]1 :i* is n %[n 9 ?is figure4 ,atta*$ to ! plug #d by ! screw #e is a heavy /rip #f1 :i* rea*es d[n ?r\gh ! tube to ! base plate ( ! /&>d & is held !re9 by a screw #g4 ,! plug #d1 c>ry+ ) x ! swit*-hook lev] #b & ! brass /rip #f1 may be lift$ bodily out ( ! /&>d #a by tak+ out ! screw #g :i* holds ! /rip #f 9 place1 z is cle>ly indicat$4 ,on ! /rip #f !re is m\nt$ ! gr\p ( swit* spr+s by :i* ! circuit *anges ( ! in/rum5t are br\ght ab\t :5 ! hook is rais$ or l[]$4 ,! spr+ #h is long] ?an ! o!rs1 & projects upw>dly f> en\gh to engage ! lug on ! swit*-hook lev] #b4 ,?is spr+1 :i* is s b5t z to close ! contacts at ! "r :5 n prev5t$ by ! swit* lev]1 also s]ves z an actuat+ spr+ to raise ! lev] #b :5 ! receiv] is remov$ f x4 ,?is spr+1 :5 ! receiv] is remov$ f ! hook1 engages ! two spr+s at ! "r1 z %[n1 or :5 ! receiv] is plac$ on ! hook1 breaks contact ) ! two "r-h& spr+s & makes contact respectively ) ! left-h& spr+ & also ) ! contact #i :i* =ms ! transmitt] t]m9al4 ,illu/ration3 ,fig4 #hf4 ,desk-,/& ,hook ,swit* ,x is se5 f an inspection ( ?is swit* hook t x has two make & two break contacts4 ,! v>i\s contact spr+s are connect$ ) ! sev]al b9d+ po/s %[n1 ^! =m+ ! connectors = ! flexible cord conductors lead+ into ! base & up ?r\gh ! /&>d ( ! desk /&4 ,by means ( ! conductors 9 ?is cord ! circuits are l$ to ! o!r p>ts ( ! in/rum5t1 su* z ! induction coil1 call bell1 & g5]ator1 if !re is "o1 :i*1 9 ! case ( ! ,we/]n ,electric ,company's desk set1 are all m\nt$ sep>ately f ! portable desk /& prop]4 ,?is hook swit* is accessible 9 an easy mann] & yet n subject to ! tamp]+ ( idle or mis*iev\s p]sons4 ,by tak+ out ! screw #g ! entire hook swit* may be lift$ out ( ! tube =m+ ! /&>d1 ! cords lead+ to ! v>i\s b9d+ po/s be+ slid along ?r\gh ! tube4 ,by ?is means ! connections to ! hook swit*1 z well z ! contact ( ! swit* itself1 are readily inspect$ or repair$ by ^? ^: duty x is to p]=m su* op]ations4 ,kellogg4 ,9 ,fig4 #hg is %[n a sectional view ( ! desk-/& hook swit* ( ! ,kellogg ,swit*bo>d & ,supply ,company4 ,9 ?is x w be se5 t in/ead ( plac+ ! swit*-hook spr+s )9 ! /&>d or tube1 z 9 ! case ( ! ,we/]n ,electric ,company1 !y are m\nt$ 9 ! base :]e !y are readily accessible by m]ely tak+ (f ! base plate f ! bottom ( ! /&4 ,! hook lev] op]ates on ! long spr+ ( ! gr\p ( swit* spr+s by means ( a toggle jo9t 9 an obvi\s mann]4 ,?is swit* spr+ itself s]ves by its own /r5g? to raise ! hook lev] :5 releas$ f ! weight ( ! receiv]4 ,illu/ration3 ,fig4 #hg4 ,desk-,/& ,hook ,swit* ,9 ?is swit*1 ! hook lev]1 & 9 fact ! entire expos$ metal portions ( ! in/rum5t1 are insulat$ f all ( ! contact spr+s &1 !re=e1 !re is little liability ( %ocks on ! "p ( ! p]son us+ ! in/rum5t4 ,conv5tional ,symbols4 ,! hook swit* plays a v important "p 9 ! op]ation ( telephone circuits2 = ?is reason readily und]/ood conv5tional symbols1 by :i* !y may be conv5i5tly repres5t$ 9 draw+s ( circuits1 are desirable4 ,9 ,fig4 #hh are %[n sev]al symbols su* z w\ld apply to almo/ any circuit1 reg>dless ( ! actual me*anical details ( ! p>ticul> hook swit* :i* happ5$ to be employ$4 ,?us diagram ,a 9 ,fig4 #hh %[s a hook swit* hav+ a s+le make contact & ?is diagram might be us$ to ref] to ! hook swit* ( ! ,dean ,electric ,company %[n 9 ,fig4 #he1 9 :i* only a s+le contact is made :5 ! receiv] is remov$1 & none is made :5 x is on ! hook4 ,simil>ly1 diagram ,b might be us$ to repres5t ! hook swit* ( ! ,kellogg ,company1 %[n 9 ,fig4 #hc1 ! arrangem5t be+ = two make & two break contacts4 ,likewise diagram ,c might be us$ to repres5t ! hook swit* ( ! ,we/]n ,electric ,company1 %[n 9 ,fig4 #hd1 :i*1 z be=e /at$1 has two make contacts only4 ,diagram ,d %[s ano!r modification 9 :i* contacts made by ! hook swit*1 :5 ! receiv] is remov$1 control two sep>ate circuits4 ,assum+ t ! solid black portion repres5ts insulation1 x is obvi\s t ! contacts are divid$ into two gr\ps1 "o insulat$ f ! o!r4 ,illu/ration3 ,fig4 #hh4 ,hook ,swit* ,symbols ,illu/ration3 ,,compress$ ,,air ,,wagon ,,= ,,pneumatic ,,drill+ ,,& ,,*ipp+ ,,9 ,,manholes ,,*apt] ,x ,,electromagnets ,,& ,,inductive ,,coils ,electromagnet4 ,! physical ?+ :i* we call an electromagnet1 consi/+ ( a coil or helix ( wire1 ! turns ( :i* are insulat$ f ea* o!r1 & )9 :i* is usually includ$ an iron core1 is by f> ! mo/ useful ( all ! s-call$ translat+ devices employ$ 9 telephony4 ,9 p]=m+ ! ord9>y functions ( an electromagnet x translates ! en]gy ( an electrical curr5t into ! en]gy ( me*anical motion4 ,an almo/ equally important function is ! conv]se ( ?is1 t is1 ! translation ( ! en]gy ( me*anical motion into t ( an electrical curr5t4 ,9 addition to ^! prim>y functions :i* und]lie ! art ( telephony1 ! electromagnetic coil or helix s]ves a wide field ( usefulness 9 cases :]e no me*anical motion is involv$4 ,z imp$ance coils1 !y s]ve to ex]t important influ5ces on ! fl[ ( curr5ts 9 circuits1 & z induction coils1 !y s]ve to translate ! en]gy ( a curr5t fl[+ 9 "o circuit into ! en]gy ( a curr5t fl[+ 9 ano!r circuit1 ! translation usually1 b n always1 be+ accompani$ by a *ange 9 voltage4 ,:5 a curr5t fl[s ?r\gh ! convolutions ( an ord9>y helix1 ! helix w exhibit ! prop]ties ( a magnet ev5 ?\gh ! sub/ance =m+ ! core ( ! helix is ( non-magnetic mat]ial1 su* z air1 or wood1 or brass4 ,if1 h[ev]1 a mass ( iron1 su* z a rod or a bundle ( s(t iron wires1 = in/ance1 is sub/itut$ z a core1 ! magnetic prop]ties w be enorm\sly increas$4 ,! reason = ?is is1 t a giv5 magnetiz+ =ce w set up 9 iron a va/ly great] numb] ( l9es ( magnetic =ce ?an 9 air or 9 any o!r non-magnetic mat]ial4 ,magnetiz+ ,=ce4 ,! magnetiz+ =ce ( a giv5 helix is t =ce :i* t5ds to drive magnetic l9es ( =ce ?r\gh ! magnetic circuit int]l9k$ ) ! helix4 ,x is call$ magnetomotive =ce & is analog\s to electromotive =ce1 t is1 ! =ce :i* t5ds to drive an electric curr5t ?r\gh a circuit4 ,! magnetiz+ =ce ( a giv5 helix dep5ds on ! product ( ! curr5t /r5g? & ! numb] ( turns ( wire 9 ! helix4 ,?us1 :5 ! curr5t /r5g? is measur$ 9 amp]es1 ?is magnetiz+ =ce is express$ z amp]e-turns1 be+ ! product ( ! numb] ( amp]es fl[+ by ! numb] ( turns4 ,! magnetiz+ =ce ex]t$ by a giv5 curr5t1 !re=e1 is indep5d5t ( any?+ except ! numb] ( turns1 & ! mat]ial )9 ! core or ! %ape ( ! core has no effect ^u x4 ,magnetic ,flux4 ,! total magnetization result+ f a magnetiz+ =ce is call$ ! magnetic flux1 & is analog\s to curr5t4 ,! int5sity ( a magnetic flux is express$ by ! numb] ( magnetic l9es ( =ce 9 a squ>e c5timet] or squ>e in*4 ,:ile ! magnetomotive =ce or magnetiz+ =ce ( a giv5 helix is indep5d5t ( ! mat]ial ( ! core1 ! flux :i* x sets up is l>gely dep5d5t on ! mat]ial & %ape ( ! core--n only ^u ?is b on ! mat]ial t lies 9 ! return pa? = ! flux outside ( ! core4 ,we may say1 !re=e1 t ! am\nt ( flux set up by a giv5 curr5t 9 a giv5 coil or helix is dep5d5t on ! mat]ial 9 ! magnetic pa? or magnetic circuit1 & on ! %ape & l5g? ( t circuit4 ,if ! magnetic circuit be ( air or brass or wood or any o!r non-magnetic mat]ial1 ! am\nt ( flux set up by a giv5 magnetiz+ =ce w be relatively small1 :ile x w be v mu* great] if ! magnetic circuit be compos$ 9 "p or :olly ( iron or /eel1 :i* are highly magnetic sub/ances4 ,p]meability4 ,! quality ( mat]ial1 :i* p]mits ( a giv5 magnetiz+ =ce sett+ up a great] or less numb] ( l9es ( =ce )9 x1 is call$ its p]meability4 ,m accurately1 ! p]meability is ! ratio exi/+ betwe5 ! am\nt ( magnetization & ! magnetiz+ =ce :i* produces su* magnetization4 ,! p]meability ( a sub/ance is usually repres5t$ by ! ,greek lett] 7pron\nc$ mu74 ,! int5sity ( ! magnetiz+ =ce is commonly symboliz$ by ,h1 & s9ce ! p]meability ( air is always tak5 z unity1 we may express ! int5sity ( magnetiz+ =ce by ! numb] ( l9es ( =ce p] squ>e c5timet] :i* x sets up 9 air4 ,n[1 if ! space on :i* ! giv5 magnetiz+ =ce ,h 7 act+ 7 fill$ ) iron in/ead ( air1 !n1 ow+ to ! great] p]meability ( iron1 !re w\ld be set up a v mu* great] numb] ( l9es ( =ce p] squ>e c5timet]1 & ?is numb] ( l9es ( =ce p] squ>e c5timet] 9 ! iron is ! measure ( ! magnetization produc$ & is commonly express$ by ! lett] ,b4 ,f ?is we h ,b_/,h ,?us1 :5 we say t ! p]meability ( a giv5 specim5 ( wr\ght iron "u giv5 conditions is #b1jjj1 we mean t #b1jjj times z _m l9es ( =ce w\ld be induc$ 9 a unit cross-section ( ?is sample z w\ld be induc$ by ! same magnetiz+ =ce 9 a correspond+ unit cross-section ( air4 ,evid5tly = air ,b ,h1 h5ce becomes unity4 ,! p]meability ( air is always a con/ant4 ,?is means t :e!r ! magnetic d5sity ( ! l9es ( =ce ?r\gh ! air be great or small ! numb] ( l9es w always be proportional to ! magnetiz+ =ce4 ,un=tunately = easy calculations 9 electromagnetic "w1 h[ev]1 ?is is n true ( ! p]meability ( iron4 ,= small magnetic d5sities ! p]meability is v great1 b = l>ge d5sities1 t is1 "u conditions :]e ! numb] ( l9es ( =ce exi/+ 9 ! iron is great1 ! p]meability becomes small]1 & an increase 9 ! magnetiz+ =ce does n produce a correspond+ increase 9 ! total flux ?r\gh ! iron4 ,magnetization ,curves4 ,?is quality ( iron is be/ %[n by ! curves ( ,fig4 #hi1 :i* illu/rate ! degree ( magnetization set up 9 v>i\s k9ds ( iron by diff]5t magnetiz+ =ces4 ,9 ^! curves ! ord9ates repres5t ! total magnetization ,b1 :ile ! abscissas repres5t ! magnetiz+ =ce ,h4 ,x is se5 f an inspection ( ^! curves t z ! magnetiz+ =ce ,h increases1 ! int5sity ( flux also increases1 b at a gradually less5+ rate1 indicat+ a r$uction 9 p]meability at ! high] d5sities4 ,^! curves are also in/ructive z %[+ ! great diff]5ces t exi/ betwe5 ! p]meability ( ! diff]5t k9ds ( iron2 & also z %[+ h[1 :5 ! magnetiz+ =ce becomes v great1 ! iron approa*es :at is call$ saturation1 t is1 a po9t at :i* ! fur!r increase 9 magnetiz+ =ce w result 9 no fur!r magnetization ( ! core4 ,f ! data ( ! curves ( ,fig4 #hi1 :i* are commonly call$ magnetization curves1 x is easy to det]m9e o!r data f :i* s-call$ p]meability curves may be plott$4 ,9 p]meability curves ! total magnetization ( ! giv5 pieces ( iron are plott$ z abscissas1 :ile ! correspond+ p]meabilities are plott$ z ord9ates4 ,illu/ration3 ,fig4 #hi4 ,magnetization ,curve ,direction ( ,l9es ( ,=ce4 ,! l9es ( =ce set up )9 ! core ( a helix always h a c]ta9 direction4 ,?is direction always dep5ds ^u ! direction ( ! fl[ ( curr5t ar\nd ! core4 ,an easy way to rememb] ! direction is to consid] ! helix z grasp$ 9 ! "r h& ) ! f+]s p>tially encircl+ x & ! ?umb po9t+ along its axis4 ,!n1 if ! curr5t ?r\gh ! convolutions ( ! helix be 9 ! direction 9 :i* ! f+]s ( ! h& are po9t$ ar\nd ! helix1 ! magnetic l9es ( =ce w proce$ ?r\gh ! core ( ! helix along ! direction 9 :i* ! ?umb is po9t$4 ,9 ! case ( a simple b> electromagnet1 su* z is %[n 9 ,fig4 #ij1 ! l9es ( =ce em]g+ f "o end ( ! b> mu/ pass back ?r\gh ! air to ! o!r end ( ! b>1 z indicat$ by dott$ l9es & arr[s4 ,! pa? foll[$ by ! magnetic l9es ( =ce is call$ ! magnetic circuit1 &1 !re=e1 ! magnetic circuit ( ! magnet %[n 9 ,fig4 #ij is compos$ p>tly ( iron & p>tly ( air4 ,f :at has be5 said conc]n+ ! relative p]meability ( air & ( iron1 x w be obvi\s t ! pres5ce ( su* a long air pa? 9 ! magnetic circuit w greatly r$uce ! numb] ( l9es ( =ce t a giv5 magnetiz+ =ce c set up4 ,! pres5ce ( an air gap 9 a magnetic circuit has mu* ! same effect on ! total fl[ ( l9es ( =ce z ! pres5ce ( a piece ( bad conductor 9 a circuit compos$ o!rwise ( good conductor1 9 ! case ( ! fl[ ( electric curr5t4 ,reluctance4 ,z ! prop]ty :i* opposes ! fl[ ( electric curr5t 9 an electrical circuit is call$ resi/ance1 s ! prop]ty :i* opposes ! fl[ ( magnetic l9es ( =ce 9 a magnetic circuit is call$ reluctance4 ,9 ! case ( ! electric circuit1 ! resi/ance is ! reciprocal ( ! conductivity2 9 ! case ( ! magnetic circuit1 ! reluctance is ! reciprocal ( ! p]meability4 ,z 9 ! case ( an electrical circuit1 ! am\nt ( fl[ ( curr5t is equal to ! electromotive =ce divid$ by ! resi/ance2 s 9 a magnetic circuit1 ! magnetic flux is equal to ! magnetiz+ =ce or magnetomotive =ce divid$ by ! reluctance4 ,illu/ration3 ,fig4 #ij4 ,b> ,electromagnet ,types ( ,l[-,reluctance ,circuits4 ,z ! pull ( an electromagnet ^u its armature dep5ds on ! total numb] ( l9es ( =ce pass+ f ! core to ! armature--t is1 on ! total flux--& z ! total flux dep5ds = a giv5 magnetiz+ =ce on ! reluctance ( ! magnetic circuit1 x is obvi\s t ! design ( ! electromagnetic circuit is ( great importance 9 influ5c+ ! action ( ! magnet4 ,obvi\sly1 any?+ t w r$uce ! am\nt ( air or o!r non-magnetic mat]ial t is 9 ! magnetic circuit w t5d to r$uce ! reluctance1 &1 !re=e1 to increase ! total magnetization result+ f a giv5 magnetiz+ =ce4 ,horse%oe ,=m4 ,"o ( ! easie/ & mo/ common ways ( r$uc+ reluctance 9 a circuit is to b5d ! ord9>y b> electromagnet into horse%oe =m4 ,9 ord] to make cle> ! direction ( curr5t fl[1 att5tion is call$ to ,fig4 #ia4 ,?is is int5d$ to repres5t a simple b> ( iron ) a w9d+ ( "o direction ?r\gh\t its l5g?4 ,! gap 9 ! middle ( ! b>1 :i* divides ! w9d+ into two p>ts1 is int5d$ m]ely to m>k ! fact t ! w9d+ ne$ n cov] ! :ole l5g? ( ! b> & /ill w be able to magnetize ! b> :5 ! curr5t passes ?r\gh x4 ,9 ,fig4 #ib a simil> b> is %[n ) simil> w9d+ ^u x1 b b5t into ,u-=m1 exactly z if x _h be5 grasp$ 9 ! h& & b5t )\t fur!r *ange4 ,! magnetic pol>ity ( ! two ends ( ! b> rema9 ! same z be=e = ! same direction ( curr5t1 & x is obvi\s t ! portion ( ! magnetic circuit :i* ext5ds ?r\gh air has be5 v greatly %ort5$ by ! b5d+4 ,z a result1 ! magnetic reluctance ( ! circuit has be5 greatly decreas$ & ! /r5g? ( ! magnet correspond+ly increas$4 ,illu/ration3 ,fig4 #ia4 ,b> ,electromagnet ,illu/ration3 ,fig4 #ib4 ,horse%oe ,electromagnet ,illu/ration3 ,fig4 #ic4 ,horse%oe ,electromagnet ,if ! armature ( ! electromagnet %[n 9 ,fig4 #ib is long en\gh to ext5d entirely across ! air gap f ! s\? to ! nor? pole1 !n ! air gap 9 ! magnetic circuit is /ill fur!r %ort5$1 & is n[ repres5t$ only by ! small gap betwe5 ! ends ( ! armature & ! ends ( ! core4 ,su* a magnet1 ) an armature closely approa*+ ! poles1 is call$ a clos$-circuit magnet1 s9ce ! only gap 9 ! iron ( ! magnetic circuit is t across :i* ! magnet pulls 9 attract+ its armature4 ,9 ,fig4 #ic is %[n ! electrical & magnetic c\nt]p>t ( ,fig4 #ib4 ,! fact t ! magnetic circuit is n a s+le iron b> b is made up ( two cores & "o backpiece rigidly secur$ toge!r1 has no be>+ ^u ! pr9ciple1 b only %[s t a modification ( con/ruction is possible4 ,9 ! con/ruction ( ,fig4 #ic ! armature #a is %[n z be+ pull$ directly aga9/ ! two cores #b & #c1 ^! two cores be+ jo9$ by a yoke #d1 :i*1 l ! armature & ! core1 is ( magnetic mat]ial4 ,! pa? ( ! l9es ( =ce is indicat$ by dott$ l9es4 ,?is is a v important =m ( electromagnet & is l>gely us$ 9 telephony4 ,iron-,clad ,=m4 ,ano!r way ( =m+ a clos$-circuit magnet t is widely us$ 9 telephony is to enclose ! helix or w9d+ 9 a %ell ( magnetic mat]ial :i* jo9s ! core at "o end4 ,?is con/ruction results 9 :at is kn[n z ! tubul> or iron-clad electromagnet1 :i* is %[n 9 section & 9 end view 9 ,fig4 #id4 ,9 ?is ! core #a is a /raight b> ( iron & x lies c5trally )9 a cyl9drical %ell #b1 also ( iron4 ,! b> is usually held 9 place )9 ! %ell by a screw1 z %[n4 ,! l9es ( =ce set up 9 ! core by ! curr5t fl[+ ?r\gh ! coil1 pass to ! c5t] ( ! bottom ( ! iron %ell & !nce return ?r\gh ! metal ( ! %ell1 ?r\gh ! air gap betwe5 ! edges ( ! %ell & ! armature1 & !n conc5trate at ! c5t] ( ! armature & pass back to ! end ( ! core4 ,?is is a highly effici5t =m ( clos$-circuit magnet1 s9ce ! magnetic circuit is ( l[ reluctance4 ,illu/ration3 ,fig4 #id4 ,iron-,clad ,electromagnet ,su* =ms ( magnets are frequ5tly us$ :]e x is necess>y to m\nt a l>ge numb] ( !m closely toge!r & :]e x is desir$ t ! curr5t fl[+ 9 "o magnet %all produce no inductive effect 9 ! coils ( ! adjac5t magnets4 ,! reason :y mutual induction betwe5 adjac5t magnets is obviat$ 9 ! case ( ! iron-clad or tubul> magnet is t practically all /ray field is elim9at$1 s9ce ! return pa? = ! magnetic l9es is s completely provid$ = by ! pres5ce ( ! iron %ell4 ,special ,horse%oe ,=m4 ,9 ,fig4 #ie is %[n a type ( relay commonly employ$ 9 telephone circuits4 ,! purpose ( illu/rat+ x 9 ?is *apt] is n to discuss relays1 b r to %[ an adaptation ( an electromagnet :]e9 l[ reluctance ( ! magnetic circuit is secur$ by provid+ a return leg = ! magnetic l9es develop$ 9 ! core1 ?us =m+ 9 effect a horse%oe magnet ) a w9d+ on "o ( its limbs only4 ,to ! end ( ! core #a !re is secur$ an ,l-%ap$ piece ( s(t iron #b4 ,?is ext5ds upw>dly & !n =w>dly ?r\gh\t ! entire l5g? ( ! magnet core4 ,an ,l-%ap$ armature #c re/s on ! front edge ( ! piece #b s t a slight rock+ motion w be p]mitt$ on ! knife-edge be>+ ?us af=d$4 ,x is se5 f ! dott$ l9es t ! magnetic circuit is almo/ a clos$ "o4 ,! only gap is t betwe5 ! l[] end ( ! armature #c & ! front end ( ! core4 ,:5 ! coil is en]giz$1 ?is gap is clos$ by ! attraction ( ! armature4 ,z a result1 ! re>w>dly project+ end ( ! armature #c is rais$ & ?is raises ! spr+ #d & causes x to break ! normally exi/+ contact ) ! spr+ #e & to e/abli% ano!r contact ) ! spr+ #f4 ,?us ! en]gy develop$ )9 ! coil ( ! magnet is made to move c]ta9 p>ts :i* 9 turn op]ate ! swit*+ devices to produce *anges 9 electrical circuits4 ,^! relays & o!r adaptations ( ! electromagnet w be discuss$ m fully lat] on4 ,illu/ration3 ,fig4 #ie4 ,electromagnet ( ,relay ,!re are almo/ numb]less =ms ( electromagnets1 b we h illu/rat$ "h examples ( ! pr9cipal types employ$ 9 telephony1 & ! modifications ( ^! types w be readily und]/ood 9 view ( ! g5]al pr9ciples laid d[n4 ,direction ( ,armature ,motion4 ,x may be said 9 g5]al t ! armature ( an electromagnet always moves or t5ds to move1 :5 ! coil is en]giz$1 9 su* a way z to r$uce ! reluctance ( ! magnetic circuit ?r\gh ! coil4 ,?us1 9 all ( ! =ms ( electromagnets discuss$1 ! armature1 :5 attract$1 moves 9 su* a direction z to %ort5 ! air gap & to introduce ! iron ( ! armature z mu* z possible into ! pa? ( ! magnetic l9es1 ?us r$uc+ ! reluctance4 ,9 ! case ( a sol5oid type ( electromagnet1 or ! coil & plung] type1 :i* is a bett] "n ?an sol5oid1 ! coil1 :5 en]giz$1 acts 9 effect to suck ! iron core or plung] )9 itself s z to include m & m ( ! iron )9 ! mo/ d5sely occupi$ portion ( ! magnetic circuit4 ,illu/ration3 ,fig4 #if4 ,p>allel ,diff]5tial ,electromagnet ,diff]5tial ,electromagnet4 ,frequ5tly 9 telephony1 ! electromagnets are provid$ ) m ?an "o w9d+4 ,"o purpose ( ! d\ble-w\nd electromagnet is to produce ! s-call$ diff]5tial action betwe5 ! two w9d+s1 i4e41 mak+ "o ( ! w9d+s develop magnetization 9 ! opposite direction f t ( ! o!r1 s t ! two w neutralize ea* o!r1 or at lea/ ex]t diff]5t & opposite influ5ces4 ,! pr9ciple ( ! diff]5tial electromagnet may be illu/rat$ 9 connection ) ,fig4 #if4 ,"h two wires #a & #b are %[n wrapp$ 9 ! same direction ab\t an iron core1 ! ends ( ! wire be+ jo9$ toge!r at #c4 ,obvi\sly1 if "o ( ^! w9d+s only is employ$ & a curr5t s5t ?r\gh x1 z by connect+ ! t]m9als ( a batt]y ) ! po9ts #d & #c1 = in/ance1 ! core w be magnetiz$ z 9 an ord9>y magnet4 ,likewise1 ! core w be en]giz$ if a curr5t be s5t f #e to #c4 ,assum+ t ! two w9d+s are ( equal resi/ance & numb] ( turns1 ! effects s produc$1 :5 ei!r ! coil #a or ! coil #b is en]giz$1 w be equal4 ,if ! batt]y be connect$ betwe5 ! t]m9als #d & #e ) ! positive pole1 say1 at #e1 !n ! curr5t w proce$ ?r\gh ! w9d+ #b & t5d to g5]ate magnetism 9 ! core 9 ! direction ( ! arr[4 ,aft] trav]s+ ! w9d+ #b1 h[ev]1 x w !n beg9 to trav]se ! o!r w9d+ #a & w pass ar\nd ! core 9 ! opposite direction ?r\gh\t ! l5g? ( t w9d+4 ,?is w t5d to set up magnetism 9 ! core 9 ! opposite direction to t indicat$ by ! arr[4 ,s9ce ! two curr5ts are equal & also ! numb] ( turns 9 ea* w9d+1 x is obvi\s t ! two magnetiz+ influ5ces w be exactly equal & opposite & no magnetic effect w be produc$4 ,su* a w9d+1 z is %[n 9 ,fig4 #if1 :]e ! two wires are laid on side by side1 is call$ a p>allel diff]5tial w9d+4 ,ano!r way ( w9d+ magnets diff]5tially is to put "o w9d+ on "o end ( ! core & ! o!r w9d+ on ! o!r end ( ! core & connect ^! s z to cause ! curr5ts ?r\gh !m to fl[ ar\nd ! core 9 opposite directions4 ,su* a con/ruction is %[n 9 ,fig4 #ig & is call$ a t&em diff]5tial w9d+4 ,! t&em arrangem5t1 :ile (t5 good en\gh = practical purposes1 _c result 9 ! complete neutralization ( magnetic effect4 ,?is is true because ( ! leakage ( "s ( ! l9es ( =ce f int]m$iate po9ts 9 ! l5g? ( ! core ?r\gh ! air1 result+ 9 "s ( ! l9es pass+ ?r\gh m ( ! turns ( "o coil ?an ( ! o!r4 ,complete neutralization c only be atta9$ by fir/ twi/+ ! two wires toge!r ) a uni=m lay & !n w9d+ !m simultane\sly on ! core4 ,illu/ration3 ,fig4 #ig4 ,t&em ,diff]5tial ,electromagnet ,me*anical ,details4 ,we w n[ consid] ! actual me*anical con/ruction ( ! electromagnet4 ,?is is a v important feature ( telephone "w1 because1 n only mu/ ! prop] electrical & magnetic effects be produc$1 b also ! :ole /ructure ( ! magnet mu/ be su* t x w n easily get out ( ord] & n be affect$ by moi/ure1 heat1 c>eless h&l+1 or o!r adv]se conditions4 ,! mo/ usual =m ( magnet con/ruction employ$ 9 telephony is %[n 9 ,fig4 #ih4 ,on ! core1 :i* is ( s(t ,norway iron1 usually cyl9drical 9 =m1 are =c$ two wa%]s ( ei!r fib] or h>d rubb]4 ,fib] is ord9>ily to be pref]r$ because x is t\gh] & less liable to breakage4 ,ar\nd ! core1 betwe5 ! two heads1 are !n wrapp$ sev]al lay]s ( pap] or specially prep>$ clo? 9 ord] t ! wire =m+ ! w9d+ may be ?or\ghly insulat$ f ! core4 ,"o end ( ! wire is !n pass$ ?r\gh a hole 9 "o ( ! spool heads or wa%]s1 ne> ! core1 & ! wire is !n w\nd on 9 lay]s4 ,sometimes a ?ickness ( pap] is plac$ ar\nd ea* lay] ( wire 9 ord] to fur!r gu>d aga9/ ! break+ d[n ( ! insulation betwe5 lay]s4 ,:5 ! la/ lay] is w\nd on1 ! end ( ! wire is pass$ out ?r\gh a hole 9 ! head1 ?us leav+ bo? ends project+4 ,illu/ration3 ,fig4 #ih ,con/ruction ( ,electromagnet ,magnet ,wire4 ,! wire us$ 9 w9d+ magnets is1 ( c\rse1 an important "p ( ! electromagnet4 ,x is always necess>y t ! adjac5t turns ( ! wire be insulat$ f ea* o!r s t ! curr5t %all be =c$ to pass ar\nd ! core ?r\gh all ! l5g? ( wire 9 ea* turn r ?an all[+ x to take ! %ort] & easi] pa? f "o turn to ! next1 z w\ld be ! case if ! turns 7 n insulat$4 ,= ?is purpose ! wire is usually cov]$ ) a coat+ ( "s insulat+ mat]ial4 ,!re are1 h[ev]1 me?ods ( w9d+ magnet coils ) b>e wire & tak+ c>e ( ! insulation betwe5 ! turns 9 ano!r way1 z w be po9t$ out4 ,insulat$ wire = ! purpose ( w9d+ magnet coils is t]m$ magnet wire4 ,copp] is ! mat]ial almo/ univ]sally employ$ = ! conductor4 ,its high conductivity1 great ductility1 & l[ co/ are ! factors :i* make x sup]ior to all o!r metals4 ,h[ev]1 9 special cases1 :]e exce$+ly high conductivity is requir$ ) a limit$ w9d+ space1 silv] wire is sometimes employ$1 & on ! o!r h&1 :]e v high resi/ance is desir$ )9 a limit$ w9d+ space1 ei!r iron or ,g]man silv] or "s o!r high-resi/ance alloy is us$4 ,wire ,gauges4 ,wire = electrical purposes is drawn to a numb] ( diff]5t /&>d gauges4 ,ea* ( ! s-call$ wire gauges consi/s ( a s]ies ( grad$ sizes ( wire1 rang+ f approximately "o-half an in* 9 diamet] d[n to ab\t ! f95ess ( a lady's hair4 ,9 c]ta9 bran*es ( telephone "w1 su* z l9e con/ruction1 ! exi/5ce ( ! sev]al wire gauges or /&>ds is v likely to lead to confusion4 ,=tunately1 h[ev]1 s f> z magnet wire is conc]n$1 ! s-call$ ,br[n & ,%>pe1 or ,am]ican1 wire gauge is almo/ univ]sally employ$ 9 ?is c\ntry4 ,! abbreviations = ?is gauge are ,b4,s4 or ,a4,w4,g4 ,,table ,,iii ,copp] ,wire ,table ,giv+ weights1 l5g?s1 & resi/ances ( wire #fh ,f41 ( ,mat?iess5's ,/&>d ,conductivity4 ---------------------------------------- ---------------------------------------- ------------- ,,resi/ance ,,l5g? ,,weight ,a4,w4,g4 ,,diamet] ,,area ---------------------------------------- -------------------------- ,b4,s4 ,,mils ,,circul> ,,ohms ,,p] ,,ohms ,,p] ,,feet ,,p] ,,feet ,,p] ,,p\nds ,,p] ,,p\nds ,,p] ,,mils ,,p\nd ,,foot ,,p\nd ,,ohm ,,foot ,,ohm ---------------------------------------- ---------------------------------------- ---------- #jjjj #dfj4 #baa1fjj4 #j4jjjjgfci #j4jjjjdhi #a4efa #bj1ddj4 #j4fdje #ac1jij4 #jjj #dji4f #afg1hjj4 #j4jjjabae #j4jjjjfag #a4ifi #af1baj4 #j4ejhj #h1bcb4 #jj #cfd4h #acc1ajj4 #j4jjjaica #j4jjjjggh #b4dhb #ab1hej4 #j4djbh #e1agg4 #j #cbd4i #aje1ejj4 #j4jjjcjga #j4jjjjiha #c4acj #aj1aij4 #j4caie #c1bef4 ---------------------------------------- ---------------------------------------- ---------- #a #bhi4c #hc1fij4 #j4jjjdhhc #j4jjjabcg #c4idg #h1jhc4 #j4becc #b1jdh4 #b #beg4f #ff1cgj4 #j4jjjggfe #j4jjjaefj #d4igg #f1daj4 #j4bjji #a1bhh4 #c #bbi4d #eb1fcj4 #j4jjabce #j4jjjaifg #f4bgf #e1jhd4 #j4aeic #haj4j #d #bjd4c #da1gdj4 #j4jjaifc #j4jjjbdhj #g4iad #d1jca4 #j4abfd #eji4d #e #aha4i #cc1ajj4 #j4jjcabb #j4jjjcabh #i4ihj #c1aig4 #j4ajjb #cbj4d #f #afb4j #bf1bej4 #j4jjdifc #j4jjjcidd #ab4eh #b1ece4 #j4jgidf #bja4e #g #add4c #bj1hbj4 #j4jjghib #j4jjjdigc #ae4hg #b1jaa4 #j4jfcjb #abf4g #h #abh4e #af1eaj4 #j4jabee #j4jjjfbga #bj4ja #a1eie4 #j4jdiih #gi4fi #i #aad4d #ac1jij4 #j4jaiie #j4jjjgijh #be4bc #a1bfe4 #j4jcifc #ej4ab #aj #aja4i #aj1chj4 #j4jcagc #j4jjjibgc #ca4hb #a1jjc4 #j4jcadc #ca4eb ---------------------------------------- ---------------------------------------- ---------- #aa #ij4gd #h1bcd4 #j4jejde #j4jjabeg #dj4ab #gie4c #j4jbdic #ai4hb #ab #hj4ha #f1ecj4 #j4jhjbb #j4jjaehf #ej4ei #fcj4g #j4jaigg #ab4dg #ac #ga4if #e1agh4 #j4abgf #j4jjaiii #fc4gi #ejj4a #j4jaefh #g4hdj #ad #fd4jh #d1ajg4 #j4bjbh #j4jjbeba #hj4dd #cif4f #j4jabdc #d4ica #ae #eg4jg #c1beg4 #j4cbbe #j4jjcagi #aja4d #cad4e #j4jjiheh #c4aja #af #ej4hb #b1ehc4 #j4eabh #j4jjdjji #abg4i #bdi4d #j4jjghah #a4iej #ag #de4bf #b1jdh4 #j4haec #j4jjejee #afa4c #aig4h #j4jjfbjj #a4bbf #ah #dj4cj #a1fbd4 #a4bif #j4jjfcgd #bjc4d #aef4i #j4jjdiag #j4ggac #ai #ce4hi #a1bhh4 #b4jfa #j4jjhjch #bef4e #abd4d #j4jjchii #j4dhea #bj #ca4if #a1jbb4 #c4bgh #j4jajad #cbc4d #ih4ff #j4jjcjib #j4cjea ---------------------------------------- ---------------------------------------- ---------- #ba #bh4df #haj4a #e4bab #j4jabgh #djg4h #gh4bd #j4jjbdeb #j4aiai #bb #be4ce #fdb4d #h4bhg #j4jafab #ead4b #fb4je #j4jjaide #j4abjg #bc #bb4eg #eji4e #ac4ah #j4jbjcb #fdh4d #di4ba #j4jjaedb #j4jgehi #bd #bj4aj #djd4j #bj4ie #j4jbefc #hag4f #ci4jb #j4jjabbc #j4jdggc #be #ag4ij #cbj4d #cc4cb #j4jcbca #a1jca4 #cj4ie #j4jjjifii #j4jcjjb #bf #ae4id #bed4a #eb4ig #j4jdjge #a1cjj4 #bd4ed #j4jjjgfib #j4aahg #bg #ad4b #bja4e #hd4bc #j4jeach #a1fci4 #ai4df #j4jjjfajj #j4jahhh #bh #ab4fd #aei4h #acc4i #j4jfdgi #b1jfg4 #ae4dc #j4jjjdhcg #j4jjgdff #bi #aa4bf #abf4g #bac4j #j4jhagj #b1fjg4 #ab4bd #j4jjjchcf #j4jjdfif #cj #aj4jc #ajj4e #cch4f #j4ajcj #c1bhg4 #i4gjg #j4jjjcjdb #j4jjbiec ---------------------------------------- ---------------------------------------- ---------- #ca #h4ibh #gi4gj #ech4d #j4abii #d1ade4 #g4fih #j4jjjbdac #j4jjaheg #cb #g4iej #fc4ba #hef4b #j4afch #e1bbg4 #f4aje #j4jjjaiac #j4jjaafh #cc #g4jhj #ej4ac #a1cfa4 #j4bjff #f1eia4 #d4hda #j4jjjaeag #j4jjjgcdf #cd #f4cje #ci4ge #b1afe4 #j4bfje #h1caa4 #c4hci #j4jjjabjc #j4jjjdfbj #ce #e4fae #ca4eb #c1dda4 #j4cbhd #aj1dhj4 #c4jde #j4jjjjiedc #j4jjjbije #cf #e4j #be4j #e1dgc4 #j4dadb #ac1baj4 #b4dad #j4jjjjgefh #j4jjjahbg #cg #d4dec #ai4hc #h1gjb4 #j4ebbb #af1ffj4 #a4iae #j4jjjjfjja #j4jjjaadi #ch #c4ife #ae4gb #ac1hgj4 #j4fehe #ba1jaj4 #a4eai #j4jjjjdgei #j4jjjjgbaj #ci #c4eca #ab4dg #bb1jjj4 #j4hcjd #bf1ejj4 #a4bjd #j4jjjjcggd #j4jjjjdede #dj #c4ade #i4hhh #cd1ihj4 #a4jdg #cc1daj4 #j4ieej #j4jjjjbiic #j4jjjjbheh ---------------------------------------- ---------------------------------------- ---------- ,illu/ration3 ,,s\? ,,(fice ,,( ,,home ,,telephone ,,company1 ,,san ,,francisco ,9 ! ,br[n & ,%>pe gauge ! sizes1 beg9n+ ) ! l>ge/1 are numb]$ #jjjj1 #jjj1 #jj1 #j1 #a1 #b1 & s on up to #dj4 ,sizes l>g] ?an ab\t ,no4 #af ,b4,s4 gauge are seldom us$ z magnet wire 9 telephony1 b = ! purpose ( mak+ ! li/ complete1 ,table ,,iii is giv51 includ+ all ( ! sizes ( ! ,b4,s4 gauge4 ,9 ,table ,,iii !re is giv5 = ea* gauge numb] ! diamet] ( ! wire 9 mils 7?\s&?s ( an in*72 ! cross-sectional area 9 circul> mils 7a unit area equal to t ( a circle hav+ a diamet] ( "o "o-?\s&? ( an in*72 ! resi/ance ( ! wire 9 v>i\s units ( l5g? & weight2 ! l5g? ( ! wire 9 t]ms ( resi/ance & ( weight2 & ! weight ( ! wire 9 t]ms ( its l5g? & resi/ance4 ,x is to be und]/ood t 9 ,table ,,iii ! wire ref]r$ to is b>e wire & is ( pure copp]4 ,x is n comm]cially practicable to use absolutely pure copp]1 & ! ord9>y magnet wire has a conductivity equal to ab\t #ih p] c5t ( t ( pure copp]4 ,! figures giv5 9 ?is table are suffici5tly accurate = all ord9>y practical purposes4 ,silk & ,cotton ,insulation4 ,! insulat+ mat]ial usually employ$ = cov]+ magnet wire is ( silk or cotton4 ,( ^!1 silk is by f> ! bett] mat]ial = all ord9>y purposes1 s9ce x has a mu* high] insulat+ prop]ty ?an cotton1 & is v mu* ?9n]4 ,cotton1 h[ev]1 is l>gely employ$1 p>ticul>ly 9 ! l>g] sizes ( magnet wire4 ,bo? ( ^! mat]ials possess ! disadvantage ( be+ hygroscopic1 t is1 ( readily absorb+ moi/ure4 ,?is disadvantage is ov]come 9 _m cases by saturat+ ! coil aft] x is w\nd 9 "s melt$ insulat+ comp\nd1 su* z wax or v>ni% or asphaltum1 :i* w solidify on cool+4 ,:]e ! coils are to be s saturat$ ! be/ practice is to place !m 9 a vacuum *amb] & exhau/ ! air1 aft] :i* ! hot insulat+ comp\nd is admitt$ & is ?us drawn into ! inn]mo/ recesses ( ! w9d+ space4 ,silk-insulat$ wire1 z regul>ly produc$1 has ei!r "o or two lay]s ( silk4 ,?is is ref]r$ to comm]cially z s+le silk wire or z d\ble silk wire4 ,! s+le silk has a s+le lay] ( silk fib]s wrapp$ ab\t x1 :ile ! d\ble silk has a d\ble lay]1 ! two lay]s be+ put on 9 rev]se direction4 ,! same holds true ( cotton insulat$ wire4 ,frequ5tly1 also1 !re is a comb9ation ( ! two1 consi/+ ( a s+le or a d\ble wrapp+ ( silk next to ! wire ) an out] wrapp+ ( cotton4 ,:]e ?is is done ! cotton s]ves pr9cipally z a me*anical protection = ! silk1 ! pr9cipal insulat+ prop]ties resid+ 9 ! silk4 ,enamel4 ,a lat] developm5t 9 ! insulation ( magnet wire has result$ 9 ! s-call$ enamel wire4 ,9 ?is1 in/ead ( coat+ ! wire ) "s fibr\s mat]ial su* z silk or cotton1 ! wire is heat$ & run ?r\gh a ba? ( fluid insulat+ mat]ial or liquid enamel1 :i* adh]es to ! wire 9 a v ?9 coat+4 ,! wire is !n run ?r\gh bak+ ov5s1 s t ! enamel is bak$ on4 ,?is process is repeat$ sev]al times s t a numb] ( ^! ?9 lay]s ( ! enamel are laid on & bak$ 9 succession4 ,! *>act]i/ics s\ght 9 good enamel insulation = magnet wire may be ?us briefly set =?3 ,x is desirable = ! insulation to possess ! highe/ insulat+ qualities2 to h a glossy1 flawless surface2 to be h>d )\t be+ brittle2 to adh]e t5aci\sly & /& all reasonable h&l+ )\t crack+ or flak+2 to h a coeffici5t ( ela/icity great] ?an ! wire itself2 to )/& high temp]atures2 to be moi/ure-pro( & in]t to corrosive ag5cies2 & n to dry out or become brittle ov] a long p]iod ( "t4 ,space ,utilization4 ,! utilization ( ! w9d+ space 9 an electromagnet is an important factor 9 design1 s9ce obvi\sly ! copp] or o!r conductor is ! only "p ( ! w9d+ t is effective 9 sett+ up magnetiz+ =ce4 ,! space occupi$ by ! insulation is1 9 ?is s5se1 wa/e space4 ,an ideally p]fect w9d+ may be conceiv$ z "o 9 :i* ! space is all occupi$ by wire2 & ?is w\ld necess>ily involve ! conception ( wire ( squ>e cross-section & insulation ( inf9ite ?9ness4 ,9 su* a w9d+ !re w\ld be no wa/e ( space & a maximum am\nt ( metal employ$ z a conductor4 ,( c\rse1 su* a condition is n possible to atta9 & 9 practice "s insulat+ mat]ial mu/ be introduc$ betwe5 ! lay]s ( wire & betwe5 ! adjac5t convolutions ( wire4 ,! ratio ( ! space occupi$ by ! conductor to ! total space occupi$ by ! w9d+1 t is1 by ! conductor & ! insulation1 is call$ ! coeffici5t ( space utilization ( ! coil4 ,= ! ideal coil j conceiv$ ! coeffici5t ( space utilization w\ld be #a4 ,ord9>ily ! coeffici5t ( space utilization is great] = co>se wire ?an = f9e wire1 s9ce obvi\sly ! ratio ( ! diamet] ( ! wire to ! ?ickness ( ! insulation increases z ! size ( ! wire gr[s l>g]4 ,! *ief advantage ( enamel insulation = magnet wire is its ?9ness1 & ! high coeffici5t ( space utilization :i* may be secur$ by its use4 ,9 good enamel wire ! insulation w av]age ab\t "o-qu>t] ! ?ickness ( ! /&>d s+le silk insulation1 & ! dielectric /r5g? is equal or great]4 ,:]e economy ( w9d+ space is desirable ! advantages ( ?is may readily be se54 ,= in/ance1 9 a giv5 coil w\nd ) ,no4 #cf s+le silk wire ab\t "o-half ( ! w9d+ space is tak5 up ) ! insulation1 :]eas :5 ! same coil is w\nd ) ,no4 #cf enamel$ wire only ab\t "o-fif? ( ! w9d+ space is tak5 up by ! insulation4 ,?us ! coeffici5t ( space utilization is increas$ f 4#ej to 4#hj4 ,! practical result ( ?is is t1 9 ! case ( any giv5 w9d+ space :]e ,no4 #cf wire is us$1 ab\t #fj p] c5t m turns c be put on ) enamel$ wire ?an ) s+le silk insulation1 & ( c\rse ?is ratio greatly increases :5 ! comp>ison is made ) d\ble silk insulation or ) cotton insulation4 ,aga91 :]e x is desir$ to r$uce ! w9d+ space & keep ! same numb] ( turns1 an equal numb] ( turns may be _h ) a correspond+ r$uction ( w9d+ space :]e enamel$ wire is us$ 9 place ( silk or cotton4 ,9 ! matt] ( heat-resi/+ prop]ties ! enamel$ wire possesses a great advantage ov] silk & cotton4 ,cotton or silk insulation w *> at ab\t #bfj ,fahr5heit1 :ile good enamel$ wire w /& #djj to #ejj ,fahr5heit )\t det]ioration ( ! insulation4 ,x is 9 ! matt] ( liability to injury 9 r\gh or c>eless h&l+1 or 9 w9d+ coils hav+ irregul> %apes1 t enamel wire is decid$ly inf]ior to silk or cotton-cov]$ wire4 ,x is likely to be damag$ if x is all[$ to /rike aga9/ ! %>p corn]s ( ! magnet spool dur+ w9d+1 or run ov] ! edge ( a h>d surface :ile x is be+ f$ on to ! spool4 ,coils hav+ o!r ?an r\nd cores1 or hav+ %>p corn]s on _! spool heads1 %\ld n ord9>ily be w\nd ) enamel wire4 ,! dielectric /r5g? ( enamel insulation is mu* great] ?an t ( ei!r silk or cotton insulation ( equal ?ickness4 ,?is is a di/9ct advantage & frequ5tly a comb9ation ( ! two k9ds ( insulation results 9 a sup]ior wire4 ,if wire insulat$ ) enamel is giv5 a s+le wrapp+ ( silk or ( cotton1 ! insulat+ & dielectric prop]ties ( ! enamel is secur$1 :ile ! pres5ce ( ! silk & cotton af=ds n only an additional safegu>d aga9/ b>e spots 9 ! enamel b also a c]ta9 degree ( me*anical protection to ! enamel4 ,w9d+ ,me?ods4 ,9 w9d+ a coil1 ! spool1 aft] be+ prop]ly prep>$1 is plac$ ^u a sp9dle :i* may be made to revolve rapidly4 ,ord9>ily ! wire is guid$ on by h&2 sometimes1 h[ev]1 ma*9]y is us$1 ! wire be+ run ov] a tool :i* moves to & fro along ! l5g? ( ! spool1 j fa/ en\gh to lay ! wire on at ! prop] rate4 ,! movem5t ( ?is tool is mu* ! same z t ( ! tool 9 a screw cutt+ la!4 ,unless high voltages are to be enc\nt]$1 x is ord9>ily n necess>y to sep>ate ! lay]s ( wire ) pap]1 9 ! case ( silk-or cotton-insulat$ magnet wire2 al?\gh :]e especially high insulation resi/ance is ne$$ ?is is (t5 done4 ,x is necess>y to sep>ate ! successive lay]s ( a magnet t is w\nd ) enamel wire1 by %eets ( pap] or ?9 oil$ clo?4 ,illu/ration3 ,fig4 #ii4 ,electromagnet ) ,b>e ,wire ,9 ,fig4 #ii is %[n a me?od1 t has be5 us$ ) "s success1 ( w9d+ magnets ) b>e wire4 ,9 ?is ! v>i\s adjac5t turns are sep>at$ f ea* o!r by a f9e ?read ( silk or cotton w\nd on beside ! wire4 ,ea* lay] ( wire & ?read z x is plac$ on ! core is completely insulat$ f ! subsequ5t lay] by a lay] ( pap]4 ,?is is ess5tially a ma*9e-w\nd coil1 & ma*9es = w9d+ x h be5 s p]fect$ t sev]al coils are w\nd simultane\sly1 ! pap] be+ f$ 9 automatically at ! end ( ea* lay]4 ,ano!r me?od ( w9d+ ! b>e wire omits ! silk ?read & dep5ds on ! p]man5t position+ ( ! wire z x is plac$ on ! coil1 due to ! slight s9k+ into ! lay] ( pap] on :i* x is w\nd4 ,9 ?is case ! fe$ ( ! wire at ea* turn ( ! spool is slightly great] ?an ! diamet] ( ! wire1 s t a small di/ance w be left betwe5 ea* pair ( adjac5t turns4 ,^u ! completion ( ! w9d+ ( a coil1 reg>dless ( :at me?od is us$1 x is cu/om>y to place a lay] ( bookb9d]s' clo? ov] ! coil s z to af=d a c]ta9 me*anical protection = ! insulat$ wire4 ,w9d+ ,t]m9als4 ,! matt] ( br++ out ! t]m9al ends ( ! w9d+ is "o t has receiv$ a great deal ( att5tion 9 ! con/ruction ( electromagnets & coils = v>i\s purposes4 ,:]e ! w9d+ is ( f9e wire1 x is always well to re9=ce its ends by a %ort piece ( l>g] wire4 ,:]e ?is is done ! l>g] wire is giv5 sev]al turns ar\nd ! body ( ! coil1 s t ! f9] wire ) :i* x connects may be reliev$ ( all /ra9 :i* may be ex]t$ ^u x f ! protrud+ ends ( ! wire4 ,great c>e is necess>y 9 ! br++ out ( ! inn] t]m9al--i4e41 ! t]m9al :i* connects ) ! inn] lay]--t ! t]m9al wire %all n come 9 contact ) any ( ! subsequ5t lay]s t are w\nd on4 ,illu/ration ,fig4 #ajj4 ,electromagnet ) ,t]m9als ,:]e economy ( space is necess>y1 a conv5i5t me?od ( t]m9at+ ! w9d+ ( ! coil consi/s 9 fa/5+ rigid t]m9als to ! spool head4 ,?is1 9 ! case ( a fib] spool head1 may be done by driv+ heavy metal t]m9als into ! fib]4 ,! connections ( ! two wires lead+ f ! w9d+ are !n made ) ^! heavy rigid t]m9als by means ( sold]4 ,a coil hav+ su* t]m9als is %[n 9 its f9i%$ condition 9 ,fig4 #ajj4 ,w9d+ ,data4 ,! two ?+s pr9cipally affect+ ! manufacture ( electromagnets = telephone purposes are ! numb] ( turns 9 a w9d+ & ! resi/ance ( ! w\nd wire4 ,! latt] gov]ns ! am\nt ( curr5t :i* may fl[ ?r\gh ! coil ) a giv5 diff]5ce ( pot5tial at its end1 :ile ! =m] control ! am\nt ( magnetism produc$ 9 ! core by ! curr5t fl[+4 ,:ile a coil is be+ w\nd1 x is a simple matt] to c\nt ! turns by any simple =m ( revolution c\nt]4 ,:5 ! coil has be5 complet$ x is a simple matt] to measure its resi/ance4 ,b x is n s simple to det]m9e 9 advance h[ _m turns ( a giv5 size wire may be plac$ on a giv5 spool1 & /ill less simple to "k :at ! resi/ance ( ! wire on t spool w be :5 ! desir$ turns %all h be5 w\nd4 ,,table ,,iv ,w9d+ ,data = ,insulat$ ,wires--,silk & ,cotton ,cov]+ ,a4,w4,g4 ,b ,s #bj #ba #bb #bc #bd #be ---------------------------------------- ----------------------------- ,,diamet] ,mils #ca4ifa #bh4dfb #be4cdg #bb4ega #bj4ajj #ag4ijj ---------------------------------------- ----------------------------- ,,area ,circul> ,mils #ajba4bj #haj4aj #fdb4gj #eji4de #djd4ja #cbj4dj ---------------------------------------- ----------------------------- ,,diamet] ,,ov] ,,insulation ,,s+le ,,cotton #cg4hfa #cd4cfb #ca4bdg #bh4dga #bf4jjj #bc4hjj ,,d\ble ,,cotton #db4afa #ch4ffb #ce4edg #cb4gga #cj4cjj #bh4ajj ,,s+le ,,silk #cd4bfa #cj4gfb #bg4fdg #bd1hga #bb4dja #bj4bjj ,,d\ble ,,silk #cf4afa #cb4ffb #bi4edg #bf4gga #bd4cjj #bb4ajj ---------------------------------------- ----------------------------- ,,turns ,,p] ,,l9e> ,,in* ,,s+le ,,cotton #be4g #bh4c #ca4j #cd4d #cf4i #ch4j ,,d\ble #bb4e #bd4e #bf4g #bh4ig #ca4ce #cc4ib ,,cotton ,,s+le ,,silk #bg4gj #cj4ig #cd4ci #ch4ai #db4cg #dg4jb ,,d\ble ,,silk #bf4bb #bi4jg #cb4aa #ce4ec #ci4ad #db4id ---------------------------------------- ----------------------------- ,,turns ,,p] ,,squ>e ,,in* ,,s+le ,,cotton #ffj4e #hjj4i #ifa4j #aahc4j #acba4f #addd4j ,,d\ble ,,cotton #ejf4c #fjj4b #gab4i #hci4b #ihb4h #aaej4h ,,s+le ,,silk #gfg4c #iei4a #aahb4g #adeh4e #agie4b #bbaj4i ,,d\ble ,,silk #fhg4e #hde4j #ajca4j #abfb4d #aecb4j #ahdc4h ---------------------------------------- ----------------------------- ,,ohms ,,p] ,,cubic ,,in* ,,s+le ,,cotton 4#fdf 4#iha #a4ejb #b4cei #c4ebh #e4hca ,,d\ble ,,cotton 4#ecc 4#gie #a4ahh #a4ggb #b4eie #c4hjb ,,s+le ,,silk 4#hja #a4bfa #a4ief #c4jdi #d4gci #g4dhi ---------------------------------------- ----------------------------- ,a4,w4,g4 ,b ,s #bf #bg #bh #bi #cj #ca ---------------------------------------- ----------------------------- ,,diamet] ,mils #ae4idj #ad4aie #ab4fda #aa4beg #aj4jbe #h4ibh ---------------------------------------- ----------------------------- ,,area ,circul> ,mils #bed4ja #bja4ej #aei4gi #abf4gb #ajj4ej #gi4ga ---------------------------------------- ----------------------------- ,,diamet] ,,ov] ,,insulation ,,s+le ,,cotton #ba4hdj #bj4jie #ah4eda #ag4aeg #ae4ibe #ad4hbh ,,d\ble ,,cotton #bf4adj #bd4cie #bb4hda #ba4deg #bj4bbe #ai4abh ,,s+le ,,silk #ah4bdj #af4die #ad4ida #ac4eeg #ab4cbe #aa4bbh ,,d\ble ,,silk #bj4adj #ah4cie #af4hda #ae4deg #ad4bbe #ac4abh ---------------------------------------- ----------------------------- ,,turns ,,p] ,,l9e> ,,in* ,,s+le ,,cotton #db4j #dh4j #ec4j #ef4e #ei4ff #fd4abe ,,d\ble ,,cotton #cf4bi #ch4ie #da4fa #dd4bg #df4ic #di4gh ,,s+le ,,silk #eb4jf #eg4fg #fc4cf #gj4aa #gg4ad #hd4fd ,,d\ble ,,silk #df4ha #ea4ei #ef4dc #fa4ef #ff4gi #gb4ci ---------------------------------------- ----------------------------- ,,turns ,,p] ,,squ>e ,,in* ,,s+le ,,cotton #agfd4j #bcjd4j #bhji4i #caib4c #ccei4b #daab4b ,,d\ble ,,cotton #acag4j #aeag4b #agca4j #aiei4i #bbjb4e #bdgh4j ,,s+le ,,silk #bgaj4c #ccbf4j #djad4e #diae4e #eiej4b #gafd4j ,,d\ble ,,silk #baia4b #bffa4f #cahd4e #cghi4h #ddfa4j #ebdj4j ---------------------------------------- ----------------------------- ,,ohms ,,p] ,,cubic ,,in* ,,s+le ,,cotton #f4ida #aj4had #ag4fag #be4ejj #cd4hjj #dh4e ,,d\ble ,,cotton #e4eeb #h4jgh #aa4ed #af4dg #bc4dc #cb4hc ,,s+le ,,silk #i4jca #ac4ib #bf4hf #da4bi #fb4ih #ie4gj ---------------------------------------- ----------------------------- ,a4,w4,g4 ,b ,s #cb #cc #cd #ce #cf #cg ---------------------------------------- ------------------------------ ,,diamet] ,mils #g4iej #g4jhj #f4cjd #e4fad #e4jjj #d4dec ---------------------------------------- ------------------------------ ,,area ,circul> ,mils #fc4bj #ej4ac #ci4gd #ca4eb #be4jj #ai4hc ---------------------------------------- ------------------------------ ,,diamet] ,,ov] ,,insulation ,,s+le ,,cotton #ac4hej #ab4ihj #ab4bjd #aa4ead #aj4ijj #aj4cec ,,d\ble ,,cotton #ah4aej #ag4bhj #af4ejd #ae4had #ae4bjj #ad4fec ,,s+le ,,silk #aj4bej #i4chj #h4ejd #g4iad #g4cjj #f4gec ,,d\ble ,,silk #ab4aej #aa4bhj #aj4ejd #i4had #i4bjj #h4fec ---------------------------------------- ------------------------------ ,,turns ,,p] ,,l9e> ,,in* ,,s+le ,,cotton #fh4fjj #gc4jej #gg4ijj #hb4fjj #hg4ajj #ia4hgj ,,d\ble ,,cotton #eb4cd #ee4aj #eg4eg #fj4jd #fb4ea #fd4gj ,,s+le ,,silk #ib4gb #aja4fe #aab4aa #aai4g #acj4ae #adj4f ,,d\ble ,,silk #gh4ai #hd4ag #ij4dd #if4ij #ajc4ee #aaj4bj ---------------------------------------- ------------------------------ ,,turns ,,p] ,,squ>e ,,in* ,,s+le #dfib4e #eccc4e #fjfh4e #fggc4c #gehf4e #hddj4j ,,cotton ,,d\ble ,,cotton #bgci4e #cjcf4a #ccad4b #cfje4j #cijg4e #dahf4a ,,s+le ,,silk #heig4e #ajccb4j #abegj4j #adcbg4j #afidj4j #aiggj4j ,,d\ble ,,silk #faad4j #gjhe4j #hagi4e #ichi4e #ajggb4j #abade4j ---------------------------------------- ----------------------------- ,,ohms ,,p] ,,cubic ,,in* ,,s+le ,,cotton #gc4h #ajd4e #aea4d #bjb4j #bih4h #dah4j ,,d\ble ,,cotton #df4ai #fd4cj #gj4eh #abe4i #aff4c #bbe4f ,,s+le ,,silk #add4gj #bag4h #cdb4a #dhi4j #gba4a #ajfb4j ---------------------------------------- ----------------------------- ,a4,w4,g4 ,b ,s #ch #ci #dj ---------------------------------------- ---- ,,diamet] ,mils #c4ife #c4eca #c4add ---------------------------------------- ---- ,,area ,circul> ,mils #ae4gb #ab4dg #i4hi ---------------------------------------- ---- ,,diamet] ,,ov] ,,insulation ,,s+le ,,cotton #i4hfe #i4dca #i4jdd ,,d\ble ,,cotton #ad4afe #ac4gca #ac4cdd ,,s+le ,,silk #f4bfe #e4hca #e4cdd ,,d\ble ,,silk #h4afe #g4gca #g4cdd ---------------------------------------- ---- ,,turns ,,p] ,,l9e> ,,in* ,,s+le ,,cotton #ie4jjj #ajj4gjj #ajf4jjj ,,d\ble ,,cotton #ff4hj #fh4hj #ga4bj ,,s+le ,,silk #aea4je #afc4jd #agg4fe ,,d\ble ,,silk #aaf4he #abb4ee #abi4bj ---------------------------------------- ---- ,,turns ,,p] ,,squ>e ,,in* ,,s+le ,,cotton #ijbe4j #ajadj4e #aabcf4j ,,d\ble #ddfb4b #dgcc4f #ejfi4h ,,cotton ,,s+le ,,silk #bbhbj4j #bfgjj4j #caeei4j ,,d\ble ,,silk #acfee4j #aejah4j #affib4j ---------------------------------------- ---- ,,ohms ,,p] ,,cubic ,,in* ,,s+le ,,cotton #efg4j #haa4j #aaac4j ,,d\ble #cje4e #dji4h #ede4e ,,cotton ,,s+le ,,silk #aeeg4j #bbff4j #cdjj4j ---------------------------------------- --- ,if ! l5g? & ! dep? ( ! w9d+ space ( ! coil z well z ! diamet] ( ! core are kn[n1 x is n difficult to det]m9e h[ mu* b>e copp] wire ( a giv5 size may be w\nd on x1 b x is m difficult to "k ^! facts conc]n+ copp] wire :i* has be5 cov]$ ) cotton or silk4 ,yet some?+ may be done1 & tables h be5 prep>$ = /&>d wire sizes ) def9ite ?icknesses ( silk & cotton insulation4 ,z a result ( facts collect$ f a l>ge numb] ( actually w\nd coils1 ! numb] ( turns p] l9e> in* & p] squ>e in* ( ,b4,s4 gauge wires f ,no4 #bj to ,no4 #dj h be5 tabulat$1 & ^!1 supplem5t$ by a tabulation ( ! numb] ( ohms p] cubic in* ( w9d+ space = wires ( ?ree diff]5t k9ds ( insulation1 are giv5 9 ,table ,,iv4 ,be>+ 9 m9d t ! calculations ( ,table ,,iv are all bas$ ^u ! diamet] ov] insulation1 :i* x /ates at ! outset = ea* ( f\r diff]5t k9ds ( cov]+1 x is evid5t :at is meant by turns p] l9e> in*4 ,! columns ref]r+ to turns p] squ>e in* mean ! numb] ( turns1 ! ends ( :i* w\ld be expos$ 9 "o squ>e in* if ! w\nd coil 7 cut 9 a plane pass+ ?r\gh ! axis ( ! core4 ,kn[+ ! di/ance betwe5 ! head1 & ! dep? to :i* ! coil is to be w\nd1 x is easy to select a size ( wire :i* w give ! requir$ numb] ( turns 9 ! provid$ space4 ,x is to be not$ t ! dep? ( w9d+ space is "o-half ( ! diff]5ce betwe5 ! core diamet] & ! complete diamet] ( ! w\nd coil4 ,! resi/ance ( ! entire volume ( w\nd wire may be det]m9$ 9 advance by kn[+ ! total cubic cont5ts ( ! w9d+ space & multiply+ ?is by ! ohms p] cubic in* ( ! select$ wire2 t is1 "o mu/ multiply 9 in*es ! di/ance betwe5 ! heads ( ! spool by ! diff]5ce betwe5 ! squ>es ( ! diamet]s ( ! core & ! w9d+ space1 & ?is 9 turn by 4#ghed4 ,?is result1 times ! ohms p] cubic in*1 z giv5 9 ! table1 gives ! resi/ance ( ! w9d+4 ,!re is a consid]able v>iation 9 ! me?od ( apply+ silk insulation to ! f9] wires1 & x is 9 ! f9] sizes t ! errors1 if any1 pile up mo/ rapidly4 ,yet ! table ?r\gh\t is bas$ on data tak5 f _m samples ( actual coil w9d+ by ! pres5t process ( w9d+ small coils4 ,x %\ld be said fur!r t ! table does n take into acc\nt ! plac+ ( any lay]s ( pap] betwe5 ! successive lay]s ( ! wires4 ,?is table has be5 comp>$ ) _m examples & has be5 us$ 9 calculat+ w9d+s 9 advance1 & is f\nd to be z close an approximation z is af=d$ by any ( ! =mulas on ! subject1 & ) ! fur!r advantage t x is n s cumb]some to apply4 ,w9d+ ,calculations4 ,9 exp]im5tal "w1 involv+ ! w9d+ ( coils1 x is frequ5tly necess>y to try "o w9d+ to det]m9e its effect 9 a giv5 circuit arrangem5t1 & f ! k s ga9$ to sub/itute ano!r j fitt$ to ! conditions4 ,x is 9 su* a sub/itution t ! table is ( mo/ value4 ,assume a case 9 :i* are requir$ a spool & core ( a giv5 size ) a w9d+ (1 say ,no4 #be s+le silk-cov]$ wire1 ( a resi/ance ( #ej ohms4 ,assume also t ! circuit regulations requir$ t ?is spool %\ld be rew\nd s z to h a resi/ance (1 say #a1jjj ohms4 ,:at size s+le silk-cov]$ wire %all be us$8 ,manife/ly1 ! w9d+ space rema9s ! same1 or ne>ly s4 ,! resi/ance is to be increas$ f #ej to #a1jjj ohms1 or tw5ty times its fir/ value4 ,!re=e1 ! wire to be us$ mu/ %[ 9 ! table tw5ty times z _m ohms p] cubic in* z are %[n 9 ,no4 #be1 ! kn[n fir/ size4 ,?is am\nt w\ld be tw5ty times #g4dhi1 :i* is #adi4h1 b !re is no size giv+ ?is exact resi/ance4 ,no4 #cb1 h[ev]1 is v ne>ly ( t resi/ance & if w\nd to exactly ! same dep? w\ld give ab\t #igj ohms4 ,a few turns m w\ld provide ! additional ?irty ohms4 ,simil>ly1 9 a coil kn[n to possess a c]ta9 numb] ( turns1 ! table w give ! size to be select$ = rew9d+ to a great] or small] numb] ( turns4 ,9 ?is case1 z 9 ! case ( sub/itut+ a w9d+ ( diff]5t resi/ance1 x is unnecess>y to measure & calculate ^u ! dim5sions ( ! spool & core4 ,assume a spool w\nd ) ,no4 #cj d\ble silk-cov]$ wire1 :i* requires to be w\nd ) a size to d\ble ! numb] ( turns4 ,! exact size to d ?is w\ld h #hibb4 turns p] squ>e in* & w\ld be betwe5 ,no4 #cd & ,no4 #ce4 ,a *oice ( ^! two wires may be made1 us+ an increas$ w9d+ dep? ) ! small] wire & a %all[] w9d+ dep? = ! l>g] wire4 ,imp$ance ,coils4 ,9 telephony electromagnets frequ5tly s]ve1 z already /at$1 to p]=m o!r functions ?an ! produc+ ( motion by attract+ or releas+ _! armatures4 ,!y are requir$ to act z imp$ance coils to pres5t a b>ri] to ! passage ( alt]nat+ or o!r rapidly fluctuat+ curr5ts1 & at ! same "t to all[ ! comp>atively free passage ( /eady curr5ts4 ,:]e x is desir$ t an electromagnet coil %all possess high imp$ance1 x is usual to employ a lam9at$ in/ead ( a solid core4 ,?is is done by build+ up a core ( suitable size by lay+ toge!r ?9 %eets ( s(t iron1 or by =m+ a bundle ( s(t iron wires4 ,! use ( lam9at$ cores is = ! purpose ( prev5t+ eddy curr5ts1 :i*1 if all[$ to fl[1 w\ld n only be wa/eful ( en]gy b w\ld also t5d to defeat ! desir$ high imp$ance4 ,sometimes 9 iron-clad imp$ance coils1 ! iron %ell is slott$ longitud9ally to break up ! fl[ ( eddy curr5ts 9 ! %ell4 ,frequ5tly electromagnetic coils h only ! function ( (f]+ imp$ance1 :]e no requirem5ts exi/ = conv]t+ any "p ( ! electric en]gy into me*anical "w4 ,:]e ?is is ! case1 su* coils are t]m$ imp$ance1 or ret>dation1 or *oke coils1 s9ce !y are employ$ to imp$e or to ret>d or to *oke back ! fl[ ( rapidly v>y+ curr5t4 ,! di/9ction1 !re=e1 betwe5 an imp$ance coil & ! coil ( an ord9>y electromagnet is "o ( function1 s9ce /ructurally !y may be ! same1 & ! same pr9ciples ( design & con/ruction apply l>gely to ea*4 ,numb] ( ,turns4 ,x %\ld be rememb]$ t an imp$ance coil ob/ructs ! passage ( fluctuat+ curr5t1 n s mu* by ohmic resi/ance z by (f]+ an oppos+ or c\nt]-electromotive =ce4 ,o!r ?+s be+ equal1 ! c\nt]-electromotive =ce ( self-induction increases directly z ! numb] ( turns on a coil & directly z ! numb] ( l9es ( =ce ?read+ ! coil1 & ?is latt] factor dep5ds also on ! reluctance ( ! magnetic circuit4 ,!re=e1 to secure high imp$ance we ne$ _m turns or l[ reluctance1 or bo?4 ,(t51 ow+ to requirem5ts = direct-curr5t c>ry+ capacity & limitations ( space1 a v l>ge numb] ( turns is n p]missible1 9 :i* case suffici5tly high imp$ance to su* rapid fluctuations z ^? ( voice curr5ts may be _h by employ+ a magnetic circuit ( v l[ reluctance1 usually a completely clos$ circuit4 ,k9d ( ,iron4 ,an important factor 9 ! design ( imp$ance coils is ! grade ( iron us$ 9 ! magnetic circuit4 ,obvi\sly1 x %\ld be ( ! highe/ p]meability &1 fur!rmore1 !re %\ld be ample cross-section ( core to prev5t ev5 an approa* to saturation4 ,! iron %\ld1 if possible1 be work$ at t d5sity ( magnetization at :i* x has ! highe/ p]meability 9 ord] to obta9 ! maximum imp$ance effects4 ,types4 ,op5-,circuit3--,:]e v feeble curr5ts are be+ dealt )1 & p>ticul>ly :]e !re is no fl[ ( direct curr5t1 an op5 magnetic circuit is mu* us$4 ,an imp$ance coil hav+ an op5 magnetic circuit is %[n 9 section 9 ,fig4 #aja1 ,fig4 #ajb %[+ its ext]nal appe>ance & illu/rat+ p>ticul>ly ! me?od ( br++ out ! t]m9als ( ! w9d+4 ,illu/ration3 ,fig4 #aja4 ,section ( ,op5-,circuit ,imp$ance ,coil ,illu/ration3 ,fig4 #ajb4 ,op5-,circuit ,imp$ance ,coil ,illu/ration3 ,fig4 #ajc4 ,clos$-,circuit ,imp$ance ,coil ,clos$-,circuit3--,a type ( ret>dation coil :i* is l>gely us$ 9 sy/ems ( simultane\s telegraphy & telephony1 kn[n z composite sy/ems1 is %[n 9 ,fig4 #ajc4 ,9 ! con/ruction ( ?is coil ! core is made ( a bundle ( f9e iron wires fir/ b5t into ,u-%ape1 & !n aft] ! coils are 9 place1 ! free ends ( ! core are br\ght toge!r to =m a clos$ magnetic circuit4 ,! coils h a l>ge numb] ( turns ( r co>se wire4 ,! conditions surr\nd+ ! use ( ?is coil are ^? :i* require v high imp$ance & r l>ge curr5t-c>ry+ capacity1 & =tunately ! add$ requirem5t1 t x %all be plac$ 9 a v small space1 does n exi/4 ,toroidal3--,ano!r type ( ret>dation coil1 call$ ! toroidal type due to ! fact t its core is a torus =m$ by w9d+ a cont9u\s l5g? ( f9e iron wire1 is %[n 9 diagram 9 ,fig4 #ajd4 ,! two w9d+s ( ?is coil may be connect$ 9 s]ies to =m 9 effect a s+le w9d+1 or x may be us$ z a split-w9d+ coil1 ! two w9d+s be+ 9 s]ies b hav+ "s o!r elem5t1 su* z a batt]y1 connect$ betwe5 !m 9 ! circuit4 ,evid5tly su* a coil1 h[ev] connect$1 is well adapt$ = high imp$ance1 on acc\nt ( ! l[ reluctance ( its core4 ,illu/ration3 ,fig4 #ajd4 ,symbol ( ,toroidal ,imp$ance ,coil ,?is coil is usually m\nt$ on a base-bo>d1 ! coil be+ enclos$ 9 a protect+ iron case1 z %[n 9 ,fig4 #aje4 ,! t]m9al wires ( bo? w9d+s ( ea* coil are br\ght out to t]m9al pun*+s on "o end ( ! base-bo>d to facilitate ! mak+ ( ! necess>y circuit connections4 ,illu/ration3 ,fig4 #aje4 ,toroidal ,imp$ance ,coil ,! usual diagrammatic symbol = an imp$ance coil is %[n 9 ,fig4 #ajf4 ,?is is ! same z = an ord9>y b> magnet1 except t ! p>allel l9es ?r\gh ! core may be tak5 z indicat+ t ! core is lam9at$1 ?us convey+ ! idea ( high imp$ance4 ,! symbol ( ,fig4 #ajd is a good "o = ! toroidal type ( imp$ance coil4 ,illu/ration3 ,fig4 #ajf4 ,symbol ( ,imp$ance ,coil ,induction ,coil4 ,an induction coil consi/s ( two or m w9d+s ( wire int]l9k$ by a common magnetic circuit4 ,9 an induction coil hav+ two w9d+s1 any *ange 9 ! /r5g? ( ! curr5t fl[+ 9 "o ( ! w9d+s1 call$ ! prim>y1 w cause correspond+ *anges 9 ! magnetic flux ?read+ ! magnetic circuit1 &1 !re=e1 *anges 9 flux ?r\gh ! o!r w9d+1 call$ ! second>y4 ,?is1 by ! laws ( electromagnetic induction1 w produce correspond+ electromotive =ces 9 ! second>y w9d+ &1 !re=e1 correspond+ curr5ts 9 t w9d+ if its circuit be clos$4 ,curr5t & ,voltage ,ratios4 ,9 a well-design$ induction coil ! en]gy 9 ! second>y1 i4e41 ! induc$ curr5t1 is = all practical purposes equal to t ( ! prim>y curr5t1 yet ! values ( ! voltage & ! amp]age ( ! induc$ curr5t may v>y widely f ! values ( ! voltage & ! amp]age ( ! prim>y curr5t4 ,) simple p]iodic curr5ts1 su* z ! comm]cial alt]nat+ light+ curr5ts1 ! ratio betwe5 ! voltage 9 ! prim>y & t 9 ! second>y w be equal to ! ratio ( ! numb] ( turns 9 ! prim>y to ! numb] ( turns 9 ! second>y4 ,s9ce ! en]gy 9 ! two circuits w be practically ! same1 x foll[s t ! ratio betwe5 ! curr5t 9 ! prim>y & t 9 ! second>y w be equal to ! ratio ( ! numb] ( turns 9 ! second>y to ! numb] ( turns 9 ! prim>y4 ,9 telephony1 :]e ! curr5ts are n simple p]iodic curr5ts1 & :]e ! v>iations 9 curr5t /r5g? take place at diff]5t rates1 su* a law z t j /at$ does n hold = all cases2 b x may be /at$ 9 g5]al t ! induc$ curr5ts w be ( high] voltage & small] curr5t /r5g? ?an ^? ( ! prim>y 9 all coils :]e ! second>y w9d+ has a great] numb] ( turns ?an ! prim>y1 & vice v]s4 ,functions4 ,! function ( ! induction coil 9 telephony is1 !re=e1 ma9ly "o ( trans=mation1 t is1 ei!r ( /epp+ up ! voltage ( a curr5t1 or 9 o!r cases /epp+ x d[n4 ,! induction coil1 h[ev]1 does s]ve ano!r purpose 9 cases :]e no *ange 9 voltage & curr5t /r5g? is desir$1 t is1 x s]ves z a means = electrically sep>at+ two circuits s f> z any conductive relation exi/s1 & yet ( all[+ ! free transmission by induction f "o ( ^! circuits to ! o!r4 ,?is is a function t 9 telephony is sc>cely ( less importance ?an ! purely trans=m+ function4 ,design4 ,induction coils1 z employ$ 9 telephony1 may be divid$ into two g5]al types3 fir/1 ^? hav+ an op5 magnetic circuit2 &1 second1 ^? hav+ a clos$ magnetic circuit4 ,9 ! design ( ei!r type x is important t ! core %\ld be ?or\ghly lam9at$1 & ?is is done usually by =m+ x ( a bundle ( s(t ,sw$i% or ,norway iron wire ab\t 4#jb ( an in* 9 diamet]4 ,! diamet] & ! l5g? ( ! coil1 & ! relation betwe5 ! numb] ( turns 9 ! prim>y & 9 ! second>y1 & ! me*anical con/ruction ( ! coil1 are all matt]s :i* are subject to v wide v>iation 9 practice4 ,:ile ! prop] relation%ip ( ^! factors is ( great importance1 yet !y may n be readily det]m9$ except by actual exp]im5t ) v>i\s coils1 ow+ to ! extreme complexity ( ! action :i* takes place 9 !m & to ! difficulty ( obta9+ fundam5tal data z to ! exi/+ facts4 ,x may be /at$1 !re=e1 t ! design ( induction coils is ne>ly always c>ri$ out by cut-&-try me?ods1 br++ to be>1 ( c\rse1 su* sci5tific & practical k z ! exp]im5t] may possess4 ,illu/ration3 ,fig4 #ajg4 ,induction ,coil ,illu/ration3 ,fig4 #ajh4 ,section ( ,induction ,coil ,use & ,advantage4 ,! use & advantages ( ! induction coil 9 s-call$ local-batt]y telephone sets h already be5 expla9$ 9 previ\s *apt]s4 ,su* induction coils are ne>ly always ( ! op5 magnetic circuit type1 consi/+ ( a long1 /raight core compris$ ( a bundle ( small anneal$ iron wires1 on :i* is w\nd a prim>y ( comp>atively co>se wire & hav+ a small numb] ( turns1 & ov] :i* is w\nd a second>y ( comp>atively f9e wire & hav+ a v mu* l>g] numb] ( turns4 ,a view ( su* a coil m\nt$ on a base is %[n 9 ,fig4 #ajg1 & a sectional view ( a simil> coil is %[n 9 ,fig4 #ajh4 ,! me?od ( br++ out ! w9d+ t]m9als is cle>ly indicat$ 9 ?is figure1 ! t]m9al wires #b & #d be+ ^? ( ! prim>y w9d+ & #a & #c ^? ( ! second>y w9d+4 ,x is cu/om>y to br+ out ^! wires & atta* !m by sold] to suitable t]m9al clips4 ,9 ! case ( ! coil %[n 9 ,fig4 #ajh ^! clips are m\nt$ on ! wood5 heads ( ! coil1 :ile 9 ! design %[n 9 ,fig4 #ajg !y are m\nt$ on ! base1 z is cle>ly indicat$4 ,repeat+ ,coil4 ,! s-call$ repeat+ coil us$ 9 telephony is really no?+ b an induction coil4 ,x is us$ 9 a v>iety ( ways & usually has = its purpose ! inductive association ( two circuits t are conductively sep>at$4 ,usually ! repeat+ coil has a "o to "o ratio ( turns1 t is1 !re are ! same numb] ( turns 9 ! prim>y z 9 ! second>y4 ,h[ev]1 ?is is n always ! case1 s9ce sometimes !y are made to h an unequal numb] ( turns1 9 :i* case !y are call$ /ep-up or /ep-d[n repeat+ coils1 accord+ to :e!r ! prim>y has a small] or a great] numb] ( turns ?an ! second>y4 ,repeat+ coils are almo/ univ]sally ( ! clos$ magnetic circuit type4 ,r++ & ,talk+ ,consid]ations4 ,s9ce repeat+ coils (t5 s]ve to connect two telephones1 x foll[s t x is sometimes necess>y to r+ ?r\gh !m z well z talk ?r\gh !m4 ,by ?is is meant t x is necess>y t ! coil %all be s design$ z to be capable ( trans=m+ ! heavy r++ curr5ts z well z ! v mu* small] telephone or voice curr5ts4 ,r++ curr5ts ord9>ily h a frequ5cy rang+ f ab\t #af to #ge cycles p] second1 :ile voice curr5ts h frequ5cies rang+ f a few hundr$ up to p]haps t5 ?\s& p] second4 ,ord9>ily1 !re=e1 ! be/ =m ( repeat+ coil = trans=m+ voice curr5ts is n ! be/ = trans=m+ ! heavy r++ curr5ts & vice v]s4 ,if ! comp>atively heavy r++ curr5ts alone 7 to be consid]$1 ! repeat+ coil might well be ( heavy con/ruction ) a l>ge am\nt ( iron 9 its magnetic circuit4 ,on ! o!r h&1 = c>ry+ voice curr5ts alone x is usually made ) a small am\nt ( iron & ) small w9d+s1 9 ord] to prev5t wa/e ( en]gy 9 ! core1 & to give a high degree ( responsiv5ess ) ! lea/ am\nt ( di/ortion ( wave =m1 s t ! voice curr5ts w reta9 z f> z possible _! orig9al *>act]i/ics4 ,:51 !re=e1 a coil is requir$ to c>ry bo? r++ & talk+ curr5ts1 a compromise mu/ be effect$4 ,types4 ,! =m ( repeat+ coil l>gely us$ = bo? r++ & talk+ ?r\gh is %[n 9 ,fig4 #aji4 ,?is coil comprises a s(t iron core made up ( a bundle ( wires ab\t 4#jb in* 9 diamet]1 ! ends ( :i* are left ( suffici5t l5g? to be b5t back ar\nd ! w9d+s aft] !y are 9 place & ?us =m a completely clos$ magnetic pa? = ! core4 ,! w9d+s ( ?is p>ticul> coil are f\r 9 numb]1 & conta9 ab\t #b1djj turns ea*1 & h a resi/ance ( ab\t #fj ohms4 ,9 ?is coil1 :5 connect$ = local batt]y "w1 ! w9d+s are connect$ 9 pairs 9 s]ies1 ?us =m+ effectively two w9d+s hav+ ab\t #abj ohms resi/ance ea*4 ,! :ole coil is enclos$ 9 a protect+ case ( iron4 ,! t]m9als are br\ght out to suitable clips on ! wood5 base1 z %[n4 ,an ext]nal p]spective view ( ?is coil is %[n 9 ,fig4 #aaj4 ,by br++ out ea* t]m9al ( ea* w9d+1 eight 9 all1 z %[n 9 ?is figure1 great latitude ( connection is provid$ =1 s9ce ! w9d+s may be connect$ 9 circuit 9 any desirable way1 ei!r by connect+ !m toge!r 9 pairs to =m virtually a prim>y & a second>y1 or1 z is frequ5tly ! case1 to split ! prim>y & ! second>y1 connect+ a batt]y betwe5 ea* pair ( w9d+s4 ,illu/ration3 ,fig4 #aji4 ,repeat+ ,coil ,illu/ration3 ,fig4 #aaj4 ,repeat+ ,coil ,fig4 #aaa illu/rates 9 section a comm]cial type ( coil design$ = talk+ ?r\gh only4 ,?is coil is provid$ ) f\r w9d+s ( #a1ceg turns ea*1 & :5 us$ = local batt]y "w ! coils are connect$ 9 pairs 9 s]ies1 ?us giv+ a resi/ance ( ab\t #aij ohms 9 ea* half ( ! repeat+ coil4 ,! core ( ?is coil consi/s ( a bundle ( s(t iron wires1 & ! %ell :i* =ms ! return pa? = ! magnetic l9es is ( v s(t %eet iron4 ,?is %ell is drawn into cup %ape & its op5 end is clos$1 aft] ! coil is ins]t$1 by ! ins]tion ( a s(t iron head1 z indicat$4 ,z 9 ! case ( ! coil %[n 9 ,figs4 #aji & #aaj1 eight t]m9als are br\ght out on ?is coil1 ?us provid+ ! necess>y flexibility ( connection4 ,illu/ration3 ,fig4 #aaa4 ,repeat+ ,coil ,illu/ration3 ,fig4 #aab4 ,diagram ( ,toroidal ,repeat+ ,coil ,illu/ration3 ,fig4 #aac4 ,toroidal ,repeat+ ,coil ,/ill ano!r type ( repeat+ coil is illu/rat$ 9 diagram 9 ,fig4 #aab1 & 9 view 9 ,fig4 #aac4 ,?is coil1 l ! imp$ance coil %[n 9 ,fig4 #ajd1 comprises a core made up ( a bundle ( s(t iron wires w\nd into ! =m ( a r+4 ,x is usually provid$ ) two prim>y w9d+s plac$ opposite ea* o!r ^u ! core1 & ) two second>y w9d+s1 "o ov] ea* prim>y4 ,9 practice ^! two prim>y w9d+s are connect$ 9 "o circuit & ! two second>ies 9 ano!r4 ,?is is ! /&>d repeat+ coil n[ us$ by ! ,bell companies 9 _! common-batt]y cord circuits4 ,illu/ration3 ,,! ,,op]at+ ,,room ,,( ,,! ,,ex*ange ,,at ,,webb ,,city1 ,,miss\ri ,illu/ration3 ,fig4 #aad4 ,symbol ( ,induction ,coil ,conv5tional ,symbols4 ,! ord9>y symbol = ! induction coil us$ 9 local batt]y "w is %[n 9 ,fig4 #aad4 ,?is consi/s m]ely ( a pair ( p>allel zig-zag l9es4 ,! prim>y w9d+ is usually indicat$ by a heavy l9e hav+ a few] numb] ( zig-zags1 & ! second>y by a f9] l9e hav+ a great] numb] ( zig-zags4 ,9 ?is way ! fact t ! prim>y is ( l>ge wire & ( comp>atively few turns is indicat$4 ,?is diagrammatic symbol may be modifi$ to suit almo/ any conditions1 & :]e a t]ti>y z well z a second>y w9d+ is provid$ x may be %[n by m]ely add+ ano!r zig-zag l9e4 ,illu/ration3 ,fig4 #aae4 ,repeat+-,coil ,symbols ,! repeat+ coil is indicat$ symbolically 9 ! two diagrams ( ,fig4 #aae4 ,:]e !re is no necessity = indicat+ ! int]nal connections ( ! coil1 ! symbol %[n 9 ! left ( ?is figure is usually employ$4 ,:]e1 h[ev]1 ! coil consi/s ( f\r w9d+s r ?an two & ! me?od ( connect+ !m is to be indicat$1 ! symbol at ! "r h& is employ$4 ,9 ,fig4 #aaf ano!r way ( indicat+ a f\r-w9d+ repeat+ coil or induction coil is %[n4 ,sometimes su* w9d+s may be comb9$ by connection to =m m]ely a prim>y & a second>y w9d+1 & 9 o!r cases ! f\r w9d+s all act sep>ately1 9 :i* case "o may be consid]$ ! prim>y & ! o!rs1 respectively1 ! second>y1 t]ti>y1 & quat]n>y4 ,illu/ration3 ,fig4 #aaf4 ,symbol ( ,f\r-,w9d+ ,repeat+ ,coil ,:]e ! toroidal type ( repeat+ coil is employ$1 ! diagram ( ,fig4 #aab1 already ref]r$ to1 is a good symbolic repres5tation4 ,,*apt] ,,xi ,,non-,,inductive ,,resi/ance ,,devices ,x is (t5 desir$ to introduce simple ohmic resi/ance into telephone circuits1 9 ord] to limit ! curr5t fl[1 or to create specific diff]5ces ( pot5tial at giv5 po9ts 9 ! circuit4 ,temp]ature ,coeffici5t4 ,! design or selection ( resi/ance devices = v>i\s purposes frequ5tly involves ! consid]ation ( ! effect ( temp]ature on ! resi/ance ( ! conductor employ$4 ,! resi/ance ( conductors is subject to *ange by *anges 9 temp]ature4 ,:ile ne>ly all metals %[ an increase1 c>bon %[s a decrease 9 its resi/ance :5 heat$4 ,! temp]ature coeffici5t ( a conductor is a factor by :i* ! resi/ance ( ! conductor at a giv5 temp]ature mu/ be multipli$ 9 ord] to det]m9e ! *ange 9 resi/ance ( t conductor br\ght ab\t by a rise 9 temp]ature ( "o degree4 ,,table ,v ,temp]ature ,coeffici5ts ---------------------------------------- ---------------- ,,pure ,,metals ,,temp]ature ,,coeffici5ts ---------------------------------------- --------------- ,,c5tigrade ,,fahr5heit ---------------------------------------- --------------- ,silv] 7anneal$7 #j4jjdjj #j4jjbbb ,copp] 7anneal$7 #j4jjdbh #j4jjbdb ,gold 7#ii4i7 #j4jjcgg #j4jjbaj ,alum9um 7#ii7 #j4jjdbc #j4jjbce ,z9c #j4jjdjf #j4jjbbf ,plat9um 7anneal$7 #j4jjbdg #j4jjacg ,iron #j4jjfbe #j4jjcdg ,nickel #j4jjfb #j4jjcde ,t9 #j4jjddj #j4jjbde ,lead #j4jjdaa #j4jjbbh ,antimony #j4jjchi #j4jjbaf ,m]cury #j4jjjgb #j4jjjdd ,bismu? #j4jjced #j4jjaig ---------------------------------------- --------------- ,positive & ,negative ,coeffici5ts4 ,^? conductors1 9 :i* a rise 9 temp]ature produces an increase 9 resi/ance1 are said to h positive temp]ature coeffici5ts1 :ile ^? 9 :i* a rise 9 temp]ature produces a l[]+ ( resi/ance are said to h negative temp]ature coeffici5ts4 ,! temp]ature coeffici5ts ( pure metals are always positive & = "s ( ! m famili> metals1 h values1 accord+ to ,fo/]1 z 9 ,table ,v4 ,iron1 x w be notic$1 has ! highe/ temp]ature coeffici5t ( all4 ,c>bon1 on ! o!r h&1 has a l>ge negative coeffici5t1 z prov$ by ! fact t ! filam5t ( an ord9>y inc&esc5t lamp has ne>ly twice ! resi/ance :5 cold z :5 heat$ to full c&le-p[]4 ,c]ta9 alloys h be5 produc$ :i* h v l[ temp]ature coeffici5ts1 & ^! are ( value 9 produc+ resi/ance units :i* h practically ! same resi/ance = all ord9>y temp]atures4 ,"s ( ^! alloys also h v high resi/ance z comp>$ ) copp] & are ( value 9 enabl+ "o to obta9 a high resi/ance 9 small space4 ,"o ( ! mo/ valuable resi/ance wires is ( an alloy kn[n z ,g]man silv]4 ,! s-call$ eighte5 p] c5t alloy has approximately #ah4c times ! resi/ance ( copp] & a temp]ature coeffici5t ( 4#jjjaf p] degree ,fahr5heit4 ,! ?irty p] c5t alloy has approximately #bh times ! resi/ance ( copp] & a temp]ature coeffici5t ( 4#jjjbd p] degree ,fahr5heit4 ,= facilitat+ ! design ( resi/ance coils ( ,g]man silv] wire1 ,tables ,,vi & ,,vii are giv51 conta9+ in=mation z to l5g?1 resi/ance1 & weight ( ! eighte5 p] c5t & ! ?irty p] c5t alloys1 respectively1 = all sizes ( wire small] ?an ,no4 #bj ,b4 ,s4 gauge4 ,special resi/ance alloys may be obta9$ hav+ temp]ature coeffici5ts z l[ z 4#jjjjjc p] degree ,fahr5heit4 ,o!r alloys ( nickel & /eel are adapt$ = use :]e ! wire mu/ c>ry heavy curr5ts & be rais$ to comp>atively high temp]atures !reby2 = su* use non-corrosive prop]ties are specially to be desir$4 ,su* wire may be obta9$ hav+ a resi/ance ( ab\t fifty times t ( copp]4 ,,table ,,vi #ah ,p] ,c5t ,g]man ,silv] ,wire ---------------------------------------- --------------------------- ,no4 ,b4 ,s4 ,,diamet] ,,weight ,,l5g? ,,resi/ance ,,gauge ,,in*es ,,p\nds ,,p] ,,foot ,,feet ,,p] ,,p\nd ,,ohms ,,p] ,,foot ---------------------------------------- --------------------------- #ba 4#jbhdf 4#jjbchi #dah4f 4#bccc #bb 4#jbece 4#jjahid #ebg4i 4#bida #bc 4#jbbeg 4#jjaejb #ffe4h 4#cgaj #bd 4#jbjaj 4#jjaaia #hci4e 4#dfgh #be 4#jagij 4#jjjiddi #ajeh4 4#ehii #bf 4#jaeid 4#jjjgdic #acce4 4#gdch #bg 4#jadai 4#jjjeidc #afhc4 4#ichf #bh 4#jabfd 4#jjjdgaa #babc4 #a4ahc #bi 4#jaabf 4#jjjcgce #bfgg4 #a4dia #cj 4#jajjc 4#jjjbifb #ccgf4 #a4hgi #ca 4#jjhibh 4#jjjbcej #dbee4 #b4cga #cb 4#jjgiej 4#jjjahfd #ecff4 #b4iij #cc 4#jjgjhj 4#jjjadgh #fgff4 #c4gga #cd 4#jjfcjd 4#jjjaagb #hecb4 #d4gef #ce 4#jjefad 4#jjjjibie #ajgeh4 #e4iig #cf 4#jjejjj 4#jjjjgcfi #acefi4 #g4efj #cg 4#jjddec 4#jjjjehde #agajh4 #i4ecb #ch 4#jjcife 4#jjjjdfcf #baefi4 #ab4jb #ci 4#jjceca 4#jjjjcfge #bgbji4 #ae4af #dj 4#jjcade 4#jjjjbiag #cdbhb4 #ai4aa ---------------------------------------- --------------------------- ,inductive ,neutrality4 ,:]e ! resi/ance unit is requir$ to be /rictly non-inductive1 & is to be 9 ! =m ( a coil1 special designs mu/ be employ$ to give ! desir$ inductive neutrality4 ,provisions ,aga9/ ,heat+4 ,9 cases :]e a consid]able am\nt ( heat is to be g5]at$ 9 ! resi/ance1 due to ! necessity ( c>ry+ l>ge curr5ts1 special precautions mu/ be tak5 z to ! heat-resi/+ prop]ties ( ! /ructure1 & also z to ! provision ( suffici5t radiat+ surface or its equival5t to provide = ! dissipation ( ! heat g5]at$4 ,types4 ,mica ,c>d ,unit4 ,"o ( ! mo/ common resi/ance coils us$ 9 practice is %[n 9 ,fig4 #aag4 ,?is comprises a coil ( f9e1 b>e ,g]man silv] wire w\nd on a c>d ( mica1 ! w9d+s be+ s spac$ t ! loops are n 9 contact ) ea* o!r4 ,! w9d+ is protect$ by two c>ds ( mica & ! :ole is b\nd 9 place by metal /rips1 to :i* ! ends ( ! w9d+ are atta*$4 ,b9d+ po/s are provid$ on ! ext5d$ portions ( ! t]m9als to assi/ 9 m\nt+ ! resi/ance on a support+ frame1 & ! po/s t]m9ate 9 sold]+ t]m9als by :i* ! resi/ance is connect$ into ! circuit4 ,,table ,,vii #cj ,p] ,c5t ,g]man ,silv] ,wire ---------------------------------------- --------------------------- ,no4 ,b4 ,s4 ,,diamet] ,,weight ,,l5g? ,,resi/ance ,,gauge ,,in*es ,,p\nds ,,p] ,,foot ,,feet ,,p] ,,p\nd ,,ohms ,,p] ,,foot ---------------------------------------- --------------------------- #ba 4#jbhdf 4#jjbdje #dae4h 4#ceha #bb 4#jbece 4#jjaijg #ebd4d 4#deac #bc 4#jbbeg 4#jjaeab #ffa4c 4#efic #bd 4#jbjaj 4#jjaaii #hcc4i 4#gagh #be 4#jagij 4#jjjieac #ajea4 4#ijea #bf 4#jaeid 4#jjjgedd #acbf4 #a4ada #bg 4#jadai 4#jjjeihc #afga4 #a4ddj #bh 4#jabfd 4#jjjdgdc #bajh4 #a4hae #bi 4#jaabf 4#jjjcgfa #bfei4 #b4bhg #cj 4#jajjc 4#jjjbihb #ccec4 #b4hhc #ca 4#jjhibh 4#jjjbcff #dbbg4 #c4fch #cb 4#jjgiej 4#jjjahgf #eccj4 #d4ehh #cc 4#jjgjhj 4#jjjadhh #fgba4 #e4ghf #cd 4#jjfcjd 4#jjjaahj #hdge4 #g4big #ce 4#jjefad 4#jjjjiceh #ajfhf4 #i4bja #cf 4#jjejjj 4#jjjjgdai #acdgh4 #aa4fj #cg 4#jjddec 4#jjjjehhe #afiid4 #ad4fc #ch 4#jjcife 4#jjjjdffh #badbd4 #ah4de #ci 4#jjceca 4#jjjjcgjj #bgjbf4 #bc4bf #dj 4#jjcade 4#jjjjbicg #cdjec4 #bi4cb ---------------------------------------- --------------------------- ,diff]5tially-,w\nd ,unit4 ,ano!r type ( resi/ance coil is t 9 :i* ! w9d+ is plac$ ^u an insulat+ core ( heat-resi/+ mat]ial & w\nd s z to ov]come inductive effects4 ,9 ord] to accompli% ?is1 ! wire to be b\nd on ! core is d\bl$ back on itself at its middle portion to =m two /r&s1 & ^! are w\nd simultane\sly on ! core1 ?us =m+ two spirals ( equal numb] ( turns4 ,! curr5t 9 trav]s+ ! entire coil mu/ fl[ ?r\gh "o spiral 9 "o direction ) relation to ! core1 & 9 ! opposite direction 9 ! o!r spiral1 !reby nullify+ ! inductive effects ( "o spiral by ^? ( ! o!r4 ,?is is call$ a non-inductive w9d+ & is 9 reality an example ( diff]5tial w9d+4 ,lamp ,filam5t4 ,an excell5t type ( non-inductive resi/ance is ! ord9>y c>bon-filam5t inc&esc5t lamp4 ,?is is us$ l>gely 9 ! circuits ( batt]ies1 g5]ators1 & o!r s\rces ( supply to prev5t ov]load 9 case ( %ort circuits on ! l9e4 ,^! are *eap1 durable1 h l>ge curr5t-c>ry+ capacities1 & are n likely to set ?+s afire :5 ov]heat$4 ,an additional advantage incid5t to _! use = ?is purpose is t an ov]load on a circuit 9 :i* !y are plac$ is visibly indicat$ by ! gl[+ ( ! lamp4 ,illu/ration3 ,fig4 #aag4 ,mica ,c>d ,resi/ance ,illu/ration3 ,fig4 #aah4 ,iron-,wire ,balla/ ,obvi\sly1 ! c>bon-filam5t inc&esc5t lamp1 :5 us$ z a resi/ance1 has1 on acc\nt ( ! negative temp]ature coeffici5t ( c>bon1 ! prop]ty ( pres5t+ ! highe/ resi/ance to ! circuit :5 c>ry+ no curr5t1 & ( pres5t+ a l[] & l[] resi/ance z ! curr5t & consequ5t heat+ increases4 ,= "s conditions ( practice ?is is n to be desir$1 & ! opposite *>act]i/ic ( pres5t+ l[ resi/ance to small curr5ts & comp>atively high resi/ance to l>ge curr5ts w\ld be/ meet ! conditions ( practice4 ,iron-,wire ,balla/4 ,claude ,d4 ,eno*s took advantage ( ! v high positive temp]ature coeffici5t ( iron to produce a resi/ance device hav+ ^! *>act]i/ics4 ,8 arrangem5t possesses ! compactness ( ! c>bon-filam5t lamp & is %[n 9 ,fig4 #aah4 ,! resi/ance elem5t prop] is an iron wire1 w\nd on a c5tral /em ( glass1 & ?is is includ$ 9 an exhau/$ bulb s z to avoid oxidation4 ,su* a resi/ance is comp>atively l[ :5 cold1 b :5 trav]s$ by curr5ts suffici5t to heat x consid]ably w (f] a v l>ge increase ( resi/ance to oppose ! fur!r increase ( curr5t4 ,9 a s5se1 x is a self-adju/+ resi/ance1 t5d+ t[>ds ! equalization ( ! fl[ ( curr5t 9 ! circuit 9 :i* x is plac$4 ,,*apt] ,,xii ,,cond5s]s ,*>ge4 ,a conduct+ body insulat$ f all o!r bodies w receive & hold a c]ta9 am\nt ( electricity 7a *>ge71 if subject$ to an electrical pot5tial4 ,?us1 ref]r+ to ,fig4 #aai1 if a metal plate1 insulat$ f o!r bodies1 be connect$ )1 say1 ! positive pole ( a batt]y1 ! negative pole ( :i* is gr\nd$1 a curr5t w fl[ into ! plate until ! plate is rais$ to ! same pot5tial z t ( ! batt]y pole to :i* x is connect$4 ,! am\nt ( electricity t w fl[ into ! plate w dep5d1 o!r ?+s be+ equal1 on ! pot5tial ( ! s\rce f :i* x is *>g$2 9 fact1 x is proportional to ! pot5tial ( ! s\rce f :i* x is *>g$4 ,?is am\nt ( electricity is a measure ( ! capacity ( ! plate1 j z ! am\nt ( wat] t a ba?-tub w hold is a measure ( ! capacity ( ! ba?-tub4 ,capacity4 ,in/ead ( measur+ ! am\nt ( electricity by ! qu>t or p\nd1 z 9 ! case ( mat]ial ?+s1 ! unit ( electrical quantity is ! c\lomb4 ,! unit ( capacity ( an insulat$ conductor is ! f>ad1 & a giv5 insulat$ conductor is said to h unit capacity1 t is1 ! capacity ( "o f>ad1 :5 x w receive a *>ge ( "o c\lomb ( electricity at a pot5tial ( "o volt4 ,ref]r+ to ,fig4 #aai1 ! pot5tial ( ! negative t]m9al ( ! batt]y may be said to be z]o1 s9ce x is connect$ to ! e>?4 ,if ! batt]y %[n be suppos$ to h exactly "o volt pot5tial1 !n ! plate w\ld be said to h ! capacity ( "o f>ad if "o c\lomb ( electricity fl[$ f ! batt]y to ! plate be=e ! plate 0 rais$ to ! same pot5tial z t ( ! positive pole1 t is1 to a pot5tial ( "o volt above ! pot5tial ( ! e>?2 x be+ assum$ t ! plate 0 also at z]o pot5tial be=e ! connection 0 made4 ,ano!r conception ( ?is quantity may be _h by rememb]+ t a c\lomb is su* a quantity ( curr5t z w result f "o amp]e fl[+ "o second4 ,! capacity ( a conductor dep5ds1 among o!r ?+s1 on its area4 ,if ! plate ( ,fig4 #aai %\ld be made twice z l>ge 9 area1 o!r ?+s rema9+ ! same1 x w\ld h twice ! capacity4 ,b !re are o!r factors gov]n+ ! capacity ( a conductor4 ,consid] ! diagram ( ,fig4 #abj1 :i* is suppos$ to repres5t two su* plates z are %[n 9 ,fig4 #aai1 plac$ opposite ea* o!r & connect$ respectively ) ! positive & ! negative poles ( ! batt]y4 ,:5 ! connection betwe5 ! plates & ! batt]y is made1 ! two plates become *>g$ to a diff]5ce ( pot5tial equal to ! electromotive =ce ( ! batt]y4 ,9 ord] to obta9 ^! *>ges1 assume t ! plates 7 ea* at z]o pot5tial be=e ! connection 0 made2 !n curr5t fl[s f ! batt]y into ! plates until !y ea* assume ! pot5tial ( ! correspond+ batt]y t]m9al4 ,if ! two plates be br\ght clos] toge!r1 x w be f\nd t m curr5t w n[ fl[ into ea* ( !m1 al?\gh ! diff]5ce ( pot5tial betwe5 ! two plates mu/ obvi\sly rema9 ! same1 s9ce ea* ( !m is /ill connect$ to ! batt]y4 ,illu/ration3 ,fig4 #aai4 ,cond5s] ,plate ,!ory4 ,due to ! proximity ( ! plates1 ! positive electricity on plate ,a is drawn by ! negative *>ge on plate ,b t[>ds plate ,b1 & likewise ! negative electricity on plate ,b is drawn to ! side t[>ds plate ,a by ! positive *>ge on t plate4 ,^! two *>ges s drawn t[>ds ea* o!r w1 s to speak1 b9d ea* o!r1 & !y are ref]r$ to z b\nd *>ges4 ,! *>ge on ! "r-h& side ( plate ,a & on ! left-h& side ( plate ,b w1 h[ev]1 be free *>ges1 s9ce !re is no?+ to attract !m1 & ^! are1 !re=e1 neutraliz$ by a fur!r fl[ ( electricity f ! batt]y to ! plate4 ,illu/ration3 ,fig4 #abj4 ,!ory ( ,cond5s] ,obvi\sly1 ! clos] toge!r ! plates are ! /rong] w be ! attractive influ5ce ( ! two *>ges on ea* o!r4 ,f ?is x foll[s t 9 ! case ( plate ,a1 :5 ! two plates are be+ mov$ clos] toge!r1 m positive electricity w fl[ into plate ,a to neutralize ! increas+ free negative *>ges on ! "r-h& side ( ! plate4 ,z ! plates are mov$ clos] toge!r /ill1 a new di/ribution ( *>ges w take place1 result+ 9 m positive electricity fl[+ into plate ,a & m negative electricity fl[+ into plate ,b4 ,! clos] proximity ( ! plates1 !re=e1 increases ! capacity ( ! plates = hold+ *>ges1 due to ! increas$ inductive action across ! dielectric sep>at+ ! plates4 ,cond5s] ,def9$4 ,a cond5s] is a device consi/+ ( two adjac5t plates ( conduct+ mat]ial1 sep>at$ by an insulat+ mat]ial1 call$ a dielectric4 ,! purpose is to increase by ! proximity ( ! plates1 ea* to ! o!r1 ! am\nt ( electricity :i* ea* plate w receive & hold :5 subject$ to a giv5 pot5tial4 ,dielectric4 ,we h already se5 t ! capacity ( a cond5s] dep5ds ^u ! area ( its plates1 & also ^u _! di/ance ap>t4 ,!re is /ill ano!r factor on :i* ! capacity ( a cond5s] dep5ds1 i4e41 on ! "* ( ! insulat+ m$ium sep>at+ its plates4 ,! inductive action :i* takes place betwe5 a *>g$ conductor & o!r conductors ne>by x1 z betwe5 plate ,a & plate ,b ( ,fig4 #abj1 is call$ electro/atic induction1 & x plays an important "p 9 telephony4 ,x is f\nd t ! ability ( a giv5 *>g$ conductor to induce *>ges on o!r neighbor+ conductors v>ies l>gely ) ! insulat+ m$ium or dielectric t sep>ates !m4 ,?is quality ( a dielectric1 by :i* x enables inductive action to take place betwe5 two sep>at$ conductors1 is call$ inductive capacity4 ,usually ?is quality ( dielectrics is measur$ 9 t]ms ( ! same quality 9 dry air1 ?is be+ tak5 z unity4 ,:5 s express$1 x is t]m$ specific inductive capacity4 ,to be m accurate ! specific inductive capacity ( a dielectric is ! ratio betwe5 ! capacity ( a cond5s] hav+ t sub/ance z a dielectric1 to ! capacity ( ! same cond5s] us+ dry air at z]o degrees ,c5tigrade & at a pressure ( #ad4g p\nds p] squ>e in* z ! dielectric4 ,to illu/rate1 if two cond5s]s hav+ plates ( equal size & equal di/ance ap>t are con/ruct$1 "o us+ air z ! dielectric & ! o!r us+ h>d cr[n glass z ! dielectric1 ! "o us+ glass w h a capacity ( #f4if times t ( ! "o us+ air4 ,f ?is we say t cr[n glass has a specific inductive capacity ( #f4if4 ,v>i\s au?orities diff] r widely z to ! specific inductive capacity ( _m common sub/ances4 ,! values giv5 9 ,table ,,viii h be5 *os5 f ! ,smi?sonian ,physical ,tables4 ,,table ,,viii ,specific ,inductive ,capacities ---------------------------------------- ------- ,,dielectric ,,ref]r$ ,,to ,,air ,,z #a ---------------------------------------- ------- ,vacuum 4#iiida ,hydrog5 4#iiifg ,c>bonic ,acid #a4jjjcf ,dry ,pap] #a4be to #a4ge ,p>aff9 #a4ie to #b4cb ,ebonite #a4i to #c4dh ,sulphur #b4bd to #c4ij ,%ellac #b4ie to #c4gc ,gutta-p]*a #c4c to #d4i ,plate ,glass #c4ca to #g4e ,porcela9 #d4ch ,mica #d4f to #h4j ,glass--,light ,fl9t #f4fa ,glass--,h>d ,cr[n #f4if ,sel5ium #aj4b ---------------------------------------- ------- ,?is data is int]e/+ z %[+ ! wide div]g5ce 9 specific inductive capacities ( v>i\s mat]ials1 & also %[+ ! wide div]g5ce 9 diff]5t obs]vations ( ! same mat]ial4 ,und\bt$ly1 ?is latt] is due ma9ly to ! fact t v>i\s mat]ials diff] l>gely 9 !mselves1 z 9 ! case ( p>aff91 = in/ance1 :i* exhibits widely diff]5t specific inductive capacities accord+ to ! diff]5ce 9 rapidity ) :i* x is cool$ 9 *ang+ f a liquid to a solid /ate4 ,we see !n t ! capacity ( a cond5s] v>ies z ! area ( its plates1 z ! specific inductive capacity ( ! dielectric employ$1 & also inv]sely z ! di/ance betwe5 ! plates4 ,obvi\sly1 !re=e1 9 mak+ a cond5s] ( l>ge capacity1 x is important to h z l>ge an area ( ! plate z possible2 to h !m z close toge!r z possible2 to h ! dielectric a good insulat+ m$ium s t !re w be practically no leakage betwe5 ! plates2 & to h ! dielectric ( z high a specific inductive capacity z economy & suitability ( mat]ial 9 o!r respects w p]mit4 ,dielectric ,mat]ials4 ,mica4 ,( all dielectrics mica is ! mo/ suitable = cond5s]s1 s9ce x has v high insulation resi/ance & also high specific inductive capacity1 & fur!rmore may be obta9$ 9 v ?9 %eets4 ,high-grade cond5s]s1 su* z are us$ = measurem5ts & /&>dization purposes1 usually h mica = ! dielectric4 ,illu/ration3 ,fig4 #aba4 ,roll$ ,cond5s] ,dry ,pap]4 ,! dem&s ( telephonic practice are1 h[ev]1 su* z to require cond5s]s ( v *eap con/ruction ) l>ge capacity 9 a small space4 ,= ?is purpose ?9 bond pap]1 saturat$ ) p>aff91 has be5 f\nd to be ! be/ dielectric4 ,! conductors 9 cond5s]s are almo/ always ( t9foil1 ?is be+ an ideal mat]ial on acc\nt ( its *eapness & its ?9ness4 ,be=e telephony made su* urg5t dem&s = a *eap compact cond5s]1 ! cu/om>y way ( mak+ !m 0 to lay up alt]nate %eets ( dielectric mat]ial1 ei!r ( oil$ pap] or mica & t9foil1 ! %eets ( t9foil be+ cut some:at small] ?an ! %eets ( dielectric mat]ial 9 ord] t ! prop] insulation might be secur$ at ! edges4 ,aft] a suffici5t numb] ( su* plates 7 built up ! alt]nate %eets ( t9foil 7 connect$ toge!r to =m "o composite plate ( ! cond5s]1 :ile ! o!r %eets 7 simil>ly connect$ toge!r to =m ! o!r plate4 ,obvi\sly1 9 ?is way a v l>ge area ( plates c\ld be secur$ ) a m9imum degree ( sep>ation4 ,illu/ration3 ,fig4 #abb4 ,roll$ ,cond5s] ,!re has be5 develop$ = use 9 telephony1 h[ev]1 & its use has s9ce ext5d$ into o!r arts requir+ cond5s]s1 :at is call$ ! roll$ cond5s]4 ,?is is =m$ by roll+ toge!r 9 a flat roll f\r %eets ( ?9 bond pap]1 #a1 #b1 #c1 & #d1 & two some:at n>r[] /rips ( t9foil1 #e & #f1 ,fig4 #aba4 ,! /rips ( t9foil & pap] are f$ on to ! roll 9 cont9u\s l5g?s & 9 su* mann] t two %eets ( pap] w lie betwe5 ! two /rips ( t9foil 9 all cases4 ,?9 %eet metal t]m9als #g & #h are roll$ into ! cond5s] z x is be+ w\nd1 & z ^! project beyond ! edges ( ! pap] !y =m conv5i5t t]m9als = ! cond5s] aft] x is f9i%$4 ,aft] x is roll$1 ! roll is boil$ 9 hot p>aff9 s z to ?or\ghly impregnate x & expel all moi/ure4 ,x is !n squeez$ 9 a press & all[$ to cool :ile "u pressure4 ,9 ?is way ! surplus p>aff9 is expell$ & ! plates are br\ght v close toge!r4 ,x !n appe>s z 9 ,fig4 #abb4 ,! cond5s] is n[ seal$ 9 a metallic case1 usually rectangul> 9 =m1 & pres5ts ! appe>ance %[n 9 ,fig4 #abc4 ,illu/ration3 ,fig4 #abc4 ,roll$ ,cond5s] ,a lat] me?od ( cond5s] mak+ :i* has n yet be5 ?or\ghly prov5 9 practice1 b :i* bids fair to produce good results1 v>ies f ! me?od j describ$ 9 t a pap] is us$ :i* 9 itself is coat$ ) a v ?9 conduct+ mat]ial4 ,?is conduct+ mat]ial is ( metallic nature & 9 reality =ms a "p ( ! pap]4 ,to =m a cond5s] ( ?is ! %eets are m]ely roll$ toge!r & !n boil$ 9 p>aff9 & compress$ z be=e4 ,sizes4 ,! cond5s]s ord9>ily us$ 9 telephone practice range 9 capacity f ab\t #a_/d micr(>ad to #b micr(>ads4 ,:5 l>g] capacities ?an #b micr(>ads are desir$1 !y may be obta9$ by connect+ sev]al ( ! small] size cond5s]s 9 multiple4 ,table ,,ix gives ! capacity1 %ape1 & dim5sions ( a v>iety ( cond5s]s select$ f ^? regul>ly on ! m>ket4 ,,table ,,ix ,cond5s] ,data ---------------------------------------- -------------------- ,,dim5sions ,,9 ,,in*es ,,capacity ,,%ape ------------------------------- ,height ,wid? ,?ickness ---------------------------------------- ------------------ #b m4 f4 ,rectangul> #i-a_/f #d-c_/d #aa_/af #a m4 f4 #i-a_/f #d-c_/d #aa_/af #a m4 f4 #d-c_/d #b-c_/cb #ac_/af #a_/b m4 f4 #b-c_/d #a-a_/d #c_/d #a m4 f4 #d-ac_/af #b-a_/cb #be_/cb #a_/b m4 f4 #d-c_/d #b-c_/cb #ac_/af #c_/aj m4 f4 #d-c_/d #b-c_/cb #ac_/af #a m4 f4 #b-c_/d #c l ---------------------------------------- ------------------ ,conv5tional ,symbols4 ,! conv5tional symbols usually employ$ to repres5t cond5s]s 9 telephone diagrams are %[n 9 ,fig4 #abd4 ,^! all convey ! idea ( ! adjac5t conduct+ plates sep>at$ by insulat+ mat]ial4 ,illu/ration3 ,fig4 #abd4 ,cond5s] ,symbols ,functions4 ,obvi\sly1 :5 plac$ 9 a circuit a cond5s] (f]s a complete b>ri] to ! fl[ ( direct curr5t1 s9ce no conduct+ pa? exi/s betwe5 its t]m9als1 ! dielectric (f]+ a v high insulation resi/ance4 ,if1 h[ev]1 ! cond5s] is connect$ across ! t]m9als ( a s\rce ( alt]nat+ curr5t1 ?is curr5t fl[s fir/ 9 "o direction & !n 9 ! o!r1 ! electromotive =ce 9 ! circuit increas+ f z]o to a maximum 9 "o direction1 & !n decreas+ back to z]o & to a maximum 9 ! o!r direction1 & s on4 ,) a cond5s] connect$ s z to be subject$ to su* alt]nat+ electromotive =ces1 z ! electromotive =ce beg9s to rise ! electromotive =ce at ! cond5s] t]m9als w also rise & a curr5t w1 !re=e1 fl[ into ! cond5s]4 ,:5 ! electromotive =ce rea*es its maximum1 ! cond5s] w h receiv$ its full *>ge = t pot5tial1 & ! curr5t fl[ into x w cease4 ,:5 ! electromotive =ce beg9s to fall1 ! cond5s] c no long] reta9 its *>ge & a curr5t w1 !re=e1 fl[ out ( x4 ,app>5tly1 !re=e1 !re is a fl[ ( curr5t ?r\gh ! cond5s] ! same z if x 7 a conductor4 ,means = ,assort+ ,curr5ts4 ,9 conclusion1 x is obvi\s t ! telephone eng9e] has )9 8 rea* 9 ! v>i\s coils--:e!r non-inductive or inductive1 or :e!r hav+ "o or sev]al w9d+s--& 9 ! cond5s]1 a v>iety ( tools by :i* he may a*ieve a great _m useful ends 9 8 circuit "w4 ,obvi\sly1 ! cond5s] af=ds a means = transmitt+ voice curr5ts or fluctuat+ curr5ts1 & = exclud+ /eady curr5ts4 ,likewise ! imp$ance coil af=ds a means = readily transmitt+ /eady curr5ts b practically exclud+ voice curr5ts or fluctuat+ curr5ts4 ,by ! use ( ^! v simple devices x is possible to sift out ! voice curr5ts f a circuit conta9+ bo? /eady & fluctuat+ curr5ts1 or x is possible 9 ! same mann] to sift out ! /eady curr5ts & to leave ! voice curr5ts alone to trav]se ! circuit4 ,great use is made 9 ! design ( telephone circuits ( ! fact t ! electromagnets1 :i* accompli% ! useful me*anical results 9 caus+ ! movem5t ( p>ts1 possess ! quality ( imp$ance4 ,?us1 ! magnets :i* op]ate v>i\s signal+ relays at ! c5tral (fice are (t5 us$ also z imp$ance coils 9 portions ( ! circuit ?r\gh :i* x is desir$ to h only /eady curr5ts pass4 ,if1 on ! o!r h&1 x is necess>y to place a relay magnet1 hav+ consid]able imp$ance1 directly 9 a talk+ circuit1 ! bad effects ( ?is on ! voice curr5ts may be elim9at$ by %unt+ ?is coil ) a cond5s]1 or ) a comp>atively high non-inductive resi/ance4 ,! voice curr5ts w fl[ ar\nd ! high imp$ance ( ! relay coil ?r\gh ! cond5s] or resi/ance1 :ile ! /eady curr5ts1 :i* are ! ones :i* mu/ be dep5d$ ^u to op]ate ! relay1 are /ill =c$ 9 :ole or 9 "p to pass ?r\gh ! relay coil :]e !y belong4 ,9 a simil> way ! induction coil af=ds a means = keep+ two circuits completely isolat$ s f> z ! direct fl[ ( curr5t betwe5 !m is conc]n$1 & yet ( readily transmitt+1 by electromagnetic induction1 curr5ts f "o ( ^! circuits to ! o!r4 ,"h is a means ( isolation s f> z direct curr5t is conc]n$1 ) complete communication = alt]nat+ curr5t4 ,,*apt] ,,xiii ,,curr5t ,,supply ,,to ,,transmitt]s ,! me?ods by :i* curr5t is suppli$ to ! transmitt] ( a telephone = en]giz+ x1 may be classifi$ "u two divisions3 fir/1 ^? :]e ! batt]y or o!r s\rce ( curr5t is locat$ at ! /ation ) ! transmitt] :i* x supplies2 & second1 ^? :]e ! batt]y or o!r s\rce ( curr5t is locat$ at a di/ant po9t f ! transmitt]1 ! batt]y 9 su* cases s]v+ z a common s\rce ( curr5t = ! supply ( transmitt]s at a numb] ( /ations4 ,! advantages ( putt+ ! transmitt] & ! batt]y :i* supplies x ) curr5t 9 a local circuit ) ! prim>y ( an induction coil1 & plac+ ! second>y ( ! induction coil 9 ! l9e1 h already be5 po9t$ out b may be briefly summ>iz$ z foll[s3 ,:5 ! transmitt] is plac$ directly 9 ! l9e circuit & ! l9e is ( consid]able l5g?1 ! curr5t :i* passes ?r\gh ! transmitt] is necess>ily r small unless a batt]y ( high pot5tial is us$2 &1 fur!rmore1 ! total *ange 9 resi/ance :i* ! transmitt] is capable ( produc+ is b a small proportion ( ! total resi/ance ( ! l9e1 &1 !re=e1 ! curr5t *anges produc$ by ! transmitt] are relatively small4 ,on ! o!r h&1 :5 ! transmitt] is plac$ 9 a local circuit ) ! batt]y1 ?is circuit may be ( small resi/ance & ! curr5t relatively l>ge1 ev5 ?\gh suppli$ by a l[-voltage batt]y2 s t ! transmitt] is capable ( produc+ relatively l>ge *anges 9 a relatively l>ge curr5t4 ,to draw a comp>ison betwe5 ^! two g5]al classes ( transmitt] curr5t supply1 a numb] ( cases w be consid]$ 9 connection ) ! foll[+ figures1 9 ea* ( :i* two /ations connect$ by a telephone l9e are %[n4 ,brief ref]5ce to ! local batt]y me?od ( supply+ curr5t w be made 9 ord] to make ?is *apt] conta91 z f> z possible1 all ( ! commonly us$ me?ods ( curr5t supply to transmitt]s4 ,illu/ration3 ,a ,,typical ,,m$ium-,,siz$ ,,multiple ,,swit*bo>d ,,equipm5t ,local ,batt]y4 ,9 ,fig4 #abe two /ations are %[n connect$ by a gr\nd$ l9e wire4 ,! transmitt] ( ea* /ation is includ$ 9 a l[-resi/ance prim>y circuit includ+ a batt]y & ! prim>y w9d+ ( an induction coil1 ! relation betwe5 ! prim>y circuits & ! l9e circuits be+ e/abli%$ by ! inductive action betwe5 ! prim>y & ! second>y w9d+s ( induction coils1 ! second>y 9 ea* case be+ 9 ! l9e circuits ) ! receiv]s4 ,illu/ration3 ,fig4 #abe4 ,local-,batt]y ,/ations ) ,gr\nd$ ,circuit ,fig4 #abf %[s exactly ! same arrangem5t b ) a metallic circuit r ?an a gr\nd$ circuit4 ,! /ud5t %\ld become accu/om$ to ! replac+ ( "o ( ! l9e wires ( a metallic circuit by ! e>?1 & to ! me?od1 employ$ 9 ,figs4 #abe & #abf1 ( indicat+ a gr\nd$ circuit z di/+ui%$ f a metallic circuit4 ,illu/ration3 ,fig4 #abf4 ,local-,batt]y ,/ations ) ,metallic ,circuit ,9 ,fig4 #abg is %[n a slight modification ( ! circuit %[n 9 ,fig4 #abf1 :i* consi/s ( connect+ "o end ( ! prim>y w9d+ to "o end ( ! second>y w9d+ ( ! induction coil1 ?us l9k+ toge!r ! prim>y circuit & ! l9e circuit1 a portion ( ea* ( ^! circuits be+ common to a %ort piece ( ! local wir+4 ,!re is no diff]5ce :atev] 9 ! action ( ! circuits %[n 9 ,figs4 #abf & #abg1 ! latt] be+ %[n m]ely = ! purpose ( br++ out ?is fact4 ,x is v common1 p>ticul>ly 9 local-batt]y circuits1 to connect "o end ( ! prim>y & ! second>y w9d+s1 z by do+ s x is (t5 possible to save a contact po9t 9 ! hook swit* & also to simplify ! wir+4 ,illu/ration3 ,fig4 #abg4 ,local-,batt]y ,/ations ) ,metallic ,circuit ,! advantages to be ga9$ by employ+ a local batt]y at ea* subscrib]'s /ation associat$ ) ! transmitt] 9 ! prim>y circuit ( an induction coil are att5d$ by c]ta9 disadvantages f a comm]cial /&po9t4 ,! prim>y batt]y is n an economical way to g5]ate electric en]gy4 ,9 all its comm]cial =ms x involves ! consumption ( z9c & z9c is an exp5sive fuel4 ,! actual am\nt ( curr5t 9 watts requir$ by a telephone is small1 h[ev]1 & ?is disadvantage due to ! inexp5sive me?od ( g5]at+ curr5t w\ld n 9 itself be ( great importance4 ,a m s]i\s objection to ! use ( local batt]ies at subscrib]s' /ations appe>s :5 ! subject is consid]$ f ! /&po9t ( ma9t5ance4 ,batt]ies1 :e!r ( ! s-call$ dry or wet type1 gradually det]iorate1 ev5 :5 n us$1 & 9 cases :]e ! telephone is us$ _m times a day ! det]ioration is comp>atively rapid4 ,?is makes necess>y ! occasional r5ewals ( ! batt]ies ) ! att5dant exp5se = new batt]ies or new mat]ial1 & ( labor & transportation 9 visit+ ! /ation4 ,! labor item becomes m s]i\s :5 ! /ations are scatt]$ 9 a sp>sely settl$ community1 9 :i* case ! visit+ ( ! /ations1 ev5 = ! p]=mance ( a task t w\ld require b a few m9utes' "t1 may consume "s h\rs on ! "p ( ! employes 9 gett+ !re & back4 ,common ,batt]y4 ,advantages4 ,x w\ld be m economical if all ( ! curr5t = ! subscrib]s' transmitt]s c\ld be suppli$ f a s+le comp>atively effici5t g5]at+ s\rce in/ead ( f a multitude ( ineffici5t small s\rces scatt]$ ?r\gh\t ! community s]v$ by ! ex*ange4 ,! advantage ( su* c5tralization lies n only 9 m economic g5]at+ means1 b also 9 hav+ ! common s\rce ( curr5t locat$ at "o place1 :]e x may be c>$ = ) a m9imum am\nt ( exp5se4 ,su* consid]ations h result$ 9 ! s-call$ common-batt]y sy/em1 :]e9 ! curr5t = all ! subscrib]s' transmitt]s is furni%$ f a s\rce locat$ at ! c5tral (fice4 ,:]e su* a me?od ( supply+ curr5t is practic$1 ! result has also be51 9 ne>ly all cases1 ! do+ away ) ! subscrib]'s magneto g5]ators1 rely+ on ! c5tral-(fice s\rce ( curr5t to furni% ! en]gy = enabl+ ! subscrib] to signal ! op]ator4 ,su* sy/ems1 !re=e1 conc5trate all ( ! s\rces ( en]gy at ! c5tral (fice & = t reason !y are frequ5tly ref]r$ to z c5tral-en]gy sy/ems4 ,,note4 ,9 ?is *apt] ! c5tral-en]gy or common-batt]y sy/em w be consid]$ only 9 s f> z ! supply ( curr5t = en]giz+ ! subscrib]s' transmitt]s is conc]n$1 ! discussion ( ! action ( signal+ be+ res]v$ = subsequ5t *apt]s4 ,s]ies ,batt]y4 ,if b a s+le pair ( l9es _h to be consid]$1 ! arrangem5t %[n 9 ,fig4 #abh might be employ$4 ,9 ?is ! batt]y is locat$ at ! c5tral (fice & plac$ 9 s]ies ) ! two gr\nd$ l9es lead+ f ! c5tral (fice to ! two subscrib]s' /ations4 ,! voltage ( ?is batt]y is made suffici5t to furni% ! requir$ curr5t ov] ! resi/ance ( ! entire l9e circuit ) its includ$ in/rum5ts4 ,obvi\sly1 *anges 9 resi/ance 9 ! transmitt] at ,/ation ,a w affect ! fl[ ( curr5t 9 ! entire l9e & ! fluctuations result+ f ! vibration ( ! transmitt] diaphragm w1 !re=e1 reproduce ^! s\nds 9 ! receiv] at ,/ation ,b1 z well z 9 t at ,/ation ,a4 ,illu/ration3 ,fig4 #abh4 ,batt]y 9 ,s]ies ) ,two ,l9es ,an exactly simil> arrangem5t appli$ to a metallic circuit is %[n 9 ,fig4 #abi4 ,9 ?us plac+ ! batt]y 9 s]ies 9 ! circuit betwe5 ! two /ations1 z %[n 9 ,figs4 #abh & #abi1 x is obvi\s t ! transmitt] at ea* /ation is compell$ to v>y ! resi/ance ( ! entire circuit compris+ ! two l9es 9 s]ies1 9 ord] to affect ! receiv] at di/ant /ations4 ,?is is 9 effect mak+ ! transmitt] circuit twice z long z is necess>y1 z w be %[n 9 ! subsequ5t sy/ems consid]$4 ,fur!rmore1 ! plac+ ( ! batt]y 9 s]ies 9 ! circuit ( ! two comb9$ l9es does n l5d itself readily to ! supply ( curr5t f a common s\rce to m ?an a s+le pair ( l9es4 ,illu/ration3 ,fig4 #abi4 ,batt]y 9 ,s]ies ) ,two ,l9es ,s]ies ,sub/ation ,circuit4 ,! arrangem5t at ! sub/ations--consi/+ 9 plac+ ! transmitt] & ! receiv] 9 s]ies 9 ! l9e circuit1 z %[n 9 ,figs4 #abh & #abi--;is ! simple/ possible "o1 & has be5 us$ to a consid]able ext5t1 b x has be5 subject to ! s]i\s objection1 :]e receiv]s hav+ p]man5t magnets 7 us$1 ( mak+ x necess>y to s connect ! receiv] 9 ! l9e circuit t ! /eady curr5t f ! batt]y w\ld n set up a magnetization 9 ! cores ( ! receiv] 9 su* a direction z to neutralize or oppose ! magnetization ( ! p]man5t magnets4 ,z long z ! curr5t fl[$ ?r\gh ! receiv] coils 9 su* a direction z to supplem5t ! magnetization ( ! p]man5t magnets1 no h>m 0 usually done1 b :5 ! curr5t fl[$ ?r\gh ! receiv] coils 9 su* a way z to neutralize or oppose ! magnetiz+ =ce ( ! p]man5t magnets1 ! action ( ! receiv] 0 greatly int]f]$ )4 ,z a result1 x 0 necess>y to always connect ! receiv]s 9 ! l9e circuit 9 a c]ta9 way1 & ?is op]ation 0 call$ pol+4 ,9 ord] to obviate ! necessity = pol+ & also to br+ ab\t o!r desirable features1 x has be51 until rec5tly1 almo/ univ]sal practice to s arrange ! receiv] t x w\ld be 9 ! circuit ( ! voice curr5ts pass+ ov] ! l9e1 b w\ld n be trav]s$ by direct curr5ts1 ?is condition be+ br\ght ab\t by v>i\s arrangem5ts ( cond5s]s1 imp$ance coils1 or induction coils1 z w be %[n lat]4 ,dur+ ! ye> #aiji1 h[ev]1 ! adoption by sev]al conc]ns ( ! s-call$ direct-curr5t receiv] has made x necess>y = ! direct curr5t to fl[ ?r\gh ! receiv] coils 9 ord] to give ! prop] magnetization to ! receiv] cores1 & ?is has br\ght ab\t a return to ! v simple =m ( sub/ation circuit1 :i* includes ! receiv] & ! transmitt] directly 9 ! circuit ( ! l9e4 ,?is illu/rates well an occurr5ce t is frequ5tly obs]v$ by ^? :o h opportunity to wat* closely ! developm5t ( an art4 ,at "o "t ! conditions w be su* z to call = complicat$ arrangem5ts1 & = ye>s ! aim ( inv5tors w be to p]fect ^! arrangem5ts2 !n1 aft] !y are p]fect$1 adopt$1 & /&>diz$1 a new idea1 or a slight alt]ation 9 ! practice 9 "s o!r respect1 w dem& a return to ! fir/ pr9ciples & wipe out ! necessity = ! ?+s t h be5 s ardu\sly /riv5 =4 ,illu/ration3 ,fig4 #acj4 ,bridg+ ,batt]y ) ,repeat+ ,coil ,bridg+ ,batt]y ) ,repeat+ ,coil4 ,z po9t$ out1 ! plac+ ( ! batt]y 9 s]ies 9 ! l9e circuit 9 ! c5tral (fice is n desirable1 &1 s f> z we are aw>e1 has nev] be5 ext5sively us$4 ,! univ]sal practice1 !re=e1 is to place x 9 a bridge pa? across ! l9e circuit1 & a numb] ( arrangem5ts employ+ ?is basic idea are 9 wide use4 ,9 ,fig4 #acj is %[n ! /&>d arrangem5t ( ! ,we/]n ,electric ,company1 employ$ by practically all ! ,bell op]at+ companies4 ,9 ?is ! batt]y at ! c5tral (fice is connect$ 9 ! middle ( ! two sides ( a repeat+ coil s t ! curr5t f ! batt]y is f$ out to ! two connect$ l9es 9 multiple4 ,ref]r+ to ! middle portion ( ?is figure %[+ ! c5tral-(fice app>atus1 #a & #b may be consid]$ z ! two halves ( "o side ( a repeat+ coil divid$ s t ! batt]y may be cut into _! circuit4 ,likewise1 #c & #d may be consid]$ z ! two halves ( ! o!r side ( ! repeat+ coil simil>ly divid$ = ! same purpose4 ,! w9d+s ( ?is repeat+ coil are ord9>ily alike2 t is1 #a & #b comb9$ h ! same resi/ance1 numb] ( turns1 & imp$ance z #c & #d comb9$4 ,! two sides ( ?is coil are alt]nately us$ z prim>y & second>y1 #a & #b =m+ ! prim>y :5 ,/ation ,a is talk+1 & #c & #d1 ! second>y2 & vice v]s :5 ,/ation ,b is talk+4 ,z w be se51 ! curr5t fl[+ f ! positive pole ( ! batt]y w divide & fl[ ?r\gh ! w9d+s #b & #d2 !nce ov] ! upp] limb ( ea* l9e1 ?r\gh ! transmitt] at ea* /ation1 & back ov] ! l[] limbs ( ! l9e1 ?r\gh ! w9d+s #a & #c1 :]e ! two pa?s reunite & pass to ! negative pole ( ! batt]y4 ,x is evid5t t :5 nei!r transmitt] is be+ us$ ! curr5t fl[+ ?r\gh bo? l9es w be a /eady curr5t & t1 !re=e1 nei!r l9e w h an inductive effect on ! o!r4 ,:51 h[ev]1 ! transmitt] at ,/ation ,a is us$ ! v>iations 9 ! resi/ance caus$ by x w cause undulations 9 ! curr5t4 ,^! undulations1 pass+ ?r\gh ! w9d+s #a & #b ( ! repeat+ coil1 w cause1 by electromagnetic induction1 alt]nat+ curr5ts to fl[ 9 ! w9d+s #c & #d1 & ^! alt]nat+ curr5ts w be sup]impos$ on ! /eady curr5ts fl[+ 9 t l9e & w affect ! receiv] at ,/ation ,b1 z w be po9t$ out4 ,! rev]se conditions exi/ :5 ,/ation ,b is talk+4 ,bell ,sub/ation ,arrangem5t4 ,! sub/ation circuits at ! /ations 9 ,fig4 #acj are illu/rative ( "o ( ! commonly employ$ me?ods ( prev5t+ ! /eady curr5t f ! batt]y f fl[+ ?r\gh ! receiv] coil4 ,?is p>ticul> arrangem5t is t employ$ by ! common-batt]y in/rum5ts ( ! v>i\s ,bell companies4 ,consid]+ ! action at ,/ation ,b1 x is evid5t t ! /eady curr5t w pass ?r\gh ! transmitt] & ?r\gh ! second>y w9d+ ( ! induction coil1 & t z long z ?is curr5t is /eady no curr5t w fl[ ?r\gh ! telephone receiv]4 ,! receiv]1 transmitt]1 & prim>y w9d+ ( ! induction coil are1 h[ev]1 includ$ 9 a local circuit ) ! cond5s]4 ,! pres5ce ( ! cond5s] precludes ! possibility ( direct curr5t fl[+ 9 ?is pa?4 ,consid]+ ,/ation ,a z a receiv+ /ation1 x is evid5t t ! voice curr5ts com+ to ! /ation ov] ! l9e w pass ?r\gh ! second>y w9d+ & w induce alt]nat+ curr5ts 9 ! prim>y w9d+ :i* w circulate ?r\gh ! local circuit conta9+ ! receiv] & ! cond5s]1 & ?us actuate ! receiv]4 ,! consid]ations are n s simple :5 ! /ation is be+ treat$ z a transmitt+ /ation4 ,"u ?is condition ! /eady curr5t passes ?r\gh ! transmitt] 9 an obvi\s mann]4 ,x is cle> t if ! local circuit conta9+ ! receiv] did n exi/1 ! circuit w\ld be op]ative z a transmitt+ circuit because ! transmitt] w\ld produce fluctuations 9 ! /eady curr5t fl[+ 9 ! l9e & ?us be able to affect ! di/ant /ation4 ,! transmitt]1 !re=e1 has a direct action on ! curr5ts fl[+ 9 ! l9e by ! v>iation 9 resi/ance :i* x produces 9 ! l9e circuit4 ,!re is1 h[ev]1 a subsidi>y action 9 ?is circuit4 ,obvi\sly1 !re is a drop ( pot5tial across ! transmitt] t]m9als due to ! fl[ ( /eady curr5t4 ,?is means t ! upp] t]m9al ( ! cond5s] w be *>g$ to ! same pot5tial z ! upp] t]m9al ( ! transmitt]1 :ile ! l[] t]m9al ( ! cond5s] w be ( ! same pot5tial z ! l[] t]m9al ( ! transmitt]4 ,:51 n[1 ! transmitt] v>ies its resi/ance1 a v>iation 9 ! pot5tial across its t]m9als w occur2 & z a result1 a v>iation 9 pot5tial across ! t]m9als ( ! cond5s] w occur1 & ?is means t alt]nat+ curr5ts w fl[ ?r\gh ! prim>y w9d+ ( ! induction coil4 ,! transmitt]1 !re=e1 by its action1 causes alt]nat+ curr5ts to fl[ ?r\gh ! prim>y ( ?is induction coil & x causes1 by direct action on ! circuit ( ! l9e1 fluctuations 9 ! /eady curr5t fl[+ 9 ! l9e4 ,! alt]nat+ curr5ts fl[+ 9 ! prim>y ( ! coil induce curr5ts 9 ! second>y ( ! coil :i* supplem5t & augm5t ! fluctuations produc$ by ! direct action ( ! transmitt]4 ,?is circuit may be look$ at1 !re=e1 9 ! light ( comb9+ ! direct action :i* ! transmitt] produces 9 ! curr5t 9 ! l9e ) ! action :i* ! transmitt] produces 9 ! local circuit conta9+ ! prim>y ( ! induction coil1 ?is action be+ repeat$ 9 ! l9e circuit ?r\gh ! second>y ( ! induction coil4 ,! receiv] 9 ?is circuit is plac$ 9 ! local circuit1 & is ?us n trav]s$ by ! /eady curr5ts fl[+ 9 ! l9e4 ,!re is ?us no necessity = pol+ x4 ,?is circuit is v effici5t1 b is subject to ! objection ( produc+ a heavy side tone 9 ! receiv] ( ! transmitt+ /ation4 ,by side tone is meant ! noises :i* are produc$ 9 ! receiv] at a /ation by virtue ( ! action ( ! transmitt] at t /ation4 ,side tone is objectionable = sev]al reasons3 fir/1 x is sometimes annoy+ to ! subscrib]2 second1 & ( m importance1 ! subscrib] :o is talk+1 he>+ a v l\d noise 9 8 own receiv]1 unconsci\sly assumes t he is talk+ too l\d &1 !re=e1 l[]s 8 voice1 sometimes to su* an ext5t t x w n prop]ly rea* ! di/ant /ation4 ,illu/ration3 ,fig4 #aca4 ,bridg+ ,batt]y ) ,imp$ance ,coils ,bridg+ ,batt]y ) ,imp$ance ,coils4 ,! me?od ( fe$+ curr5t to ! l9e f ! common batt]y1 %[n 9 ,fig4 #acj1 is call$ ! split repeat+-coil me?od4 ,z di/+ui%$ f ?is is ! imp$ance-coil me?od :i* is %[n 9 ,fig4 #aca4 ,9 ?is ! batt]y is bridg$ across ! circuit ( ! comb9$ l9es 9 s]ies ) two imp$ance coils1 #a & #b1 "o on ea* side ( ! batt]y4 ,! /eady curr5ts f ! batt]y f9d ready pa? ?r\gh ^! imp$ance coils :i* are ( comp>atively l[ ohmic resi/ance1 & ! curr5t divides & passes 9 multiple ov] ! circuits ( ! two l9es4 ,voice curr5ts1 h[ev]1 orig9at+ at ei!r "o ( ! /ations1 w n pass ?r\gh ! %unt across ! l9e at ! c5tral (fice on acc\nt ( ! high imp$ance (f]$ by ^! coils1 & z a result !y are compell$ to pass on to ! di/ant /ation & affect ! receiv] !re1 z desir$4 ,?is imp$ance-coil me?od seems to pres5t ! advantage ( great] simplicity ov] ! repeat+-coil me?od %[n 9 ,fig4 #acj1 & s f> z talk+ effici5cy is conc]n$1 !re is little to *oose betwe5 ! two4 ,! repeat+-coil me?od1 h[ev]1 has ! advantage ov] ?is imp$ance-coil me?od1 because by x ! two l9es are practically divid$ except by ! inductive connection betwe5 ! two w9d+s1 & z a result an unbalanc$ condition ( "o ( ! connect$ l9es is n z likely to produce an unbalanc$ condition 9 ! o!r z :]e ! two l9es are connect$ /raight ?r\gh1 z ) ! imp$ance-coil me?od4 ,! sub/ation arrangem5t ( ,fig4 #aca is ! same z t ( ,fig4 #acj4 ,illu/ration3 ,fig4 #acb4 ,d\ble-,batt]y ,kellogg ,sy/em ,d\ble ,batt]y ) ,imp$ance ,coils4 ,a modification ( ! imp$ance-coil me?od is us$ 9 all ( ! c5tral-(fice "w ( ! ,kellogg ,swit*bo>d & ,supply ,company4 ,?is employs a comb9ation ( imp$ance coils & cond5s]s1 & 9 effect isolates ! l9es conductively f ea* o!r z completely z ! repeat+-coil me?od4 ,x is *>act]i/ic ( all ! ,kellogg common-batt]y sy/ems t !y employ two batt]ies in/ead ( "o1 "o ( ^! be+ connect$ 9 all cases ) ! call+ l9e ( a pair ( connect$ l9es & ! o!r 9 all cases ) ! call$ l9e4 ,z %[n 9 ,fig4 #acb1 ! left-h& batt]y is connect$ ) ! l9e lead+ to ,/ation ,a ?r\gh ! imp$ance coils #a & #b4 ,likewise1 ! "r-h& batt]y is connect$ to ! l9e ( ,/ation ,b ?r\gh ! imp$ance coils #c & #d4 ,^! f\r imp$ance coils are w\nd on sep>ate cores & d n h any inductive relation :atsoev] ) ea* o!r4 ,cond5s]s #e & #f are employ$ to completely isolate ! l9es conductively4 ,curr5t f ! left-h& batt]y1 !re=e1 passes only to ,/ation ,a1 & curr5t f ! "r-h& batt]y to ,/ation ,b4 ,:5ev] ! transmitt] at ,/ation ,a is actuat$ ! undulations ( curr5t :i* x produces 9 ! l9e cause a v>y+ diff]5ce ( pot5tial across ! outside t]m9als ( ! two imp$ance coils #a & #b4 ,?is means t ! two left-h& t]m9als ( cond5s]s #e & #f are subject$ to a v>y+ diff]5ce ( pot5tial & ^!1 ( c\rse1 by electro/atic induction1 cause ! "r-h& t]m9als ( ^! cond5s]s to be subject to a correspond+ly v>y+ diff]5ce ( pot5tial4 ,f ?is x foll[s t alt]nat+ curr5ts w be impress$ ^u ! "r-h& l9e & ^! w affect ! receiv] at ,/ation ,b4 ,a r\gh way ( express+ ! action ( ?is circuit is to consid] x 9 ! same light z t ( ! imp$ance-coil circuit %[n 9 ,fig4 #aca1 & to consid] t ! voice curr5ts orig9at+ 9 "o l9e are prev5t$ f pass+ ?r\gh ! bridge pa?s at ! c5tral (fice on acc\nt ( ! imp$ance1 & are1 !re=e1 =c$ to cont9ue on ! l9e1 be+ all[$ to pass readily by ! cond5s]s 9 s]ies betwe5 ! two l9es4 ,kellogg ,sub/ation ,arrangem5t4 ,an int]e/+ =m ( sub/ation circuit :i* is employ$ by ! ,kellogg ,company 9 all ( its common-batt]y telephones is %[n 9 ,fig4 #acb4 ,9 pass+1 x may be well to /ate t almo/ any ( ! sub/ation circuits %[n 9 ?is *apt] are capable ( work+ ) any ( ! c5tral-(fice circuits4 ,! diff]5t ones are %[n = ! purpose ( giv+ a k ( ! v>i\s sub/ation circuits t are employ$1 &1 z f> z possible1 to associate !m ) ! p>ticul> c5tral-(fice arrangem5ts ) :i* !y are commonly us$4 ,9 ?is ,kellogg sub/ation arrangem5t ! l9e circuit passes fir/ ?r\gh ! transmitt] & !n divides1 "o bran* pass+ ?r\gh an imp$ance coil #g & ! o!r ?r\gh ! receiv] & ! cond5s] #h1 9 s]ies4 ,! /eady curr5t f ! c5tral-(fice batt]y f9ds ready pa? ?r\gh ! transmitt] & ! imp$ance coil1 b is prev5t$ f pass+ ?r\gh ! receiv] by ! b>ri] set up by ! cond5s] #h4 ,voice curr5ts1 h[ev]1 com+ ov] ! l9e to ! /ation1 f9d ready pa? ?r\gh ! receiv] & ! cond5s] b are b>r$ f pass+ ?r\gh ! imp$ance coil by virtue ( its high imp$ance4 ,9 consid]+ ! action ( ! /ation z a transmitt+ /ation1 ! v>iations set up by ! transmitt] pass ?r\gh ! cond5s] & ! receiv] at ! same /ation1 :ile ! /eady curr5t :i* supplies ! transmitt] passes ?r\gh ! imp$ance coil4 ,imp$ance coils us$ = ?is purpose are made ( l[ ohmic resi/ance b ( a comp>atively great numb] ( turns1 &1 !re=e1 pres5t a good pa? = /eady curr5ts & a difficult pa? = voice curr5ts4 ,?is divid$ circuit arrangem5t employ$ by ! ,kellogg ,company is "o ( ! v simple ways ( elim9at+ direct curr5ts f ! receiv] pa?1 at ! same "t all[+ ! free passage ( voice curr5ts4 ,illu/ration3 ,fig4 #acc4 ,dean ,sy/em ,dean ,sub/ation ,arrangem5t4 ,9 m>k$ contra/ to ! s*eme = keep+ /eady curr5t out ( ! receiv] circuit employ$ by ! ,kellogg ,company1 is t %[n 9 ,fig4 #acc1 :i* has be5 l>gely us$ by ! ,dean ,electric ,company1 ( ,elyria1 ,ohio4 ,! c5tral-(fice arrangem5t 9 ?is case is t us+ ! split repeat+ coil1 :i* ne$s no fur!r description4 ,! sub/ation arrangem5t1 h[ev]1 is unique & is a beautiful example ( :at c be done 9 ! way ( prev5t+ a fl[ ( curr5t ?r\gh a pa? )\t 9 any way insulat+ t pa? or plac+ any b>ri] 9 ! way ( ! curr5t4 ,x is an example ( ! prev5tion ( ! direct fl[ ( curr5t ?r\gh ! receiv] by s arrang+ ! circuits t !re w always be an equal pot5tial on ea* side ( x1 &1 !re=e1 no t5d5cy = curr5t to fl[ ?r\gh x4 ,9 ?is sub/ation arrangem5t f\r coils ( wire--#a1 #b1 #c1 & #d--;are s arrang$ z to be connect$ 9 ! circuit ( ! l9e1 two 9 s]ies & two 9 multiple4 ,! curr5t fl[+ f ! batt]y at ! c5tral (fice1 aft] pass+ ?r\gh ! transmitt]1 divides betwe5 ! two pa?s conta9+1 respectively1 ! coils #a & #c & ! coils #b & #d4 ,! receiv] is connect$ betwe5 ! junction ( ! coils #b & #d & t ( #a & #c4 ,! resi/ances ( ! coils are s *os5 t ! drop ( pot5tial ?r\gh ! coil #b w be equal to t ?r\gh ! coil #a1 & likewise t ?r\gh ! coil #d w be equal to t ?r\gh ! coil #c4 ,z a result1 ! receiv] w be connect$ betwe5 two po9ts ( equal pot5tial1 & no direct curr5t w fl[ ?r\gh x4 ,h[1 !n1 d voice curr5ts f9d _! way ?r\gh ! receiv]1 z !y evid5tly mu/1 if ! circuit is to fulfill any useful function8 ,! coils #b & #c are made to h high imp$ance1 :ile #a & #d are s w\nd z to be non-inductive &1 !re=e1 (f] no imp$ance save t ( _! ohmic resi/ance4 ,:at is true1 !re=e1 ( direct curr5ts does n hold = voice curr5ts1 & z a result1 ! voice curr5ts1 in/ead ( tak+ ! divid$ pa? :i* ! direct curr5ts pursu$1 are deb>r$ f ! coils #b & #c by _! high imp$ance & ?us pass ?r\gh ! non-inductive coil #a1 ! receiv]1 & ! non-inductive coil #d4 ,?is circuit employs a ,:eat/one-bridge arrangem5t1 adju/$ to a /ate ( balance ) respect to direct curr5ts1 su* curr5ts be+ exclud$ f ! receiv]1 n because ! receiv] circuit is 9 any s5se opaque to su* direct curr5ts1 b because !re is no diff]5ce ( pot5tial betwe5 ! t]m9als ( ! receiv] circuit1 &1 !re=e1 no t5d5cy = curr5t to fl[ ?r\gh ! receiv]4 ,9 ord] t fluctuat+ curr5ts may n1 = ! same reason1 be caus$ to pass by1 r ?an ?r\gh1 ! receiv] circuit1 ! diametrically-oppos$ arms ( ! ,:eat/one bridge are made to possess1 9 l>ge degree1 self-induction1 !reby giv+ ^! two arms a high imp$ance to fluctuat+ curr5ts4 ,! conditions :i* exi/ = direct curr5ts d n1 !re=e1 exi/ = fluctuat+ curr5ts1 & x is ?is di/9ction :i* all[s alt]nat+ curr5ts to pass ?r\gh ! receiv] & at ! same "t excludes direct curr5ts !refrom4 ,9 practice1 ! coils #a1 #b1 #c1 & #d ( ! ,dean sub/ation circuit are w\nd on ! same core1 b coils #a & #d--! non-inductive ones--are w\nd by d\bl+ ! wire back on itself s z to neutralize _! self-induction4 ,/romb]g-,c>lson4 ,ano!r modification ( ! c5tral-(fice arrangem5t & also ( ! subscrib]s' /ation circuits1 is %[n 9 ,fig4 #acd1 ?is be+ a simplifi$ repres5tation ( ! circuits commonly employ$ by ! ,/romb]g-,c>lson ,telephone ,manufactur+ ,company4 ,! batt]y fe$ at ! c5tral (fice diff]s only f t %[n 9 ,fig4 #acb1 9 t a s+le batt]y r ?an two batt]ies is us$1 ! curr5t be+ suppli$ to "o ( ! l9es ?r\gh ! imp$ance coils #a & #b1 & to ! o!r l9e ?r\gh ! imp$ance coils #c & #d2 cond5s]s #e & #f s]ve conductively to isolate ! two l9es4 ,at ! subscrib]'s /ation ! l9e circuit passes ?r\gh ! second>y ( an induction coil & ! transmitt]4 ,! receiv] is kept entirely 9 a local circuit s t !re is no t5d5cy = direct curr5t to fl[ ?r\gh x1 b x is receptive to voice curr5ts ?r\gh ! electromagnetic induction betwe5 ! prim>y & ! second>y ( ! induction coil4 ,illu/ration3 ,fig4 #acd4 ,/romb]g-,c>lson ,sy/em ,illu/ration3 ,fig4 #ace4 ,nor? ,electric ,company ,sy/em ,nor?4 ,ano!r arrangem5t ( c5tral-(fice batt]y fe$ is employ$ by ! ,nor? ,electric ,company1 & is %[n 9 ,fig4 #ace4 ,9 ?is two batt]ies are us$ :i* supply curr5t respectively to ! two connect$ l9es1 cond5s]s be+ employ$ to conductively isolate ! l9es4 ,?is diff]s f ! ,kellogg arrangem5t %[n 9 ,fig4 #acb 9 t ! two coils #a & #b are w\nd on ! same core1 :ile ! coils #c & #d are w\nd toge!r ^u ano!r core4 ,9 ?is case1 9 ord] t ! inductive action ( "o ( ! coils may n neutralize t ( ! o!r coil on ! same core1 ! two coils are w\nd 9 su* relative direction t _! magnetiz+ influ5ce w always be cumulative r ?an diff]5tial4 ,! c5tral-(fice arrangem5ts discuss$ 9 ,figs4 #acj to #ace1 inclusive1 are ^? :i* are 9 pr9cipal use 9 comm]cial practice 9 common-batt]y ex*anges4 ,curr5t ,supply ov] ,limbs ( ,l9e 9 ,p>allel4 ,z indicat+ fur!r int]e/+ possibilities 9 ! me?od ( supply+ curr5t f a common s\rce to a numb] ( sub/ations1 sev]al o!r sy/ems w be briefly ref]r$ to z be+ ( int]e/1 al?\gh ^! h n gone into wide comm]cial use4 ,! sy/em %[n 9 ,fig4 #acf is "o propos$ by ,dean 9 ! e>ly days ( common-batt]y work+1 & ?is arrangem5t 0 put into actual s]vice & gave satisfactory results1 b 0 aft]w>ds supplant$ by ! ,bell equipm5t op]at+ "u ! sy/em %[n 9 ,fig4 #acj1 :i* became /&>diz$ by t company4 ,9 ?is ! curr5t f ! common batt]y at ! c5tral (fice is n f$ ov] ! two l9e wires 9 s]ies1 b 9 multiple1 us+ a gr\nd return f ! subscrib]'s /ation to ! c5tral (fice4 ,across ! metallic circuit =m$ by two connect$ l9es !re is bridg$1 at ! c5tral (fice1 an imp$ance coil #a1 & betwe5 ! c5t] po9t ( ?is imp$ance coil & ! gr\nd is connect$ ! common batt]y4 ,at ! subscrib]'s /ation is plac$ an imp$ance coil #b1 also bridg$ across ! two limbs ( ! l9e1 & betwe5 ! c5t] po9t ( ?is imp$ance coil & ! gr\nd is connect$ ! transmitt]1 :i* is %unt$ by ! prim>y w9d+ ( an induction coil4 ,connect$ betwe5 ! two limbs ( ! l9e at ! sub/ation !re is also ! receiv] & ! second>y ( an induction coil 9 s]ies4 ,illu/ration3 ,fig4 #acf4 ,curr5t ,supply ov] ,p>allel ,limbs ( ,l9e ,! action ( ?is circuit at fir/ seems a little complex1 b if tak5 /ep by /ep may readily be und]/ood4 ,! transmitt] supply circuit may be trac$ f ! c5tral-(fice batt]y ?r\gh ! two halves ( ! imp$ance coil #a 9 multiple2 !nce ov] ! two limbs ( ! l9e 9 multiple to ,/ation ,a1 = in/ance2 !nce 9 multiple ?r\gh ! two halves ( imp$ance coil #b1 to ! c5t] po9t ( t coil2 !nce ?r\gh ! two pa?s (f]$ respectively by ! prim>y ( ! induction coil & by ! transmitt]2 !n to gr\nd & back to ! o!r pole ( ! c5tral-(fice batt]y4 ,by ?is circuit ! transmitt] at ! sub/ation is suppli$ ) curr5t4 ,v>iations 9 ! resi/ance ( ! transmitt] :5 9 action1 cause complem5t>y v>iations 9 ! supply curr5t fl[+ ?r\gh ! prim>y ( ! induction coil4 ,^! v>iations induce simil> alt]nat+ curr5ts 9 ! second>y ( ?is coil1 :i* is 9 s]ies 9 ! l9e circuit4 ,! curr5ts1 s induc$ 9 ?is second>y1 fl[ 9 s]ies ?r\gh "o side ( ! l9e to ! di/ant /ation2 !nce ?r\gh ! second>y & ! receiv] at t /ation to ! o!r side ( ! l9e & back ?r\gh t side ( ! l9e to ! receiv]4 ,^! curr5ts are n p]mitt$ to pass ?r\gh ! bridg$ pa?s across ! metallic circuit t are (f]$ by ! imp$ance coils #a & #b1 because !y are voice curr5ts & are1 !re=e1 deb>r$ f ^! pa?s by virtue ( ! imp$ance4 ,illu/ration3 ,fig4 #acg4 ,curr5t ,supply ov] ,p>allel ,limbs ( ,l9e ,an objection to ?is =m ( curr5t supply & to o!r simil> =ms1 :]e9 ! transmitt] curr5t is f$ ov] ! two sides ( ! l9e 9 multiple ) a gr\nd return1 is t ! gr\nd-return circuit =m$ by ! two sides ( ! l9e 9 multiple is subject to inductive di/urbances f o!r l9es 9 ! same way z an ord9>y gr\nd$ l9e is subject to inductive di/urbance4 ,! curr5t-supply circuit is ?us subject to ext]nal di/urbances & su* di/urbances f9d _! way into ! metallic circuit &1 !re=e1 ?r\gh ! in/rum5ts by means ( ! electromagnetic induction betwe5 ! prim>y & ! second>y coils at ! sub/ations4 ,ano!r int]e/+ me?od ( curr5t supply f a c5tral-(fice batt]y is %[n 9 ,fig4 #acg4 ,?is1 l ! circuit j consid]$1 fe$s ! en]gy to ! subscrib]'s /ation ov] ! two sides ( ! l9e 9 multiple ) a gr\nd return4 ,9 ?is case1 h[ev]1 a local circuit is provid$ at ! sub/ation1 9 :i* is plac$ a /orage batt]y #a & ! prim>y #b ( an induction coil1 toge!r ) ! transmitt]4 ,! idea 9 ?is is t ! curr5t supply f ! c5tral (fice w pass ?r\gh ! /orage batt]y & *>ge x4 ,^u ! use ( ! transmitt]1 ?is /orage batt]y acts to supply curr5t to ! local circuit conta9+ ! transmitt] & ! prim>y coil #b 9 exactly ! same mann] z 9 a local batt]y sy/em4 ,! fluctuat+ curr5t s produc$ by ! action ( ! transmitt] 9 ?is local circuit acts on ! second>y w9d+ #c ( ! induction coil1 & produces !re9 alt]nat+ curr5ts :i* pass to ! c5tral (fice & are 9 turn repeat$ to ! di/ant /ation4 ,supply ,_m ,l9es f ,common ,s\rce4 ,we come n[ to ! consid]ation ( ! arrangem5t by :i* a s+le batt]y may be made to supply curr5t at ! c5tral (fice to a l>ge numb] ( pairs ( connect$ l9es simultane\sly4 ,up to ?is po9t 9 ?is discussion x has be5 %[n only h[ ea* batt]y s]v$ a s+le pair ( connect$ l9es & no o!rs4 ,repeat+ ,coil3--,9 ,fig4 #ach is %[n h[ a s+le batt]y supplies curr5t simultane\sly to f\r diff]5t pairs ( l9es1 ! l9es ( ea* pair be+ connect$ = conv]sation4 ,x is se5 t ! pairs ( l9es %[n 9 ?is figure are arrang$ 9 ea* case 9 accordance ) ! sy/em %[n 9 ,fig4 #acj4 ,let u inquire :y x is t1 al?\gh all ( ^! f\r pairs ( l9es are connect$ ) a common s\rce ( en]gy & are1 !re=e1 all conductively jo9$1 ! /ations w be able to communicate 9 pairs )\t int]f]5ce betwe5 ! pairs4 ,9 o!r words1 :y is x t voice curr5ts orig9at+ at ,/ation ,a w pass only to ! receiv] at ,/ation ,b & n to ! receiv]s at ,/ation ,c or ,/ation ,h1 = in/ance8 ,! reason is t sep>ate supply conductors lead f ! po9ts su* z #a & #b at ! junctions ( ! repeat+-coil w9d+s on ea* pair ( circuits to ! batt]y t]m9als1 & ! resi/ance & imp$ance ( ! batt]y itself & ( ! common leads to x are s small t al?\gh ! feeble voice curr5ts orig9at+ 9 ! pair ( l9es connect+ ,/ation ,a & ,/ation ,b pass ?r\gh ! batt]y1 !y are n able to alt] ! pot5tial ( ! batt]y 9 any appreciable degree4 ,z a result1 !re=e1 ! supply wires lead+ f ! common-batt]y t]m9als to ! po9ts #g & #h1 = in/ance1 _c be subject$ to any v>iations 9 pot5tial by virtue ( curr5ts fl[+ ?r\gh ! batt]y f ! po9ts #a & #b ( ! l9es jo9+ ,/ation ,a & ,/ation ,b4 ,illu/ration3 ,,ma9 ,,(fice1 ,,key/one ,,telephone ,,company1 ,,philadelphia1 ,,pa4 ,illu/ration3 ,fig4 #ach4 ,common ,s\rce = ,_m ,l9es ,illu/ration3 ,fig4 #aci4 ,common ,s\rce = ,_m ,l9es ,ret>dation ,coil--,s+le ,batt]y3--,9 ,fig4 #aci is %[n 9 simil> mann] ! curr5t supply f a s+le batt]y to f\r diff]5t pairs ( l9es1 ! batt]y be+ associat$ ) ! l9es by ! comb9$ imp$ance coil & cond5s] me?od1 :i* 0 specifically dealt ) 9 connection ) ,fig4 #acc4 ,! reasons :y !re w be no int]f]5ce betwe5 ! conv]sations c>ri$ on 9 ! v>i\s pairs ( connect$ l9es 9 ?is case are ! same z ^? j consid]$ 9 connection ) ! sy/em %[n 9 ,fig4 #ach4 ,! imp$ance coils 9 ?is case s]ve to keep ! telephone curr5ts conf9$ to _! respective pairs ( l9es 9 :i* !y orig9ate1 & ?is same consid]ation applies to ! sy/em ( ,fig4 #ach1 = ea* ( ! sep>ate repeat+-coil w9d+s ( ,fig4 #ach is 9 itself an imp$ance coil ) respect to su* curr5ts z might leak away f "o pair ( l9es on to ano!r4 ,ret>dation ,coil--,d\ble ,batt]y3--,! arrangem5t ( fe$+ a numb] ( pairs ( l9es accord+ to ! ,kellogg two-batt]y sy/em is indicat$ 9 ,fig4 #adj1 :i* ne$s no fur!r explanation 9 view ( ! description ( ! prec$+ figures4 ,x is int]e/+ to note 9 ?is case t ! left-h& batt]y s]ves only ! left-h& l9es & ! "r-h& batt]y only ! "r-h& l9es4 ,z ?is is work$ out 9 practice1 ! left-h& batt]y is always connect$ to ^? l9es :i* orig9ate a call & ! "r-h& batt]y always to ^? l9es t are call$ =4 ,! en]gy suppli$ to a call+ l9e is always1 !re=e1 f a diff]5t s\rce ?an t :i* supplies a call$ l9e4 ,illu/ration3 ,fig4 #adj4 ,two ,s\rces = ,_m ,l9es ,illu/ration3 ,fig4 #ada4 ,curr5t ,supply f ,di/ant ,po9t ,curr5t ,supply f ,di/ant ,po9t4 ,sometimes x is conv5i5t to supply curr5t to a gr\p ( l9es c5t]+ at a c]ta9 po9t f a s\rce ( curr5t locat$ at a di/ant po9t4 ,?is is (t5 ! case 9 ! s-call$ private bran* ex*ange1 :]e a giv5 bus9ess h\se or o!r in/itution is provid$ ) its own swit*bo>d = int]connect+ ! l9es lead+ to ! v>i\s telephones ( t conc]n or in/itution among !mselves1 & also = connect+ !m ) l9es lead+ to ! city ex*ange4 ,x is n always easy or conv5i5t to ma9ta9 at su* private swit*bo>ds a sep>ate batt]y = supply+ ! curr5t ne$$ by ! local ex*ange4 ,9 su* cases ! arrangem5t %[n 9 ,fig4 #ada is sometimes employ$4 ,?is %[s two pairs ( l9es connect$ by ! imp$ance-coil sy/em ) common t]m9als #a & #b1 betwe5 :i* ord9>ily ! common batt]y w\ld be connect$4 ,in/ead ( putt+ a batt]y betwe5 ^! t]m9als1 h[ev]1 at ! local ex*ange1 a cond5s] ( l>ge capacity is connect$ betwe5 !m & f ^! t]m9als circuit wires #c & #d are l$ to a batt]y ( suitable voltage at a di/ant c5tral (fice4 ,! cond5s] 9 ?is case is us$ to af=d a %ort-circuit pa? = ! voice curr5ts t leak f "o side ( "o pair ( l9es to ! o!r1 ?r\gh ! imp$ance coils bridg$ across ! l9e4 ,9 ?is way ! effect ( ! necess>ily high resi/ance 9 ! common leads #c & #d1 lead+ to ! /orage batt]y1 is ov]come & ! t5d5cy to cross-talk betwe5 ! v>i\s pairs ( connect$ l9es is elim9at$4 ,frequ5tly1 in/ead ( employ+ ?is arrangem5t1 a /orage batt]y ( small capacity w be connect$ betwe5 ! t]m9als #a & #b1 in/ead ( ! cond5s]1 & ^! w be *>g$ ov] ! wires #c & #d f a s\rce ( curr5t at a di/ant po9t4 ,a consid]ation ( ! v>i\s me?ods ( supply+ curr5t f a common s\rce to a numb] ( l9es w %[ t x is ess5tial t ! resi/ance ( ! batt]y itself be v l[4 ,x is also necess>y t ! resi/ance & ! imp$ance ( ! common leads f ! batt]y to ! po9t ( di/ribution to ! v>i\s pairs ( l9es be v l[1 9 ord] t ! voice curr5ts :i* fl[ ?r\gh !m1 by virtue ( ! conv]sations go+ on 9 ! diff]5t pairs ( l9es1 %all n produce any appreciable alt]ation 9 ! diff]5ce ( pot5tial betwe5 ! batt]y t]m9als4 ,,*apt] ,,xiv ,,! ,,telephone ,,set ,we h consid]$ :at may be call$ ! elem5tal p>ts ( a complete telephone2 t is1 ! receiv]1 transmitt]1 hook swit*1 batt]y1 g5]ator1 call bell1 cond5s]1 & ! v>i\s k9ds ( coils :i* g to make up ! app>atus by :i* "o is enabl$ to transmit & receive spee* & signals4 ,we w n[ consid] ! gr\p+ ( ^! v>i\s elem5ts into a complete work+ organization kn[n z a telephone4 ,be=e consid]+ ! v>i\s types x is well to /ate t ! t]m telephone is (t5 r loosely us$4 ,we sometimes he> ! receiv] prop] call$ a telephone or a h& telephone4 ,s9ce ?is 0 ! orig9al speak+ telephone1 !re is "s reason = s call+ ! receiv]4 ,! mod]n cu/om m (t5 applies ! t]m telephone to ! complete organization ( talk+ & signal+ app>atus1 toge!r ) ! associat$ wir+ & cab9et or /&>d on :i* x is m\nt$4 ,! "n telephone set is p]haps to be pref]r$ to ! ^w telephone1 s9ce x t5ds to avoid misund]/&+ z to exactly :at is meant4 ,frequ5tly1 also1 ! telephone or telephone set is ref]r$ to z a subscrib]'s /ation equipm5t1 indicat+ ! equipm5t t is to be f\nd at a subscrib]'s /ation4 ,?is1 z apply+ to a telephone alone1 is n prop]1 s9ce ! subscrib]'s /ation equipm5t includes m ?an a telephone4 ,x includes ! local wir+ )9 ! premises ( ! subscrib] & also ! lightn+ arre/] & o!r protective devices1 if su* exi/4 ,to avoid confusion1 !re=e1 ! collection ( talk+ & signal+ app>atus ) its wir+ & conta9+ cab9et or /&>d w be ref]r$ to 9 ?is "w z a telephone or telephone set4 ,! receiv] w1 z a rule1 be designat$ z su*1 r ?an z a telephone4 ,! t]m subscrib]'s /ation equipm5t w ref] to ! complete equipm5t at a subscrib]'s /ation1 & w include ! telephone set1 ! int]ior wir+1 & ! protective devices1 toge!r ) any o!r app>atus t may be associat$ ) ! telephone l9e & be locat$ )9 ! subscrib]'s premises4 ,classification ( ,sets4 ,telephones may be classifi$ "u two g5]al head+s1 magneto telephones & common-batt]y telephones1 accord+ to ! "* ( ! sy/ems 9 :i* !y are adapt$ to "w4 ,magneto ,telephone4 ,! t]m magneto telephone1 z x 0 orig9ally employ$ 9 telephony1 ref]r$ to ! type ( in/rum5t n[ kn[n z a receiv]1 p>ticul>ly :5 ?is 0 us$ also z a transmitt]4 ,z ! use ( ?is in/rum5t z a transmitt] has practically ceas$1 ! t]m magneto telephone has lo/ its significance z apply+ to ! receiv]1 &1 s9ce _m telephones are equipp$ ) magneto g5]ators = call+ purposes1 ! t]m magneto telephone has1 by common cons5t1 come to be us$ to designate any telephone includ+1 z a "p ( its equipm5t1 a magneto g5]ator4 ,magneto telephones usually1 also1 include local batt]ies = furni%+ ! transmitt] ) curr5t1 & ?is has l$ to ^! telephones be+ frequ5tly call$ local batt]y telephones4 ,h[ev]1 a local batt]y telephone is n necess>ily a magneto telephone & vice v]s1 s9ce sometimes magneto telephones h no local batt]ies & sometimes local batt]y telephones h no magnetos4 ,ne>ly all ( ! telephones :i* are equipp$ ) magneto g5]ators are1 h[ev]1 also equipp$ ) local batt]ies = talk+ purposes1 &1 !re=e1 ! t]ms magneto telephone & local batt]y telephone usually ref] to ! same ?+4 ,common-,batt]y ,telephone4 ,common-batt]y telephones1 on ! o!r h&1 are ^? :i* h no local batt]y & no magneto g5]ator1 all ! curr5t = bo? talk+ & signal+ be+ furni%$ f a common s\rce ( curr5t at ! c5tral (fice4 ,wall & ,desk ,telephones4 ,aga9 we may classify telephones or telephone sets 9 accordance ) ! mann] 9 :i* _! v>i\s p>ts are associat$ ) ea* o!r = use1 reg>dless ( :at p>ts are conta9$ 9 ! set4 ,we may ref] to all sets adapt$ to be m\nt$ on a wall or p>tition z wall telephones1 & to all 9 :i* ! receiv]1 transmitt]1 & hook are provid$ ) a /&>d ( _! own to enable !m to re/ on any flat surface1 su* z a desk or table1 z desk telephones4 ,^! latt] are also ref]r$ to z portable telephones & z portable desk telephones4 ,9 g5]al1 magneto or local batt]y telephones diff] f common-batt]y telephones 9 _! compon5t p>ts1 ! diff]5ce resid+ pr9cipally 9 ! fact t ! magneto telephone always has a magneto g5]ator & usually a local batt]y1 :ile ! common-batt]y telephone has no local s\rce ( curr5t :atev]4 ,on ! o!r h&1 ! diff]5ces betwe5 wall telephones & desk telephones are pr9cipally /ructural1 & obvi\sly ei!r ( ^! types ( telephones may be = common-batt]y or magneto "w4 ,! same compon5t p>ts g to make up a desk telephone z a wall telephone1 provid$ ! two in/rum5ts are adapt$ = ! same class ( s]vice1 b ! diff]5ce betwe5 ! two lies 9 ! /ructural features by :i* ^! same p>ts are associat$ ) ea* o!r & protect$ f exposure4 ,illu/ration3 ,fig4 #adb4 ,magneto ,wall ,set ,illu/ration3 ,fig4 #adc4 ,magneto ,wall ,set ,magneto-,telephone ,sets4 ,wall4 ,9 ,fig4 #adb is %[n a famili> type ( wall set4 ,! conta9+ box includes )9 x all ( ! work+ p>ts ( ! app>atus except t :i* is necess>ily left outside 9 ord] to be )9 ! rea* ( ! us]4 ,fig4 #adc %[s ! same set ) ! door op54 ,?is gives a good idea ( ! ord9>y arrangem5t ( ! app>atus )94 ,x is se5 t ! pol>iz$ bell or r+] has its work+ p>ts m\nt$ on ! inside ( ! door or cov] ( ! box1 ! tapp] project+ ?r\gh s z to play betwe5 ! gongs on ! outside4 ,likewise ! transmitt] arm1 :i* supports ! transmitt] & all[s its adju/m5t up & d[n to accommodate itself to ! height ( ! us]1 is m\nt$ on ! front ( ! door1 & ! conductors lead+ to x may be se5 fa/5$ to ! re> ( ! door 9 ,fig4 #adc4 ,9 "s wall sets ! wires lead+ to ! bell & transmitt] are connect$ to ! wir+ ( ! re/ ( ! set ?r\gh ! h+es ( ! door1 ?us all[+ ! door to be op5$ & clos$ repeat$ly )\t break+ (f ! wires4 ,9 ord] to always insure positive electrical contact betwe5 ! /ation>y & movable p>ts ( ! h+e a small wire is w\nd ar\nd ! h+e p91 "o end be+ sold]$ to ! /ation>y "p & ! o!r end to ! movable "p ( ! h+e4 ,9 o!r =ms ( wall set ! wires to ! bell & ! transmitt] lead directly f ! /ation>y portion ( ! cab9et to ! back ( ! door1 ! wires be+ left long en\gh to h suffici5t flexibility to all[ ! door to be op5$ & clos$ )\t injur+ ! wires4 ,at ! upp] portion ( ! box !re is m\nt$ ! hook swit*1 ?is be+1 9 ?is case1 ( ! %ort lev] type4 ,! lev] ( ! hook projects ?r\gh ! side ( ! box s z to make ! hook available z a support = ! receiv]4 ,imm$iately at ! "r ( ! hook swit* is m\nt$ ! induction coil1 & imm$iately bel[ ?is ! g5]ator1 its crank h&le project+ ?r\gh ! "r-h& side ( ! box s z to be available = use !re4 ,! g5]ator is usually m\nt$ on a transv]se %elf across ! middle ( ! cab9et1 ?is %elf s]v+ to =m a comp>tm5t bel[ x 9 :i* ! dry batt]y ( two or ?ree cells is plac$4 ,! wall telephone-set cab9ets h assum$ a multitude ( =ms4 ,:5 wet cells r ?an dry cells 7 ord9>ily employ$1 z 0 ! case up to ab\t ! ye> #ahie1 ! magneto g5]ator1 pol>iz$ bell1 & hook swit* 7 usually m\nt$ 9 a rectangul> box plac$ at ! top ( a long backbo>d4 ,imm$iately bel[ ?is on ! backbo>d 0 m\nt$ ! transmitt] arm1 & sometimes ! base ( ?is includ$ ! induction coil4 ,bel[ ?is 0 ! batt]y box1 ?is be+ a l>ge affair usually adapt$ to accommodate two & sometimes ?ree ord9>y ,le,clanch cells side by side4 ,! dry cell has almo/ completely replac$ ! wet cell 9 ?is c\ntry1 & z a result1 ! g5]al type ( wall set z %[n 9 ,figs4 #adb & #adc1 has gradually replac$ ! old wet-cell type1 :i* 0 m cumbr\s & unsightly4 ,x is usual on wall sets to provide "s sort ( a %elf1 z indicat$ 9 ,fig4 #adb1 = ! conv5i5ce ( ! us] 9 mak+ notes & memor&a4 ,desk4 ,9 ! magneto desk-telephone sets1 ! s-call$ desk /&1 conta9+ ! transmitt]1 ! receiv]1 & ! hook swit*1 ) ! /&>d ^u :i* !y are m\nt$1 is %[n 9 ,fig4 #add4 ,?is desk /& evid5tly does n comprise ! complete equipm5t = a magneto desk-telephone set1 s9ce ! g5]ator1 pol>iz$ bell1 & batt]y are lack+4 ,! g5]ator & bell are usually m\nt$ toge!r 9 a box1 ei!r on ! "u side ( ! desk ( ! us] or on ! wall )9 easy rea* ( 8 *air4 ,connections are made betwe5 ! app>atus 9 ! desk /& prop] & ! batt]y1 g5]ator1 & bell by means ( flexible conduct+ cords1 ^! c>ry+ a plurality ( conductors1 z requir$ by ! p>ticul> circuit ( ! telephone 9 "q4 ,su* a complete magneto desk-telephone set is %[n 9 ,fig4 #ade1 ?is be+ "o ( ! types manufactur$ by ! ,/romb]g-,c>lson ,manufactur+ ,company4 ,illu/ration3 ,fig4 #add4 ,desk ,/& ,a great v>iety ( arrangem5ts ( ! v>i\s p>ts ( magneto desk-telephone app>atus is employ$ 9 practice4 ,sometimes1 z %[n 9 ,fig4 #ade1 ! magneto bell box is equipp$ ) b9d+ po/s = t]m9at+ all ( ! conductors 9 ! cord1 ! l9e wires also runn+ to "s ( ^! b9d+ po/s4 ,9 ! magneto-telephone set illu/rat$ ! box is made l>ge en\gh to accommodate only ! g5]ator & call bell1 & ! batt]ies are m\nt$ else:]e1 z 9 a draw] ( ! desk1 :ile 9 o!r cases !re is no o!r equipm5t b t %[n 9 ! cut1 ! batt]ies be+ m\nt$ )9 ! magneto bell box itself4 ,9 /ill o!r cases1 ! pol>iz$ bell is conta9$ 9 "o box1 ! g5]ator 9 ano!r1 ! batt]ies 9 ! draw] ( ! desk1 ! induction coil be+ m\nt$ ei!r 9 ! base ( ! desk /&1 9 ! bell box1 or 9 ! g5]ator box4 ,9 su* cases all ( ! circuits ( ! v>i\s scatt]$ p>ts are wir$ to a t]m9al /rip1 locat$ at "s conv5i5t po9t1 ?is /rip conta9+ t]m9als = all ! wires lead+ f ! v>i\s p>ts & = ! l9e wires !mselves4 ,by comb9+ ! v>i\s wires on ! t]m9als ( ?is t]m9al /rip1 ! complete circuits ( ! telephone are built up4 ,9 /ill o!r cases ! induction coil is m\nt$ on ! t]m9al /rip & sep>ate wires or sets ( wires are run to ! pol>iz$ bell & g5]ator1 to ! desk /& itself1 & to ! batt]ies4 ,^! v>i\s arrangem5ts are subject l>gely to ! desire or p]sonal ideas ( ! manufactur] or us]4 ,all ( !m "w on ! same pr9ciple s f> z ! op]ation ( ! talk+ & signal+ circuits is conc]n$4 ,illu/ration3 ,fig4 #ade4 ,magneto ,desk ,set ,circuits ( ,magneto-,telephone ,sets4 ,magneto telephones1 :e!r ( ! wall or desk type1 may be divid$ into two g5]al classes1 s]ies & bridg+1 accord+ to :e!r ! magnet ( ! bell is includ$ 9 s]ies or bridge relation ) ! telephone l9e :5 ! hook is d[n4 ,s]ies4 ,9 ! s-call$ s]ies telephone l9e1 :]e sev]al telephones are plac$ 9 s]ies 9 a s+le l9e circuit1 ! employm5t ( ! s]ies type ( telephone results 9 all ( ! telephone bells be+ 9 s]ies 9 ! l9e circuit4 ,?is means t ! voice curr5ts orig9at+ 9 ! telephones t are 9 use at a giv5 "t mu/ pass 9 s]ies ?r\gh ! magnets ( ! bells ( ! /ations t are n 9 use4 ,9 ord] t ^! magnets1 ?r\gh :i* ! voice curr5ts mu/ pass1 may int]f]e to z small a degree z possible ) ! voice curr5ts1 x is common to employ l[-resi/ance magnets 9 s]ies telephones1 ^! magnets be+ w\nd ) comp>atively few turns & on r %ort cores s t ! imp$ance w be z small z possible4 ,likewise1 s9ce ! g5]ators are requir$ to r+ all ( ! bells 9 s]ies1 !y ne$ n h a l>ge curr5t output1 b mu/ h suffici5t voltage to r+ ?r\gh all ( ! bells 9 s]ies & ?r\gh ! resi/ance ( ! l9e4 ,= ?is reason ! g5]ators are usually ( ! ?ree-b> type & sometimes h only two b>s4 ,9 ,fig4 #adf are %[n1 9 simplifi$ =m1 ! circuits ( an ord9>y s]ies telephone4 ,! receiv] 9 ?is is %[n z be+ remov$ f ! hook & ?us ! talk+ app>atus is br\ght into play4 ,! l9e wires #a & #b connect respectively to ! b9d+ po/s #c & #d :i* =m ! t]m9als ( ! in/rum5t4 ,:5 ! hook is up1 ! circuit betwe5 ! b9d+ po/s #c & #d includes ! receiv] & ! second>y w9d+ ( ! induction coil1 toge!r ) "o ( ! upp] contacts #e ( ! swit* hook & ! hook lev] itself4 ,?is completes ! circuit = receiv+ spee*4 ,! hook swit* is provid$ ) ano!r upp] contact #f1 betwe5 :i* & ! contact #e is connect$ ! local circuit conta9+ ! transmitt]1 ! batt]y1 & ! prim>y ( ! induction coil 9 s]ies4 ,! prim>y & ! second>y w9d+s are connect$ toge!r at "o end & connect$ ) ! swit* contact #e1 z %[n4 ,x is ?us se5 t :5 ! hook is up ! circuit ?r\gh ! receiv] is automatically clos$ & also ! local circuit conta9+ ! prim>y1 ! batt]y1 & ! transmitt]4 ,?us1 all ! conditions = transmitt+ & receiv+ spee* are fulfill$4 ,fig4 #adf4 ,circuit ( ,s]ies ,magneto ,set ,:5 ! hook is d[n1 h[ev]1 ! receiv+ & transmitt+ circuits are brok51 b ano!r circuit is complet$ by ! engagem5t ( ! hook-swit* lev] ) ! l[] hook contact #g4 ,betwe5 ?is contact & "o side ( ! l9e is connect$ ! pol>iz$ r+] & ! g5]ator4 ,) ! hook d[n1 !re=e1 ! circuit may be trac$ f ! l9e wire #a to b9d+ po/ #c1 !nce ?r\gh ! g5]ator %unt to ! call bell1 & !nce ?r\gh ! l[] swit*+ contact #g to ! b9d+ po/ #d & l9e wire #b4 ,! g5]ator %unt1 z already describ$ 9 ,*apt] ,,viii1 normally keeps ! g5]ator %unt$ out ( circuit4 ,:51 h[ev]1 ! g5]ator is op]at$ ! %unt is brok51 :i* all[s ! armature ( ! g5]ator to come into ! circuit 9 s]ies ) ! w9d+ ( ! pol>iz$ bell4 ,! normal %unt+ ( ! g5]ator armature f ! circuit ( ! l9e is advantage\s 9 sev]al ways4 ,9 ! fir/ place1 ! imp$ance ( ! g5]ator w9d+ is normally cut out ( ! circuit s t 9 ! case ( a l9e ) sev]al /ations ! talk+ or voice curr5ts d n h to fl[ ?r\gh ! g5]ator armatures at ! /ations :i* are n 9 use4 ,aga91 ! normal %unt+ ( ! g5]ator t5ds to save ! g5]ator armature f injury by lightn+4 ,illu/ration3 ,fig4 #adg4 ,circuit ( ,s]ies ,magneto ,set4 ,! m complete circuits ( a s]ies magneto telephone are %[n 9 ,fig4 #adg4 ,9 ?is ! l9e b9d+ po/s are %[n z #a & #b4 ,at ! bottom ( ! telephone cab9et are f\r o!r b9d+ po/s m>k$ #c1 #d1 #e1 & #f4 ,( ^! #c & #d s]ve = ! receiv] t]m9als & #e & #f = ! transmitt] & batt]y t]m9als4 ,! circuits ( ?is diagram w be f\nd to be ess5tially ! same z ^? ( ,fig4 #adf1 except t !y are %[n 9 great] detail4 ,?is p>ticul> type ( circuit is "o commonly employ$ :]e ! g5]ator1 r+]1 hook swit*1 & induction coil are all m\nt$ 9 a s-call$ magneto bell box at ! top ( ! in/rum5t1 & :]e ! transmitt] is m\nt$ on an arm j bel[ ?is box1 & ! batt]y 9 a sep>ate comp>tm5t bel[ ! transmitt]4 ,! only wir+ t has to be done betwe5 ! bell box & ! o!r p>ts ( ! in/rum5t 9 assembl+ ! complete telephone is to connect ! receiv] to ! b9d+ po/s #c & #d & to connect ! batt]y & transmitt] circuit to ! b9d+ po/s #e & #f4 ,bridg+4 ,9 o!r cases1 :]e sev]al telephones are plac$ on a s+le-l9e circuit1 ! bells are arrang$ 9 multiple across ! l9e4 ,= ?is reason _! magnets are w\nd ) a v great numb] ( turns & consequ5tly to a high resi/ance4 ,9 ord] to fur!r increase ! imp$ance1 ! cores are made long & heavy4 ,s9ce ! g5]ators on ^! l9es mu/ be capable ( giv+ out a suffici5t volume ( curr5t to divide up betwe5 all ( ! bells 9 multiple1 x foll[s t ^! g5]ators mu/ h a l>ge curr5t output1 & at ! same "t a suffici5t voltage to r+ ! bells at ! f>!/ end ( ! l9e4 ,su* in/rum5ts are commonly call$ bridg+ in/rum5ts1 on acc\nt ( ! me?od ( connect+ _! bells across ! circuit ( ! l9e4 ,illu/ration3 ,fig4 #adh4 ,circuit ( ,bridg+ ,magneto ,set ,! fundam5tal *>act]i/ic ( ! bridg+ telephone is t x conta9s ?ree possible bridge pa?s across ! l9e wires4 ,! fir/ ( ^! bridge pa?s is ?r\gh ! talk+ app>atus1 ! second ?r\gh ! g5]ator1 & ! ?ird ?r\gh ! r+]4 ,?is is %[n 9 simplifi$ =m 9 ,fig4 #adh4 ,! talk+ app>atus is associat$ ) ! two upp] contacts ( ! hook swit* 9 ! usual mann] & ne$s no fur!r description4 ,! g5]ator is ! second sep>ate bridge pa?1 normally op51 b adapt$ to be clos$ :5 ! g5]ator is op]at$1 ?is automatic closure be+ p]=m$ by ! movem5t ( ! crank %aft4 ,! ?ird bridge conta9s ! pol>iz$ bell1 & ?is1 z a rule1 is p]man5tly clos$4 ,sometimes1 h[ev]1 ! arrangem5t is su* t ! bell pa? is normally clos$ ?r\gh ! swit* :i* is op]at$ by ! g5]ator crank %aft1 & ?is pa? is automatically brok5 :5 ! g5]ator is op]at$1 at :i* "t1 also1 ! g5]ator pa? is automatically clos$4 ,?is arrangem5t br+s ab\t ! result t ! g5]ator nev] c r+ its own bell1 because its swit* always op]ates to cut out ! bell at its own /ation j be=e ! g5]ator itself is cut into ! circuit4 ,9 ,fig4 #adi is %[n ! complete circuit ( a bridg+ telephone4 ,! circuit giv5 9 ?is figure is = a local-batt]y wall set simil> 9 type to t %[n 9 ,figs4 #adb & #adc4 ,a simplifi$ diagrammatic arrangem5t is %[n 9 ! l[] left-h& corn] ( ?is figure1 & f a consid]ation ( ?is x w be se5 t ! bell circuit across ! l9e is normally complet$ ?r\gh ! two "r-h& normally clos$ contacts ( ! swit* on ! g5]ator4 ,:51 h[ev]1 ! g5]ator is op]at$ ^! two contacts are made to dis5gage ea* o!r :ile ! long spr+ ( ! g5]ator swit* engages ! left-h& spr+ & ?us br+s ! g5]ator itself into ! circuit4 ,illu/ration3 ,fig4 #adi4 ,circuit ( ,bridg+ ,magneto ,set ,( ! ?ree b9d+ po/s1 #a1 #b1 & #c1 at ! top ( ,fig4 #adi1 #a & #b are = connect+ ) ! l9e wires1 :ile #h is = a gr\nd connection1 act+ 9 conjunction ) ! lightn+ arre/] m\nt$ at ! top ( ! telephone & indicat$ at #d 9 ,fig4 #adi4 ,?is has no function 9 talk+ or r++1 & w be ref]r$ to m fully 9 ,*apt] ,,xix4 ,suffice x to say at ?is po9t t ^! arre/]s usually consi/ ( two conduct+ bodies1 "o connect$ p]man5tly to ea* ( ! l9e b9d+ po/s1 & a ?ird conduct+ body connect$ to ! gr\nd b9d+ po/4 ,^! ?ree conduct+ bodies are 9 close proximity b c>efully insulat$ f ea* o!r2 ! idea be+ t :5 ! l9e wires are /ruck by lightn+ or subject$ o!rwise to a dang]\s pot5tial1 ! *>ge on ! l9e w jump across ! space betwe5 ! conduct+ bodies & pass h>mlessly to gr\nd4 ,,note4 ,! /ud5t %\ld practice mak+ simplifi$ diagrams f actual wir+ diagrams4 ,! diff]5ce betwe5 ! two is t "o is laid out = ease 9 und]/&+ x1 :ile ! o!r is laid out to %[ ! actual c\rse ( ! wires z in/all$4 ,if ! l>ge detail$ circuit ( ,fig4 #adi be comp>$ ) ! small !oretical circuit 9 ! same figure1 ! v>i\s conduct+ pa?s w be f\nd to be ! same4 ,su* a simplifi$ circuit does m to enable "o to grasp ! fundam5tal s*eme ( a complex circuit ?an mu* description1 s9ce x %[s at a glance ! g5]al arrangem5t4 ,! m detail$ circuits are1 h[ev]1 necess>y to %[ ! actual pa?s foll[$ by ! wir+4 ,! circuits ( desk /&s d n diff] f ^? ( wall sets 9 any mat]ial degree1 except z may be necessitat$ by ! fact t ! v>i\s p>ts ( ! telephone set are n all m\nt$ 9 ! same cab9et or on ! same /&>d4 ,to provide = ! necess>y relative movem5t betwe5 ! desk /& & ! o!r portions ( ! set1 flexible conductors are run f ! desk /& itself to ! /ation>y portions ( ! equipm5t1 su* z ! batt]y & ! p>ts conta9$ 9 ! g5]ator & bell box4 ,illu/ration3 ,fig4 #aej4 ,circuit ( ,bridg+ ,magneto ,desk ,set ,9 ,fig4 #aej is %[n ! circuit ( ! ,/romb]g-,c>lson magneto desk-telephone set1 illu/rat$ 9 ,fig4 #ade4 ,?is diagram ne$s no explanation 9 view ( :at has already be5 said4 ,! conductors1 lead+ f ! desk-/& gr\p ( app>atus to ! bell-box gr\p ( app>atus1 are gr\p$ toge!r 9 a flexible cord1 z %[n 9 ,fig4 #ade1 & are connect$ respectively to ! v>i\s b9d+ po/s or contact po9ts )9 ! desk /& at "o end & at ! base ( ! bell box at ! o!r end4 ,^! flexible conductors are insulat$ individually & cov]$ by a common braid$ cov]+4 ,!y usually are individualiz$ by hav+ a color$ ?read wov5 into _! insulat+ braid1 s t x is an easy matt] to id5tify ! two ends ( ! same conductor at ei!r end ( ! flexible cord or cable4 ,illu/ration3 ,fig4 #aea4 ,common-,batt]y ,wall ,set ,illu/ration3 ,fig4 #aeb4 ,common-,batt]y ,wall ,set ,common-,batt]y ,telephone ,sets4 ,ow+ to ! fact t common-batt]y telephones conta9 no s\rces ( curr5t1 !y are usually some:at simpl] ?an ! magneto type4 ,! compon5t p>ts ( a common-batt]y telephone1 :e!r ( ! wall or desk type1 are ! transmitt]1 receiv]1 hook swit*1 pol>iz$ bell1 cond5s]1 & sometimes an induction coil4 ,! purpose ( ! cond5s] is to prev5t direct or /eady curr5ts f pass+ ?r\gh ! w9d+s ( ! r+] :ile ! r+] is connect$ across ! circuit ( ! l9e dur+ ! "t :5 ! telephone is n 9 use4 ,! requirem5ts ( common-batt]y signal+ dem& t ! r+] %all be connect$ ) ! l9e s z to be receptive ( a call at any "t :ile ! telephone is n 9 use4 ,! requirem5ts also dem& t no conduct+ pa? %all normally exi/ betwe5 ! two sides ( ! l9e4 ,^! two app>5tly contradictory requirem5ts are met by plac+ a cond5s] 9 s]ies ) ! r+] s t ! r+] w be 9 a pa? t w readily transmit ! alt]nat+ r++ curr5ts s5t out f ! c5tral-(fice g5]ator1 :ile at ! same "t ! cond5s] w af=d a complete b> to ! passage ( /eady curr5ts4 ,sometimes ! cond5s] is also us$ z a portion ( ! talk+ app>atus1 z w be po9t$ out4 ,illu/ration3 ,,ma9 ,,(fice1 ,,kansas ,,city ,,home ,,telephone ,,co41 ,,kansas ,,city1 ,,mo4 ,wall4 ,9 ,figs4 #aea & #aeb are giv5 two views ( a *>act]i/ic =m ( common-batt]y wall-telephone set1 made by ! ,/romb]g-,c>lson ,manufactur+ ,company4 ,! common-batt]y wall set has usually tak5 ?is g5]al =m4 ,9 x ! transmitt] is m\nt$ on an adju/able arm at ! top ( ! backbo>d1 :ile ! box conta9+ ! bell & all work+ p>ts ( ! in/rum5t is plac$ bel[ ! transmitt]1 ! top ( ! box af=d+ a %elf = writ+ purposes4 ,9 ,fig4 #aea are %[n ! hook swit* & ! receiv]2 j bel[ ^! may be se5 ! magnets ( ! pol>iz$ bell1 back ( :i* is %[n a rectangul> box conta9+ ! cond5s]4 ,imm$iately 9 front ( ! r+] magnets is ! induction coil4 ,illu/ration3 ,fig4 #aec4 ,/romb]g-,c>lson ,common-,batt]y ,wall ,set ,9 ,fig4 #aec are %[n ! details ( ! circuit ( ?is in/rum5t4 ,?is figure also includes a simplifi$ circuit arrangem5t f :i* ! pr9ciples involv$ may be m readily und]/ood4 ,x is se5 t ! prim>y ( ! induction coil & ! transmitt] are includ$ 9 s]ies across ! l9e4 ,! second>y ( ! induction coil1 9 s]ies ) ! receiv]1 is connect$ also across ! l9e 9 s]ies ) a cond5s] & ! transmitt]4 ,hotel4 ,sometimes1 9 ord] to economize space1 ! %elf ( common-batt]y wall sets is omitt$ & ! entire app>atus m\nt$ 9 a small rectangul> box1 ! front ( :i* c>ries ! transmitt] m\nt$ on ! %ort arm or on no arm at all4 ,su* in/rum5ts are commonly t]m$ hotel sets1 because ( ! fact t _! use 0 fir/ conf9$ l>gely to ! rooms 9 hotels4 ,lat]1 h[ev]1 ^! in/rum5ts h become v popul> 9 g5]al use1 p>ticul>ly 9 resid5ces4 ,sometimes ! boxes or cab9ets ( ^! sets are made ( wood1 b ( rec5t ye>s ! t5d5cy has be5 gr[+ to make !m ( press$ /eel4 ,! /eel box is usually f9i%$ 9 black enamel1 bak$ on1 ! color be+ sometimes v>i$ to mat* ! color ( ! surr\nd+ woodwork4 ,9 ,figs4 #aed & #aee are %[n two views ( a common-batt]y hotel set manufactur$ by ! ,dean ,electric ,company4 ,su* sets are extremely neat 9 appe>ance & h ! advantage ( tak+ up little room on ! wall & ! comm]cial advantage ( be+ light & compact = %ipp+ purposes4 ,a possible disadvantage ( ?is type ( in/rum5t is ! some:at cr[d$ condition :i* necess>ily foll[s f ! plac+ ( all ! p>ts 9 s conf9$ a space4 ,?is int]f]es some:at ) ! accessibility ( ! v>i\s p>ts1 b great +5uity has be5 manife/$ 9 mak+ ! p>ts readily get-at-able 9 case ( necessity = repairs or alt]ations4 ,illu/ration3 ,fig4 #aed4 ,/eel ,box ,hotel ,illu/ration3 ,fig4 #aee4 ,/eel ,box ,hotel ,set ,desk4 ,! common-batt]y desk telephone pres5ts a some:at simpl] problem ?an ! magneto desk telephone = ! reason t ! g5]ator & local batt]y1 ! two mo/ bulky p>ts ( a magneto telephone1 d n h to be provid$ =4 ,"s companies1 9 manufactur+ desk /&s = common-batt]y purposes1 m\nt ! cond5s] & ! induction coil or imp$ance coil1 or :atev] device is us$ 9 connection ) ! talk+ circuit1 9 ! base ( ! desk /& itself1 & m\nt ! pol>iz$ r+] & ! cond5s] us$ = r++ purposes 9 a sep>ate bell box adapt$ to be m\nt$ on ! wall or "s portion ( ! desk4 ,o!r companies m\nt only ! transmitt]1 receiv]1 & hook swit* on ! desk /& prop] & put ! cond5s] or induction coil1 or o!r device associat$ ) ! talk+ circuit1 9 ! bell box4 ,!re is little to *oose betwe5 ! two g5]al practices4 ,! numb] ( conduct+ /r&s 9 ! flexible cord is some:at dep5d5t on ! arrangem5t ( ! circuit employ$4 ,illu/ration3 ,fig4 #aef4 ,common-,batt]y ,desk ,set ,illu/ration3 ,fig4 #aeg4 ,bell = ,common-,batt]y ,desk ,set4 ,! ,kellogg ,swit*bo>d & ,supply ,company is "o :i* places all ! p>ts1 except ! pol>iz$ r+] & ! associat$ cond5s]1 9 ! desk /& itself4 ,9 ,fig4 #aef is %[n a bottom view ( ! desk /& ) ! bottom plate remov$4 ,9 ! upp] portion ( ! circle ( ! base is %[n a small cond5s] :i* is plac$ 9 ! talk+ circuit 9 s]ies ) ! receiv]4 ,9 ! "r-h& portion ( ! circle ( ! base is %[n a small imp$ance coil1 :i* is plac$ 9 s]ies ) ! transmitt] b 9 %unt relation ) ! cond5s] & ! receiv]4 ,illu/ration3 ,fig4 #aeh4 ,bell = ,common-,batt]y ,desk ,set ,9 ,figs4 #aeg & #aeh are %[n two views ( ! type ( bell box employ$ by ! ,kellogg ,company 9 connection ) ! common-batt]y desk sets1 ?is box be+ ( press$-/eel con/ruction & hav+ a removable lid1 z %[n 9 ,fig4 #aeh1 by :i* ! work+ p>ts ( ! r+] are made readily accessible1 z are also ! t]m9als = ! cord lead+ f ! desk /& & = ! wires ( ! l9e circuit4 ,! cond5s] t is plac$ 9 s]ies ) ! r+] is also m\nt$ 9 ?is same box4 ,by employ+ two cond5s]s1 "o 9 ! bell box l>ge en\gh to transmit r++ curr5ts & ! o!r 9 ! base ( ! desk /& l>ge en\gh only to transmit voice curr5ts1 a duplication ( cond5s]s is involv$1 b x has ! correspond+ advantages ( requir+ only two /r&s to ! flexible cord lead+ f ! bell box to ! desk /& prop]4 ,illu/ration3 ,fig4 #aei4 ,microtelephone ,set ,a =m ( desk-telephone set t is us$ l>gely abroad1 b t has f\nd v little use 9 ?is c\ntry1 is %[n 9 ,fig4 #aei4 ,9 ?is ! transmitt] & ! receiv] are p]man5tly atta*$ toge!r1 ! receiv] be+ ( ! wat*-case v>iety & s position$ relatively to ! transmitt] t :5 ! receiv] is held at ! e>1 ! m\?piece ( ! transmitt] w be j 9 front ( ! lips ( ! us]4 ,9 ord] to ma9ta9 ! transmitt] 9 a v]tical position dur+ use1 ?is necessitates ! use ( a curv$ m\?piece z %[n4 ,?is transmitt] & receiv] s comb9$ is commonly call$1 9 ?is c\ntry1 ! microtelephone set1 al?\gh !re seems to be no logical reason = ?is "n4 ,! comb9$ transmitt] & receiv]1 in/ead ( be+ support$ on an ord9>y =m ( hook swit*1 are support$ on a =k$ bracket z %[n1 ?is bracket s]v+ to op]ate ! swit* spr+s :i* are held 9 "o position :5 ! bracket is subject$ to ! weight ( ! microtelephone1 & 9 ! alt]nate position :5 reliev$ !refrom4 ,?is p>ticul> microtelephone set is ! product ( ! ,l4,m4 ,ericsson ,telephone ,manufactur+ ,company1 ( ,buffalo1 ,new ,york4 ,! circuits ( su* sets d n diff] mat]ially f ^? ( ! ord9>y desk telephone set4 ,illu/ration3 ,fig4 #afj4 ,kellogg ,common-,batt]y ,desk ,set ,illu/ration3 ,fig4 #afa4 ,dean ,common-,batt]y ,set ,circuits ( ,common-,batt]y ,telephone ,sets4 ,! complete circuits ( ! ,kellogg desk-/& arrangem5t are %[n 9 ,fig4 #afj1 ! desk-/& p>ts be+ %[n at ! left & ! bell-box p>ts at ! "r4 ,z is se51 b two conductors ext5d f ! =m] to ! latt]4 ,a simplifi$ !oretical sket* is also %[n 9 ! upp] "r-h& corn] ( ?is figure4 ,! details ( ! common-batt]y telephone circuits ( ! ,dean ,electric ,company are %[n 9 ,fig4 #afa4 ,?is involves ! use ( ! balanc$ ,:eat/one bridge4 ,! only o!r ?+ ab\t ?is circuit t ne$s description1 9 view ( :at has previ\sly be5 said ab\t x1 is t ! pol>iz$ bell is plac$ 9 s]ies ) a cond5s] s t ! two sides ( ! circuit may be insulat$ f ea* o!r :ile ! telephone is n 9 use1 & yet p]mit ! passage ( r++ curr5t ?r\gh ! bell4 ,illu/ration3 ,fig4 #afb4 ,mon>* ,common-,batt]y ,wall ,set ,! use ( ! s-call$ direct-curr5t receiv] has br\ght ab\t a great simplification 9 ! common-batt]y telephone circuits ( sev]al ( ! manufactur+ companies4 ,by ?is use ! transmitt] & ! receiv] are plac$ 9 s]ies across ! l9e1 ?is pa? be+ normally op5$ by ! hook-swit* contacts4 ,! pol>iz$ bell & cond5s] are plac$ 9 ano!r bridge pa? across ! l9e1 ?is pa? n be+ affect$ by ! hook-swit* contacts4 ,all t !re is to su* a complete common-batt]y telephone set1 !re=e1 is a receiv]1 transmitt]1 hook swit*1 bell1 cond5s]1 & cab9et1 or o!r support4 ,! extreme simplicity ( ! circuits ( su* a set is illu/rat$ 9 ,fig4 #afb1 :i* %[s h[ ! ,mon>* ,telephone ,manufactur+ ,company connect up ! v>i\s p>ts ( _! telephone set1 us+ ! direct-curr5t receiv] already describ$ 9 connection ) ,fig4 #ed4 ,illu/ration3 ,,v5tilat+ ,,plant ,,= ,,l>ge ,,telephone ,,(fice ,,build+ ,,*apt] ,,xv ,,non-,,selective ,,p>ty-,,l9e ,,sy/ems ,a p>ty l9e is a l9e t is = ! jo9t use ( sev]al /ations4 ,x is1 !re=e1 a l9e t connects a c5tral (fice ) two or m subscrib]s' /ations1 or :]e no c5tral (fice is involv$1 a l9e t connects ?ree or m isolat$ /ations ) ea* o!r4 ,! di/+ui%+ feature ( a p>ty l9e1 !re=e1 is t x s]ves m ?an two /ations1 c\nt+ ! c5tral (fice1 if !re is "o1 z a /ation4 ,/rictly speak+1 ! t]m p>ty l9e %\ld be us$ 9 contradi/9ction to ! t]m private l9e4 ,companies op]at+ telephone ex*anges1 h[ev]1 frequ5tly lease _! wires to individuals = private use1 ) no c5tral-(fice swit*bo>d connections1 & su* l9es are1 by common usage1 ref]r$ to z private l9es4 ,su* l9es may be us$ to connect two or m isolat$ /ations4 ,a private l9e1 9 ! p>lance ( telephone ex*ange work+1 may1 !re=e1 be a p>ty l9e1 z inconsi/5t z ?is may seem4 ,a telephone l9e t is connect$ ) an ex*ange is an ex*ange l9e1 & x is a p>ty l9e if x has m ?an "o /ation on x4 ,x is an individual l9e or a s+le p>ty l9e if x has b a s+le /ation on x4 ,a l9e :i* has no c5tral-(fice connection is call$ an isolat$ l9e1 & x is a p>ty l9e if x has m ?an two /ations on x4 ,! problem ( m]e spee* transmission on p>ty l9es is comp>atively easy1 be+ sc>cely m complex ?an t involv$ 9 private or s+le p>ty l9es4 ,?is is n true1 h[ev]1 ( ! problem ( signal+ ! v>i\s /ations4 ,?is is because ! l9e is = ! common use ( all its patrons or subscrib]s1 z !y are t]m$1 & ! necessity !re=e exi/s t ! p]son s5d+ a signal1 :e!r op]ator or subscrib]1 %all be able 9 "s way to in=m a p]son at ! desir$ /ation t ! call is int5d$ = t /ation4 ,!re are two g5]al ways ( accompli%+ ?is purpose4 7#a7 ,! fir/ & simple/ ( ^! ways is to make no provision = r++ any "o bell on ! l9e to ! exclusion ( ! o!rs1 & ?us all[ all bells to r+ at once :5ev] any /ation on ! l9e is want$4 ,:]e ?is is done1 9 ord] to prev5t all /ations f answ]+1 x is necess>y1 9 "s way1 to convey to ! desir$ /ation ! in=mation t ! call is int5d$ = t /ation1 & to all ( ! o!r /ations ! in=mation t ! call is n int5d$ = !m4 ,?is is done on su* l9es by :at is call$ code r++1 ! code consi/+ ( v>i\s comb9ations ( long & %ort r+s4 7#b7 ,! o!r & m complex way is to arrange = selective r++1 s t ! p]son s5d+ ! call may r+ ! bell at ! /ation desir$1 all[+ ! bells at all ! o!r /ations to rema9 quiet4 ,illu/ration3 ,fig4 #afc4 ,gr\nd$-,circuit ,s]ies ,l9e ,^! two g5]al classes ( p>ty-l9e sy/ems may1 !re=e1 be t]m$ non-selective & selective sy/ems4 ,non-selective p>ty l9es are l>gely us$ bo? on l9es hav+ connection ) a c5tral (fice1 & ?r\gh ! c5tral (fice ! privilege ( connection ) o!r l9es1 & on isolat$ l9es hav+ no c5tral-(fice connection4 ,! greate/ field ( usefulness ( non-selective l9es is 9 rural di/ricts & 9 connection ) ex*anges 9 s]v+ r sp>sely settl$ di/ricts :]e ! co/ ( individual l9es or ev5 l9es s]v+ b a few subscrib]s1 is prohibitive4 ,non-selective telephone p>ty l9es mo/ (t5 employ magneto telephones4 ,! e>ly =ms ( p>ty l9es employ$ ! ord9>y s]ies magneto telephone1 ! bells be+ ( l[ resi/ance & comp>atively l[ imp$ance1 :ile ! g5]ators 7 provid$ ) automatic %unt+ devices1 s t _! resi/ance w\ld normally be remov$ f ! circuit ( ! l9e4 ,s]ies ,sy/ems4 ,! g5]al arrangem5t ( a s]ies p>ty l9e employ+ a gr\nd return is %[n 9 ,fig4 #afc4 ,9 ?is ?ree ord9>y s]ies in/rum5ts are connect$ toge!r 9 s]ies1 ! end /ations be+ gr\nd$1 9 ord] to af=d a return pa? = ! r++ & voice curr5ts4 ,illu/ration3 ,fig4 #afd4 ,metallic-,circuit ,s]ies ,l9e ,9 ,fig4 #afd !re is %[n a metallic-circuit s]ies l9e on :i* five ord9>y s]ies telephones are plac$ 9 s]ies4 ,9 ?is no gr\nd is employ$1 ! return be+ ?r\gh a l9e wire1 ?us mak+ ! circuit entirely metallic4 ,illu/ration3 ,fig4 #afe4 ,s]ies ,p>ty ,l9e ,! limitations ( ! ord9>y s]ies p>ty l9e may be be/ und]/ood by ref]5ce to ,fig4 #afe1 9 :i* ! circuits ( ?ree s]ies telephones are %[n connect$ ) a s+le l9e4 ,! receiv] ( ,/ation ,a is repres5t$ z be+ on its hook1 :ile ! receiv]s ( ,/ations ,b & ,c are remov$ f _! hooks1 z :5 ! subscrib]s at ^? two /ations are c>ry+ on a conv]sation4 ,! hook swit*es ( ,/ations ,b & ,c be+ 9 rais$ positions1 ! g5]ators & r+]s ( ^? /ations are cut out ( ! circuit1 & only ! telephone app>atus prop] is includ$1 b ! hook swit* ( ,/ation ,a be+ depress$ by ! weight ( its receiv]1 includes ! r+] ( t /ation 9 circuit1 & ?r\gh ?is r+]1 !re=e1 ! voice curr5ts ( ,/ations ,b & ,c mu/ pass4 ,! g5]ator ( ,/ation ,a is n 9 ! circuit ( voice curr5ts1 h[ev]1 because ( ! automatic %unt ) :i* ! g5]ator is provid$1 z describ$ 9 ,*apt] ,,viii4 ,a slight consid]ation ( ! s]ies sy/em z %[n 9 ?is figure1 indicates t ! voice curr5ts ( any two /ations t are 9 use1 mu/ pass 7z indicat$ by ! heavy l9es7 ?r\gh ! r+]s ( all ! /ations t are n 9 use2 & :5 a great numb] ( /ations are plac$ ^u a s+le l9e1 z has be5 frequ5tly ! case1 ! imp$ance (f]$ by ^! r+]s becomes a s]i\s b>ri] to ! passage ( ! voice curr5ts4 ,?is defect 9 ! s]ies p>ty l9e is fundam5tal1 z x is obvi\s t ! r+]s mu/ be left 9 ! circuit ( ! /ations :i* are n 9 use1 9 ord] t ^? /ations may always be 9 su* condition z to be able to receive a call4 ,?is defect may 9 "s measure be r$uc$ by mak+ ! r+]s ( l[ imp$ance4 ,?is is ! g5]al practice ) s]ies telephones1 ! r+]s ord9>ily hav+ %ort cores & a comp>atively small numb] ( turns1 ! resi/ance be+ z a rule ab\t #hj ohms4 ,bridg+ ,sy/ems4 ,v mu* bett] ?an ! s]ies plan ( p>ty-l9e connections1 is ! arrangem5t by :i* ! in/rum5ts are plac$ 9 bridges across ! l9e1 su* l9es be+ commonly kn[n z bridg$ or bridg+ l9es4 ,?is 0 fir/ /rongly advocat$ & put into wide practical use by ,j4,j4 ,c>ty1 n[ ! ,*ief ,eng9e] ( ! ,am]ican ,telephone & ,telegraph ,company4 ,a simple illu/ration ( a bridg+ telephone l9e is %[n 9 ,fig4 #aff1 :]e ! ?ree telephones %[n are ea* connect$ 9 a bridge pa? f ! l9e wire to gr\nd1 a type kn[n z a gr\nd$ bridg+ l9e4 ,its use is v common 9 rural di/ricts4 ,a bett] arrangem5t is %[n 9 ,fig4 #afg1 :i* repres5ts a metallic-circuit bridg+ l9e1 ?ree telephone in/rum5ts be+ %[n 9 p>allel or bridge pa?s across ! two l9e wires4 ,! actual circuit arrangem5ts ( a bridg+ p>ty l9e are bett] %[n 9 ,fig4 #afh4 ,!re are ?ree /ations & x w be se5 t at ea* /ation !re are ?ree possible bridges1 or bridge pa?s1 across ! two limbs ( ! l9e4 ,! fir/ ( ^! bridges is controll$ by ! hook swit* & is normally op54 ,:5 ! hook is rais$1 h[ev]1 ?is pa? is clos$ ?r\gh ! receiv] & second>y ( ! induction coil1 ! prim>y circuit be+ also clos$ s z to include ! batt]y & transmitt]4 ,?is con/itutes an ord9>y local-batt]y talk+ set4 ,illu/ration3 ,fig4 #aff4 ,gr\nd$ ,bridg+ ,l9e ,illu/ration3 ,fig4 #afg4 ,metallic ,bridg+ ,l9e ,illu/ration3 ,fig4 #afh4 ,metallic ,bridg+ ,l9e ,a second bridge at ea* /ation is l$ ?r\gh ! r+] or call-bell1 & ?is1 9 mo/ bridg+ telephones1 is p]man5tly clos$1 ! cont9uity ( ?is pa? betwe5 ! two limbs ( ! l9e n be+ affect$ ei!r by ! hook swit* or by ! automatic swit* 9 connection ) ! g5]ator4 ,a ?ird bridge pa? at ea* /ation is l$ ?r\gh ! g5]ator4 ,?is1 z indicat$1 is normally op51 b ! automatic cut-9 swit* ( ! g5]ator s]ves1 :5 ! g5]ator is op]at$1 to close its pa? across ! l9e1 s t x may s5d its curr5ts to ! l9e & r+ ! bells ( all ! /ations4 ,:5 any g5]ator is op]at$1 its curr5t divides & passes ov] ! l9e wires & ?r\gh all ( ! r+]s 9 multiple4 ,x is se51 !re=e1 t ! requirem5ts = a bridg+ g5]ator are t x %all be capable ( g5]at+ a l>ge curr5t1 suffici5t :5 divid$ up among/ all ! bells to r+ ea* ( !m2 & t x %all be capable ( produc+ a suffici5t voltage to s5d ! requir$ curr5t n only to ! ne>-by /ations1 b to ! /ations at ! di/ant end ( ! l9e4 ,x might seem at fir/ t ! bridg+ sy/em avoid$ "o difficulty only to enc\nt] ano!r4 ,x cle>ly avoids ! difficulty ( ! s]ies sy/em 9 t ! voice curr5ts1 9 ord] to rea* di/ant /ations1 d n h to pass ?r\gh all ( ! bells ( ! idle /ations 9 s]ies4 ,!re is1 h[ev]1 pres5t$ at ea* /ation a leakage pa? ?r\gh ! bell bridg$ across ! l9e1 ?r\gh :i* x w\ld appe> ! voice curr5ts might leak uselessly f "o side ( ! l9e to ! o!r & n pass on 9 suffici5t volume to ! di/ant /ation4 ,?is difficulty is1 h[ev]1 m app>5t ?an real4 ,x is f\nd t1 by mak+ ! r+]s ( high imp$ance1 ! leakage ( voice curr5ts ?r\gh !m f "o side ( ! l9e to ! o!r is practically negligible4 ,x is obvi\s t 9 a heavily load$ bridg$ l9e1 ! bell at ! home /ation1 t is at ! /ation f :i* ! call is be+ s5t1 w take slightly m ?an its %>e ( ! curr5t1 & x is also obvi\s t ! r++ ( ! home bell p]=ms no useful function4 ,! plan is frequ5tly adopt$1 !re=e1 ( hav+ ! op]ation ( ! g5]ator s]ve to cut its own bell out ( ! circuit4 ,! arrangem5t by :i* ?is is done is cle>ly %[n 9 ,fig4 #afi4 ,! circuit ( ! bell is normally complete across ! l9e1 :ile ! circuit ( ! g5]ator is normally op54 ,:51 h[ev]1 ! g5]ator crank is turn$ ^! conditions are rev]s$1 ! bell circuit be+ brok5 & ! g5]ator circuit clos$1 s z to all[ its curr5t all to pass ! l9e4 ,?is feature ( hav+ ! local bell rema9 sil5t ^u ! op]ation ( its own g5]ator is also ( advantage because o!r p>ties at ! same /ation are n di/urb$ by ! r++ ( ! bell :5 a call is be+ made by t /ation4 ,a difficulty enc\nt]$ on non-selective bridg+ p>ty l9es1 :i* at fir/ seems amus+ r ?an s]i\s1 b :i* nev]!less is (t5 a vexati\s tr\ble1 is t due to ! prop5sity ( "s p to li/5 9 on ! l9e on he>+ calls int5d$ = o!r ?an _! own /ations4 ,p ^: e?ical /&>ds w\ld n p]mit !m to li/5 at1 or peep ?r\gh1 a keyhole1 (t5 engage 9 ?is telephonic eavesdropp+4 ,frequ5tly1 n only "o b _m subscrib]s w respond to a call int5d$ = o!rs & w li/5 to ! ensu+ conv]sation4 ,?is is disadvantage\s 9 sev]al respects3 ,x de/roys ! privacy ( conv]sation betwe5 any two p>ties2 x subjects ! local batt]ies to an unnecess>y & useless dra92 & x greatly impairs ! r++ effici5cy ( ! l9e4 ,! reason = ?is int]f]5ce ) r++ is t ! pres5ce ( ! l[-resi/ance receiv]s across ! l9e all[s ! curr5t s5t out by any ( ! g5]ators to pass 9 l>ge measure ?r\gh ! receiv]s1 ?us depriv+ ! r+]s1 :i* are ( comp>atively high resi/ance & imp$ance1 ( ! en]gy necess>y to op]ate !m4 ,z a result ( ?is x is frequ5tly impossible = "o p>ty to repeat ! call = ano!r because1 dur+ ! int]val betwe5 ! fir/ & second call1 a numb] ( p>ties remove _! receiv]s f _! hooks 9 ord] to li/54 ,r+-(f or cle>+-out signals are likewise int]f]$ )4 ,illu/ration3 ,fig4 #afi4 ,circuits ( ,bridg+ ,/ation ,a p>tial rem$y = ?is int]f]5ce ) r++1 due to eavesdropp+1 is to introduce a l[-capacity cond5s] into ! receiv] circuit at ea* /ation1 z %[n 9 ,fig4 #afi4 ,?is does n s]i\sly int]f]e ) ! spee* transmission s9ce ! cond5s]s w readily transmit ! high-frequ5cy voice curr5ts4 ,su* cond5s]s1 h[ev]1 h n suffici5t capacity to enable !m readily to transmit ! l[-frequ5cy r++ curr5ts & h5ce ^! are =c$1 9 l>ge measure1 to pass ?r\gh ! bells = :i* !y are int5d$ r ?an leak+ ?r\gh ! l[-resi/ance receiv] pa?s4 ,! be/ cond5s] = ?is use is ( ab\t #a_/b-micr(>ad capacity1 :i* is ample = voice-transmitt+ purposes1 :ile x s]ves to effectively b> ! major portion ( ! g5]ator curr5ts4 ,a high] capacity cond5s] w\ld c>ry ! g5]ator curr5ts mu* m readily & ?us defeat ! purpose = :i* x 0 int5d$4 ,9 ord] t ! requisite imp$ance may be giv5 to ! r+]s employ$ = bridg+ p>ty l9es1 x is cu/om>y to make ! cores r long & ( some:at l>g] diamet] ?an 9 s]ies r+]s & at ! same "t to w9d ! coils ) r f9e wire s z to secure ! requisite numb] ( turns4 ,bridg+ bells are ord9>ily w\nd to a resi/ance ( #a1jjj or #a1fjj ohms1 ^! two figures hav+ become /&>d practice4 ,x is n1 h[ev]1 ! high resi/ance s mu* z ! high imp$ance t is /riv5 = 9 bridg+ bells2 x is ! numb] ( turns t is ( pr9cipal importance4 ,z has already be5 /at$1 ! g5]ators us$ = bridg+ l9es are made capable ( giv+ a great] curr5t output ?an is necess>y 9 s]ies in/rum5ts1 & = ?is purpose !y are usually provid$ ) at lea/ f\r1 & usually five1 b> magnets4 ,! armature is made correspond+ly long & is w\nd1 z a rule1 ) ab\t ,no4 #cc wire4 ,sometimes :]e a bridg$ p>ty l9e t]m9ates 9 a c5tral-(fice swit*bo>d x is desir$ to s op]ate ! l9e t ! subscrib]s %all n be able to call up ea* o!r1 b %all1 in/ead1 be able to signal only ! c5tral-(fice op]ator1 :o1 9 turn1 w be enabl$ to call ! p>ty desir$1 designat+ 8 /ation by a suitable code r+4 ,"o common way to d ?is is to use bias$ bells in/ead ( ! ord9>y pol>iz$ bells4 ,9 ord] t ! bells may n be rung by ! subscrib]s' g5]ators1 ^! g5]ators are made ( ! direct-curr5t type & ^! are s associat$ ) ! l9e t ! curr5ts :i* !y s5d out w be 9 ! wrong direction to actuate ! bells4 ,on ! o!r h&1 ! c5tral-(fice g5]ator is ( direct-curr5t type & is associat$ ) ! l9e 9 ! "r direction to en]gize ! bells4 ,?us any subscrib] on ! l9e may call ! c5tral (fice by m]ely turn+ 8 g5]ator crank1 :i* action w n r+ ! bells ( ! subscrib]s on ! l9e4 ,! op]ator w !n be able to receive ! call & 9 turn s5d out curr5ts ( ! prop] direction to r+ all ! bells &1 by code1 call ! desir$ p>ty to ! telephone4 ,illu/ration3 ,,"o ,,w+ ,,( ,,op]at+ ,,room1 ,,b]l91 ,,g]many ,ultimate ,capacity #bd1jjj ,subscrib]s' ,l9es & #b1ajj ,trunk ,l9es4 ,siem5s-,halske ,equipm5t4 ,note ,horizontal ,disposal ( ,multiple ,signal ,code4 ,! code by :i* /ations are designat$ on non-selective p>ty l9es usually consi/s 9 comb9ations ( long & %ort r+s simil> to ! dots & da%es 9 ! ,morse code4 ,?us1 "o %ort r+ may indicate ,/ation ,no4 #a2 two %ort r+s ,/ation ,no4 #b2 & s on up to1 say1 five %ort r+s1 indicat+ ,/ation ,no4 #e4 ,x is n good practice to employ m ?an five successive %ort r+s because ( ! confusion :i* (t5 arises 9 p's m9ds z to ! numb] ( r+s t !y he>4 ,:51 !re=e1 ! numb] ( /ations to be rung by code exce$s five1 x is bett] to employ comb9ations ( long & %ort r+s1 & a good way is to adopt a p>tial decimal sy/em1 omitt+ ! numb]s high] ?an five 9 ea* t51 & employ+ long r+s to indicate ! t5s digits & %ort r+s to indicate ! units digit1 ,table ,x4 ,,table ,x ,signal ,code ---------------------------------------- ------------------ ,,/ation ,,numb],,r+ ,,/ation ,,numb],,r+ #a #a %ort #ab #a long1 #b %ort #b #b %ort #ac #a long1 #c %ort #c #c %ort #ad #a long1 #d %ort #d #d %ort #ae #a long1 #e %ort #e #e %ort #ba #b long1 #a %ort #aa #a long1 #a %ort#bb #b long1 #b %ort ---------------------------------------- ------------------ ,o!r arrangem5ts are (t5 employ$ & by almo/ any ( !m a great v>iety ( readily di/+ui%able signals may be secur$4 ,! patrons ( su* l9es le>n to di/+ui%1 ) comp>atively few errors1 betwe5 ! calls int5d$ = !m & ^? int5d$ = o!rs1 b frequ5tly !y d n obs]ve ! di/9ction1 z has already be5 po9t$ out4 ,limitations4 ,) good telephones ! limit z to ! numb] ( /ations t x is possible to op]ate ^u a s+le l9e is usually due m to limitations 9 r++ ?an 9 talk+4 ,z ! numb] ( /ations is increas$ indef9itely a condition w be rea*$ at :i* ! g5]ators w n be able to g5]ate suffici5t curr5t to r+ all ( ! bells1 & ?is condition is likely to occur be=e ! talk+ effici5cy is s]i\sly impair$ by ! numb] ( bridges across ! l9e4 ,nei!r ( ^! consid]ations1 h[ev]1 %\ld det]m9e ! maximum numb] ( /ations to be plac$ on a l9e4 ,! prop] limit z to ! numb] ( /ations is n ! numb] t c be rung by a s+le g5]ator1 or ! numb] ) :i* x is possible to transmit spee* prop]ly1 b r ! numb] ( /ations t may be employ$ )\t caus+ undue int]f]5ce betwe5 ! v>i\s p>ties :o may desire to use ! l9e4 ,ov]load$ p>ty l9es cause mu* annoyance1 n only = ! reason t ! subscrib]s are (t5 n able to use ! l9e :5 !y want x1 b also1 9 non-selective l9es1 because ( ! incessant r++ ( ! bells1 & ! liability ( confusion 9 ! int]pretation ( ! signal+ code1 :i* ( c\rse becomes m complex z ! numb] ( /ations increases4 ,! am\nt ( bus9ess t is done ov] a telephone l9e is usually ref]r$ to z ! traffic4 ,x w be und]/ood1 h[ev]1 9 consid]+ p>ty-l9e work+ t ! numb] ( calls p] day or p] h\r1 or p] %ort] unit1 is n ! true measure ( ! traffic &1 !re=e1 n ! true measure ( ! am\nt ( possible int]f]5ce betwe5 ! v>i\s subscrib]s on ! l9e4 ,an almo/ equally great factor is ! av]age l5g? ( ! conv]sation4 ,9 city l9es1 t is1 9 l9es 9 city ex*anges1 ! conv]sation is usually %ort & av]ages p]haps two m9utes 9 duration4 ,9 c\ntry l9es1 h[ev]1 s]v+ p 9 rural di/ricts1 :o h poor facilities = see+ ea* o!r1 p>ticul>ly dur+ ! w9t] "t1 ! conv]sations w av]age v mu* long]4 ,9 rural communities ! p (t5 d mu* ( _! visit+ by telephone1 & conv]sations ( half an h\r 9 l5g? are n unusual4 ,x is obvi\s t "u su* conditions a p>ty l9e hav+ a great _m /ations w be subject to v grave int]f]5ce betwe5 ! p>ties1 p desir+ to use ! l9e = bus9ess purposes (t5 be+ compell$ to wait an undue "t be=e !y may secure ! use ( ! l9e4 ,x is obvi\s1 !re=e1 t ! am\nt ( traffic on ! l9e1 :e!r due to _m %ort conv]sations or to a comp>atively few long ones1 is ! ma9 factor t %\ld det]m9e ! numb] ( /ations t1 economically1 may be plac$ on a l9e4 ,! facilities also = build+ l9es ent] z a factor 9 ?is respect1 s9ce x is obvi\s t 9 comp>atively poor communities ! money may n be =?com+ to build z _m l9es z are ne$$ to prop]ly take c>e ( ! traffic4 ,a compromise is1 !re=e1 (t5 necess>y1 & ! only rule t may be safely laid d[n is to place z few p>ties on a giv5 l9e z conditions w admit4 ,no def9ite limit may be set to apply to all conditions b x may be safely /at$ t "u ord9>y circum/ances no m ?an t5 /ations %\ld be plac$ on a non-selective l9e4 ,tw5ty /ations are1 h[ev]1 common1 & sometimes =ty & ev5 fifty h be5 connect$ to a s+le l9e4 ,9 su* cases ! confusion :i* results1 ev5 if ! talk+ & ! r++ effici5cy are tol]able1 makes ! s]vice ov] su* ov]load$ l9es unsatisfactory to all conc]n$4 ,,*apt] ,,xvi ,,selective ,,p>ty-,,l9e ,,sy/ems ,! problem :i* confronts "o 9 ! production ( a sy/em ( selective r++ on p>ty l9es is t ( caus+ ! bell ( any *os5 "o ( ! sev]al p>ties on a circuit to respond to a signal s5t out f ! c5tral (fice )\t s\nd+ any ( ! o!r bells4 ,?is1 ( c\rse1 mu/ be accompli%$ )\t int]f]+ ) ! regul> functions ( ! telephone l9e & app>atus4 ,by ?is is meant t ! subscrib]s mu/ be able to call ! c5tral (fice & to signal = disconnection :5 desir$1 & also t ! association ( ! selective-signal+ devices ) ! l9e %all n int]f]e ) ! transmission ( spee* ov] ! l9e4 ,a great _m ways ( accompli%+ selective r++ on p>ty l9es h be5 propos$1 & a l>ge numb] ( !m h be5 us$4 ,all ( ^! ways may be classifi$ "u f\r diff]5t classes accord+ to ! und]ly+ pr9ciple involv$4 ,classification4 7#a7 ,pol>ity sy/ems are s call$ because !y dep5d = _! op]ation on ! use ( bells or o!r responsive devices s pol>iz$ t !y w respond to "o direction ( curr5t only4 ,^! bells or o!r devices are s arrang$ 9 connection ) ! l9e t ! "o to be rung w be trav]s$ by curr5t 9 ! prop] direction to actuate x1 :ile all ( ! o!rs w ei!r n be trav]s$ by any curr5t at all1 or by curr5t 9 ! wrong direction to cause _! op]ation4 7#b7 ,! h>monic sy/ems h = _! und]ly+ pr9ciple ! fact t a p5dulum or ela/ic re$1 s support$ z to be capable ( vibrat+ freely1 w h "o p>ticul> rate ( vibration :i* x may easily be made to assume4 ,?is p5dulum or re$ is plac$ "u ! influ5ce ( an electromagnet associat$ ) ! l9e1 & ow+ to ! fact t x w vibrate easily at "o p>ticul> rate ( vibration & ) extreme difficulty at any o!r rate1 x is cle> t = curr5t impulses ( a frequ5cy correspond+ to its natural rate ! re$ w take up ! vibration1 :ile = o!r frequ5cies x w fail to respond4 ,selection on p>ty l9es by means ( ?is sy/em is provid$ = by tun+ all ( ! re$s on ! l9e at diff]5t rates ( vibration & is accompli%$ by s5d+ out on ! l9e r++ curr5ts ( prop] frequ5cy to r+ ! desir$ bell4 ,! curr5t-g5]at+ devices = r++ ^! bells are capable ( s5d+ out diff]5t frequ5cies correspond+ respectively to ! rates ( vibration ( ea* ( ! vibrat+ re$ tongues4 ,to select any "o /ation1 !re=e1 ! curr5t frequ5cy correspond+ to ! rate ( vibration ( ! re$ tongue at t /ation is s5t & ?is1 be+ out ( tune ) ! re$ tongues at all ( ! o!r /ations1 op]ates ! tongue ( ! desir$ /ation1 b fails to op]ate ^? at all ( ! o!r /ations4 7#c7 ,9 ! /ep-by-/ep sy/em ! bells on ! l9e are normally n 9 op]ative relation ) ! l9e & ! bell ( ! desir$ p>ty on ! l9e is made responsive by s5d+ ov] ! l9e a c]ta9 numb] ( impulses prelim9>y to r++ x4 ,^! impulses move /ep-by-/ep me*anisms at ea* ( ! /ations 9 unison1 ! arrangem5t be+ su* t ! bells at ! sev]al /ations are ea* made op]ative aft] ! s5d+ ( a c]ta9 numb] ( prelim9>y impulses1 ?is numb] be+ diff]5t = all ! /ations4 7#d7 ,! brok5-l9e sy/ems are new 9 telephony & = c]ta9 fields ( "w look promis+4 ,9 ^! ! l9e circuit is normally brok5 up into sections1 ! fir/ section t]m9at+ at ! fir/ /ation out f ! c5tral (fice1 ! second section at ! second /ation1 & s on4 ,:5 ! l9e is 9 its normal or inactive condition only ! bell at ! fir/ /ation is s connect$ ) ! l9e circuit z to enable x to be rung1 ! l9e be+ op5 beyond4 ,s5d+ a s+le prelim9>y impulse w1 h[ev]1 op]ate a swit*+ device s z to disconnect ! bell at ! fir/ /ation & to connect ! l9e ?r\gh to ! second /ation4 ,?is may be c>ri$ out1 by s5d+ ! prop] numb] ( prelim9>y impulses1 s z to build up ! l9e circuit to ! desir$ /ation1 aft] :i* ! s5d+ ( ! r++ curr5t w cause ! bell to r+ at t /ation only4 ,pol>ity ,me?od4 ,! pol>ity me?od ( selective signal+ on p>ty l9es is probably ! mo/ ext5sively us$4 ,! /&>d selective sy/em ( ! ,am]ican ,telephone & ,telegraph ,company op]ates on ?is pr9ciple4 ,two-,p>ty ,l9e4 ,x is obvi\s t selection may be _h betwe5 two p>ties on a s+le metallic-circuit l9e )\t ! use ( bias$ bells or curr5t ( diff]5t pol>ities4 ,?us1 "o limb ( a metallic circuit may be us$ z "o gr\nd$ l9e to r+ ! bell at "o ( ! /ations1 & ! o!r limb ( ! metallic circuit may be us$ z ano!r gr\nd$ l9e to r+ ! bell ( ! o!r /ation2 & ! two limbs may be us$ toge!r z a metallic circuit = talk+ purposes z usual4 ,?is is %[n 9 ,fig4 #agj1 :]e ! r++ keys at ! c5tral (fice are diagrammatically %[n 9 ! left-h& portion ( ! figure z ,k#a & ,k#b4 ,! op]ation ( ^! keys w be m fully po9t$ out 9 a subsequ5t *apt]1 b a correct und]/&+ w be _h if x be rememb]$ t ! circuits are normally ma9ta9$ by ^! keys 9 ! position %[n4 ,:51 h[ev]1 ei!r "o ( ! keys is op]at$1 ! two long spr+s may be consid]$ z press$ ap>t s z to dis5gage ! normal contacts betwe5 ! spr+s & to engage ! two out] contacts1 ) :i* !y are %[n 9 ! cut to be dis5gag$4 ,! two out] contacts are connect$ respectively to an ord9>y alt]nat+-curr5t r++ g5]ator & to gr\nd1 b ! connection is rev]s$ on ! two keys4 ,illu/ration3 ,fig4 #agj4 ,simple ,two-,p>ty ,l9e ,selection ,at ,/ation ,a ! ord9>y talk+ set is %[n 9 simplifi$ =m1 consi/+ m]ely ( a receiv]1 transmitt]1 & hook swit* 9 a s+le bridge circuit across ! l9e4 ,an ord9>y pol>iz$ bell is %[n connect$ 9 s]ies ) a cond5s] betwe5 ! l[] limb ( ! l9e & gr\nd4 ,at ,/ation ,b ! same talk+ circuit is %[n1 b ! pol>iz$ bell & cond5s] are bridg$ betwe5 ! upp] limb ( ! l9e & gr\nd4 ,if ! op]ator desires to call ,/ation ,a1 %e w press key ,k#a :i* w gr\nd ! upp] side ( ! l9e & connect ! l[] side ( ! l9e ) ! g5]ator ,g#a1 & ?is1 obvi\sly1 w cause ! bell at ,/ation ,a to r+4 ,! bell at ,/ation ,b w n r+ because x is n 9 ! circuit4 ,if1 on ! o!r h&1 ! op]ator desires to r+ ! bell at ,/ation ,b1 %e w depress key ,k#b1 :i* w all[ ! curr5t f g5]ator ,g#b to pass ov] ! upp] side ( ! l9e ?r\gh ! bell & cond5s] at ,/ation ,b & return by ! pa? ?r\gh ! gr\nd4 ,! object ( gr\nd+ ! opposite sides ( ! keys at ! c5tral (fice is to prev5t cross-r++1 t is1 r++ ! wrong bell4 ,7 ! keys n gr\nd$ ?is might occur :5 a r++ curr5t 0 be+ s5t out :ile ! receiv] at "o ( ! /ations 0 (f its hook2 ! r++ curr5t f1 say1 g5]ator ,g#a !n pass+ n only ?r\gh ! bell at ,/ation ,a z int5d$1 b also ?r\gh ! bell at ,/ation ,b by way ( ! bridge pa? ?r\gh ! receiv] t happ5$ to be connect$ across ! l9e4 ,) ! r++ keys gr\nd$ z %[n1 x is obvi\s t ?is w n occur1 s9ce ! pa? = ! r++ curr5t ?r\gh ! wrong bell w always be %unt$ by a direct pa? to gr\nd on ! same side ( ! l9e4 ,9 su* a two-p>ty-l9e selective sy/em ! two g5]ators ,g#a & ,g#b may be ! same g5]ator & may be ( ! ord9>y alt]nat+-curr5t type4 ,! bells likewise may be ( ! ord9>y alt]nat+-curr5t type4 ,! two-p>ty selective l9e j describ$ virtually employs two sep>ate circuits = r++4 ,n[ ea* ( ^! circuits alone may be employ$ to accompli% selective r++ betwe5 two /ations by us+ two bias$ bells oppositely pol>iz$1 & employ+ pulsat+ r++ curr5ts ( "o direction or ! o!r accord+ to :i* bell x is desir$ to r+4 ,"o side ( a circuit s equipp$ is %[n 9 ,fig4 #aga4 ,9 ?is ! two bias$ bells are at ,/ation ,a & ,/ation ,b1 ^! be+ bridg$ to gr\nd 9 ea* case & adapt$ to respond only to positive & negative impulses respectively4 ,at ! c5tral (fice ! two keys ,k#a & ,k#b are %[n4 ,a s+le alt]nat+-curr5t g5]ator ,g is %[n1 hav+ its bru% #a gr\nd$ & bru% #b connect$ to a commutator disk #c m\nt$ on ! g5]ator %aft s z to revolve !re)4 ,"o-half ( ! p]iph]y ( ?is disk is ( insulat+ mat]ial s t ! bru%es #d & #e1 :i* be> aga9/ ! disk1 w be alt]nately connect$ ) ! disk &1 !re=e1 ) ! bru% #b ( ! g5]ator4 ,n[ ! bru% #b1 be+ "o t]m9al ( an alt]nat+-curr5t ma*9e1 is alt]nately positive & negative1 & ! arrangem5t ( ! commutator is su* t ! disk1 :i* is always at ! pot5tial ( ! bru% #b1 w be connect$ to ! bru% #e only :ile x is positively *>g$ & ) ! bru% #d only :ile x is negatively *>g$4 ,z a result1 bru% #e has a succession ( positive impulses & bru% #d a succession ( negative ones4 ,obvi\sly1 !re=e1 :5 key ,k#a is depress$ only ! bell at ,/ation ,a w be rung1 & likewise ! depression ( key ,k#b w result only 9 ! r++ ( ! bell at ,/ation ,b4 ,illu/ration3 ,fig4 #aga4 ,pr9ciple ( ,selection by ,pol>ity ,f\r-,p>ty ,l9e4 ,f ! two =ego+ two-p>ty l9e sy/ems x is evid5t t a f\r-p>ty l9e sy/em may be readily obta9$1 t is1 by employ+ two oppositely pol>iz$ bias$ bells on ea* side ( ! metallic circuit4 ,! selection ( any ( ! f\r bells may be obta9$1 *oos+ betwe5 ! pairs connect$1 respectively1 ) ! two limbs ( ! l9e1 by *oos+ ! limb on :i* ! curr5t is to be s5t1 & *oos+ betwe5 ! two bells ( ! pair on t side ( ! l9e by *oos+ :i* pol>ity ( curr5t to s5d4 ,su* a f\r-p>ty l9e sy/em is %[n 9 ,fig4 #agb4 ,9 ?is ! g5]ators are n %[n1 b ! wires lead+ f ! f\r keys are %[n m>k$ plus or m9us1 accord+ to ! t]m9al ( ! g5]ator to :i* !y are suppos$ to be connect$4 ,likewise ! two bells connect$ ) ! l[] side ( ! l9e are m>k$ positive & negative1 z are ! two bells connect$ ) ! upp] side ( ! l9e4 ,f ! =ego+ description ( ,figs4 #agj & #aga1 x is cle> t if key ,k#a is press$ ! bell at ,/ation ,a w be rung1 & t bell only1 s9ce ! bells at ,/ation ,c & ,/ation ,d are n 9 ! circuit & ! positive curr5t s5t ov] ! l[] side ( ! l9e is n ( ! prop] pol>ity to r+ ! bell at ,/ation ,b4 ,! sy/em %[n 9 ,fig4 #agb is subject to "o r grave defect4 ,9 subsequ5t *apt]s x w be po9t$ out t 9 common-batt]y sy/ems ! display ( ! l9e signal at ! c5tral (fice is affect$ by any "o ( ! subscrib]s m]ely tak+ 8 receiv] (f its hook & ?us e/abli%+ a connection betwe5 ! two limbs ( ! metallic circuit4 ,su* common-batt]y sy/ems %\ld h ! two limbs ( ! l9e1 normally1 entirely insulat$ f ea* o!r4 ,x is se5 t ?is is n ! case 9 ! sy/em j describ$1 s9ce !re is a conduct+ pa? f "o limb ( ! l9e ?r\gh ! two bells on t side to gr\nd1 & !nce ?r\gh ! o!r pair ( bells to ! o!r limb ( ! l9e4 ,?is means t unless ! resi/ance ( ! bell w9d+s is made v high1 ! pa? ( ! signal+ circuit w be ( suffici5tly l[ resi/ance to actuate ! l9e signal at ! c5tral (fice4 ,illu/ration3 ,fig4 #agb4 ,f\r-,p>ty ,pol>ity ,selection ,x is n feasible to ov]come ?is objection by ! use ( cond5s]s 9 s]ies ) ! bells1 z 0 done 9 ! sy/em %[n 9 ,fig4 #agj1 s9ce ! bells are necess>ily bias$ & su* bells1 z may readily be se51 w n "w prop]ly ?r\gh cond5s]s1 s9ce ! plac+ ( a cond5s] 9 _! circuit means t ! curr5t :i* passes ?r\gh ! bell is alt]nat+ r ?an pulsat+1 al?\gh ! orig9al s\rce may h be5 ( pulsat+ nature only4 ,illu/ration3 ,fig #agc4 ,/&>d ,pol>ity ,sy/em ,! rem$y = ?is difficulty1 !re=e1 has be5 to place 9 s]ies ) ea* bell a v high non-inductive resi/ance ( ab\t #ae1jjj or #bj1jjj ohms1 & also to make ! w9d+s ( ! bells ( comp>atively high resi/ance1 usually ab\t #b1ejj ohms4 ,ev5 ) ?is precaution !re is a consid]able leakage ( ! c5tral-(fice batt]y curr5t f "o side ( ! l9e to ! o!r ?r\gh ! two pa?s to gr\nd 9 s]ies4 ,?is me?od ( selective signal+ has1 !re=e1 be5 m frequ5tly us$ ) magneto sy/ems4 ,an endeavor to apply ?is pr9ciple to common-batt]y sy/ems )\t ! objections not$ above has l$ to ! adoption ( a modification1 :]e9 a relay at ea* /ation normally holds ! gr\nd connection op54 ,?is is %[n 9 ,fig4 #agc & is ! /&>d f\r-p>ty l9e r++ circuit employ$ by ! ,am]ican ,telephone & ,telegraph ,company & _! lic5sees4 ,9 ?is sy/em ! bias$ bells are normally disconnect$ f ! l9e1 &1 !re=e1 ! leakage pa? ?r\gh !m f "o side ( ! l9e to ! o!r does n exi/4 ,at ea* /ation !re is a relay w9d+ adapt$ to be op]at$ by ! r++ curr5t bridg$ across ! l9e 9 s]ies ) a cond5s]4 ,z a result1 :5 r++ curr5t is s5t out on ! l9e all ( ! relays1 i4e41 "o at ea* /ation1 are en]giz$ & attract _! armatures4 ,?is e/abli%es ! connection ( all ! bells to l9e & really br+s ab\t tempor>ily a condition equival5t to t ( ,fig4 #agb4 ,z a result1 ! s5d+ ( a positive curr5t on ! l[] l9e ) a gr\nd return w cause ! op]ation ( ! bell at ,/ation ,a4 ,x w n r+ ! bell at ,/ation ,b because ( ! wrong pol>ity4 ,x w n r+ ! bells ( ,/ation ,c & ,/ation ,d because !y are 9 ! circuit betwe5 ! o!r side ( ! l9e & gr\nd4 ,z soon z ! r++ curr5t ceases all ( ! relays release _! armatures & disconnect all ! bells f ! l9e4 ,by ?is v simple device ! tr\ble1 due to m>g9al work+ ( ! l9e signal1 is done away )1 s9ce normally !re is no leakage f "o side ( ! l9e to ! o!r on acc\nt ( ! pres5ce ( ! cond5s]s 9 ! bridge at ea* /ation4 ,illu/ration3 ,fig4 #agd4 ,r++-,key ,arrangem5t ,9 ,fig4 #agd1 ! m complete connections ( ! c5tral-(fice r++ keys are %[n1 by means ( :i* ! prop] positive or negative r++ curr5ts are s5t to l9e 9 ! prop] way to cause ! r++ ( any "o ( ! f\r bells on a p>ty l9e ( ei!r ( ! types %[n 9 ,figs4 #agb & #agc4 ,9 ?is ! g5]ator ,g & its commutator disk #c1 ) ! v>i\s bru%es1 #a1 #b1 #d1 & #e1 are arrang$ 9 ! same mann] z is %[n 9 ,fig4 #aga4 ,x is evid5t f :at has be5 said t wire #f lead+ f g5]ator bru% #b & commutator disk #c w c>ry alt]nat+ pot5tial2 t wire #g w c>ry positive pulsations ( pot5tial2 & t wire #h w c>ry negative pulsations ( pot5tial4 ,!re are five keys 9 ! set illu/rat$ 9 ,fig4 #agd1 ( :i* f\r1 viz1 ,k#a1 ,k#b1 ,k#c1 & ,k#d1 are connect$ 9 ! same mann] z diagrammatically indicat$ 9 ,figs4 #agb & #agc1 & w1 obvi\sly1 s]ve to s5d ! prop] curr5t ov] ! prop] limb ( ! l9e to r+ "o ( ! bells4 ,key ,k#e1 ! fif? "o 9 ! set1 is add$ s z to enable ! op]ator to r+ an ord9>y unbias$ bell on a s+le p>ty l9e :5 connection is made ) su* l9e4 ,z ! two outside contacts ( ?is key are connect$ respectively to ! two bru%es ( ! alt]nat+-curr5t dynamo ,g1 x is cle> t x w impress an alt]nat+ curr5t on ! l9e :5 its contacts are clos$4 ,circuits ( ,two-,p>ty ,l9e ,telephones4 ,9 ,fig4 #age is %[n 9 detail ! wir+ ( ! telephone set usually employ$ 9 connection ) ! p>ty-l9e selective-r++ sy/em illu/rat$ 9 ,fig4 #agj4 ,9 ! wir+ ( ?is set & ! two foll[+1 x mu/ be borne 9 m9d t ! portion ( ! circuit us$ dur+ conv]sation might be wir$ 9 a numb] ( ways )\t affect+ ! pr9ciple ( selective r++ employ$2 h[ev]1 ! circuits %[n are ^? mo/ commonly employ$ ) ! respective selective r++ sy/ems :i* !y are int5d$ to illu/rate4 ,9 connect+ ! circuits ( ?is telephone in/rum5t to ! l9e1 ! two l9e conductors are connect$ to b9d+ po/s #a & #b & a gr\nd connection is made to b9d+ po/ #c4 ,9 practice1 9 ord] to avoid ! necessity ( *ang+ ! p]man5t wir+ ( ! telephone set 9 connect+ x z an ,a or ,b ,/ation 7,fig4 #agj71 ! l9e conductors are connect$ to ! b9d+ po/s 9 rev]se ord] at ! two /ations2 t is1 = ,/ation ,a ! upp] conductor1 ,fig4 #agj1 is connect$ to b9d+ po/ #a & ! l[] conductor to b9d+ po/ #b1 :ile at ,/ation ,b ! upp] conductor is connect$ to b9d+ po/ #b & ! l[] conductor to b9d+ po/ #a4 ,! p]man5t wir+ ( ?is telephone set is ! same z t frequ5tly us$ = a set connect$ to a l9e hav+ only "o /ation1 ! prop] r++ circuit be+ made by ! me?od ( connect+ up ! b9d+ po/s4 ,= example1 if ?is telephone set 7 to be us$ on a s+le /ation l9e1 ! b9d+ po/s #a & #b w\ld be connect$ to ! two conductors ( ! l9e z be=e1 :ile b9d+ po/ #c w\ld be connect$ to po/ #a in/ead ( be+ gr\nd$4 ,illu/ration3 ,fig4 #age4 ,circuit ( ,two-,p>ty ,/ation ,circuits ( ,f\r-,p>ty-,l9e ,telephones4 ,! wir+ ( ! telephone set us$ ) ! sy/em illu/rat$ 9 ,fig4 #agb is %[n 9 detail 9 ,fig4 #agf4 ,! wir+ ( ?is set is arrang$ = local batt]y or magneto work+1 z ?is me?od ( selective r++ is m frequ5tly employ$ ) magneto sy/ems1 on acc\nt ( ! objectionable features :i* arise :5 appli$ to common-batt]y sy/ems4 ,9 ?is figure ! l9e conductors are connect$ to b9d+ po/s #a & #b1 & a gr\nd connection is made to b9d+ po/ #c4 ,9 ord] t all sets may be wir$ alike & yet p]mit ! in/rum5t to be connect$ = any "o ( ! v>i\s /ations1 ! bell is n p]man5tly wir$ to any portion ( ! circuit b has flexible connections :i* w all[ ( ! set be+ prop]ly connect$ = any desir$ /ation4 ,! t]m9als ( ! bell are connect$ to b9d+ po/s #i & #aj1 to :i* are connect$ flexible conductors t]m9at+ 9 t]m9als #g & #h4 ,^! t]m9als may be connect$ to ! b9d+ po/s #d1 #e1 & #f 9 ! prop] mann] to connect ! set z an ,a1 ,b1 ,c1 or ,d /ation1 z requir$4 ,= example1 9 connect+ ! set = ,/ation ,a1 ,fig4 #agb1 t]m9al #g is connect$ to b9d+ po/ #f & #h to #e4 ,= connect+ ! set = ,/ation ,b t]m9al #g is connect$ to b9d+ po/ #e & #h to #f4 ,= connect+ ! set = ,/ation ,c t]m9al #g is connect$ to b9d+ po/ #f & #h to #d4 ,= connect+ ! set = ,/ation ,d t]m9al #g is connect$ to b9d+ po/ #d & #h to #f4 ,illu/ration3 ,fig4 #agf4 ,circuit ( ,f\r-,p>ty ,/ation )\t ,relay ,illu/ration3 ,fig4 #agg4 ,circuit ( ,f\r-,p>ty ,/ation ) ,relay ,! detail$ wir+ ( ! telephone set employ$ 9 connection ) ! sy/em illu/rat$ 9 ,fig4 #agc is %[n 9 ,fig4 #agg4 ,! wir+ ( ?is set is arrang$ = a common-batt]y sy/em1 inasmu* z ?is arrangem5t ( signal+ circuit is m especially adapt$ = common-batt]y work+4 ,h[ev]1 ?is arrangem5t is frequ5tly adapt$ to magneto sy/ems z ev5 ) magneto sy/ems a p]man5t gr\nd connection at a subscrib]'s /ation is objectionable inasmu* z x increases ! difficulty ( det]m9+ ! exi/5ce or location ( an accid5tal gr\nd on "o ( ! l9e conductors4 ,! wir+ ( ?is set is also arrang$ s t "o /&>d type ( wir+ may be employ$ & yet all[ any telephone set to be connect$ z an ,a1 ,b1 ,c1 or ,d /ation4 ,h>monic ,me?od4 ,pr9ciples4 ,to be/ und]/& ! pr9ciple ( op]ation ( ! h>monic p>ty-l9e signal+ sy/ems1 x is to be rememb]$ t a flexible re$1 m\nt$ rigidly at "o end & hav+ its o!r end free to vibrate1 w1 l a viol9 /r+1 h a c]ta9 natural p]iod ( vibration2 t is1 if x be />t$ 9 vibration1 z by snapp+ x ) ! f+]s1 x w take up a c]ta9 rate ( vibration :i* w cont9ue at a uni=m rate until ! vibration ceases altoge!r4 ,su* a re$ w be mo/ easily ?r[n into vibration by a s]ies ( impulses hav+ a frequ5cy correspond+ exactly to ! natural rate ( vibration ( ! re$ itself2 x may be ?r[n into vibration by v slight impulses if !y occur at exactly ! prop] times4 ,x is famili> to all t a p]son pu%+ ano!r 9 a sw+ may cause a consid]able amplitude ( vibration ) ! ex]tion ( b a small am\nt ( =ce1 if he w s "t 8 pu%es z to con=m exactly to ! natural rate ( vibration ( ! sw+4 ,x is ( c\rse possible1 h[ev]1 to make ! sw+ take up o!r rates ( vibrations by ! application ( suffici5t =ce4 ,z ano!r example1 consid] a clock p5dulum beat+ seconds4 ,by g5tle bl[s furni%$ by ! escapem5t at exactly ! prop] times1 ! heavy p5dulum is kept 9 motion4 ,h[ev]1 if a p]son grasps ! p5dulum weight & %akes x1 x may be made to vibrate at almo/ any desir$ rate1 dep5d5t on ! /r5g? & agility ( ! individual4 ,! conclusion is1 !re=e1 t a re$ or p5dulum may be made to />t & vibrate easily by ! application ( impulses at prop] int]vals1 & only ) great difficulty by ! application ( impulses at o!r ?an ! prop] int]vals2 & ^! facts =m ! basis on :i* h>monic-r++ sy/ems re/4 ,! fa!r ( h>monic r++ 9 telephony 0 ,jacob ,b4 ,curri]1 an und]tak] ( ,l[ell1 ,mass4 ,8 h>monic bells 7 plac$ 9 s]ies 9 ! telephone l9e1 & 7 consid]ably us$ 9 ,new ,engl& 9 comm]cial practice 9 ! e>ly eighties4 ,some:at lat] ,james ,a4 ,ligh?ipe ( ,san ,francisco indep5d5tly inv5t$ a h>monic-r++ sy/em1 :i* 0 put 9 successful comm]cial use at ,sacram5to & a few o!r small] ,cali=nia t[ns4 ,ligh?ipe pol>iz$ 8 bells & bridg$ !m across ! l9e 9 s]ies ) cond5s]s1 z 9 mod]n practice1 & save = "s crudities 9 design1 8 app>atus closely resembl$1 bo? 9 pr9ciple & con/ruction1 "s ( t 9 successful use today4 ,ligh?ipe's sy/em w5t out ( use & 0 almo/ =gott51 :5 ab\t #aijc1 ,wm4 ,w4 ,dean aga9 indep5d5tly r$evelop$ ! h>monic sy/em1 & produc$ a bell a/oni%+ly l t ( ,ligh?ipe1 b ( m ref9$ design1 ?us />t+ ! developm5t :i* has result$ 9 ! pres5t wide use ( ?is sy/em4 ,! signal-receiv+ device 9 h>monic-r++ sy/ems takes ! =m ( a r+]1 hav+ its armature & /rik] m\nt$ on a r /iff spr+ r ?an on trunnions4 ,by ?is means ! mov+ p>ts ( ! bell con/itute 9 effect a re$ tongue1 :i* has a natural rate ( vibration at :i* x may easily be made to vibrate ) suffici5t amplitude to /rike ! gongs4 ,! h>monic r+] diff]s f ! ord9>y pol>iz$ bell or r+]1 !re=e1 9 t its armature w vibrate mo/ easily at "o p>ticul> rate1 :ile ! armature ( ! ord9>y r+] is almo/ indiff]5t1 betwe5 r wide limits1 z to ! rate at :i* x vibrates4 ,z a rule h>monic p>ty-l9e sy/ems are limit$ to f\r /ations on a l9e4 ,! frequ5cies employ$ are usually #af-b_/c1 #cc-a_/c1 #ej1 & #ff-b_/c cycles p] second1 ?is correspond+ to #a1jjj1 #b1jjj1 #c1jjj1 & #d1jjj cycles p] m9ute4 ,! reason :y ?is p>ticul> set ( frequ5cies 0 *os5 is t !y repres5t approximately ! range ( desirable frequ5cies1 & t ! fir/ r++-curr5t ma*9es 9 su* sy/ems 7 made by m\nt+ ! armatures ( f\r diff]5t g5]ators on a s+le %aft1 ^! hav+1 respectively1 two poles1 f\r poles1 six poles1 & eight poles ea*4 ,! two-pole g5]ator gave "o cycle p] revolution1 ! f\r-pole two1 ! six-pole ?ree1 & ! eight-pole f\r1 s t by runn+ ! %aft ( ! ma*9e at exactly #a1jjj revolutions p] m9ute ! frequ5cies be=e m5tion$ 7 atta9$4 ,?is range ( frequ5cies hav+ prov$ ab\t "r = g5]al practice & ! e>ly r+]s all hav+ be5 attun$ s z to op]ate on ?is basis1 ! practice ( adh]+ to ^! numb]s ( vibrations has be5 kept up ) "o exception by all ! manufactur]s :o make ?is type ( r+]4 ,tun+4 ,! process ( adju/+ ! armature ( a r+] to a c]ta9 rate ( vibration is call$ tun+1 & x is cu/om>y to ref] to a r+] z be+ tun$ to a c]ta9 rate ( vibration1 j z x is cu/om>y to ref] to a viol9 /r+ z be+ tun$ to a c]ta9 pit* or rate ( vibration4 ,! physical diff]5ce betwe5 ! r+]s ( ! v>i\s frequ5cies consi/s ma9ly 9 ! size ( ! weights at ! end ( ! vibrat+ re$1 t is1 ( ! weights :i* =m ! tapp] = ! bell4 ,! l[-frequ5cy r+]s h ! l>ge/ weights & ! high-frequ5cy ! smalle/1 ( c\rse4 ,! r+]s are r\ghly tun$ to ! desir$ frequ5cies by m]ely plac+ on ! tapp] rod ! desir$ weight & !n a m ref9$ tun+ is giv5 !m by slightly alt]+ ! positions ( ! weights on ! tapp] rod4 ,to make ! re$ h a slightly l[] natural rate ( vibration1 ! weight is mov$ fur!r f ! /ation>y end ( ! re$1 :ile to give x a slightly high] natural rate ( vibration ! weight is mov$ t[>d ! /ation>y4 ,9 ?is way v nice adju/m5ts may be made1 & ! aim ( ! v>i\s factories manufactur+ ^! bells is to make ! adju/m5t p]man5t s t x w nev] h to be alt]$ by ! op]at+ companies4 ,sev]al ye>s ( exp]i5ce ) ^! bells has %[n t :5 once prop]ly assembl$ !y ma9ta9 ! same rate ( vibration ) great con/ancy4 ,!re are two g5]al me?ods ( op]at+ h>monic bells4 ,"o ( ^! may be call$ ! 9-tune sy/em & ! o!r ! "u-tune sy/em4 ,! "u-tune sy/em 0 ! fir/ employ$4 ,illu/ration3 ,,op]at+ ,,room ,,at ,,tokyo1 ,,japan ,"u-,tune ,sy/em4 ,! e>ly work]s 9 ! field ( h>monic-selective signal+ discov]$ t :5 ! tapp] ( ! re$ /ruck aga9/ gongs ! natural rate ( vibration ( ! re$ 0 *ang$1 or m prop]ly1 ! re$ 0 made to h a diff]5t rate ( vibration f its natural rate4 ,?is 0 caus$ by ! fact t ! ela/icity ( ! gongs prov$ ano!r factor 9 ! set ( conditions caus+ ! re$s to take up a c]ta9 rate ( vibration1 & ! effect ( ?is add$ factor 0 always to accel]ate ! rate ( vibration :i* ! re$ _h :5 x 0 n /rik+ ! gongs4 ,! reb\nd ( ! hamm] f ! gongs t5d$1 9 o!r words1 to accel]ate ! rate ( vibration1 :i*1 z might be expect$1 caus$ a s]i\s difficulty 9 ! practical op]ation ( ! bells4 ,to illu/rate3 ,if a re$ 7 to h a natural rate ( vibration1 :5 n /rik+ ! gongs1 ( #ej p] second & a curr5t ( #ej cycles p] second 7 impress$ on ! l9e1 ! re$ w\ld take up ?is rate ( vibration easily1 b :5 a suffici5t amplitude ( vibration 0 atta9$ to cause ! tapp] to /rike ! gongs1 ! re$ w\ld be ?r[n out ( tune1 on acc\nt ( ! t5d5cy ( ! gongs to make ! re$ vibrate at a high] rate4 ,?is caus$ irregul> r++ & 0 frequ5tly suffici5t to make ! bells cease r++ altoge!r or to r+ 9 an entirely unsatisfactory mann]4 ,9 ord] to provide = ?is difficulty ! e>ly bells ( ,curri] & ,ligh?ipe 7 made on :at has s9ce be5 call$ ! "u-tun$ pr9ciple4 ,! fir/ bells ( ! ,kellogg ,swit*bo>d & ,supply ,company1 develop$ by ,dean1 7 bas$ on ?is idea z _! c>d9al pr9ciple4 ,! re$s 7 all giv5 a natural rate ( vibration1 :5 n /rik+ ! gongs1 some:at bel[ t ( ! curr5t frequ5cies to be employ$2 & yet n suffici5tly bel[ ! correspond+ curr5t frequ5cy to make ! bell s f> out ( tune t ! curr5t frequ5cy w\ld n be able to />t x4 ,?is 0 done s t :5 ! tapp] began to /rike ! gongs ! tapp] w\ld be accel]at$ & br\ght practically into tune ) ! curr5t frequ5cy1 & ! r++ w\ld cont9ue regul>ly z long z ! curr5t fl[$4 ,x w be se5 t ! "u-tun$ sy/em 01 !re=e1 "o involv+ "s difficulty 9 />t+ 9 ord] to provide = prop] regul>ity :ile actually r++4 ,r+]s ( ?is k9d 7 always made ) b a s+le gong1 x be+ f\nd difficult to secure uni=mity ( r++ & uni=mity ( adju/m5t :5 two gongs 7 employ$4 ,al?\gh no r+]s ( ?is type are be+ made at pres5t1 yet a l>ge numb] ( !m are 9 use & !y w consequ5tly be describ$4 ,_! action is int]e/+ 9 ?r[+ bett] light on ! m improv$ types1 if = no o!r reason4 ,figs4 #agh & #agi %[1 respectively1 side & front views ( ! orig9al ,kellogg bell4 ,! entire me*anism is self-conta9$1 all p>ts be+ m\nt$ on ! base plate #a4 ,! electromagnet is ( ! two-coil type1 & is support$ on ! brackets #b & #c4 ,! bracket #b is ( iron s z to af=d a magnetic yoke = ! field ( ! electromagnet1 :ile ! bracket #c is ( brass s z n to %ort-circuit ! magnetic l9es across ! air-gap4 ,! re$ tongue--consi/+ ( ! /eel spr+ #e1 ! s(t-iron armature pieces #f1 ! auxili>y spr+ #g1 & ! tapp] ball #h1 all ( :i* are rivet$ toge!r1 z %[n 9 ,fig4 #agh--;con/itutes ! only mov+ "p ( ! bell4 ,! /eel spr+ #e is rigidly m\nt$ 9 ! clamp+ piece #i at ! upp] "p ( ! bracket #c1 & ! re$ tongue is p]mitt$ to vibrate only by ! flexibility ( ?is spr+4 ,! auxili>y spr+ #g is mu* light] ?an ! spr+ #e & has = its purpose ! provision ( a c]ta9 small am\nt ( flexibility betwe5 ! tapp] ball & ! m rigid portion ( ! armature =m$ by ! iron /rips #f-f4 ,! front ends ( ! magnet pole pieces ext5d ?r\gh ! bracket #c & are !re provid$ ) squ>e s(t-iron pole pieces #aj set at "r angles to ! magnet cores s z to =m a r n>r[ air-gap 9 :i* ! armature may vibrate4 ,illu/ration3 ,fig4 #agh4 ,"u-,tun$ ,r+] ,! cores ( ! magnet & also ! re$ tongue are pol>iz$ by means ( ! ,l-%ap$ b> magnet #d1 m\nt$ on ! iron yoke #b at "o end 9 su* mann] t its o!r end w lie q close to ! end ( ! spr+ #e1 :i*1 be+ ( /eel1 w af=d a pa? = ! l9es ( =ce to ! armature prop]4 ,we see1 !re=e1 t ! two magnet cores are1 by ?is p]man5t magnet1 giv5 "o pol>ity1 :ile ! re$ tongue itself is giv5 ! o!r pol>ity1 ?is be+ exactly ! condition t has already be5 describ$ 9 connection ) ! regul> pol>iz$ bell or r+]4 ,! electromagnetic action by :i* ?is re$ tongue is made to vibrate is1 !re=e1 exactly ! same z t ( an ord9>y pol>iz$ r+]1 b ! diff]5ce betwe5 ! two is t1 9 ?is h>monic r+]1 ! re$ tongue w respond only to "o p>ticul> rate ( vibrations1 :ile ! regul> pol>iz$ r+] w respond to almo/ any4 ,z %[n 9 ,fig4 #agh1 ! tapp] ball /rikes on ! inside surface ( ! s+le gong4 ,! function ( ! auxili>y spr+ #g betwe5 ! ball & ! ma9 portion ( ! armature is to all[ "s resili5ce betwe5 ! ball & ! balance ( ! armature s z to c\nt]act 9 "s measure ! accel]at+ influ5ce ( ! gong on ! armature4 ,9 ^! bells1 z already /at$1 ! natural rate ( vibration ( ! re$ tongue 0 made some:at l[] ?an ! rate at :i* ! bell 0 to be op]at$1 s t ! re$ tongue _h to be />t$ by a curr5t slightly out ( tune ) x1 & !n1 z ! tapp] /ruck ! gong1 ! accel]ation due to ! gong w\ld br+ ! vibration ( ! re$ tongue1 z modifi$ by ! gong1 into tune ) ! curr5t t 0 op]at+ x4 ,9 e!r words1 9 ?is sy/em ! r++ curr5ts t 7 appli$ to ! l9e _h frequ5cies correspond+ to :at may be call$ ! op]ative rates ( vibration ( ! re$ tongues1 :i* op]ative rates ( vibration 7 9 ea* case ! resultant ( ! natural pit* ( ! re$ z modifi$ by ! action ( ! bell gong :5 /ruck4 ,illu/ration3 ,fig4 #agi4 ,"u-,tun$ ,r+] ,9-,tune ,sy/em4 ,! m mod]n me?od ( tun+ is to make ! natural rate ( vibration ( ! re$ tongue1 t is1 ! rate at :i* x naturally vibrates :5 n /rik+ ! gongs1 su* z to accurately correspond to ! rate ( vibration at :i* ! bells are to be op]at$--t is1 ! natural rate ( vibration ( ! re$ tongues is made ! same z ! op]ative rate4 ,?us ! bells are attun$ = easy />t+1 a great advantage ov] ! "u-tun$ sy/em4 ,9 ! "u-tun$ sy/em1 ! re$s be+ out ( tune 9 />t+ require heavi] />t+ curr5t1 & ?is is obvi\sly conducive to cross-r++1 t is1 to ! response ( bells to o!r ?an ! int5d$ frequ5cy4 ,aga91 easy />t+ is desirable because :5 ! armature is at re/1 or 9 v slight vibration1 x is at a maximum di/ance f ! poles ( ! electromagnet1 &1 !re=e1 subject to ! weake/ influ5ce ( ! poles4 ,a curr5t1 !re=e1 :i* is /rong en\gh to />t ! vibration1 w be /rong en\gh to keep ! bell r++ prop]ly4 ,illu/ration3 ,fig4 #ahj4 ,dean ,9-,tune ,r+] ,:5 ) ?is 9-tune mode ( op]ation1 ! armature is ?r[n into suffici5tly wide vibration to cause ! tapp] to /rike ! gong1 ! gong may t5d to accel]ate ! vibration ( ! re$ tongue1 b ! curr5t impulses ?r\gh ! electromagnet coils cont9ue at precisely ! same rates z be=e4 ,"u ?is condition ( vibration1 :5 ! re$ tongue has an amplitude ( vibration wide en\gh to cause ! tapp] to /rike ! gongs1 ! ends ( ! armature come close/ to ! pole pieces1 s t ! pole pieces h _! maximum magnetic effect on ! armature1 ) ! result t ev5 if ! accel]at+ t5d5cy ( ! gongs 7 consid]able1 ! comp>atively l>ge magnetic attractive impulses occurr+ at ! same rate z ! natural rate ( vibration ( ! re$ tongue1 s]ve :olly to prev5t any actual accel]ation ( ! re$ tongue4 ,! magnetic attractions ^u ! ends ( ! armature1 cont9u+ at ! initial rate1 s]ve1 !re=e1 z a *eck to (fset any accel]at+ t5d5cy :i* ! /rik+ ( ! gong may h ^u ! vibrat+ re$ tongue4 ,x is obvi\s1 !re=e1 t 9 ! 9-tune sy/em ! electromagnetic effect on ! armature %\ld1 :5 ! armature is close/ to ! pole pieces1 be ( su* an ov]p[]+ nature z to prev5t :atev] accel]at+ t5d5cy ! gongs may h f ?r[+ ! armature out ( its /ride 9 /ep ) ! curr5t4 ,= ?is reason x is usual 9 ?is type to s adju/ ! armature t its ends w actually /rike aga9/ ! pole pieces ( ! electromagnet :5 ?r[n into vibration4 ,suffici5t flexibility is giv5 to ! tapp] rod to all[ x to cont9ue slightly beyond ! po9t at :i* x w\ld be br\ght to re/ by ! /rik+ ( ! armature ends aga9/ ! pole pieces & ?us ex]t a :ipp+ action s z to all[ ! ball to cont9ue 9 its movem5t f> en\gh to /rike aga9/ ! gongs4 ,! reb\nd ( ! gong is !n tak5 up by ! ela/icity ( ! tapp] rod1 :i* returns to an unflex$ position1 & at ab\t ?is "t ! pole piece releases ! armature s t x may sw+ ov] 9 ! o!r direction to cause ! tapp] to /rike ! o!r gong4 ,illu/ration3 ,fig4 #aha4 ,tapp]s = ,dean ,r+]s ,! con/ruction ( ! 9-tune h>monic r+] employ$ by ! ,dean ,electric ,company1 ( ,elyria1 ,ohio1 is illu/rat$ 9 ,figs4 #ahj1 #aha1 & #ahb4 ,x w be se5 f ,fig4 #ahj t ! g5]al arrangem5t ( ! magnet & armature is ! same z t ( ! ord9>y pol>iz$ r+]2 ! ess5tial diff]5ce is t ! armature is spr+-m\nt$ in/ead ( pivot$4 ,! armature & ! tapp] rod normally /& 9 ! normal c5tral position ) ref]5ce to ! pole pieces ( ! magnet & ! gongs4 ,fig4 #aha %[s ! complete vibrat+ p>ts ( f\r r+]s1 adapt$1 respectively1 to ! f\r diff]5t frequ5cies ( ! sy/em4 ,! assembl$ armature1 tapp] rod1 & tapp] are all rivet$ toge!r & are non-adju/able4 ,all ( ! adju/m5t t is done ^u !m is done 9 ! factory & is accompli%$1 fir/1 by *oos+ ! prop] size ( weight1 & second1 by =c+ ?is weight into ! prop] position on ! tapp] rod to give exactly ! rate ( vibration t is desir$4 ,illu/ration3 ,fig4 #ahb4 ,dean ,9-,tune ,r+] ,an int]e/+ feature ( ?is ,dean h>monic r+] is ! gong adju/m5t4 ,z w be se51 ! gongs are m\nt$ on po/s :i* are c>ri$ on lev]s pivot$ to ! r+] frame4 ,^! lev]s h at _! out] end a curv$ rack provid$ ) ge> tee? adapt$ to engage a worm or screw ?read m\nt$ on ! r+] frame4 ,obvi\sly1 by turn+ ?is worm screw 9 "o direction or ! o!r1 ! gongs are mov$ slightly t[>d or f ! armature or tapp]4 ,?is af=ds a v delicate means ( adju/+ ! gongs1 & at ! same "t "o :i* has no t5d5cy to "w loose or to get out ( adju/m5t4 ,illu/ration3 ,fig4 #ahc4 ,kellogg ,9-,tune ,r+] ,9 ,fig4 #ahc is %[n a draw+ ( ! 9-tune h>monic r+] manufactur$ by ! ,kellogg ,swit*bo>d & ,supply ,company4 ,?is diff]s 9 no ess5tial respect f t ( ! ,dean ,company1 except 9 ! gong adju/m5t1 ?is latt] be+ affect$ by a screw pass+ ?r\gh a nut 9 ! gong po/1 z cle>ly indicat$4 ,9 bo? ! ,kellogg & ! ,dean 9-tune r+]s1 on acc\nt ( ! comp>ative /iffness ( ! armature spr+s & on acc\nt ( ! normal position ( ! armature ) maximum air gaps & consequ5t m9imum magnetic pull1 ! armature w practically n be affect$ unless ! en]giz+ curr5t is accurately attun$ to its own natural rate4 ,:5 ! prop] curr5t is ?r[n on to ! l9e1 ! ball w be ?r[n into viol5t vibration1 & ! ends ( ! armature br\ght into actual contact ) ! pole pieces1 :i* are ( b>e iron & %ield$ 9 no way4 ,! armature 9 ?is position is v /rongly attract$ & comes to a sudd5 /op on ! pole pieces4 ,! gongs are s adju/$ t ! tapp] ball w h to spr+ ab\t "o ?irty-second ( an in* 9 ord] to hit !m4 ,! armature is held aga9/ ! pole piece :ile ! tapp] ball is engag$ 9 /rik+ ! gong & 9 p>tially return+ !refrom1 & s /rong is ! pull ( ! pole piece on ! armature 9 ?is position t ! accel]at+ influ5ce ( ! gong has no effect 9 accel]at+ ! rate ( vibration ( ! re$4 ,illu/ration3 ,fig4 #ahd4 ,circuits ( ,dean ,h>monic ,sy/em ,circuits4 ,9 ,fig4 #ahd are %[n 9 simplifi$ =m ! circuits ( a f\r-/ation h>monic p>ty l9e4 ,x is se5 t at ! c5tral (fice !re are f\r r++ keys1 adapt$1 respectively1 to impress on ! l9e r++ curr5ts ( f\r diff]5t frequ5cies4 ,at ! f\r /ations on ! l9e1 lett]$ ,a1 ,b1 ,c1 & ,d1 !re are f\r h>monic bells tun$ accord+ly4 ,at ,/ation ,a !re is %[n ! talk+ app>atus employ+ ! ,:eat/one bridge arrangem5t4 ,! talk+ app>atus at all ( ! o!r /ations is exactly ! same1 b is omitt$ = ! sake ( simplicity4 ,a cond5s] is plac$ 9 s]ies ) ea* ( ! bells 9 ord] t !re may be no direct-curr5t pa? f "o side ( ! l9e to ! o!r :5 all ( ! receiv]s are on _! hooks at ! sev]al /ations4 ,9 ,fig4 #ahe is %[n exactly ! same arrangem5t1 ) ! exception t ! talk+ app>atus illu/rat$ 9 detail at ,/ation ,a is t ( ! ,kellogg ,swit*bo>d & ,supply ,company4 ,o!rwise ! circuits ( ! ,dean & ! ,kellogg ,company1 & 9 fact ( all ! o!r companies manufactur+ h>monic r++ sy/ems1 are ! same4 ,advantages4 ,a great advantage ( ! h>monic p>ty-l9e sy/em is ! simplicity ( ! app>atus at ! subscrib]'s /ation4 ,! h>monic bell is sc>cely m complex ?an ! ord9>y pol>iz$ r+]1 & ! only diff]5ce betwe5 ! h>monic-r++ telephone & ! ord9>y telephone is 9 ! r+] itself4 ,! abs5ce ( all relays & o!r me*anism & also ! abs5ce ( ! necessity = gr\nd connections at ! telephone are all po9ts 9 favor ( ! h>monic sy/em4 ,illu/ration3 ,fig4 #ahe4 ,circuits ( ,kellogg ,h>monic ,sy/em ,limitations4 ,z already /at$1 ! h>monic sy/ems ( ! v>i\s companies1 ) "o exception1 are limit$ to f\r frequ5cies4 ,! exception is 9 ! case ( ! ,nor? ,electric ,company1 :i* sometimes employs f\r & sometimes five frequ5cies & ?us gets a selection betwe5 five /ations4 ,9 ! f\r-p>ty ,nor? sy/em1 ! frequ5cies1 unlike ^? 9 ! ,dean & ,kellogg sy/ems1 :]e9 ! high] frequ5cies are multiples ( ! l[]1 are arrang$ s z to be proportional to ! :ole numb]s #e1 #g1 #i1 & #aa1 :i*1 ( c\rse1 h no common d5om9ator4 ,! frequ5cies ?us employ$ 9 ! ,nor? sy/em are1 9 cycles p] second1 #cj4c1 #db4d1 #ed4e1 & #ff4g4 ,9 ! five-p>ty sy/em1 ! frequ5cy ( #af4g is arbitr>ily add$4 ,:ile all ( ! comm]cial h>monic sy/ems on ! m>ket are limit$ to f\r or five frequ5cies1 x does n foll[ t a great] numb] ?an f\r or five /ations may n be selectively rung4 ,d\ble ^! numb]s may be plac$ on a p>ty l9e & selectively actuat$1 if ! fir/ set ( f\r or five is bridg$ across ! l9e & ! second set ( f\r or five is connect$ betwe5 "o limb ( ! l9e & gr\nd4 ,! fir/ set ( ^! is selectively rung1 z already describ$1 by s5d+ ! r++ curr5ts ov] ! metallic circuit1 :ile ! second set may be likewise selectively rung by s5d+ ! r++ curr5ts ov] "o limb ( ! l9e ) a gr\nd return4 ,?is me?od is frequ5tly employ$ ) success on c\ntry l9es1 :]e x is desir$ to place a great] numb] ( in/rum5ts on a l9e ?an f\r or five4 ,/ep-by-,/ep ,me?od4 ,a v l>ge numb] ( /ep-by-/ep sy/ems h be5 propos$ & r$uc$ to practice1 b z yet !y h n met ) great success 9 comm]cial telephone "w1 & are n[h]e ne> z commonly us$ z are ! pol>ity & h>monic sy/ems4 ,pr9ciples4 ,an idea ( ! g5]al features ( ! /ep-by-/ep sy/ems may be _h by conceiv+ at ea* /ation on ! l9e a rat*et :eel1 hav+ a pawl adapt$ to drive x "o /ep at a "t1 ?is pawl be+ associat$ ) ! armature ( an electromagnet :i* receives curr5t impulses f ! l9e circuit4 ,!re is ?us "o ( ^! driv+ magnets at ea* /ation1 ea* bridg$ across ! l9e s t :5 a s+le impulse ( curr5t is s5t out f ! c5tral (fice all ( ! rat*et :eels w be mov$ "o /ep4 ,ano!r impulse w move all ( ! rat*et :eels ano!r /ep1 & s on ?r\gh\t any desir$ numb] ( impulses4 ,! rat*et :eels1 !re=e1 are all /epp$ 9 unison4 ,let u fur!r conceive t all ( ^! rat*et :eels are provid$ ) a not* or a hole or a projection1 alike 9 all respects at all /ations save 9 ! position :i* ?is not* or hole or projection occupies on ! :eel4 ,! ?+ to get cle> 9 ?is "p ( ! conception is t all ( ^! not*es1 holes1 or projections are alike on all ( ! :eels1 b !y occupy a diff]5t position on ! :eel = ea* "o ( ! /ations4 ,consid] fur!r t ! bell circuit at ea* ( ! /ations is normally op51 b t 9 ea* case x is adapt$ to be clos$ :5 ! not*1 hole1 or projection is br\ght to a c]ta9 po9t by ! revolution ( ! :eel4 ,let u conceive fur!r t ?is di/+ui%+ not*1 hole1 or projection is s arrang$ on ! :eel ( ! fir/ /ation z to close ! bell circuit :5 "o impulse has be5 s5t1 t t on ! second /ation w close ! bell circuit aft] ! second impulse has be5 s5t1 & s on ?r\gh\t ! entire numb] ( /ations4 ,x w1 !re=e1 be app>5t t ! bell circuits at ! v>i\s /ations w1 z ! :eels are rotat$ 9 unison1 be clos$ "o aft] ! o!r4 ,9 ord] to call a giv5 /ation1 !re=e1 x is only necess>y to rotate all ( ! :eels 9 unison1 by s5d+ out ! prop] /epp+ impulses until !y all occupy su* a position t ! "o at ! desir$ /ation is 9 su* position z to close ! bell circuit at t /ation4 ,s9ce all ( ! not*es1 holes1 or projections are arrang$ to close ! bell circuits at _! respective /ations at diff]5t times1 x foll[s t :5 ! bell circuit at ! desir$ /ation is clos$ ^? at all ( ! o!r /ations w be op54 ,if1 !re=e1 aft] ! prop] numb] ( /epp+ impulses has be5 s5t to ! l9e to close ! bell circuit ( ! desir$ /ation1 r++ curr5t be appli$ to ! l9e1 x is obvi\s t ! bell ( t "o /ation w be rung to ! exclusion ( all o!rs4 ,x is1 ( c\rse1 necess>y t provision be made :]eby ! magnets :i* furni% ! en]gy = /epp+ ! :eels w n be en]giz$ by ! r++ curr5t4 ,?is is accompli%$ 9 "o ( sev]al ways1 ! mo/ common ( :i* is to h ! /epp+ magnets pol>iz$ or bias$ 9 "o direction & ! bells at ! v>i\s /ations oppositely bias$1 s t ! r++ curr5t w n affect ! /epp+ magnet & ! /epp+ curr5t w n affect ! r+] magnets4 ,aft] a conv]sation is f9i%$1 ! l9e may be re/or$ to its normal position 9 "o ( sev]al ways4 ,usually s-call$ release magnets are employ$1 = op]at+ on ! releas+ device at ea* /ation4 ,^!1 :5 en]giz$1 w )draw ! hold+ pawls f ! rat*ets & all[ !m all to return to _! normal positions4 ,sometimes ^! release magnets are op]at$ by a long impulse ( curr5t1 be+ made too sluggi% 9 _! action to respond to ! quick-/epp+ impulses2 sometimes ! release magnets are tapp$ f "o limb ( ! l9e to gr\nd1 s z n to be affect$ by ! /epp+ or r++ curr5ts s5t ov] ! metallic circuit2 & sometimes o!r exp$i5ts are us$ = obta9+ ! release ( ! rat*ets at ! prop] "t1 a l>ge am\nt ( +5uity hav+ be5 sp5t to ?is end4 ,z practically all /ep-by-/ep p>ty-l9e sy/ems 9 comm]cial use h also c]ta9 o!r features int5d$ to assure privacy ( conv]sation to ! us]s1 &1 !re=e1 come "u ! g5]al head+ ( lock-out p>ty-l9e sy/ems1 ! discussion ( comm]cial examples ( ^! sy/ems w be left = ! next *apt]1 :i* is devot$ to su* lock-out sy/ems4 ,brok5-,l9e ,me?od4 ,! brok5-l9e sy/em1 l ! /ep-by-/ep sy/em1 is also ess5tially a lock-out sy/em & = t reason only its g5]al features1 by :i* ! selective r++ is accompli%$1 w be dealt ) "h4 ,pr9ciples4 ,9 ?is sy/em !re are no tun$ bells1 no positively & negatively pol>iz$ bells bridg$ to gr\nd on ea* side ( ! l9e1 & no /ep-by-/ep devices 9 ! ord9>y s5se1 by :i* selective signal+ has ord9>ily be5 accompli%$ on p>ty l9es4 ,in/ead ( ?is1 ea* in/rum5t on ! l9e is exclusively br\ght into op]ative relation ) ! l9e1 & !n remov$ f su* op]ative relation until ! subscrib] want$ is connect$1 at :i* "t all ( ! o!r in/rum5ts are lock$ out & ! l9e is n encumb]$ by any bridge circuits at any ( ! in/rum5ts t are n engag$ 9 ! conv]sation4 ,fur!rmore1 9 ! select+ ( a subscrib] or ! r++ ( 8 bell !re is no splitt+ up ( curr5t among ! magnets at ! v>i\s /ations z 9 ord9>y practice1 b ! op]at+ curr5t goes /raight to ! /ation desir$ & to t /ation alone :]e its entire /r5g? is available = p]=m+ its prop] "w4 ,9 ord] to make ! sy/em cle> x may be /at$ at ! outset t "o side ( ! metallic circuit l9e is cont9u$ z 9 ord9>y practice1 pass+ ?r\gh all ( ! /ations z a cont9u\s conductor4 ,! o!r side ( ! l9e1 h[ev]1 is divid$ into sections1 its cont9uity be+ brok5 at ea* ( ! subscrib]'s /ations4 ,fig4 #ahf is int5d$ to %[ 9 ! simple/ possible way h[ ! circuit ( ! l9e may be ext5d$ f /ation to /ation 9 su* mann] t only ! r+] ( "o /ation is 9 circuit at a "t4 ,! two sides ( ! l9e are %[n 9 ?is figure1 & x w be se5 t limb ,l ext5ds f ! c5tral (fice on ! left to ! la/ /ation on ! "r )\t a break4 ,! limb ,r1 h[ev]1 ext5ds to ! fir/ /ation1 at :i* po9t x is cut (f f ! ext5sion ,rx by ! op5 contacts ( a swit*4 ,= ! purpose ( simplicity ?is swit* is %[n z an ord9>y h& swit*1 b z a matt] ( fact x is a "p ( a relay1 ! op]at+ coil ( :i* is %[n at #f1 j above x1 9 s]ies ) ! r+]4 ,illu/ration3 ,fig4 #ahf4 ,pr9ciple ( ,brok5-,l9e ,sy/em ,obvi\sly1 if a prop] r++ curr5t is s5t ov] ! metallic circuit f ! c5tral (fice1 only ! bell at ,/ation ,a w op]ate1 s9ce ! bells at ! o!r /ations are n 9 ! circuit4 ,if by any means ! swit* lev] #b at ,/ation ,a 7 mov$ out ( engagem5t ) contact #a & into engagem5t ) contact #c1 x is obvi\s t ! bell ( ,/ation ,a w\ld no long] be 9 circuit1 b ! limb ,r ( ! l9e w\ld be cont9u$ to ! ext5sion ,rx & ! bell ( ,/ation ,b w\ld be 9 circuit4 ,any curr5t !n s5t ov] ! circuit ( ! l9e f ! c5tral (fice w\ld r+ ! bell ( ?is /ation4 ,9 ,fig4 #ahg ! swit*es ( bo? ,/ation ,a & ,/ation ,b h be5 ?us op]at$1 & ,/ation ,c is ?us plac$ 9 circuit4 ,inspection ( ?is figure w %[ t ! bells ( ,/ation ,a1 ,/ation ,b1 & ,/ation ,d are all cut out ( circuit1 & t1 !re=e1 no curr5t f ! c5tral (fice c affect !m4 ,?is g5]al s*eme ( selection is a new-com] 9 ! field1 & = c]ta9 classes ( "w x is ( und\bt$ promise4 ,illu/ration3 ,fig4 #ahg4 ,pr9ciple ( ,brok5-,l9e ,sy/em ,,*apt] ,,xvii ,,lock-,,out ,,p>ty-,,l9e ,,sy/ems ,! p>ty-l9e problem 9 rural di/ricts is some:at diff]5t f t )9 urban limits4 ,9 ! latt] cases1 ow+ to ! clos] gr\p+ ( ! subscrib]s1 x is n n[ g5]ally consid]$ desirable1 ev5 f ! /&po9t ( economy1 to place m ?an f\r subscrib]s on a s+le l9e4 ,= su* a l9e selective r++ is simple1 bo? f ! /&po9t ( app>atus & op]ation2 & moreov] ow+ to ! small numb] ( /ations on a l9e1 & ! small am\nt ( traffic to & f su* subscrib]s z usually take p>ty-l9e s]vice1 ! int]f]5ce betwe5 p>ties on ! same l9e is n a v s]i\s matt]4 ,= rural di/ricts1 p>ticul>ly ^? tribut>y to small t[ns1 ^! conditions d n exi/4 ,ow+ to ! remot5ess ( ! /ations f ea* o!r x is n feasible f ! /&po9t ( l9e co/ to limit ! numb] ( /ations to f\r4 ,a mu* great] numb] ( /ations is employ$ & ! confusion result+ is di/ress+ n only to ! subscrib]s !mselves b also to ! managem5t ( ! company4 ,!re exi/s !n ! ne$ ( a p>ty-l9e sy/em :i* w give ! limit$ us] 9 rural di/ricts a s]vice1 at lea/ approa*+ t :i* he w\ld get if s]v$ by an individual l9e4 ,! pr9cipal inve/m5t necess>y to provide facilities = telephone s]vice is t requir$ to produce ! telephone l9e4 ,9 _m cases ! co/ ( in/rum5ts & app>atus is small 9 comp>ison ) ! co/ ( ! l9e4 ,by f> ! great] numb] ( subscrib]s 9 rural di/ricts are ^? :o use _! in/rum5ts a comp>atively small numb] ( times a day1 & to ma9ta9 an exp5sive telephone l9e = ! exclusive use ( "o su* subscrib] :o w use x b a few m9utes ea* day is on its face an economic wa/e4 ,z a result1 :]e individual l9e s]vice is practic$ exclusively "o ( two ?+s mu/ be true3 ei!r ! av]age subscrib] pays m = 8 s]vice ?an he %\ld1 or else ! op]at+ company sells ! s]vice = less ?an x co/s1 or at be/ = an insuffici5t pr(it4 ,bo? ( ^! conditions are unnatural & _c be p]man5t4 ,! p>ty-l9e me?od ( giv+ s]vice1 by :i* a s+le l9e is made to s]ve a numb] ( subscrib]s1 (f]s a solution to ?is difficulty1 b ! ord9>y non-selective or ev5 selective p>ty l9e has _m undesirable features if ! attempt is made to place on x su* a l>ge numb] ( /ations z is consid]$ economically necess>y 9 rural "w4 ,^! undesirable features "w to ! detrim5t ( bo? ! us] ( ! telephone & ! op]at+ company4 ,_m attempts h be5 made to ov]come ^! disadvantages ( ! p>ty l9e 9 sp>sely settl$ communities1 by produc+ :at are commonly call$ lock-out sy/ems4 ,^!1 z _! "n implies1 employ su* an arrangem5t ( p>ts t :5 ! l9e is 9 use by any two p>ties1 all o!r p>ties are lock$ out f ! circuit & _c ga9 access to x until ! p>ties :o are us+ x are ?r\gh4 ,sy/em aft] sy/em = accompli%+ ?is purpose has be5 ann\nc$ b = ! mo/ "p ^! h involv$ su* a degree ( complexity & h introduc$ s _m undesirable features z to s]i\sly affect ! smoo? op]ation ( ! sy/em & ! reliability ( ! s]vice4 ,we believe1 h[ev]1 9 spite ( num]\s failures1 t ! lock-out selective-signal+ p>ty l9e has a real field ( usefulness & t op]at+ companies z well z manufactur+ companies are beg9n+ to appreciate ?is ne$1 & z a result t ! relief ( ! rural subscrib] f ! almo/ intol]able s]vice he has (t5 _h to endure is at h&4 ,a few ( ! mo/ promis+ lock-out p>ty-l9e sy/ems n[ be=e ! public w1 !re=e1 be describ$ 9 "s detail4 ,poole ,sy/em4 ,! ,poole sy/em is a lock-out sy/em pure & simple1 its devices be+ 9 ! nature ( a lock-out atta*m5t = selective-signal+ l9es1 ei!r ( ! pol>ity or ( ! h>monic type :]e9 common-batt]y transmission is employ$4 ,x w be "h describ$ z employ$ 9 connection ) an ord9>y h>monic-r++ sy/em4 ,9 ,fig4 #ahh !re is %[n a f\r-/ation p>ty l9e equipp$ ) ,poole lock-out devices1 x be+ assum$ t ! r+]s at ea* /ation are h>monic & t ! keys at ! c5tral (fice are ! ord9>y keys adapt$ to impress ! prop] frequ5cy on ! l9e = r++ any "o ( ! /ations4 ,9 addition to ! ord9>y talk+ & r++ app>atus at ea* subscrib]'s /ation1 !re is a relay ( special =m & also a pu%-button key4 ,illu/ration3 ,fig4 #ahh4 ,poole ,lock-,out ,sy/em ,ea* ( ! relays has two w9d+s1 "o ( high resi/ance & ! o!r ( l[ resi/ance4 ,rememb]+ t ! sy/em to :i* ?is device is appli$ is always a common-batt]y sy/em1 & t1 !re=e1 ! normal condition ( ! l9e w be "o 9 :i* !re is a diff]5ce ( pot5tial betwe5 ! two limbs1 x w be evid5t t :5ev] any subscrib] on a l9e t is n 9 use raises 8 receiv] f its hook1 a circuit w be e/abli%$ f ! upp] contact ( ! hook ?r\gh ! lev] ( ! hook to ! high-resi/ance w9d+ #a ( ! relay & !nce to ! o!r side ( ! l9e by way ( wire #f4 ,?is w result 9 curr5t pass+ ?r\gh ! high-resi/ance w9d+ ( ! relay & ! relay w pull up its armature4 ,z soon z x does s x e/abli%es two o!r circuits by ! closure ( ! relay armature aga9/ ! contacts #d & #e4 ,! clos+ ( ! contact #d e/abli%es a circuit f ! upp] side ( ! l9e ?r\gh ! upp] contact ( ! swit* hook1 !nce ?r\gh ! contacts ( ! pu% button #c1 !nce ?r\gh ! l[-resi/ance w9d+ #b ( ! relay to ! t]m9al #d1 !nce ?r\gh ! relay armature & ! transmitt] to ! l[] side ( ! l9e4 ,?is l[-resi/ance pa? across ! l9e s]ves to hold ! relay armature attract$ & also to furni% curr5t to ! transmitt] = talk+4 ,! e/abli%m5t ( ?is l[-resi/ance pa? across ! l9e does ano!r important ?+1 h[ev]2 x practically %ort-circuits ! l9e ) respect to all ! high-resi/ance relay w9d+s1 & ?us prev5ts any ( ! o!r high-resi/ance relay w9d+s f receiv+ en\gh curr5t to actuate !m1 %\ld ! subscrib] at any o!r /ation remove 8 receiv] f ! hook 9 an attempt to li/5 9 or to make a call :ile ! l9e is 9 use4 ,z a subscrib] c only e/abli% ! prop] conditions = talk+ & li/5+ by ! attraction ( ?is relay armature at 8 /ation1 x is obvi\s t unless he c cause ! pull+ up ( 8 relay armature he c n place himself 9 communication ) ! l9e4 ,! second ?+ t is accompli%$ by ! pull+ up ( ! relay armature is ! closure ( ! contacts #e1 & t completes ! talk+ circuit ?r\gh ! cond5s] & receiv] across ! l9e 9 an obvi\s fa%ion4 ,! result ( ?is arrangem5t is t x is ! fir/ p>ty :o raises 8 receiv] f its hook :o is enabl$ to successfully e/abli% a connection ) ! l9e1 all subsequ5t ef=ts1 by o!r subscrib]s1 fail+ to d s because ( ! fact t ! l9e is %ort-circuit$ by ! pa? ?r\gh ! l[-resi/ance w9d+ & ! transmitt] ( ! /ation t is already connect$ ) ! l9e4 ,a little t>get is mov$ by ! action ( ! relay s t a visual indication is giv5 to ! subscrib] 9 mak+ a call to %[ :e!r or n he is successful 9 gett+ ! use ( ! l9e4 ,if ! relay op]ates & he secures control ( ! l9e1 ! t>get indicates ! fact by its movem5t1 :ile if someone else is us+ ! l9e & ! relay does n op]ate1 ! t>get1 by its failure to move1 indicates t fact4 ,:5 "o p>ty desires to conv]se ) ano!r on ! same l9e1 he depresses ! button #c at 8 /ation until aft] ! call$ p>ty has be5 rung & has respond$4 ,?is holds ! circuit ( 8 l[-resi/ance w9d+ op51 & ?us prev5ts ! lock-out f becom+ effective until ! call$ p>ty is connect$ ) ! l9e4 ,! relay armature ( ! call+ p>ty does n fall back ) ! e/abli%m5t ( ! l[-resi/ance pa? at ! call$ /ation1 because1 ev5 ?\gh %unt$1 x /ill receives suffici5t curr5t to hold its armature 9 its attract$ position4 ,aft] ! call$ p>ty has respond$1 ! button at ! call+ /ation is releas$ & bo? l[-resi/ance hold+ coils act 9 multiple4 ,illu/ration3 ,,"o ,,w+ ,,( ,,op]at+ ,,room1 ,,b]l91 ,,g]many ,ultimate ,capacity #bd1jjj ,subscrib]s' ,l9es & #b1ajj ,trunk ,l9es4 ,siem5s-,halske ,equipm5t4 ,note ,horizontal ,disposal ( ,multiple ,jack ,field4 ,no induction coil is us$ 9 ?is sy/em & ! imp$ance ( ! hold+ coil is su* t incom+ voice curr5ts fl[ ?r\gh ! cond5s] & ! receiv]1 :i*1 by ref]5ce to ! figure1 w be se5 to be 9 %unt ) ! hold+ coil4 ,! hold+ coil is 9 s]ies ) ! local transmitt]1 ?us mak+ a circuit simil> to t ( ! ,kellogg common-batt]y talk+ circuit already discuss$4 ,a possible defect 9 ! use ( ?is sy/em is "o t has be5 common to a great _m o!r lock-out sy/ems1 dep5d+ = _! op]ation on ! same g5]al plan ( action4 ,?is appe>s :5 ! in/rum5ts are us$ on a comp>atively long l9e4 ,s9ce ! lock+-out ( all ! in/rum5ts t are n 9 use by ! "o t is 9 use dep5ds on ! l[-resi/ance %unt t is plac$ across ! l9e by ! in/rum5t t is 9 use1 x is obvi\s t1 9 ! case ( a long l9e1 ! resi/ance ( ! l9e wire w ent] into ! problem 9 su* a way z to t5d to defeat ! lock+-out function 9 "s cases4 ,?us1 :]e ! fir/ in/rum5t to use ! l9e is at ! remote end ( ! l9e1 ! %unt+ effect t ?is in/rum5t c ex]t ) respect to ano!r in/rum5t ne> ! c5tral (fice is t due to ! resi/ance ( ! l9e plus ! resi/ance ( ! hold+ coil at ! end in/rum5t4 ,! resi/ance ( ! l9e wire may be s high z to /ill all[ a suffici5t curr5t to fl[ ?r\gh ! high-resi/ance coil at ! ne>] /ation to all[ its op]ation1 ev5 ?\gh ! m remote in/rum5t is already 9 use4 ,com+ n[ to a consid]ation ( ! complete selective-signal+ lock-out sy/ems1 :]e9 ! selection ( ! p>ty & ! lock+ out ( ! o!rs are bo? inh]5t features1 a s+le example ( ! /ep-by-/ep1 & ( ! brok5-l9e selective lock-out sy/ems w be discuss$4 ,/ep-by-,/ep ,sy/em4 ,! s-call$ ,k4,b4 sy/em1 manufactur$ by ! ,dayton ,telephone ,lock-out ,manufactur+ ,company ( ,dayton1 ,ohio1 op]ates on ! /ep-by-/ep pr9ciple4 ,! ess5tial feature ( ! subscrib]'s telephone equipm5t 9 ?is sy/em is ! /ep-by-/ep actuat+ me*anism :i* p]=ms also ! functions ( a relay4 ,?is device consi/s ( an electromagnet hav+ two cores1 ) a p]man5t pol>iz+ magnet !rebetwe51 ! arrangem5t 9 ?is respect be+ ! same z 9 an ord9>y pol>iz$ bell4 ,! armature ( ?is magnet works a rock] arm1 :i*1 besides /epp+ ! selector segm5t ar\nd1 also1 "u c]ta9 conditions1 closes ! bell circuit & ! talk+ circuit1 z w be describ$4 ,illu/ration3 ,fig4 #ahi4 ,k4,b4 ,lock-,out ,sy/em ,ref]r+ fir/ to ,fig4 #ahi1 :i* %[s 9 simplifi$ =m a f\r-/ation ,k4,b4 lock-out l9e1 ! electromagnet is %[n at #a & ! rock] arm at #b4 ,! rat*et #c 9 ?is case is n a complete :eel b r a segm5t !re(1 & x is provid$ ) a s]ies ( not*es ( diff]5t dep?s4 ,x is obvi\s t ! dep? ( ! not*es w det]m9e ! degree ( movem5t :i* ! upp] end ( ! rock] arm may h t[>d ! left1 ?is be+ dep5d5t on ! ext5t to :i* ! pawl #f is p]mitt$ to ent] into ! segm5t4 ,! fir/ or normal not*1 i4e41 ! top not*1 is always ( su* a dep? t x w all[ ! rock]-arm lev] #b to engage ! contact lev] #d1 b w n p]mit ! rock] arm to sw+ f> en\gh to ! left to cause t contact to engage ! bell contact #e4 ,z w be %[n lat]1 ! condition = ! talk+ circuit to be clos$ is t ! rock] arm #b %all re/ aga9/ ! contact #d2 & f ?is we see t ! normal not* ( ea* ( ! segm5ts #c is ( su* a dep? z to all[ ! talk+ circuit at ea* /ation to be clos$4 ,! next not*1 i4e41 ! second "o 9 ea* disk1 is always %all[1 z are all ( ! o!r not*es except "o4 ,a deep not* is plac$ on ea* disk any:]e f ! ?ird to ! next to ! la/ on ! segm5t4 ,?is deep not* is call$ ! selective not*1 & x is ! "o t all[s ( contact be+ made ) ! r+] circuit ( t /ation :5 ! pawl #f drops into x4 ,! position ( ?is not* diff]s on all ( ! segm5ts on a l9e1 & obvi\sly1 !re=e1 ! r+] circuit at any /ation may be clos$ to ! exclusion ( all ! o!rs by /epp+ all ( ! segm5ts 9 unison until ! deep not* on ! segm5t ( ! desir$ /ation lies opposite to ! pawl #f1 :i* w p]mit ! rock] arm #b to sw+ s f> to ! left z to close n only ! circuit betwe5 #b & #d1 b also betwe5 #b1 #d1 & #e4 ,9 ?is position ! talk+ & ! r++ circuits are bo? clos$4 ,! position ( ! deepe/ not*1 i4e41 ! selective not*1 on ! circumf]5ce ( ! segm5t at any /ation dep5ds ^u ! numb] ( t /ation2 ?us1 ! segm5t ( ,/ation #d w h a deep not* 9 ! six? position2 ! segm5t = ,/ation #i w h a deep not* 9 ! elev5? position2 ! segm5t = any /ation w h a deep not* 9 ! position correspond+ to ! numb] ( t /ation plus two4 ,f :at has be5 said1 !re=e1 x is evid5t t ! fir/1 or normal1 not* on ea* segm5t is ( su* a dep? z to all[ ! mov+ pawl #f to fall to su* a dep? 9 ! segm5t z to p]mit ! rock] arm #b to close ! talk+ circuit only4 ,all ( ! o!r not*es1 except "o1 are comp>atively %all[1 & :ile !y p]mit ! mov+ pawl #f "u ! influ5ce ( ! rock] arm #b to move ! segm5t #c1 yet !y d n p]mit ! rock] arm #b to move s f> to ! left z to close ev5 ! talk+ circuit4 ,! exception is ! deep not*1 or selective not*1 :i* is ( su* dep? z to p]mit ! pawl #f to fall s f> into ! segm5t z to all[ ! rock] arm #b to close bo? ! talk+ & ! r++ circuits4 ,besides ! mov+ pawl #f !re is a det5t pawl #g4 ,?is always holds ! segm5t #c 9 ! position to :i* x has be5 la/ mov$ by ! mov+ pawl #f4 ,! actuat+ magnet #a1 z has be5 /at$1 is pol>iz$ & :5 en]giz$ by curr5ts 9 "o direction1 ! rock] arm moves ! pawl #f s z to /ep ! segm5t "o not*4 ,:5 ?is relay is en]giz$ by curr5t 9 ! opposite direction1 ! op]ation is su* t bo? ! mov+ pawl #f & ! det5t pawl #g w be pull$ away f ! segm5t1 ?us all[+ ! segm5t to return to its normal position by gravity4 ,?is is accompli%$ by ! foll[+ me*anism3 ,an armature /op is pivot$ ^u ! face ( ! rock] arm s z to sw+ 9 a plane p>allel to ! pole faces ( ! relay1 & is adapt$1 :5 ! relay is actuat$ by selective impulses ( "o pol>ity1 to be pull$ t[>ds "o ( ! pole faces :]e x acts1 ?r\gh impact ) a plate atta*$ to ! pole face ( ! relay1 z a limit+ means = ! motion ( ! rock] arm :5 ! rock] arm is actuat$ by ! magnet4 ,:51 h[ev]1 ! relay is en]giz$ by curr5t 9 ! opposite direction1 z on a releas+ impulse1 ! armature /op sw+s ^u its pivot t[>ds ! opposite pole face1 9 :i* position ! lug on ! end ( ! armature /op regi/]s ) a hole 9 ! plate on ! relay1 ?us all[+ ! full motion ( ! rock] arm :5 x is attract$ by ! magnet4 ,?is motion ( ! rock] arm )draws ! det5t pawl f engagem5t ) ! segm5t z well z ! mov+ pawl1 & !reby p]mits ! segm5t to return to its normal position4 ,z w be se5 f ,fig4 #ahi1 ea* ( ! relay magnets #a is p]man5tly bridg$ across ! two limbs ( ! l9e4 ,ea* /ation is provid$ ) a pu% button1 n %[n1 by means ( :i* ! subscrib] :o makes a call may prev5t ! rock] arm ( 8 in/rum5t f be+ actuat$ :ile selective impulses are be+ s5t ov] ! l9e4 ,! purpose ( ?is is to enable "o p>ty to make a call = ano!r on ! same l9e1 depress+ 8 pu% button :ile ! op]ator is select+ & r++ ! call$ p>ty4 ,! segm5t at 8 own /ation1 !re=e1 rema9s 9 its normal position1 9 :i* position1 z we h already se51 8 talk+ circuit is clos$2 all ( ! o!r segm5ts are1 h[ev]1 /epp$ up until ! r++ & talk+ circuits ( ! desir$ /ation are 9 prop] position1 at :i* "t r++ curr5t is s5t ov] ! l9e4 ,! segm5ts 9 ,fig4 #ahi1 except at ,/ation ,c1 are %[n z hav+ be5 /epp$ up to ! six? position1 :i* corresponds to ! r++ position ( ! f\r? /ation1 or ,/ation ,d4 ,! condition %[n 9 ?is figure corresponds to t 9 :i* ! subscrib] at ,/ation ,c orig9at$ ! call & press$ 8 button1 ?us reta9+ 8 own segm5t 9 its normal position s t ! talk+ circuits w\ld be e/abli%$ ) ,/ation ,d4 ,:5 ! l9e is 9 normal position any subscrib] may call c5tral by 8 magneto g5]ator1 n %[n 9 ,fig4 #ahi1 :i* w op]ate ! drop at c5tral1 b w n op]ate any ( ! subscrib]s' bells1 because all bell circuits are normally op54 ,:5 a subscrib] desires connection ) ano!r l9e1 ! op]ator s5ds an impulse back on ! l9e :i* /eps up & locks out all in/rum5ts except t ( ! call+ subscrib]4 ,illu/ration3 ,fig4 #aij4 ,k4,b4 ,lock-,out ,/ation ,a complete ,k4,b4 lock-out telephone is %[n 9 ,fig4 #aij4 ,?is is ! type ( in/rum5t t is usually furni%$ :5 new equipm5t is ord]$4 ,if1 h[ev]1 x is desir$ to use ! ,k4,b4 sy/em 9 connection ) telephones ( ! ord9>y bridg+ type t are already 9 s]vice1 ! lock-out & selective me*anism1 :i* is %[n on ! upp] inn] face ( ! door 9 ,fig4 #aij1 is furni%$ sep>ately 9 a box t may be m\nt$ close to ! regul> telephone & connect$ !reto by suitable wires1 z %[n 9 ,fig4 #aia4 ,x is se5 t ?is in/rum5t employs a local batt]y = talk+ & also a magneto g5]ator = call+ ! c5tral (fice4 ,! c5tral-(fice equipm5t consi/s ( a dial connect$ ) an impulse :eel1 toge!r ) suitable keys by :i* ! v>i\s circuits may be manipulat$4 ,?is dial & its associat$ me*anism may be m\nt$ 9 ! regul> swit*bo>d cab9et1 or x may be furni%$ 9 a sep>ate box & m\nt$ alongside ( ! cab9et 9 ei!r ( ! positions %[n at #a or #b ( ,fig4 #aib4 ,9 ord] to s5d ! prop] numb] ( impulses to ! l9e to call a giv5 p>ty1 ! op]ator places h] f+] 9 ! hole 9 ! dial t be>s ! numb] correspond+ to ! /ation want$ & rotates ! dial until ! f+] is br\ght into engagem5t ) ! fix$ /op %[n at ! bottom ( ! dial 9 ,fig4 #aib4 ,! dial is !n all[$ to return by ! action ( a spr+ to its normal position1 & 9 do+ s x op]ates a swit* )9 ! box to make & break ! batt]y circuit ! prop] numb] ( times4 ,op]ation4 ,a complete description ( ! op]ation may n[ be _h 9 connection ) ,fig4 #aic1 :i* is simil> to ,fig4 #ahi1 b conta9s ! details ( ! call+ arrangem5t at ! c5tral (fice & also ( ! talk+ circuits at ! v>i\s subscrib]s' /ations4 ,illu/ration3 ,fig4 #aia4 ,k4,b4 ,lock-,out ,/ation ,ref]r+ to ! c5tral-(fice app>atus ! usual r++ key is %[n1 ! inside contacts ( :i* lead to ! li/5+ key & to ! op]ator's telephone set z 9 ord9>y swit*bo>d practice4 ,betwe5 ! outside contact ( ?is r++ key & ! r++ g5]ator !re is int]pos$ a pair ( contact spr+s #h-h & ano!r pair #i-i4 ,! contact spr+s #h are adapt$ to be mov$ backw>d & =w>d by ! impulse :eel :i* is directly controll$ by ! dial "u ! manipulation ( ! op]ator4 ,:5 ^! spr+s #h are 9 _! normal position1 ! r++ circuit is cont9u$ ?r\gh ! release-key spr+s #i to ! r++ g5]ator4 ,^! spr+s #h occupy _! normal position only :5 ! dial is 9 its normal position1 ?is be+ due to ! not* #aj 9 ! contact :eel4 ,at all o!r times1 i4e41 :ile ! impulse :eel is out ( its normal position1 ! spr+s #h-h are ei!r depress$ s z to engage ! l[] batt]y contacts1 or else held 9 an int]m$iate position s z to engage nei!r ! batt]y contacts nor ! g5]ator contacts4 ,illu/ration3 ,fig4 #aib4 ,call+ ,app>atus ,k4,b4 ,sy/em ,:5 x is desir$ to call a giv5 /ation1 ! op]ator pulls ! subscrib]'s numb] on ! dial & holds ! r++ key clos$1 all[+ ! dial to return to normal4 ,?is connects ! impulse batt]y to ! subscrib]'s l9e z _m times z is requir$ to move ! subscrib]'s sectors to ! prop] position1 & 9 su* direction z to cause ! /epp+ movem5t ( ! v>i\s relays4 ,z ! impulse :eel comes to its normal position1 ! spr+s #h1 associat$ ) x1 aga9 engage _! upp] contacts1 by virtue ( ! not* #aj 9 ! impulse :eel1 & ?is e/abli%es ! connection betwe5 ! r++ g5]ator & ! subscrib]'s l9e1 ! r++ key be+ /ill held clos$4 ,! pull+ ( ! transmitt] dial & hold+ ! r++ key clos$1 !re=e1 n only s5ds ! /epp+ impulses to l9e1 b also foll[s x by ! r++ curr5t4 ,! s5d+ ( five impulses to l9e moves all ( ! sectors to ! six? not*1 & ?is corresponds to ! position necess>y to make ! f\r? /ation op]ative4 ,su* a condition is %[n 9 ,fig4 #aic1 x be+ assum$ t ! subscrib] at ,/ation ,c orig9at$ ! call & press$ 8 own button s z to prev5t 8 sector f be+ mov$ out ( its normal position4 ,z a result ( ?is1 ! talk+ circuit at ,/ation ,c is left clos$1 & ! talk+ & ! r++ circuit ( ,/ation ,d1 ! call$ /ation1 are clos$1 :ile bo? ! talk+ & ! r++ circuits ( all ! o!r /ations are left op54 ,/ation ,d may1 !re=e1 be rung & may communicate ) ,/ation ,c1 :ile all ( ! o!r /ations on ! l9e are lock$ out1 because ( ! fact t bo? _! talk+ & r++ circuits are left op54 ,illu/ration3 ,fig4 #aic4 ,circuit ,k4,b4 ,sy/em ,:5 conv]sation is end$1 ! op]ator is notifi$ by ! usual cle>+-out signal1 & %e !n depresses ! release button1 :i* br+s ! spr+s #i out ( engagem5t ) ! g5]ator contact b into engagem5t ) ! batt]y contact 9 su* relation z to s5d a batt]y curr5t on ! l9e 9 ! rev]se direction f t s5t out by ! impulse :eel4 ,?is s5ds curr5t ?r\gh all ( ! relays 9 su* direction z to )draw bo? ! mov+ & ! hold+ pawls f ! segm5ts & ?us all[ all ( ! segm5ts to return to _! normal positions4 ,( c\rse1 9 ?us e/abli%+ ! release curr5t1 x is necess>y = ! op]ator to depress ! r++ key z well z ! release key4 ,a "o-half micr(>ad cond5s] is plac$ 9 ! receiv] circuit at ea* /ation s t ! l9e w n be ti$ up %\ld "s subscrib] inadv]t5tly leave 8 receiv] (f its hook4 ,?is p]mits ! passage ( voice curr5ts1 b n ( ! direct curr5ts us$ 9 /epp+ ! relays or 9 releas+ !m4 ,! circuit ( ,fig4 #aic is some:at simplifi$ f t 9 actual practice1 & x %\ld be rememb]$ t ! hook swit*1 :i* is n %[n 9 ?is figure1 controls 9 ! usual way ! cont9uity ( ! receiv] & ! transmitt] circuits z well z ( ! g5]ator circuits1 ! g5]ator be+ atta*$ to ! l9e z 9 an ord9>y telephone4 ,brok5-,l9e ,sy/em4 ,! brok5-l9e me?od ( accompli%+ selective signal+ & lock+-out on telephone p>ty l9es is due to ,hom] ,rob]ts & 8 associates4 ,illu/ration3 ,fig4 #aid4 ,rob]ts ,lat*+ ,relay ,to und]/& j h[ ! pr9ciples illu/rat$ 9 ,figs4 #ahf & #ahg are put into effect1 x w be necess>y to und]/& ! lat*+ relay %[n diagrammatically 9 its two possible positions 9 ,fig4 #aid1 & 9 p]spective 9 ,fig4 #aie4 ,ref]r+ to ,fig4 #aid1 ! left-h& cut ( :i* %[s ! l9e relay 9 its normal position1 x is se5 t ! framework ( ! device resembles t ( an ord9>y pol>iz$ r+]4 ,"u ! influ5ce ( curr5t 9 "o direction fl[+ ?r\gh ! left-h& coil1 ! armature ( ?is device depresses ! h>d rubb] /ud #d1 & ! spr+s #a1 #b1 & #c are =c$ d[nw>dly until ! spr+ #b has pass$ "u ! lat* c>ri$ on ! spr+ #e4 ,:5 ! op]at+ curr5t ?r\gh ! coil #f ceases1 ! pressure ( ! armature on ! spr+ #a is reliev$1 all[+ ?is spr+ to resume its normal position & spr+ #c to engage ) spr+ #b4 ,! spr+ #b _c rise1 s9ce x is held by ! lat* #e1 & ! condition %[n 9 ! "r-h& cut ( ,fig4 #aid exi/s4 ,x w be se5 t ! spr+ #b has 9 ?is op]ation c>ri$ out j ! same function z ! swit* lev] p]=m$ z describ$ 9 connection ) ,figs4 #ahf & #ahg4 ,an analysis ( ?is action w %[ t ! normal contact betwe5 ! spr+s #a & #b1 :i* contact controls ! circuit ?r\gh ! relay coil & ! bell1 is n brok5 until ! coil #f is de-en]giz$1 :i* means t ! magnet is effective until x has accompli%$ its "w4 ,x is impossible1 !re=e1 = ?is relay to cut itself out ( circuit be=e x has caus$ ! spr+ #b to engage "u ! lat* #e4 ,if curr5t ( ! prop] direction 7 s5t ?r\gh ! coil #g ( ! relay1 ! opposite end ( ! armature w\ld be pull$ d[n & ! h>d rubb] /ud at ! left-h& end ( ! armature w\ld be> aga9/ ! b5t portion ( ! spr+ #e 9 su* mann] z to cause ! lat* ( ?is spr+ to release ! spr+ #b & ?us all[ ! relay to assume its normal1 or unlat*$1 position4 ,a good idea ( ! me*anical con/ruction ( ?is relay may be obta9$ f ,fig4 #aie4 ,! entire select+ function ( ! ,rob]ts sy/em is p]=m$ by ?is simple piece ( app>atus at ea* /ation4 ,illu/ration3 ,fig4 #aie4 ,rob]ts ,lat*+ ,relay ,! diagram ( ,fig4 #aif %[s1 9 simplifi$ =m1 a f\r-/ation l9e1 ! circuits be+ giv5 m 9 detail ?an 9 ! diagrams ( ,*apt] ,,xvi4 ,x w be notic$ t ! r+] & ! relay coil #f at ! fir/ /ation are bridg$ across ! sides ( ! l9e lead+ to ! c5tral (fice4 ,9 l mann] ! bell & ! relay magnets are bridg$ across ! two limbs ( ! l9e lead+ into ea* succe$+ /ation1 b ?is bridge at ea* ( ! /ations beyond ,/ation ,a is ineffective because ! l9e ext5sion ,rx is op5 at ! next /ation ne>e/ ! c5tral (fice4 ,illu/ration3 ,fig4 #aif4 ,simplifi$ ,circuits ( ,rob]ts ,sy/em ,9 ord] to r+ ,/ation ,a x is only necess>y to s5d out r++ curr5t f ! c5tral (fice4 ,?is curr5t is 9 su* direction z n to cause ! op]ation ( ! relay1 al?\gh x passes ?r\gh ! coil #f4 ,if1 on ! o!r h&1 x is desir$ to r+ ,/ation ,b1 a prelim9>y impulse w\ld be s5t ov] ! metallic circuit f ! c5tral (fice1 :i* impulse w\ld be ( su* direction z to op]ate ! relay at ,/ation ,a1 b n to op]ate ! bell at t /ation4 ,! op]ation ( ! relay at ,/ation ,a causes ! spr+ #b ( ?is relay to engage ! spr+ #c1 ?us ext5d+ ! l9e on to ! second /ation4 ,aft] ! spr+ #b at ,/ation ,a has be5 =c$ into contact ) ! spr+ #c1 x is caught by ! lat* ( ! spr+ #e & held me*anically4 ,:5 ! impulse f ! c5tral (fice ceases1 ! spr+ #a resumes its normal position1 ?us break+ ! bridge circuit ?r\gh ! bell at t /ation4 ,x is app>5t n[ t ! action ( coil #f at ,/ation ,a has made ! relay p[]less to p]=m any fur!r action1 & at ! same "t ! l9e has be5 ext5d$ on to ! second /ation4 ,a second simil> impulse f ! c5tral (fice w cause ! relay at ,/ation ,b to ext5d ! l9e on to ,/ation ,c1 & at ! same "t break ! circuit ?r\gh ! op]at+ coil & ! bell at ,/ation ,b4 ,9 ?is way any /ation may be pick$ out by s5d+ ! prop] numb] ( impulses to op]ate ! l9e relays ( all ! /ations betwe5 ! /ation desir$ & ! c5tral (fice1 & hav+ pick$ out a /ation x is only necess>y to s5d out r++ curr5t1 :i* curr5t is 9 su* direction z to r+ ! bell b n to op]ate ! relay magnet at t /ation4 ,9 ,fig4 #aig1 a f\r-/ation l9e1 su* z is %[n 9 ,fig4 #aif1 is illu/rat$1 b ! condition %[n 9 ?is is t exi/+ :5 two prelim9>y impulses h be5 s5t ov] ! l9e1 :i* caus$ ! l9e relays at ,/ation ,a & ,/ation ,b to be op]at$4 ,! bell at ,/ation ,c is1 !re=e1 ! only "o susceptible to r++ curr5t f ! c5tral (fice4 ,illu/ration3 ,fig4 #aig4 ,simplifi$ ,circuits ( ,rob]ts ,sy/em ,s9ce only "o bell & "o relay are 9 circuit at any "o "t1 x is obvi\s t all ( ! curr5t t passes ov] ! l9e is effective 9 op]at+ a s+le bell or relay only4 ,!re is no splitt+ up ( ! curr5t among a l>ge numb] ( bells z 9 ! bridg+ sy/em ( op]at+ /ep-by-/ep devices1 :i* me?od sometimes s greatly r$uces ! effective curr5t = ea* bell t x is ) great difficulty made to respond4 ,all ! en]gy available is appli$ directly to ! piece ( app>atus at ! "t x is be+ op]at$4 ,?is has a t5d5cy t[>d great] surety ( action1 & ! adju/m5t ( ! v>i\s pieces ( app>atus may be made ) less delicacy ?an is requir$ :]e _m pieces ( app>atus1 ea* hav+ consid]able "w to d1 mu/ necess>ily be op]at$ 9 multiple4 ,! me?od ( unlat*+ ! relays has be5 briefly ref]r$ to4 ,aft] a connection has be5 e/abli%$ ) a /ation 9 ! mann] already describ$1 ! op]ator may cle> ! l9e :5 x is prop] to d s by s5d+ impulses ( su* a nature z to cause ! l9e relays ( ! /ations beyond ! "o *os5 to op]ate1 ?us cont9u+ ! circuit to ! end ( ! l9e4 ,! op]ation ( ! l9e relay at ! la/ /ation br+s into circuit ! coil #h1 ,figs4 #aif & #aig1 ( a gr\nd+ device4 ,?is is simil> to ! l9e relay1 b x holds its op]at+ spr+ 9 a normally lat*$ position s z to ma9ta9 ! two limbs ( ! l9e disconnect$ f ! gr\nd4 ,! next impulse foll[+ ov] ! metallic circuit passes ?r\gh ! coil #h & causes ! op]ation ( ?is gr\nd+ device :i*1 by becom+ unlat*$1 gr\nds ! limb ,l ( ! l9e ?r\gh ! coil #h4 ,?is tempor>y gr\nd at ! end ( ! l9e makes x possible to s5d an unlock+ or re/or+ curr5t f ! c5tral (fice ov] ! limb ,l1 :i* curr5t passes ?r\gh all ( ! unlock+ coils #g1 %[n 9 ,figs4 #aid1 #aif1 & #aig1 ?us caus+ ! simultane\s unlock+ ( all ( ! l9e relays & ! re/oration ( ! l9e to its normal condition1 z %[n 9 ,fig4 #aif4 ,illu/ration3 ,fig4 #aih4 ,details ( ,lat*+ ,relay ,connections ,z has be5 /at$1 ! w9d+s #g on ! l9e relays are ! unlat*+ w9d+s4 ,9 ,figs4 #aif & #aig1 = ! purpose ( simplicity1 ^! w9d+s are n %[n connect$1 b z a matt] ( fact ea* ( !m is includ$ 9 s]ies 9 ! cont9u\s limb ,l ( ! l9e4 ,?is w\ld introduce a highly objectionable feature f ! /&po9t ( talk+ ov] ! l9e 7 x n = ! balanc+ coils #ga1 ea* w\nd on ! same core z ! correspond+ w9d+ #g1 & ea* includ$ 9 s]ies 9 ! limb ,r ( ! l9e1 & 9 su* direction z to be diff]5tial !reto ) respect to curr5ts pass+ 9 s]ies ov] ! two limbs ( ! l9e4 ,! w9d+s #g are ! true unlock+ w9d+s1 :ile ! w9d+s #ga h no o!r function ?an to neutralize ! inductive effects ( ^! unlock+ w9d+s necess>ily plac$ 9 s]ies 9 ! talk+ circuit4 ,all ( ^! w9d+s are ( l[ ohmic resi/ance1 a con/ruction :i*1 z has previ\sly be5 not$1 br+s ab\t ! desir$ effect )\t introduc+ any self-induction 9 ! l9e1 & )\t produc+ any appreciable effect ^u ! transmission4 ,a /udy ( ,fig4 #aih w make cle> ! connections ( ^! unlock+ & balanc+ w9d+s at ea* /ation4 ,! /atem5t ( op]ation s f> giv5 discloses ! g5]al me?od ( build+ up ! l9e 9 sections 9 ord] to *oose any p>ty & ( aga9 break+ x up into sections :5 ! conv]sation is f9i%$4 ,x has be5 /at$ t ! same op]ation :i* selects ! p>ty want$ also s]ves to give t p>ty ! use ( ! l9e & to lock ! o!rs (f4 ,t ?is is true w be und]/ood :5 x is /at$ t ! r+] is ( su* con/ruction t :5 op]at$ to r+ ! subscrib] want$1 x also op]ates to unlat* a set ( spr+s simil> to ^? %[n 9 ,fig4 #aid1 ?is unlat*+ caus+ ! prop] connection ( ! subscrib]'s talk+ circuit across ! limbs ( ! l9e1 & also clos+ ! local circuit ?r\gh 8 transmitt]4 ,! v fir/ motion ( ! bell armature p]=ms ?is unlat*+ op]ation aft] :i* ! bell behaves exactly z an ord9>y pol>iz$ bias$ r+]4 ,illu/ration3 ,fig4 #aii4 ,brok5-,back ,r+] ,! con/ruction ( ?is r+] is int]e/+ & is %[n 9 its two possible positions 9 ,fig4 #aii4 ,! gr\p ( spr+s c>ri$ on its frame is entirely indep5d5t ( ! movem5t ( ! armature dur+ ! r++ op]ation4 ,) rev]s$ curr5ts1 h[ev]1 ! armature is mov$ 9 ! opposite direction f t necess>y to r+ ! bells1 & ?is causes ! lat*+ ( ! spr+s into _! normal position4 ,9 ord] t ?is device may p]=m ! d\ble function ( r+] & relay ! tapp] rod ( ! bell is h+$ on ! armature s z to p>take ( ! movem5ts ( ! armature 9 "o direction only4 ,?is has be5 call$ by ! inv5tor & eng9e]s ( ! ,rob]ts sy/em a brok5-back r+]1 a "n sugge/ive ( ! movable relation betwe5 ! armature & ! tapp] rod4 ,! con/ruction ( ! r+] is ( ! same nature z t ( ! /&>d pol>iz$ r+] univ]sally employ$1 b a h+e action betwe5 ! armature & ! tapp] rod1 ( su* nature z to make ! tapp] p>take positively ( ! movem5ts ( ! armature 9 "o direction1 b to rema9 p]fectly quiesc5t :5 ! armature moves 9 ! o!r direction1 is provid$4 ,illu/ration3 ,fig4 #bjj4 ,details ( ,r+] ,connection ,h[ ?is brok5-back r+] controls ! talk+ & ! lock+-out conditions may be/ be und]/ood 9 connection ) ,fig4 #bjj4 ,! r+] spr+s are normally lat*$ at all /ations4 ,"u ^! conditions ! receiv] is %ort-circuit$ by ! engagem5t ( spr+s #aj & #aa1 ! receiv] circuit is op5 betwe5 spr+s #aj & #ab1 & ! local-batt]y circuit is op5 betwe5 spr+s #i & #ab4 ,! subscrib]s ^: r+]s are lat*$ are1 !re=e1 lock$ out 9 m ways ?an "o4 ,:5 ! bell is rung1 ! fir/ /roke x makes unlat*es ! spr+s1 :i* assume ! position %[n 9 ! "r-h& cut ( ,fig4 #aii1 & ?is1 x w be se5 f ,fig4 #bjj1 e/abli%es prop] conditions = enabl+ ! subscrib] to transmit & to receive spee*4 ,! hook swit* breaks bo? transmitt] & receiv] circuits :5 d[n & 9 rais+ x e/abli%es a mom5t>y circuit betwe5 ! gr\nd & ! limb ,l ( ! l9e1 bo? upp] & l[] hook contacts engag+ ! hook lev] simultane\sly dur+ ! ris+ ( ! hook4 ,! me*anism at ! c5tral (fice by :i* selection ( ! prop] /ation is made 9 a rapid mann] is %[n 9 ,fig4 #bja4 ,x has already be5 /at$ t ! selection ( ! prop] subscrib] is br\ght ab\t by ! s5d+ ( a pr$et]m9$ numb] ( impulses f ! c5tral (fice1 ^! impulses pass+ 9 "o direction only & ov] ! metallic circuit4 ,aft] ! prop] p>ty has be5 rea*$1 ! r++ curr5t is put on 9 ! rev]se direction4 ,illu/ration3 ,fig4 #bja4 ,c5tral-,(fice ,impulse ,transmitt] ,! op]ator e/abli%es ! numb] ( impulses to be s5t by plac+ ! po9t] opposite ! numb] on ! dial correspond+ to ! /ation want$4 ,! rat*et :eel is /epp$ ar\nd automatically by ea* impulse ( curr5t f an ord9>y pole *ang] su* z is employ$ 9 r++ bias$ bells4 ,:5 ! requir$ numb] ( impulses has be5 s5t1 a projection1 c>ri$ on a gr\p ( spr+s1 drops into a not* on ! drum ( ! selector %aft1 :i* op]ation in/antly /ops ! select+ curr5t impulses & at ! same "t ?r[s on ! r++ curr5t :i* consi/s ( impulses 9 ! rev]se direction4 ,s rapidly does ?is device op]ate t x w readily foll[ ! impulses ( an ord9>y pole *ang]1 ev5 :5 ?is is adju/$ to its maximum rate ( vibration4 ,illu/ration3 ,,view ,,( ,a ,,l>ge ,,=eign ,,multiple ,,swit*bo>d ,op]ation4 ,space w n p]mit a full discussion ( ! details ( ! c5tral-(fice selective app>atus1 b a g5]al resum ( ! op]ation ( ! sy/em may n[ be giv51 ) ! aid ( ,fig4 #bjb1 :i* %[s a f\r-/ation l9e ) ! circuits ( ?ree ( ! /ations some:at simplifi$4 ,9 ?is figure ,/ation ,a1 ,/ation ,b1 & ,/ation ,d are %[n 9 _! lock$-out positions1 ,a & ,b hav+ be5 pass$ by ! selection & r++ ( ,/ation ,c1 :ile ,/ation ,d is inop]ative because x 0 n rea*$ 9 ! selection & ! l9e is /ill brok5 at ,/ation ,c4 ,/ation ,c1 !re=e1 has possession ( ! l9e4 ,:5 ! subscrib] at ,/ation ,c rais$ 8 receiv] 9 ord] to call c5tral1 a fla% contact 0 made z ! hook mov$ up1 :i* mom5t>ily gr\nd$ ! limb ,l ( ! l9e4 7,see ,fig4 #bjj47 ,?is fla% contact is produc$ by ! arrangem5t ( ! hook :i* assures t ! l[] contact %all1 by virtue ( its flexibility1 foll[ up ! hook lev] until ! hook lev] engages ! upp] contact1 aft] :i* ! l[] contact breaks4 ,?is results 9 ! mom5t>y connection ( bo? ! upp] & ! l[] contacts ( ! hook ) ! lev]1 &1 !re=e1 ! mom5t>y gr\nd+ ( ! limb ,l ( ! l9e4 ,?is limb always be+ cont9u\s s]ves1 :5 ?is fla% contact is made1 to actuate ! l9e signal at ! c5tral (fice4 ,illu/ration3 ,fig4 #bjb4 ,circuits ( ,rob]ts ,l9e ,s9ce1 h[ev]1 all p>ties on ! l9e are normally lock$ out ( talk+ circuits1 "s means mu/ be provid$ :]eby ! op]ator may place ! signal+ p>ty 9 talk+ connection & leave all ! o!r in/rum5ts on ! l9e 9 _! normally lock$-out position4 ,9 fact1 ! op]ator mu/ be able automatically to pick out ! /ation t signal$ 91 & op]ate ! r+] to unlat* ! spr+s controll+ ! talk+ circuit ( t /ation4 ,accord+ly ! op]ator s5ds impulses on ! l9e1 f a gr\nd$ batt]y1 :i* are 9 ! direction to op]ate ! l9e relays & to cont9ue ! l9e circuit to ! /ation call+4 ,:51 aft] a suffici5t numb] ( impulses1 ?is curr5t rea*es t /ation x f9ds a pa? to gr\nd f ! limb ,l4 ,?is pa? is made possible by ! fact t ! subscrib]'s receiv] is (f its hook at t /ation4 ,9 ord] to und]/& j h[ ?is gr\nd connection is made1 x mu/ be rememb]$ t ea* ( ! r+] magnets is en]giz$ ) ea* select+ impulse1 b 9 su* a direction z n to r+ ! bells1 x be+ und]/ood t all ( ! r+] me*anisms are normally lat*$4 ,:5 ! select+ impulse = ,/ation ,c arrives1 x passes ?r\gh ! r+] & ! select+ relay coils at t /ation & />ts to op]ate ! rema9d] ( ! r+]s suffici5tly to cause ! spr+ #ab to engage ! spr+ #ac4 ,?is e/abli%es ! gr\nd connection f ! limb ,l ( ! l9e1 ! circuit be+ trac$ ?r\gh limb ,l ?r\gh ! upp] contact ( ! swit*1 !nce ?r\gh spr+s #ab & #ac to gr\nd1 & ?is1 be=e ! l9e relay has "t to lat*1 op]ates ! quick-act+ relay at ! c5tral (fice1 :i* acts to cut (f fur!r impulses1 & ?us automatically /ops at ! call+ /ation4 ,r++ curr5t 9 ! opposite direction is !n s5t to l9e2 ?is unlat*es ! r+] spr+s & places ! call+ subscrib] 9 talk+ circuit4 ,:5 ! op]ator has communicat$ ) ! call+ subscrib]1 & f\nd1 = example1 t ano!r p>ty on ano!r simil> l9e is desir$1 %e turns ! dial po9t] on ! selector to ! numb] correspond+ to ! call$-= p>ty's numb] on t l9e1 & presses ! signal key4 ,press+ ?is key causes impulses to run d[n ! l9e1 select+ ! prop] p>ty & r++ 8 bell 9 ! mann] already describ$4 ,! connection betwe5 ! two p>ties is !n e/abli%$1 & no "o else c 9 any possible way1 except by p]mission ( ! op]ator1 obta9 access to ! l9e4 ,x is obvi\s t "s means mu/ be provid$ = re/or+ ! select+ relays to normal aft] a conv]sation is f9i%$4 ,by ref]r+ to ,fig4 #aid x w be se5 t ! upp] end ( ! lat* spr+ #e is b5t ov] 9 su* a mann] t :5 ! armature is attract$ by curr5t fl[+ ?r\gh ! coil #g1 ! knob on ! left-h& end ( ! armature on ris+ engages ) ! b5t cam surface & =ces back ! lat*1 p]mitt+ spr+ #b to return to its normal position4 ,to re/ore ! l9e ! op]ator s5ds out suffici5t additional selective impulses to ext5d ! circuit to ! end ( ! l9e1 & ?us br+s ! gr\nd] into circuit4 ,! w9d+ ( ! gr\nd] is connect$ 9 su* a mann] t ! next pass+ impulse ?r[s (f its lat*1 p]mitt+ ! long spr+ to contact ) ! gr\nd spr+4 ,! op]ator n[ s5ds a gr\nd$ impulse ov] ! cont9u\s limb ,l ( ! l9e :i* passes ?r\gh ! re/or+ coils #g at all ! /ations & ?r\gh ! "r-h& coil ( ! gr\nd+ device to gr\nd4 ,! select+ relays are1 !re=e1 simultane\sly re/or$ to normal4 ,! gr\nd] is also en]giz$ & re/or$ to its normal position by ! same curr5t4 ,if a p>ty 9 call+ f9ds t 8 own l9e is busy & he _c get c5tral1 he may leave 8 receiv] (f its hook4 ,:5 ! p>ty :o is us+ ! l9e hangs up 8 receiv] ! fact t ano!r p>ty desires a connection is automatically indicat$ to ! op]ator1 :o !n locks out ! in/rum5t ( ! p>ty :o has j f9i%$ conv]sation & passes 8 /ation by4 ,:5 ! op]ator aga9 ?r[s ! key1 ! wait+ subscrib] is automatically select$ 9 ! same mann] z 0 ! fir/ p>ty4 ,if !re are no subscrib]s wait+ = s]vice1 ! /op relay at c5tral w n op]ate until ! gr\nd] end ( ! l9e is unlat*$1 ! select+ relays be+ !n re/or$ automatically to normal4 ,! circuits are s organiz$ t at all times :e!r ! l9e is busy or n1 ! movem5t up & d[n ( ! swit* hook1 at any sub-/ation1 op]ates a signal be=e ! op]ator4 ,su* a movem5t1 :5 made sl[ly & repeat$ly1 indicates to ! op]ator t ! subscrib] has an em]g5cy call & %e may use h] judgm5t z to tak+ ! l9e away f ! p>ties :o are us+ x1 & f9d+ out :at ! em]g5cy call is =4 ,if ! op]ator f9ds t ! subscrib] has misus$ ?is privilege ( mak+ ! em]g5cy call1 %e may re/ore ! connection to ! p>ties previ\sly engag$ 9 conv]sation4 ,"o ( ! sali5t po9ts ( ?is ,rob]ts sy/em is t ! op]ator always has control ( ! l9e4 ,a subscrib] is n able ev5 to use 8 own batt]y till p]mitt$ to d s4 ,a subscrib] :o leaves 8 receiv] (f its hook 9 ord] t he may be signal$ by ! op]ator :5 ! l9e is free1 causes no det]ioration ( ! local batt]y because ! batt]y circuit is held op5 by ! swit* contacts c>ri$ on ! r+]4 ,x _c be d5i$1 h[ev]1 t ?is sy/em is complicat$1 & t x has o!r faults4 ,= in/ance1 z describ$ h]e91 bo? sides ( ! l9e mu/ be loop$ into ea* subscrib]'s /ation1 ?us requir+ f\r drop1 or s]vice1 wires in/ead ( two4 ,x is possible to ov]come ?is objection by plac+ ! l9e relays on ! pole 9 a suitably protect$ cas+1 9 :i* case x is suffici5t to run b two drop wires f ! ne>] l9e to /ation4 ,!re are und\bt$ly o!r objections to ?is sy/em1 & yet ) all its faults x is ( great int]e/1 & al?\gh radical 9 _m respects1 x tea*es lessons ( und\bt$ value4 ,,*apt] ,,xviii ,,electrical ,,haz>ds ,all telephone sy/ems are expos$ to c]ta9 electrical haz>ds4 ,:5 ^! haz>ds become actively op]ative z causes1 h>mful results ensue4 ,! h>mful results are ( two k9ds3 ^? caus+ damage to prop]ty & ^? caus+ damage to p]sons4 ,! damage to p]sons may be s s]i\s z to result 9 dea?4 ,damage to prop]ty may de/roy ! usefulness ( a piece ( app>atus or ( "s portion ( ! wire plant4 ,or ! prop]ty damage may initiate itself z a h>m to app>atus or wir+ & may result 9 great] & ext5d+ damage by />t+ a fire4 ,electrical curr5ts :i* endang] life & prop]ty may be furni%$ by natural or artificial causes4 ,natural electricity :i* does su* damage usually displays itself z lightn+4 ,9 r>e cases1 curr5ts t5d+ to fl[ ov] gr\nd$ l9es because ( extraord9>y diff]5ces ( pot5tial betwe5 sections ( ! e>?'s surface h damag$ app>atus 9 su* l9es1 or only h be5 prev5t$ f caus+ su* damage by ! op]ation ( protective devices4 ,telegraph & telephone sy/ems h be5 ?reat5$ by natural electrical haz>ds s9ce ! beg9n+ ( ! arts & by artificial electrical haz>ds s9ce ! developm5t ( electric light & p[] sy/ems4 ,at ! pres5t "t1 contr>y to ! g5]al supposition1 x is 9 ! artificial1 & n 9 ! natural electrical haz>ds t ! great] v>iety & degree ( dang] lies4 ,( ! ways 9 :i* artificial electricity may injure a telephone sy/em1 ! entrance ( curr5t f an ext]nal electrical p[] sy/em is a great] m5ace ?an an abnormal fl[ ( curr5t f a s\rce belong+ to ! telephone sy/em itself4 ,yet mod]n practice provides opportunities = a telephone sy/em to inflict damage ^u itself 9 t way4 ,telephone eng9e]+ designs ne$ to provide means = protect+ all p>ts ( a sy/em aga9/ damage1 f ext]nal 7=eign7 z well z int]nal 7dome/ic7 haz>ds1 & to cause ?is protection to be inclusive en\gh to protect p]sons aga9/ injury & prop]ty f damage by any =m ( ov]heat+ or electrolytic action4 ,a "p ( a telephone sy/em = :i* !re is ev5 a remote possibility ( contact ) an ext]nal s\rce ( electrical p[]1 :e!r natural or artificial1 is said to be expos$ to electrical haz>d4 ,! degree or "* ( possible contact or o!r int]f]5ce (t5 is ref]r$ to 9 relative t]ms ( exposure4 ,! same t]ms are us$ conc]n+ inductive relations betwe5 circuits4 ,! :ole t5d5cy ( design1 p>ticul>ly ( wire plants1 is to arrange ! circuits 9 su* a way z to limit ! exposure z greatly z possible1 ! int5t be+ to produce a condition 9 :i* all p>ts ( ! sy/em w be unexpos$ to haz>ds4 ,me?ods ( design are n yet suffici5tly advanc$ = any plant to be =m$ ( circuits :olly unexpos$1 s t protective means are requir$ to safegu>d app>atus & circuits 9 case ! haz>d1 h[ev] remote1 becomes op]ative4 ,lightn+ dis*>ges betwe5 ! cl\ds & e>? frequ5tly *>ge op5 wires to pot5tials suffici5tly high to damage app>atus2 & less frequ5tly1 to de/roy ! wires ( ! l9es !mselves4 ,lightn+ dis*>ges betwe5 cl\ds frequ5tly induce *>ges 9 l9es suffici5t to damage app>atus connect$ ) ! l9es4 ,heavy ru%es ( curr5t 9 l9es1 f lightn+ causes1 occasionally induce damag+ curr5ts 9 adjac5t l9es n suffici5tly expos$ to ! orig9al cause to h be5 injur$ )\t ?is induction4 ,! lightn+ haz>d is lea/ :]e ! mo/ l9es are expos$4 ,9 a small city ) all ( ! l9es =m$ ( expos$ wires & all ( !m us$ z gr\nd$ circuits1 a s+le lightn+ dis*>ge may damage _m swit*bo>d signals & telephone r+]s if !re be b #ajj or #bjj l9es1 :ile ! damage might h be5 no?+ _h !re be5 #hjj to #a1jjj l9es 9 ! same area4 ,means ( protect+ l9es & app>atus aga9/ damage by lightn+ are little m elaborate ?an 9 ! e>lie/ days ( telegraph work+4 ,!y are adequate = ! almo/ entire protection ( life & ( app>atus4 ,p[] circuits are classifi$ by ! rules ( v>i\s gov]n+ bodies z high-pot5tial & l[-pot5tial circuits4 ,! classification ( ! ,national ,bo>d ( ,fire ,und]writ]s 9 ! ,unit$ ,/ates def9es l[-pot5tial circuits z hav+ pressures bel[ #eej volts2 high-pot5tial circuits z hav+ pressures f #eej to #c1ejj volts1 & extra high-pot5tial circuits z hav+ pressures above #c1ejj volts4 ,pressures ( #ajj1jjj volts are becom+ m common4 ,:]e p[] is valuable & ! di/ance ov] :i* x is to be transmitt$ is great1 su* high voltages are ju/ifi$ by ! economics ( ! p[] problem4 ,!y are a great haz>d to telephone sy/ems1 h[ev]4 ,an unprotect$ telephone sy/em meet+ su* a haz>d by contact w endang] life & prop]ty ) great c]ta9ty4 ,a v common =m ( di/ribution = light+ & p[] purposes is ! ?ree-wire sy/em hav+ a gr\nd$ neutral wire1 ! maximum pot5tial above ! e>? be+ ab\t #aae volts4 ,telephone l9es & app>atus are subject to damage by any p[] circuit :e!r ( high or l[ pot5tial4 ,! cause ( prop]ty damage 9 all cases is ! fl[ ( curr5t4 ,p]sonal damage1 if x be dea? f %ock1 ord9>ily is ! result ( a high pot5tial betwe5 two p>ts ( ! body4 ,! be/ k indicates t dea? uni=mly results f %ock to ! he>t4 ,x is believ$ t dea? has occurr$ f %ock due to pressure z l[ z #ajj volts4 ,! critical m9imum voltage :i* c n cause dea? is n kn[n4 ,a good rule is nev] will+ly to subject ano!r p]son to p]sonal contact ) any electrical pressure :atev]4 ,electricity c produce actions ( f\r pr9cipal k9ds3 physiological1 !rmal1 *emical1 & magnetic4 ,view+ electricity z e/abli%+ haz>ds1 ! physiological action may injure or kill liv+ ?+s2 ! !rmal action may produce heat en\gh to melt metals1 to *> ?+s :i* c be burn$1 or to cause !m actually to burn1 p]haps ) a fire :i* c spread2 ! *emical action may de/roy prop]ty values by *ang+ ! /ate ( metals1 z by dissolv+ !m f a solid /ate :]e !y are ne$$ into a /ate ( solution :]e !y are n ne$$2 ! magnetic action introduces no direct haz>d4 ,! greate/ haz>d to :i* prop]ty values are expos$ is ! electro-!rmal action2 t is1 ! same useful prop]ties by :i* electric light+ & electric heat+ ?rive may produce heat :]e x is n want$ & 9 an am\nt great] ?an c safely be borne4 ,! t5d5cy ( design is to make all app>atus capable ( c>ry+ )\t ov]heat+ any curr5t to :i* voltage )9 ! telephone sy/em may subject x1 & to provide ! sy/em s design$ ) specific devices adapt$ to isolate x f curr5ts orig9at+ )\t4 ,app>atus :i* is design$ 9 ?is way1 adapt$ n only to c>ry its own normal work+ curr5ts b to c>ry ! curr5t :i* w\ld result if a giv5 piece ( app>atus 7 connect$ directly across ! maximum pressure )9 ! telephone sy/em itself1 is said to be self-protect+4 ,app>atus amply able to c>ry its maximum work+ curr5t b likely to be ov]heat$1 to be injur$1 or p]haps to de/roy itself & set fire to o!r ?+s if subject$ to ! maximum pressure )9 ! sy/em1 is n self-protect+ app>atus4 ,to make all electrical devices self-protect+ by surr\nd+ !m ) special arrangem5ts = w>d+ (f abnormal curr5ts f ext]nal s\rces1 is n z simple z might appe>4 ,a lamp1 = example1 :i* c be> ! entire pressure ( a c5tral-(fice batt]y1 is n suitable = direct use 9 a l9e sev]al miles long because x w\ld n give a practical signal 9 s]ies ) t l9e & ) ! telephone set1 z x is requir$ to d4 ,a lamp suitable = use 9 s]ies ) su* a l9e & a telephone set w\ld burn out by curr5t f its own normal s\rce if ! l9e %\ld become %ort-circuit$ 9 or ne> ! c5tral (fice4 ,! balla/ ref]r$ to 9 ! *apt] on ,signals 0 design$ = ! v purpose ( provid+ rapidly-ris+ resi/ance to (fset ! t5d5cy t[>d rapidly-ris+ curr5t :i* c\ld burn out ! lamp4 ,z ano!r example1 a v small direct-curr5t electric motor c be turn$ on at a snap swit* & w ga9 spe$ quickly en\gh s t its armature w9d+ w n be ov]heat$4 ,a l>g] motor ( t k9d c n be />t$ safely )\t introduc+ resi/ance into ! armature circuit on />t+1 & cutt+ x out gradually z ! armature ga9s spe$4 ,su* a motor c\ld be made self-protect+ by hav+ ! armature w9d+ ( mu* l>g] wire ?an really is requir$ = m]e runn+1 *oos+ its size great en\gh to c>ry ! l>ge />t+ curr5t )\t ov]heat+ itself & its insulation4 ,x is bett]1 & = long has be5 /&>d practice1 to use />t+ boxes1 frankly admitt+ t su* motors are n self-protect+ until />t$1 ?\gh !y are self-protect+ :ile runn+ at normal spe$s4 ,su* a motor1 once />t$1 may be ov]load$ s z to be sl[$ d[n4 ,s mu* m curr5t n[ c pass ?r\gh ! armature t its w9d+ is aga9 9 dang]4 ,ov]load circuit-break]s are provid$ = ! v purpose ( tak+ motors out ( circuit 9 cases :]e1 once up to spe$1 !y are me*anically br\ght d[n aga9 & into dang]4 ,su* a circuit-break] is a device = protect+ aga9/ an int]nal haz>d2 t is1 int]nal to ! p[] sy/em ( :i* ! motor is a "p4 ,ano!r example3 ,9 c]ta9 situations1 app>atus int5d$ to op]ate "u impulses ( l>ge curr5t may be capable ( c>ry+ its normal impulses successfully b incapable ( c>ry+ curr5ts f ! same pressure cont9u\sly4 ,protective means may be provid$ = deta*+ su* app>atus f ! circuit :5ev] ! p]iod 9 :i* ! curr5t acts is n %ort en\gh to insure safety4 ,?is is cit$ z a case :]e9 a curr5t1 normal 9 am\nt b abnormal 9 duration1 becomes a haz>d4 ,! la/ m5tion$ example ( damage f int]nal haz>ds br+s u to ! law ( ! electrical g5]ation ( heat4 ,! great] ! curr5t or ! great] ! resi/ance ( ! conductor heat$ or ! long] ! "t1 ! great] w he ! heat g5]at$ 9 t conductor4 ,b ?is g5]at$ heat v>ies directly z ! resi/ance & z ! "t & z ! squ>e ( ! curr5t1 t is1 ! law is ,heat g5]at$ ,c#b,rt 9 :i* ,c ! curr5t2 ,r! resi/ance ( ! conductor2 & t ! "t4 ,x is obvi\s t a protective device1 su* z an ov]load circuit-break] = a motor1 or a protector = telephone app>atus1 ne$s to op]ate m quickly = a l>ge curr5t ?an = a small "o1 & ?is is j :at all well-design$ protective devices are int5d$ to d4 ,! g5]al problem :i* ^! heat+ haz>ds pres5t ) relation to telephone app>atus & circuits is3 ,to cause all p>ts ( ! telephone sy/em to be made s z to c>ry successfully all curr5ts :i* may fl[ 9 !m because ( any int]nal or ext]nal pressure1 or to supplem5t !m by devices :i* w /op or div]t curr5ts :i* c\ld ov]heat !m4 ,electrolytic haz>ds dep5d n on ! heat+ effects ( curr5ts b on _! *emical effects4 ,! same natural law :i* enables prim>y & second>y batt]ies to be useful provides a haz>d :i* m5aces telephone-cable %ea?s & o!r conductors4 ,:5 a curr5t leaves a metal 9 contact ) an electrolyte1 ! metal t5ds to dissolve into ! electrolyte4 ,9 ! processes ( electroplat+ & electrotyp+1 curr5t ent]s ! ba? at ! anode1 passes f ! anode ?r\gh ! solution to ! ca?ode1 remov+ metal f ! =m] & deposit+ x ^u ! latt]4 ,9 a prim>y batt]y us+ z9c z ! positive elem5t & ! negative t]m9al1 curr5t is caus$ to pass1 )9 ! cell1 f ! z9c to ! negative elem5t & z9c is dissolv$4 ,foll[+ ! same law1 any pipe buri$ 9 ! e>? may s]ve to c>ry curr5t f "o region to ano!r4 ,z s+le-trolley traction sy/ems ) positive trolley wires con/antly are s5d+ l>ge curr5ts ?r\gh ! e>? t[>d _! p[] /ations1 su* a pipe may be ( positive pot5tial ) relation to moi/ e>? at "s po9t 9 its l5g?4 ,curr5t leav+ x at su* a po9t may cause its metal to dissolve en\gh to de/roy ! usefulness ( ! pipe = its int5d$ purpose4 ,lead-%ea!d telephone cables 9 ! e>? are p>ticul>ly expos$ to su* damage by electrolysis4 ,! reasons are t su* cables (t5 are long1 h a good conductor z ! %ea?-metal1 & t metal dissolves readily 9 ! pres5ce ( mo/ aque\s solutions :5 electrolytic diff]5ces ( pot5tial exi/4 ,! l5g? ( ! cables enables !m to connect betwe5 po9ts ( consid]able diff]5ce ( pot5tial4 ,x is lack ( ?is l5g? :i* prev5ts electrolytic damage to masses ( /ructural metal 9 ! e>?4 ,electrical p[] is suppli$ to s+le-trolley railroads pr9cipally 9 ! =m ( direct curr5t4 ,usually all ! trolley wires ( a city are s connect$ to ! g5]at+ units z to be positive to ! rails4 ,?is causes curr5t to fl[ f ! c>s t[>d ! p[] /ations1 ! return pa? be+ made up jo9tly ( ! rails1 ! e>? itself1 actual return wires :i* may supplem5t ! rails1 & also all o!r conduct+ ?+s 9 ! e>?1 ^! be+ pr9cipally lead-cov]$ cables & o!r pipes4 ,^! conditions e/abli% def9ite areas 9 :i* ! curr5ts t5d to leave ! cables & pipes1 i4e41 9 :i* ! latt] are positive to o!r ?+s4 ,^! positive areas usually are mu* small] ?an ! negative areas1 t is1 ! regions 9 :i* curr5ts t5d to ent] ! cables =m a l>g] total ?an ! regions 9 :i* ! curr5ts t5d to leave ! cables4 ,^! facts simplify ! ways 9 :i* ! cables may be protect$ aga9/ damage by direct curr5ts leav+ !m & also !y r$uce ! am\nt1 complication1 & co/ ( apply+ ! corrective & prev5tive measures4 ,all electric roads d n use direct curr5t4 ,c]ta9 simplifications 9 ! use ( s+le-phase alt]nat+ curr5ts 9 traction motors h increas$ ! numb] ( roads us+ a sy/em ( alt]nat+-curr5t p[] supply4 ,:]e alt]nat+ curr5t is us$1 ! electrolytic conditions are diff]5t & a new problem is set1 =1 z ! curr5t fl[s 9 recurr5tly diff]5t directions1 an area :i* at "o in/ant is positive to o!rs1 is *ang$ ! next in/ant into a negative area4 ,! protective means1 !re=e1 mu/ be adapt$ to ! *ang$ requirem5ts4 ,,*apt] ,,xix ,,protective ,,means ,any ( ! heat+ haz>ds describ$ 9 ! =ego+ *apt] may cause curr5ts :i* w damage app>atus4 ,all devices = ! protection ( app>atus f su* damage1 op]ate ei!r to /op ! fl[ ( ! dang]\s curr5t1 or to s5d t fl[ ov] "s o!r pa?4 ,protection ,aga9/ ,high ,pot5tials4 ,lightn+ is ! mo/ ne>ly univ]sal haz>d4 ,all op5 wires are expos$ to x 9 "s degree4 ,damag+ curr5ts f lightn+ are caus$ by extraord9>ily high pot5tials4 ,fur!rmore1 a lightn+ dis*>ge is oscillatory2 t is1 alt]nat+1 & ( v high frequ5cy4 ,drops1 r+]s1 receiv]s1 & o!r devices subject to lightn+ damage suff] by hav+ _! w9d+s burn$ by ! dis*>ge4 ,! imp$ance ^! w9d+s (f] to ! high frequ5cy ( lightn+ oscillations is great4 ,! imp$ance ( a few turns ( heavy wire may be negligible to alt]nat+ curr5ts ( ord9>y frequ5cies because ! resi/ance ( ! wire is l[1 its inductance small1 & ! frequ5cy f9ite4 ,on ! o!r h&1 ! imp$ance ( su* a coil to a lightn+ dis*>ge is mu* high]1 due to ! v high frequ5cy ( ! dis*>ge4 ,7 x n = ! extremely high pressure ( lightn+ dis*>ges1 _! high frequ5cy ( oscillation w\ld enable ord9>y coils to be self-protect+ aga9/ !m4 ,b a dis*>ge ( electricity c take place ?r\gh ! air or o!r insulat+ m$ium if its pressure be high en\gh4 ,a pressure ( #gj1jjj volts c /rike across a gap 9 air ( "o in*1 & l[] pressures c /rike across small] di/ances4 ,:5 lightn+ enc\nt]s an imp$ance1 ! dis*>ge seldom takes place ?r\gh ! entire w9d+1 z an ord9>y curr5t w\ld fl[1 usually /rik+ across :atev] %ort pa?s may exi/4 ,v (t5 ^! pa?s are across ! insulation betwe5 ! out] turns ( a coil4 ,x is n unusual = a lightn+ dis*>ge to pl[ its way across ! out] lay] ( a w\nd spool1 melt+ ! copp] ( ! turns z x goes4 ,(t5 ! dis*>ge w take place f inn] turns directly to ! core ( ! magnet4 ,?is is m likely :5 ! core is gr\nd$4 ,air-,gap ,arre/]4 ,! t5d5cy ( a w9d+ to oppose lightn+ dis*>ges & ! ease ) :i* su* dis*>ge may /rike across insulat+ gaps1 po9ts ! way to protection aga9/ !m4 ,su* devices consi/ ( two conductors sep>at$ by an air space or o!r insulator & are v>i\sly kn[n z lightn+ arre/]s1 sp>k gaps1 op5-space cut\ts1 or air-gap arre/]s4 ,! conductors betwe5 :i* ! gap exi/s may be bo? ( metal1 may be "o ( metal & "o ( c>bon1 or bo? ( c>bon4 ,"o comb9ation consi/s ( c>bon & m]cury1 a liquid metal4 ,! space betwe5 ! conductors may be fill$ ) ei!r air or solid matt]1 or x may be a vacuum4 ,speak+ g5]ally1 ! conductors are sep>at$ by "s insulator4 ,two conductors sep>at$ by an insulator =m a cond5s]4 ,! insulator ( an op5-space arre/] (t5 is call$ ! dielectric4 ,illu/ration ,fig4 #bjc4 ,saw ,too? ,arre/] ,dis*>ge ,across ,gaps3--,electrical dis*>ges across a giv5 di/ance occur at l[] pot5tials if ! dis*>ge be betwe5 po9ts ?an if betwe5 smoo? surfaces4 ,arre/]s1 !re=e1 are provid$ ) po9ts4 ,fig4 #bjc %[s a device kn[n z a saw-too? arre/] because ( its metal plates be+ provid$ ) tee?4 ,su* an arre/] br+s a gr\nd connection close to plates connect$ ) ! l9e & is adapt$ to protect app>atus ei!r connect$ across a metallic circuit or 9 s]ies ) a s+le wire circuit4 ,fig4 #bja %[s ano!r =m ( metal plate air-gap arre/] hav+ ! fur!r possibility ( a dis*>ge tak+ place f "o l9e wire to ! o!r4 ,ins]t+ a plug 9 ! hole betwe5 ! two l9e plates connects ! l9e wires directly toge!r at ! arre/]4 ,?is practice 0 design$ = use ) s]ies l9es1 ! plug %ort-circuit+ ! telephone set :5 9 place4 ,a defect ( mo/ ord9>y types ( metal air-gap lightn+ arre/]s is t heavy dis*>ges t5d to melt ! tee? or edges ( ! plates & (t5 to weld !m toge!r1 requir+ special att5tion to re-e/abli% ! necess>y gap4 ,advantages ( ,c>bon3--,solid c>bon is f\nd to be a mu* bett] mat]ial ?an metal = ! reasons t a dis*>ge w n melt x & t its surface is compos$ ( multitudes ( po9ts f :i* dis*>ges take place m readily ?an f metals4 ,illu/ration ,fig4 #bjd4 ,saw-,too? ,arre/] ,illu/ration ,fig4 #bje4 ,c>bon ,block ,arre/] ,c>bon arre/]s n[ are widely us$ 9 ! g5]al =m %[n 9 ,fig4 #bje4 ,a c>bon block connect$ ) a wire ( ! l9e is sep>at$ f a c>bon block connect$ to gr\nd by "s =m ( insulat+ sep>ator4 ,mica is widely us$ z su* a sep>ator1 & holes ( "s =m 9 a mica slip enable ! dis*>ge to /rike freely f block to block1 :ile prev5t+ ! blocks f t\*+ ea* o!r4 ,celluloid ) _m holes is us$ z a sep>ator betwe5 c>bon blocks4 ,silk & v>i\s special compositions also h _! uses4 ,illu/ration ,fig4 #bjf4 ,arre/] ,sep>ators ,du/ ,betwe5 ,c>bons3--,dis*>ges betwe5 ! c>bon blocks t5d to ?r[ (f p>ticles ( c>bon f !m4 ,! sep>ation betwe5 ! blocks be+ small--f 4#jje to 4#jae in*--! c>bon p>ticles may lodge 9 ! air-gap1 on ! edges ( ! sep>ator1 or o!rwise1 s z to leave a conduct+ pa? betwe5 ! two blocks4 ,slight moi/ure on ! sep>ator may help to collect ?is du/1 ?us plac+ a gr\nd on t wire ( ! l9e4 ,?is gr\nd may be ( v high resi/ance1 b is probably "o ( _m su*--"o at ea* arre/] connect$ to ! l9e4 ,9 special =ms ( c>bon arre/]s an attempt has be5 made to limit ?is dang] ( gr\nd+ by ! deposit ( c>bon du/4 ,! object ( ! ,u-%ap$ sep>ator ( ,fig4 #bjf is to enable ! arre/] to be m\nt$ s t ?is op5+ 9 ! sep>ator is d[nw>d1 9 ! hope t loos5$ c>bon p>ticles may fall out ( ! space betwe5 ! blocks4 ,! deposit ( c>bon on ! inside edges ( ! ,u-%ap$ sep>ator (t5 is s f9e & cl+s s tightly z n to fall out4 ,! sep>ator projects beyond ! blocks s z to avoid ! collection ( c>bon on ! out] edges4 ,comm]cial ,types3--,fig4 #bjg is a comm]cial =m ( ! arrangem5t %[n 9 ,fig4 #bje & is "o ( ! _m =ms made by ! ,am]ican ,electric ,fuse ,company4 ,l9e wires are atta*$ to outside b9d+ po/s %[n 9 ! figure & ! gr\nd wire to ! metal b9d+ po/ at ! front4 ,! c>bon blocks ) _! sep>ator slide betwe5 clips & a gr\nd plate4 ,! air-gap is det]m9$ by ! ?ickness ( ! sep>ator betwe5 ! c>bon blocks4 ,illu/ration3 ,fig4 #bjg4 ,c>bon ,block ,arre/] ,illu/ration3 ,fig4 #bjh ,rob]ts ,self-,clean+ ,arre/] ,! ,rob]ts c>bon arre/] is design$ ) p>ticul> ref]5ce to ! disposal ( c>bon du/ & is t]m$ self-clean+ = t reason4 ,! arrangem5t ( c>bons & dielectric 9 ?is device is %[n 9 ,fig4 #bjh2 mica is cem5t$ to ! l9e c>bon & is l>ge en\gh to provide a project+ m>g9 all ar\nd4 ,! sp>k gap is n uni=m ov] ! entire surface ( ! block b is made w$ge-%ap$ by gr9d+ away ! l9e c>bon z %[n4 ,x is claim$ t a cont9u\s arc+ fills ! w$ge-%ap$ *amb] ) heat$ air or gas1 conv]t+ ! :ole ( ! space into a field ( l[ resi/ance to gr\nd1 & t ?is gas 9 exp&+ drives out e p>ticle ( c>bon t may be ?r[n (f4 ,x seems obvi\s t ! w$ge-%ap$ space (f]s great] fre$om = c>bon du/ to fall out ?an 9 ! case ( ! p>allel arrangem5t ( ! block faces4 ,an outdoor arre/] = metallic circuits1 design$ by ,f4,b4 ,cook1 is %[n 9 ,fig4 #bji4 ,! device is adapt$ to m\nt on a pole or else:]e & to be cov]$ by a protect+ cap4 ,! c>bons are l>ge & are sep>at$ by a special comp\nd int5d$ to assi/ ! self-clean+ feature4 ,! ?ree c>bons be+ gr\p$ toge!r z a unit1 ! device has ! ability to c>e = dis*>ges f "o t]m9al to ei!r ( ! o!rs direct1 )\t hav+ to pass ?r\gh two gaps4 ,9 ?is p>ticul>1 ! arrangem5t is ! same z t ( ,fig4 #bjd4 ,illu/ration3 ,fig4 #bji4 ,cook ,air-,gap ,arre/] ,a =m ( ,we/]n ,electric arre/] p>ticul>ly adapt$ = outside use on railway l9es is %[n ) its cov] 9 ,fig4 #baj4 ,illu/ration3 ,fig4 #baj4 ,we/]n ,electric ,air-,gap ,arre/] ,! ,kellogg ,company regul>ly equips its magneto telephones ) air-gap arre/]s ( ! type %[n 9 ,fig4 #baa4 ,! two l9e plates are semicircul> & ( metal4 ,! gr\nd plate is ( c>bon1 circul> 9 =m1 cov]+ bo? l9e plates ) a mica sep>ator4 ,?is is m\nt$ on ! back bo>d ( ! telephone & p]man5tly wir$ to ! l9e & gr\nd b9d+ po/s4 ,illu/ration3 ,,old ,,swit*bo>d ,,( ,,bell ,,ex*ange ,,s]v+ ,,*9at[n1 ,,san ,,francisco1 ,,cali=nia ,illu/ration3 ,fig4 #baa4 ,kellogg ,air-,gap ,arre/] ,vacuum ,arre/]s3--,all ( ! c>bon arre/]s s f> m5tion$ dep5d on ! dis*>ge tak+ place ?r\gh air4 ,a giv5 pressure w dis*>ge fur!r 9 a fairly good vacuum ?an 9 air4 ,! ,national ,electric ,specialty ,company m\nts ?ree conductors 9 a vacuum ( ! inc&esc5t lamp type1 ,fig4 #bab4 ,a great] sep>ation & less likelihood ( %ort-circuit+ c be provid$ 9 ?is way4 ,ei!r c>bon or metal plates are adapt$ = use 9 su* vacuum devices4 ,! plates may be fur!r ap>t = a giv5 dis*>ge pressure if ! surfaces are ( c>bon4 ,illu/ration3 ,fig4 #bab4 ,vacuum ,arre/] ,introduction ( ,imp$ance3--,x has be5 not$ t ! exi/5ce ( imp$ance t5ds to *oke back ! passage ( lightn+ dis*>ge ?r\gh a coil4 ,fig4 #bac sugge/s ! relation betwe5 su* an imp$ance & air-gap arre/]4 ,if ! coil %[n !re9 be consid]$ an arrangem5t ( conductors hav+ inductance1 x w be se5 t a favorable place = an air-gap arre/] is betwe5 t imp$ance & ! l9e4 ,?is fact is made kn[n 9 practice by frequ5t damage to arial cables by electricity br\ght into !m ov] long op5 wires1 ! dis*>ge tak+ place at ! fir/ turn or b5d 9 ! arial cable2 ?is dis*>ge (t5 damages bo? core & %ea?4 ,x is well to h su* b5ds z ne> ! end ( ! cable z possible1 & turns or goos5ecks at entrances to t]m9als h t advantage4 ,illu/ration3 ,fig4 #bac4 ,imp$ance & ,air-,gap ,?is same pr9ciple is utiliz$ 9 "s =ms ( arre/]s1 su* z ! "o %[n 9 ,fig4 #bad1 :i* provides an imp$ance ( its own directly 9 ! arre/] elem5t4 ,9 ?is device an insulat+ base c>ries a gr\nd$ c>bon rod & two imp$ance coils4 ,! imp$ance coils are w\nd on insulat+ rods1 :i* hold !m ne>1 b n t\*+1 ! gr\nd c>bon4 ,! coils are arrang$ s t !y may be turn$ :5 dis*>ges r\gh5 ! surfaces ( ! wires4 ,illu/ration3 ,fig4 #bad4 ,holtz]-,cabot ,arre/] ,metallic ,electrodes3--,copp] or o!r metal blocks ) r\gh5$ surfaces sep>at$ by an insulat+ slip may be sub/itut$ = ! c>bon blocks ( mo/ ( ! arre/]s previ\sly describ$4 ,metal blocks lack ! advantage ( c>bon 9 t ! latt] all[s dis*>ges at l[] pot5tials = a giv5 sep>ation1 b !y h ! advantage t a conduct+ du/ is n ?r[n (f f !m4 ,illu/ration3 ,fig4 #bae4 ,c>bon ,air-,gap ,arre/] ,provision ,aga9/ ,cont9u\s ,arc3--,= ! purpose ( %ort-circuit+ an arc1 a globule ( l[-melt+ alloy may be plac$ 9 "o c>bon block ( an arre/]4 ,?is feature is n ess5tial 9 an arre/] int5d$ solely to div]t lightn+ dis*>ges4 ,its purpose is to provide an imm$iate pa? to gr\nd if an arc aris+ f artificial electricity has be5 ma9ta9$ betwe5 ! blocks long en\gh to melt ! globule4 ,fig4 #bae is a plan & section ( ! ,we/]n ,electric ,company's arre/] us$ z ! high pot5tial elem5t 9 conjunction ) o!rs = abnormal curr5ts & sneak curr5ts2 ! latt] are curr5ts too small to op]ate air-gap arre/]s or sub/antial fuses4 ,protection ,aga9/ ,/rong ,curr5ts4 ,fuses4 ,a fuse is a metal conductor ( l[] c>ry+ capacity ?an ! circuit ) :i* x is 9 s]ies at ! "t x is requir$ to op]ate4 ,fuses 9 use 9 electrical circuits g5]ally are compos$ ( "s alloy ( lead1 :i* melts at a reasonably l[ temp]ature4 ,alloys ( lead h l[] conductivity ?an copp]4 ,a small copp] wire1 h[ev]1 may fuse at ! same volume ( curr5t z a l>g] lead alloy wire4 ,prop] ,functions3--,a fuse is n a good lightn+ arre/]4 ,z lightn+ damage is caus$ by curr5t & z x is curr5t :i* de/roys a fuse1 a lightn+ dis*>ge c op5 a circuit ov] :i* x passes by melt+ ! fuse metal4 ,b lightn+ may de/roy a fuse & at ! same dis*>ge de/roy app>atus 9 s]ies ) ! fuse4 ,!re are two reasons = ?is3 ,"o is t lightn+ dis*>ges act v quickly & may h de/roy$ app>atus be=e heat+ ! fuse en\gh to melt x2 ! o!r reason is t :5 a fuse is op]at$ ) en\gh curr5t ev5 to vaporize x1 ! vapor s]ves z a conduct+ pa? = an in/ant aft] be+ =m$4 ,?is conduct+ pa? may be ( high resi/ance & /ill all[ curr5ts to fl[ ?r\gh x1 because ( ! extremely high pressure ( ! lightn+ dis*>ge4 ,a compreh5sive protective sy/em may include fuses1 b x is n to be expect$ t !y always w arre/ lightn+ or ev5 assi/ o!r ?+s 9 arre/+ lightn+4 ,!y %\ld be consid]$ z ( no value = t purpose4 ,fur!rmore1 fuses are be/ adapt$ to be a "p ( a g5]al protective sy/em :5 !y d all t !y mu/ d 9 /opp+ abnormal curr5ts & yet )/& lightn+ dis*>ges :i* may pass ?r\gh !m4 ,o!r ?+s be+ equal1 t sy/em ( protection is be/ 9 :i* all lightn+ dis*>ges are arre/$ by gap arre/]s & 9 :i* no fuses ev] are op]at$ by lightn+ dis*>ges4 ,mica ,fuse3--,a conv5i5t & widely us$ =m ( fuse is t %[n 9 ,fig4 #baf4 ,a mica slip has metal t]m9als at its ends & a fuse wire jo9s ^! t]m9als4 ,! fuse is ins]t$ 9 ! circuit by clamp+ ! t]m9als "u screws or slid+ !m betwe5 clips z 9 ,figs4 #bag & #bah4 ,advantages ( ?is me?od ( fuse m\nt+ = protect+ circuits ne$+ small curr5ts are t ! fuse wire c be se51 ! fuses are readily replac$ :5 bl[n1 & _! m\nt+s may be made compact4 ,z elem5ts ( a compreh5sive protective sy/em1 h[ev]1 ! ord9>y types ( mica-slip fuses are objectionable because too %ort1 & because !y h no means ( _! own = ext+ui%+ an arc :i* may foll[ ! bl[+ ( ! fuses4 ,z protectors = use 9 di/ribut+ l[ pot5tial curr5ts f c5tral-(fice p[] plants !y are admirable4 ,by simple means1 !y may be made to ann\nce audibly or visibly t !y h op]at$4 ,illu/ration3 ,fig4 #baf4 ,mica ,slip ,fuse ,illu/ration3 ,fig4 #bag4 ,po/al ,type ,mica ,fuse ,illu/ration3 ,fig4 #bah4 ,we/]n ,union ,type ,mica ,fuse ,enclos$ ,fuses3--,if a fuse wire )9 an insulat+ tube be made to connect metal caps on t tube & ! space ar\nd ! tube be fill$ ) a non-conduct+ p[d]1 ! gases ( ! vaporiz$ fuse metal w be absorb$ m quickly ?an :5 =m$ )\t su* imb$d+ 9 a p[d]4 ,! fill+ ( su* a tubul> fuse also muffles ! explosion :i* occurs :5 ! fuse is vaporiz$4 ,illu/ration3 ,fig4 #bai4 ,pair ( ,enclos$ ,fuses ,fuses ( ! enclos$ type1 ) or )\t fill+1 are widely us$ 9 p[] circuits g5]ally & are recomm5d$ by fire insurance bodies4 ,fig4 #bai illu/rates an arre/] hav+ a fuse ( ! enclos$ type1 ?is example be+ t ( ! ,h4 ,w4 ,johns-,manville ,company4 ,illu/ration ,fig4 #bbj4 ,bank ( ,enclos$ ,fuses ,9 telephony x is frequ5tly necess>y to m\nt a l>ge numb] ( fuses or o!r protective devices toge!r 9 a re/rict$ space4 ,9 ,fig4 #bbj a gr\p ( ,we/]n ,electric tubul> fuses1 s m\nt$1 is %[n4 ,^! fuses h ord9>ily a c>ry+ capacity ( #f or #g amp]es4 ,x is n expect$ t ?is arre/] w bl[ because #f or #g amp]es ( abnormal curr5ts are fl[+ ?r\gh x & ! app>atus to be protect$4 ,:at is int5d$ is t ! fuse %all )/& lightn+ dis*>ges & :5 a =eign curr5t passes ?r\gh x1 o!r app>atus w increase t curr5t en\gh to bl[ ! fuse4 ,x w be notic$ t ! fuses ( ,fig4 #bbj are op5 at ! upp] end1 :i* is ! end connect$ to ! expos$ wire ( ! l9e ,! fuses are clos$ at ! l[] end1 :i* is ! end connect$ to ! app>atus4 ,:5 ! fuse bl[s1 its dis*>ge is some:at muffl$ by ! l9+ ( ! tube1 b en\gh explosion rema9s s t ! heat$ gases1 9 driv+ outw>d1 t5d to break ! arc :i* is e/abli%$ ?r\gh ! vaporiz$ metal4 ,a pair ( ,cook tubul> fuses 9 an individual m\nt+ is %[n 9 ,fig4 #bba4 ,fuses ( ?is type are n op5 at "o end l a gun1 b opportunity = ! heat$ gases to escape exi/s at ! caps4 ,! tubes are made ( wood1 ( lava1 or ( porcela94 ,fig4 #bbb is ano!r tubul> fuse1 ! section %[+ ! arrangem5t ( asbe/os l9+ :i* s]ves ! two purposes ( muffl+ ! s\nd ( ! dis*>ge & absorb+ & cool+ ! result+ gases4 ,illu/ration3 ,fig4 #bba4 ,pair ( ,wood5 ,tube ,fuses ,air-,gap vs4 ,fuse ,arre/]s4 ,x is hop$ t ! /ud5t grasps cle>ly ! di/9ction betwe5 ! purposes ( air-gap & fuse arre/]s4 ,! air-gap arre/] acts 9 response to high voltages1 ei!r ( lightn+ or ( high-t5sion p[] circuits4 ,! fuse acts 9 response to a c]ta9 curr5t value fl[+ ?r\gh x & ?is m9imum curr5t 9 well-design$ protectors = telephone l9es is n v small4 ,usually x is sev]al times l>g] ?an ! maximum curr5t app>atus 9 ! l9e c safely c>ry4 ,fuses c be made s delicate z to op]ate on ! v smalle/ curr5t :i* c\ld injure app>atus & ! e>li] protective sy/ems dep5d$ on su* an arrangem5t4 ,! difficulty ) su* delicate fuses is t !y are n robu/ en\gh to be reliable1 &1 worse /ill1 !y *ange _! c>ry+ capacity ) age & are n uni=m 9 op]ation 9 diff]5t surr\nd+s & at diff]5t temp]atures4 ,!y are also s5sitive to lightn+ dis*>ges1 :i* !y h no p[] to /op or to div]t4 ,protection ,aga9/ ,sneak ,curr5ts4 ,= ^! reasons1 a sy/em conta9+ fuses & air-gap arre/]s only1 does n protect aga9/ abnormal curr5ts :i* are cont9u\s & small1 ?\gh l>ge en\gh to injure app>atus because cont9u\s4 ,^! curr5ts h come to be kn[n z sneak curr5ts1 a t]m m descriptive ?an elegant4 ,sneak curr5ts ?\gh small1 may1 :5 all[$ to fl[ = a long "t ?r\gh ! w9d+ ( an electromagnet = in/ance1 develop en\gh heat to *> or injure ! insulation4 ,!y are ! m dang]\s because insidi\s4 ,illu/ration3 ,fig4 #bbb4 ,tubul> ,fuse ) ,asbe/os ,fill+ ,sneak-,curr5t ,arre/]s4 ,z typical ( sneak-curr5t arre/]s1 ,fig4 #bbc %[s ! pr9ciple1 ?\gh n ! exact =m1 ( an arre/] once widely us$ 9 telephone & signal l9es4 ,! normal pa? f ! l9e to ! app>atus is ?r\gh a small coil ( f9e wire imb$d$ 9 seal+ wax4 ,a spr+ =ms a bran* pa? f ! l9e & has a t5sion :i* w\ld cause x to be> aga9/ ! gr\nd contact if x 7 all[$ to d s4 ,x is prev5t$ f t\*+ t contact normally by a /r+ betwe5 itself & a rigid support4 ,! /r+ is cut at its middle & ! knott$ ends z ?us cut are imb$d$ 9 ! seal+ wax :i* conta9s ! coil4 ,illu/ration3 ,fig4 #bbc4 ,pr9ciple ( ,sneak-,curr5t ,arre/] ,a small curr5t ?r\gh ! little coil w w>m ! wax en\gh to all[ ! /r+ to "p4 ,! spr+ !n w gr\nd ! l9e4 ,ev5 s simple an app>atus z ?is op]ates ) consid]able accuracy4 ,all curr5ts bel[ a c]ta9 critical am\nt may fl[ ?r\gh ! heat+ coil indef9itely1 ! heat be+ radiat$ rapidly en\gh to keep ! wax f s(t5+ & ! /r+ f p>t+4 ,all curr5ts above ?is critical am\nt w op]ate ! arre/]2 ! l>g] ! curr5t1 ! %ort] ! "t ( op]at+4 ,x w be rememb]$ t ! law ( ^! heat+ effects is t ! heat g5]at$ ,c#b,rt1 s t if a c]ta9 curr5t op]ates ! arre/] 91 say #dj seconds1 twice z great a curr5t %\ld op]ate ! arre/] 9 #aj seconds4 ,9 o!r words1 ! "t ( op]ation v>ies inv]sely z ! squ>e ( ! curr5t & inv]sely z ! resi/ance4 ,to make ! arre/] m s5sitive = a giv5 curr5t--i4e41 to op]ate 9 a %ort] "t--"o w\ld increase ! resi/ance ( ! coil 9 ! wax ei!r by us+ m turns or f9] wire1 or by mak+ ! wire ( a metal hav+ high] specific resi/ance4 ,! pres5t /&>d sneak-curr5t arre/] embodies ! two elem5ts ( ! devices ( ,fig4 #bbc3 a resi/ance mat]ial to trans=m ! dang]\s sneak curr5t into localiz$ heat2 & a fusible mat]ial s(t5$ by ?is heat to release "s swit*+ me*anism4 ,! resi/ance mat]ial is ei!r a resi/ance wire or a bit ( c>bon1 ! latt] be+ ! bett] mat]ial1 al?\gh bo? are good4 ,! fusible mat]ial is "s alloy melt+ at a l[ temp]ature4 ,lead1 t91 bismu?1 & cadmium c be comb9$ 9 su* proportions z w enable ! alloy to melt at temp]atures f #adj to #ahj ,f4 ,su* an alloy is a sold] :i*1 at ord9>y temp]atures1 is firm en\gh to resi/ ! =ce ( p[]ful spr+s2 yet x w melt s z to be entirely fluid at a temp]ature mu* less ?an t ( boil+ wat]4 ,illu/ration3 ,fig4 #bbd4 ,heat ,coil ,heat ,coil4 ,fig4 #bbd %[s a practical way ( br++ ! heat+ & to-be-heat$ elem5ts toge!r4 ,a copp] spool is w\nd ) resi/ance wire4 ,a metal p9 is sold]$ 9 ! bore ( ! spool by an easily melt+ alloy4 ,:5 curr5t heats ! spool en\gh1 ! p9 may slide or turn 9 ! spool4 ,x may slide or turn 9 _m ways & ?is happily enables _m types ( arre/]s to result4 ,= example1 ! p9 may pull out1 or pu% 91 or pu% ?r\gh1 or rotate l a %aft 9 a be>+1 or ! spool may turn on x l a hub on an axle4 ,messrs4 ,hayes1 ,rolfe1 ,cook1 ,mc,berty1 ,kaisl+1 & _m o!r inv5tors h utiliz$ ^! comb9ations & motions 9 ! production ( sneak-curr5t arre/]s4 ,all ( !m dep5d on "o action3 ! s(t5+ ( a l[-melt+ alloy by heat g5]at$ 9 a resi/ance4 ,:5 a heat coil is associat$ ) ! prop] swit*+ spr+s1 x becomes a sneak-curr5t arre/]4 ,! swit*+ spr+s always are arrang$ to gr\nd ! l9e wire4 ,9 "s arre/]s1 ! l9e wire is cut (f f ! wire lead+ t[>d ! app>atus by ! same movem5t :i* gr\nds x4 ,9 o!rs1 ! l9e is n brok5 at all1 b m]ely gr\nd$4 ,ea* me?od has its advantages4 ,complete ,l9e ,protection4 ,fig4 #bbe %[s ! entire s*eme ( protectors 9 an expos$ l9e & _! relation to app>atus 9 ! c5tral-(fice equipm5t & at ! subscrib]'s telephone4 ,! c5tral-(fice equipm5t conta9s heat coils1 spr+s1 & c>bon arre/]s4 ,at "s po9t betwe5 ! c5tral (fice & ! subscrib]'s premises1 ea* wire conta9s a fuse4 ,at ! subscrib]'s premises ea* wire conta9s o!r fuses & ^! are associat$ ) c>bon arre/]s4 ,! figure %[s a c5tral batt]y equipm5t1 9 :i* ! r+] ( ! telephone is 9 s]ies ) a cond5s]4 ,a sneak-curr5t arre/] is n requir$ at ! subscrib]'s /ation ) su* equipm5t4 ,assume ! l9e to meet an electrical haz>d at ! po9t ,x4 ,if ?is be lightn+1 x w dis*>ge to gr\nd at ! c5tral (fice or at ! subscrib]'s in/rum5t or at bo? ?r\gh ! c>bon arre/]s connect$ to t side ( ! l9e4 ,if x be a high pot5tial f a p[] circuit & ( m ?an #cej volts1 x w /rike an arc at ! c>bon arre/] connect$ to t wire ( ! l9e 9 ! c5tral (fice or at ! subscrib]'s telephone or at bo?1 if ! sep>ation ( ! c>bons 9 ^? arre/]s is 4#jje in* or less4 ,if ! c>bon arre/]s are sep>at$ by celluloid1 x w burn away & all[ ! c>bons to come toge!r1 ext+ui%+ ! arc4 ,if !y are sep>at$ by mica & "o ( ! c>bons is equipp$ ) a globule ( l[-melt+ alloy1 ! heat ( ! arc w melt ?is1 %ort-circuit+ ! gap & ext+ui%+ ! arc4 ,! passage ( curr5t to gr\nd at ! arre/]1 h[ev]1 w be ov] a pa? conta9+ no?+ b wire & ! arre/]4 ,! result+ curr5t1 !re=e1 may be v l>ge4 ,! voltage at ! arre/] hav+ be5 #cej volts or m1 9 ord] to e/abli% ! arc1 %ort-circuit+ ! gap w make ! curr5t #g amp]es or m1 unless ! appli$ voltage miracul\sly falls to #ej volts or less4 ,! curr5t ?r\gh ! fuse be+ m ?an #g amp]es1 x w bl[ promptly1 op5+ ! l9e & isolat+ ! app>atus4 ,x w be not$ t ?is explanation applies to equipm5t at ei!r end ( ! l9e1 z ! fuse lies betwe5 ! po9t ( contact & ! c>bon arre/]4 ,illu/ration3 ,fig4 #bbe4 ,complete ,l9e ,protection ,assume1 on ! o!r h&1 t ! contact is made at ! po9t ,y4 ,! c5tral-(fice c>bon arre/] w op]ate1 gr\nd+ ! l9e & increas+ ! am\nt ( curr5t fl[+4 ,!re be+ no fuse to bl[1 a worse ?+ w befall1 9 ! ov]heat+ ( ! l9e wire & ! probable />t+ ( a fire 9 ! c5tral (fice4 ,x is obvi\s1 !re=e1 t a fuse mu/ be locat$ betwe5 ! c>bon arre/] & any "p ( ! l9e :i* is subject to contact ) a pot5tial :i* c give an abnormal curr5t :5 ! c>bon arre/] acts4 ,assume1 z a ?ird case1 t ! contact at ! po9t ,x ei!r is ) a l[ =eign pot5tial or is s poor a contact t ! diff]5ce ( pot5tial across ! gap ( ! c>bon arre/] is l[] ?an its arc+ po9t4 ,curr5t w t5d to fl[ by ! c>bon arre/] )\t op]at+ x1 b su* a curr5t mu/ pass ?r\gh ! w9d+ ( ! heat coil if x is to ent] ! app>atus4 ,! sneak curr5t may be l>ge en\gh to ov]heat ! app>atus if all[$ to fl[ long en\gh1 b be=e x has fl[$ long en\gh x w h w>m$ ! heat-coil w9d+ en\gh to s(t5 its fusible alloy & to release spr+s :i* gr\nd ! l9e1 j z did ! c>bon arre/] 9 ! case la/ assum$4 ,aga9 ! curr5t w become l>ge & w bl[ ! fuse :i* lies betwe5 ! sneak-curr5t arre/] & ! po9t ( contact ) ! s\rce ( =eign curr5t4 ,9 ?is case1 also1 contact at ! po9t ,y w\ld h op]at$ me*anism to gr\nd ! l9e at ! c5tral (fice1 &1 no fuse int]pos+1 ! wir+ w\ld h be5 ov]heat$4 ,expos$ & ,unexpos$ ,wir+4 ,und]gr\nd cables1 cables =m$ ( rubb] insulat$ wires1 & int]ior wir+ :i* is prop]ly done1 all may be consid]$ to be wir+ :i* is unexpos$1 t is1 n expos$ to =eign high pot5tials1 dis*>ges1 sneak1 or abnormal curr5ts4 ,all o!r wir+1 su* z b>e wires1 arial cables1 etc41 %\ld be consid]$ z expos$ to su* haz>ds & a fuse %\ld exi/ 9 ea* wire betwe5 its expos$ portion & ! c5tral (fice or subscrib]'s in/rum5t4 ,! rule ( action1 !re=e1 becomes3 ,! prop] position ( ! fuse is betwe5 expos$ & unexpos$ wir+4 ,x may appe> to ! /ud5t t wires 9 an arial cable ) a lead %ea?--t %ea? be+ ei!r gr\nd$ or ungr\nd$--are n expos$ to electrical haz>ds2 9 ! case ( ! gr\nd$ %ea?1 ?is w\ld presume t a contact betwe5 ! cable & a high pot5tial wire w\ld result m]ely 9 ! =eign curr5ts go+ to gr\nd ?r\gh ! cable %ea?1 ! arc burn+ (f ! high-pot5tial wire & all[+ ! contact to cle> itself by ! fall+ ( ! wire4 ,if ! assumption be t ! %ea? is n gr\nd$1 !n ! /ud5t may say t no curr5t at all w\ld fl[ f ! high-pot5tial wire4 ,bo? assumptions are wrong4 ,9 ! case ( ! gr\nd$ %ea?1 ! curr5t fl[s to x at ! contact ) ! high-pot5tial wire2 ! lead %ea? is melt$1 arcs /rike to ! wires )91 & curr5ts are l$ directly to ! c5tral (fice & to subscrib]s' premises4 ,9 ! case ( ! ungr\nd$ %ea?1 ! latt] *>ges at once ?r\gh all its l5g? to ! voltage ( ! high-pot5tial wire2 at "s po9t1 a wire )9 ! cable is close en\gh to ! %ea? = an arc to /rike across1 & ! tr\ble beg9s4 ,all ! wires 9 ! cable are endang]$ if ! cross be ) a wire ( ! prim>y circuit ( a high-t5sion transmission l9e4 ,any s]ies arc-light circuit is a high-pot5tial m5ace4 ,ev5 a #dej-volt trolley wire or fe$] c burn a lead-cov]$ cable entirely 9 two 9 a few seconds4 ,! au?ors h se5 ?is done by ! wayw>d trolley pole ( a /reet c>1 "o side ( ! pole t\*+ ! trolley wire & ! extreme end j t\*+ ! telephone cable4 ,! answ] lies 9 ! =ego+ rule4 ,place ! fuse betwe5 ! wires :i* c & ! wires :i* c n get into contact ) high pot5tials4 ,9 application1 ! rule has "s flexibility4 ,9 ! case ( a cable :i* is arial z soon z x leaves ! c5tral (fice1 place ! fuses 9 ! c5tral (fice2 9 a cable :olly und]gr\nd1 f c5tral (fice to subscrib]--z1 = example1 ! fe$ = an (fice build+--use no fuses at all2 9 a cable :i* leaves ! c5tral (fice und]gr\nd & becomes arial1 fuse ! wires j :]e !y *ange f und]gr\nd to arial4 ,! sev]al bran*es ( an und]gr\nd cable into arial ones %\ld be fus$ z !y bran*4 ,wires prop]ly in/all$ 9 subscrib]s' premises are consid]$ unexpos$4 ,! position ( ! fuse ?us is at or ne> ! po9t ( entrance ( ! wires into t build+ if ! wires ( ! subscrib]'s l9e outside ! premises are expos$1 z det]m9$ by ! def9itions giv54 ,if ! l9e is unexpos$1 by ^? def9itions1 no protector is requir$4 ,if "o is indicat$1 x %\ld be us$1 z compliance ) ! be/-kn[n practice is a cle> duty4 ,less ?an :at is kn[n to be be/ is n hone/ practice 9 a matt] :i* involves life1 limb1 & indef9ite degrees ( prop]ty values4 ,protectors 9 c5tral-batt]y subscrib]s' equipm5ts ne$ no sneak-curr5t arre/]s1 z ! cond5s] r$uces t haz>d to a negligible am\nt4 ,magneto subscrib]s' equipm5ts usually lack cond5s]s 9 r+] circuits1 ?\gh !y may h !m 9 talk+ circuits on p>ty l9es4 ,! r+] circuit is ! only pa? ?r\gh ! telephone set = ab\t #ih p] c5t ( ! "t4 ,sneak-curr5t arre/]s1 !re=e1 %\ld be a "p ( subscrib]s' /ation protectors 9 magneto equipm5t1 except 9 su* rural di/ricts z may h no light+ or p[] wires4 ,:5 sneak-curr5t arre/]s are s us$ ! arrangem5t ( ! p>ts !n is ! same z 9 ! c5tral-(fice portion ( ,fig4 #bbe4 ,types ( ,c5tral-,(fice ,protectors4 ,a =m ( comb9$ heat coil & air-gap arre/]1 widely us$ by ,bell companies = c5tral-(fice protection1 is %[n 9 ,fig4 #bbf4 ,! two inn] spr+s =m ! t]m9als = ! two limbs ( ! metallic-circuit l9e1 :ile ! two outside spr+s are t]m9als = ! cont9uation ( ! l9e lead+ to ! swit*bo>d4 ,! heat coils1 "o on ea* side1 are support$ betwe5 ! inn] & out] spr+s4 ,high-t5sion curr5ts jump to gr\nd ?r\gh ! air-gap arre/]1 :ile sneak curr5ts p]mit ! p9 ( ! heat coil to slide )9 ! sleeve1 ?us gr\nd+ ! outside l9e & ! l9e to ! swit*bo>d4 ,illu/ration3 ,fig4 #bbf4 ,sneak-,curr5t & ,air-,gap ,arre/] ,self-,sold]+ ,heat ,coils4 ,ano!r =m design$ by ,kaisl+ & manufactur$ by ! ,am]ican ,electric ,fuse ,company is %[n 9 ,fig4 #bbg4 ,9 ?is ! p9 9 ! heat coil projects unequally f ! ends ( ! coil1 & "u ! action ( a sneak curr5t ! melt+ ( ! sold] :i* holds x all[s ! out] spr+ to pu% ! p9 ?r\gh ! coil until x presses ! l9e spr+ aga9/ ! gr\nd plate & at ! same "t op5s ! pa? to ! swit*bo>d4 ,:5 ! heat-coil p9 assumes ?is new position x cools (f1 due to ! cessation ( ! curr5t1 & resold]s itself1 & ne$ only be turn$ end = end by ! att5dant to be reset4 ,_m are ! v>iations t h be5 made on ?is self-sold]+ idea1 & !re has be5 mu* controv]sy z to its desirability4 ,x is c]ta9ly a feature ( conv5i5ce4 ,illu/ration3 ,fig4 #bbg4 ,self-,sold]+ ,heat-,coil ,arre/] ,in/ead ( us+ a wire-w\nd resi/ance elem5t 9 heat-coil con/ruction "s manufactur]s employ a mass ( high-resi/ance mat]ial1 int]pos$ 9 ! pa? ( ! curr5t4 ,! ,kellogg ,company has long employ$ = its sneak-curr5t arre/] a %ort graphite rod1 :i* =ms ! resi/ance elem5t4 ,! ends ( ?is rod are electroplat$ ) copp] to :i* ! brass t]m9al heads are sold]$4 ,^! heads af=d means = mak+ ! connection ) ! prop] reta9+ spr+s4 ,illu/ration3 ,fig4 #bbh4 ,cook ,arre/] ,ano!r c5tral-(fice protector1 :i* uses a mass ( special metal composition = its heat produc+ elem5t is t design$ by ,frank ,b4 ,cook & %[n 9 ,fig4 #bbh4 ,9 ?is ! c>bon blocks are cyl9drical 9 =m & specially treat$ to make !m self-clean+4 ,in/ead ( employ+ a self-sold]+ feature 9 ! sneak-curr5t arre/] ( ?is device1 ,cook provides = electrically resold]+ !m aft] op]ation1 a clip be+ design$ = hold+ ! elem5ts 9 prop] position & pass+ a batt]y curr5t ?r\gh !m to remelt ! sold]4 ,9 small magneto ex*anges x is n uncommon to employ comb9$ fuse & air-gap arre/]s = c5tral-(fice l9e protection1 ! fuses be+ ( ! mica-m\nt$ type already ref]r$ to4 ,a gr\p ( su* arre/]s1 z manufactur$ by ! ,dean ,electric ,company1 is %[n 9 ,fig4 #bbi4 ,illu/ration3 ,fig4 #bbi4 ,mica ,fuse & ,air-,gap ,arre/]s ,types ( ,subscrib]s' ,/ation ,protectors4 ,figs4 #bcj & #bca %[ types ( subscrib]s' /ation protectors adapt$ to ! requirem5ts ( c5tral-batt]y & magneto sy/ems4 ,^!1 z has be5 said1 %\ld be m\nt$ at or ne> ! po9t ( entrance ( ! subscrib]'s l9e into ! premises1 if ! l9e is expos$ outside ( ! premises4 ,x is possible to arrange ! fuses s t !y w be safe & suitable = _! purposes if !y are m\nt$ out-(-doors ne> ! po9t ( entrance to ! premises4 ,! sneak-curr5t arre/]1 if "o exi/s1 & ! c>bon arre/] also1 mu/ be m\nt$ inside ( ! premises or 9 a protect+ case1 if outside1 on acc\nt ( ! necessity ( %ield+ bo? ( ^! devices f ! wea!r4 ,speak+ g5]ally1 ! wid] practice is to put all ! elem5ts ( ! subscrib]'s /ation protector inside ( ! h\se4 ,x is ne>] to ! ideal arrangem5t ( conditions if ! protector be plac$ imm$iately at ! po9t ( entrance ( ! outside wires into ! build+4 ,illu/ration3 ,fig4 #bcj4 ,we/]n ,electric ,/ation ,arre/] ,illu/ration3 ,fig4 #bca4 ,cook ,arre/] = ,magneto ,/ations ,ribbon ,fuses4 ,a po9t ( int]e/ ) relation to tubul> fuses is t 9 "s ( ! be/ types ( su* fuses1 ! resi/ance mat]ial is n 9 ! =m ( a r\nd wire b 9 ! =m ( a flat ribbon4 ,?is arrangem5t disposes ! necess>y am\nt ( fusible metal 9 a =m to give ! greate/ am\nt ( surface1 :ile a r\nd wire (f]s ! lea/ surface = a giv5 weight ( metal--a circle encloses its area ) less p]iph]y ?an any o!r figure4 ,! reason = giv+ ! fuse ! l>ge/ possible surface area is to decrease ! likelihood ( ! fuse be+ ruptur$ by lightn+4 ,! fact t su* fuses d )/& lightn+ dis*>ges mu* m ?or\ghly ?an r\nd fuses ( ! same rat+ is an int]e/+ pro( ( ! oscillat+ nature ( lightn+ dis*>ges1 = ! d5sity ( ! curr5t ( ^? dis*>ges is great] on & ne> ! surface ( ! conductor ?an )9 ! metal &1 !re=e1 flatt5+ ! fuse increases its c>ry+ capacity = high-frequ5cy curr5ts1 )\t appreciably *ang+ its c>ry+ capacity = direct curr5ts4 ,! reason its capacity = direct curr5ts is increas$ at all by flatt5+ x1 is t ! surface = ! radiation ( heat is increas$4 ,h[ev]1 :5 enclos$ 9 a tube1 radiation ( heat is limit$1 s t = direct curr5ts ! c>ry+ capacity ( fuses v>ies closely ) ! area ( cross-section4 ,city-,ex*ange ,requirem5ts4 ,! =ego+ has set d[n ! requirem5ts ( good practice 9 an av]age city-ex*ange sy/em4 ,no?+ %ort ( ! g5]al arrangem5t %[n 9 ,fig4 #bbe meets ! usual assortm5t ( haz>ds ( su* an ex*ange4 ,x is good mod]n practice to di/ribute l9es by means ( cables1 supplem5t$ 9 "p by %ort insulat$ drop wires twi/$ 9 pairs4 ,abs5ce ( b>e wires r$uces electrical haz>ds enorm\sly4 ,nev]!less1 haz>ds rema94 ,?\gh no less ?an ! _s ( ?is plan ( protection %\ld be foll[$1 additional haz>ds may exi/1 :i* may require additional elem5ts ( protection4 ,at ! end ( a cable1 ei!r arial or und]gr\nd1 long op5 wires may ext5d into ! op5 c\ntry z rural or long-di/ance circuits4 ,if ^! be long] ?an a mile or two1 9 mo/ regions !y w be subject$ to lightn+ dis*>ges4 ,^! may be subject$ to high-pot5tial contacts z well4 ,if a specific case ( su* exposure indicates t ! cables may be 9 dang]1 ! long op5 l9es !n are equipp$ ) additional air-gap arre/]s at ! po9t ( junction ( ^? op5 l9es ) ! cable4 ,practice v>ies z to ! type4 ,ma9t5ance *>ges are increas$ if c>bon arre/]s sep>at$ 4#jje in* are us$1 because ( ! co/ ( s5d+ to ! end ( ! long cable to cle> ! blocks f c>bon du/ aft] ea* slight dis*>ge4 ,r\gh5$ metal blocks d n become gr\nd$ z readily z d c>bon blocks4 ,! occasions ( visit to ! arre/]s1 !re=e1 usually foll[ actual heavy dis*>ges ?r\gh !m4 ,! recomm5dations & ! practice ( ! ,am]ican ,telephone & ,telegraph ,company diff] on ?is po9t1 :ile ! practice ( o!r companies v>ies ) ! temp]am5ts ( ! eng9e]s4 ,! ,am]ican ,company specifies copp]-block arre/]s :]e long c\ntry l9es ent] cables1 if ^? l9es are expos$ to lightn+ dis*>ges only4 ,! expos$ l9e is call$ long if m ?an "o-half mile 9 l5g?4 ,if x is expos$ to high-pot5tial haz>ds1 c>bon blocks are specifi$ in/ead ( copp]4 ,o!r specifications ( t company h call$ = ! use ( copp]-block arre/]s on l9es expos$ to haz>ds above #b1ejj volts4 ,illu/ration3 ,,"o ,,( ,,! ,,f\r ,,w+s ,,( ,,! ,,old ,,kellogg ,,divid$ ,,multiple ,,bo>d ,,( ,,! ,,cuyahoga ,,telephone ,,company1 ,,clevel&1 ,,ohio ,ultimate ,capacity1 #bd1jjj ,l9es4 ,"o ( ! ,two ,examples 9 ! ,unit$ ,/ates ( a ,multiple ,swit*bo>d ,hav+ an ,ultimate ,capacity ov] #ah1jjj ,l9es4 ,replac$ ,rec5tly by a ,kellogg ,/raight ,multiple ,bo>d ,hav+ an ,ultimate ,capacity ( #ah1jjj ,l9es & a ,pres5t ,capacity ( #aj1jjj ,l9es4 ,! fre$om ( metal-block arre/]s f du/ tr\bles gives !m a l>ge economical advantage ov] c>bon4 ,= simil> sep>ations1 ! ratio ( /rik+ voltages betwe5 c>bon blocks & metal blocks respectively is z #g to #af4 ,9 c]ta9 regions ( ! ,pacific ,coa/ :]e ! lightn+ haz>d is negligible & ! high t5sion haz>d is great1 metal-block arre/]s at ! out] ends ( cables give acceptable protection4 ,high w9ds :i* drive sn[ or du/ aga9/ b>e wires ( a long l9e1 create ^u or place ^u ^? wires a *>ge ( /atic electricity :i* makes its way f ! l9e 9 su* ways z x c4 ,usually x dis*>ges across arre/]s & :5 ?is dis*>ge takes place1 ! l9e is di/urb$ 9 its balance & l\d noises are he>d 9 ! telephones ^u x4 ,fig4 #bcb4 ,dra9age ,coils ,a telephone l9e :i* = a long di/ance is ne> a high-t5sion transmission l9e may h electro/atic or electromagnetic pot5tials1 or bo?1 induc$ ^u x4 ,if ! l9e be balanc$ 9 its prop]ties1 includ+ balance by transposition ( its wires1 ! electro/atic induction may neutralize itself4 ,! electromagnetic induction /ill may di/urb x4 ,dra9age ,coils4 ,! device %[n 9 ,fig4 #bcb1 :i* am\nts m]ely to an inductive leak to e>?1 is int5d$ to cure bo? ! sn[/orm & electromagnetic induction difficulties4 ,x is requir$ t its imp$ance be high en\gh to keep voice-curr5t losses l[1 :ile be+ l[ en\gh to dra9 ! l9e effectively ( ! di/urb+ *>ges4 ,su* devices are t]m$ dra9age coils4 ,electrolysis4 ,! means ( protection aga9/ ! dang] due to *emical action1 set =? 9 ! prec$+ *apt]1 =m su* a di/9ct phase ( ! subject ( gu>d+ prop]ty aga9/ electrical haz>ds z to w>rant treatm5t 9 a sep>ate *apt] devot$ to ! subject ( electrolysis4 ,illu/ration3 ,,ma9 ,,ex*ange1 ,,clevel&1 ,,ohio4 ,l>ge/ ,f\r-,p>ty ,selective ,r++ ,swit*bo>d 9 ! ,_w4 ,kellogg ,swit*bo>d & ,supply ,co4 ,,*apt] ,,xx ,,g5]al ,,features ,,( ,,! ,,telephone ,,ex*ange ,up to ?is po9t only ^? classes ( telephone s]vice :i* c\ld be giv5 betwe5 two or m /ations on a s+le l9e h be5 consid]$4 ,v soon aft] ! practical conception ( ! telephone1 came ! conception ( ! telephone ex*ange2 t is1 ! conception ( c5t]+ a numb] ( l9es at a common po9t & !re t]m9at+ !m 9 app>atus to facilitate _! int]connection1 s t any subscrib] on any l9e c\ld talk ) any subscrib] on any o!r l9e4 ,! complete equipm5t ( l9es1 telephone in/rum5ts1 & swit*+ facilities by :i* ! telephone /ations ( ! community are giv5 telephone s]vice is call$ a telephone ex*ange4 ,! build+ :]e a gr\p ( telephone l9es c5t] = int]connection is call$ a c5tral (fice1 & its telephonic equipm5t ! c5tral-(fice equipm5t4 ,! t]ms telephone (fice & telephone ex*ange are frequ5tly confus$4 ,al?\gh a telephone (fice build+ may be prop]ly ref]r$ to z a telephone ex*ange build+1 x is h>dly prop] to ref] to ! telephone (fice z a telephone ex*ange1 z is frequ5tly done4 ,9 mod]n p>lance ! telephone ex*ange ref]s n only to ! c5tral (fice & its equipm5t b to ! l9es & in/rum5ts connect$ !re) z well2 fur!rmore1 a telephone ex*ange may embrace a numb] ( telephone (fices t are int]connect$ by means ( s-call$ trunk l9es = p]mitt+ ! communication ( subscrib]s ^: l9es t]m9ate 9 "o (fice ) ^? subscrib]s ^: l9es t]m9ate 9 any o!r (fice4 ,s9ce a giv5 telephone ex*ange may conta9 "o or m c5tral (fices1 x is prop] to di/+ui% betwe5 !m by ref]r+ to an ex*ange :i* conta9s b a s+le c5tral (fice z a s+le (fice ex*ange1 & to an ex*ange :i* conta9s a plurality ( c5tral (fices z a multi-(fice ex*ange4 ,9 telephone ex*ange work+1 ?ree classes ( l9es are dealt )--subscrib]s' l9es1 trunk l9es1 & toll l9es4 ,subscrib]s' ,l9es4 ,! t]m subscrib] is commonly appli$ to ! patron ( ! telephone s]vice4 ,8 /ation is1 !re=e1 ref]r$ to z a subscrib]'s /ation1 & ! telephone equipm5t at any subscrib]'s /ation is ref]r$ to z a subscrib]'s /ation equipm5t4 ,likewise1 a l9e lead+ f a c5tral (fice to "o or m subscrib]s' /ations is call$ a subscrib]'s l9e4 ,a subscrib]'s l9e may1 z has be5 %[n 9 a previ\s *apt]1 be an individual l9e if x s]ves b "o /ation1 or a p>ty l9e if x s]ves to connect m ?an "o /ation ) ! c5tral (fice4 ,trunk ,l9es4 ,a trunk l9e is a l9e :i* is n devot$ to ! s]vice ( any p>ticul> subscrib]1 b :i* may =m a connect+ l9k betwe5 any "o ( a gr\p ( subscrib]s' l9es :i* t]m9ate 9 "o place & any "o ( a gr\p ( subscrib]s' l9es :i* t]m9ate 9 ano!r place4 ,if ! two gr\ps ( subscrib]s' l9es t]m9ate 9 ! same build+ or 9 ! same swit*bo>d1 s t ! trunk l9e =m+ ! connect+ l9k betwe5 !m is entirely )9 ! c5tral-(fice build+1 x is call$ a local trunk l9e1 or a local trunk4 ,if1 on ! o!r h&1 ! trunk l9e is = connect+ gr\ps ( subscrib]s' l9es :i* t]m9ate 9 diff]5t c5tral (fices1 x is call$ an int]-(fice trunk4 ,toll ,l9es4 ,a toll l9e is a telephone l9e = ! use ( :i* a special fee or toll is *>g$2 t is1 a fee t is n includ$ 9 ! *>ges made to ! subscrib] = 8 regul> local ex*ange s]vice4 ,toll l9es ext5d f "o ex*ange di/rict to ano!r1 m or less remote1 & !y are commonly t]m$ local toll & long-di/ance toll l9es accord+ to ! degree ( remot5ess4 ,a toll l9e1 :e!r local or long-di/ance1 may be look$ ^u 9 ! nature ( an int]-ex*ange trunk4 ,di/ricts4 ,! di/rict 9 a giv5 community :i* is s]v$ by a s+le c5tral (fice is call$ an (fice di/rict4 ,likewise1 ! di/rict :i* is s]v$ by a complete ex*ange is call$ an ex*ange di/rict4 ,an ex*ange di/rict may1 !re=e1 consi/ ( a numb] ( c5tral-(fice di/ricts1 j z an ex*ange may comprise a numb] ( c5tral (fices4 ,to illu/rate1 ! entire area s]v$ by ! ex*ange ( ! ,*icago ,telephone ,company 9 ,*icago1 embrac+ ! entire city & "s ( its suburbs1 is ! ,*icago ex*ange di/rict4 ,! area s]v$ by "o ( ! c5tral (fices1 su* z ! ,hyde ,p>k (fice1 ! ,oakl& (fice1 ! ,h>rison (fice1 or any ( ! o!rs1 is an (fice di/rict4 ,swit*bo>ds4 ,! app>atus at ! c5tral (fice by :i* ! telephone l9es are connect$ = conv]sation & aft]w>ds disconnect$1 & by :i* ! v>i\s o!r functions necess>y to ! giv+ ( complete telephone s]vice are p]=m$1 is call$ a swit*bo>d4 ,?is may be simple 9 ! case ( small ex*anges1 or ( va/ complexity 9 ! case ( ! l>g] ex*anges4 ,sometimes ! swit*bo>ds are ( su* nature z to require ! pres5ce ( op]ators1 usually girls1 to connect & disconnect ! l9e & p]=m ! o!r necess>y functions1 & su* swit*bo>ds1 :e!r l>ge or small1 are t]m$ manual4 ,sometimes ! swit*bo>ds are ( su* a nature z n to require ! pres5ce ( op]ators1 ! v>i\s functions ( connection1 disconnection1 & signal+ be+ p]=m$ by ! aid ( special =ms ( app>atus :i* are "u ! control ( ! subscrib] :o makes ! call4 ,su* swit*bo>ds are t]m$ automatic4 ,( rec5t ye>s !re has appe>$ ano!r class ( swit*bo>ds1 employ+ 9 "s measure ! features ( ! automatic & 9 "s measure ^? ( ! manual swit*bo>d4 ,^! bo>ds are commonly ref]r$ to z semi-automatic swit*bo>ds1 presumably because !y are suppos$ to be half automatic & half manual4 ,manual4 ,manual swit*bo>ds may be subdivid$ into two classes accord+ to ! me?od ( di/ribut+ en]gy = talk+ purposes4 ,?us we may h magneto swit*bo>ds1 :i* are ^? capable ( s]v+ l9es equipp$ ) magneto telephones1 local batt]ies be+ us$ = talk+ purposes4 ,on ! o!r h&1 we may h common-batt]y swit*bo>ds1 adapt$ to connect l9es employ+ common-batt]y telephones 9 :i* all ! curr5t = bo? talk+ & signal+ is furni%$ f ! c5tral (fice4 ,9 /ill ano!r way we may classify manual swit*bo>ds if ! me?od ( di/ribut+ ! en]gy = talk+ & signal+ purposes is ignor$4 ,?us1 entirely irrespective ( :e!r ! swit*bo>ds are adapt$ to s]ve common-batt]y or local-batt]y l9es1 we may h non-multiple swit*bo>ds & multiple swit*bo>ds4 ,! t]m multiple swit*bo>d is appli$ to t class ( swit*bo>ds 9 :i* ! connection t]m9als or jacks = all ! l9es are repeat$ at int]vals along ! face ( ! swit*bo>d1 s t ea* op]ator may h )9 h] rea* a t]m9al = ea* l9e & may ?us be able to complete by h]self any connection betwe5 two l9es t]m9at+ 9 ! swit*bo>d4 ,! t]m non-multiple swit*bo>d is appli$ to t class ( bo>ds :]e ! provision = repeat+ ! l9e t]m9als at int]vals along ! face ( ! bo>d is n employ$1 b :]e1 z a consequ5ce1 ea* l9e has b a s+le t]m9al on ! face ( ! bo>d4 ,non-multiple swit*bo>ds h _! ma9 use 9 small ex*anges :]e n m ?an a few hundr$ l9es t]m9ate4 ,:]e su* is ! case1 x is an easy matt] to h&le all ! traffic by "o1 two1 or ?ree op]ators1 & z all ( ^! op]ators may rea* all ov] ! face ( ! swit*bo>d1 !re is no ne$ = giv+ any l9e any m ?an "o connection t]m9al4 ,su* bo>ds may be call$ simple swit*bo>ds4 ,!re is ano!r type ( non-multiple swit*bo>d adaptable = use 9 l>g] ex*anges ?an ! simple swit*bo>d4 ,a correct idea ( ! fundam5tal pr9ciple involv$ 9 ^! may be _h by imag9+ a r[ ( simple swit*bo>ds ea* conta9+ t]m9als or jacks = its own gr\p ( l9es4 ,9 ord] to provide = ! connection ( a l9e 9 "o ( ^! simple swit*bo>ds ) a l9e 9 ano!r "o1 out ( rea* ( ! op]ator at ! fir/1 %ort connect+ l9es ext5d+ betwe5 ! two swit*bo>ds are provid$1 ^! be+ call$ transf] or trunk l9es4 ,9 ord] t connections may be made betwe5 any two ( ! simple bo>ds1 a gr\p ( transf] l9es is run f ea* bo>d to e o!r "o4 ,9 su* swit*bo>ds an op]ator at "o ( ! bo>ds or positions may complete ! connection h]self betwe5 any two l9es t]m9at+ at h] own bo>d4 ,if1 h[ev]1 ! l9e call$ = t]m9ates at ano!r "o ( ! bo>ds1 ! op]ator makes use ( ! transf] or trunk l9e ext5d+ to t bo>d1 & ! op]ator at ?is latt] bo>d completes ! connection1 s t ! two subscrib]s' l9es are connect$ ?r\gh ! trunk or transf] l9e4 ,a di/+ui%+ feature1 !re=e1 9 ! op]ation ( s-call$ transf] swit*bo>ds1 is t an op]ator c n always complete a connection h]self1 ! connection frequ5tly requir+ ! att5tion ( two op]ators4 ,transf] sy/ems are n n[ l>gely us$1 ! multiple swit*bo>d hav+ almo/ entirely supplant$ !m 9 manual ex*anges ( su* size z to be beyond ! limitation ( ! simple swit*bo>d4 ,at multi-(fice manual ex*anges1 h[ev]1 :]e !re are a numb] ( multiple swit*bo>ds employ$ at v>i\s c5tral (fices1 ! same sort ( a requirem5t exi/s z t :i* 0 met by ! provision ( trunk l9es betwe5 ! v>i\s simple swit*bo>ds 9 a transf] sy/em4 ,obvi\sly1 ! l9es 9 "o c5tral (fice mu/ be connect$ to ^? ( ano!r 9 ord] to give univ]sal s]vice 9 ! community 9 :i* ! ex*ange op]ates4 ,= ?is purpose int]-(fice trunk l9es are us$1 ! arrangem5t be+ su* t :5 an op]ator at "o (fice receives a call = a subscrib] 9 ano!r (fice1 %e w proce$ to connect ! call+ subscrib]'s l9e1 n directly ) ! l9e ( ! call$ subscrib] because t p>ticul> l9e is n )9 h] rea*1 b r ) a trunk l9e lead+ to ! (fice 9 :i* ! call$-= subscrib]'s l9e t]m9ates2 hav+ done ?is %e w !n in=m an op]ator at t second (fice ( ! connection desir$1 usually by means ( a s-call$ ord]-wire circuit4 ,! connection betwe5 ! trunk l9e s us$ & ! l9e ( ! call$-= subscrib] w !n be complet$ by ! connect+ l9k or trunk l9e ext5d+ betwe5 ! two (fices4 ,9 su* cases ! multiple swit*bo>d at ea* (fice is divid$ into two portions1 t]m$ respectively ! ,a bo>d & ! ,b bo>d4 ,ea* ( ^! bo>ds1 ) ! exception t w be po9t$ out 9 a subsequ5t *apt]1 is provid$ ) a full complem5t ( multiple jacks = all ( ! l9es ent]+ t (fice4 ,at ! ,a bo>d are locat$ op]ators1 call$ ,a op]ators1 :o answ] all ! calls f ! subscrib]s ^: l9es t]m9ate 9 t (fice4 ,9 ! case ( calls = l9es 9 t same (fice1 !y complete ! connection !mselves )\t ! assi/ance ( ! o!r op]ators4 ,on ! o!r h&1 ! calls = l9es 9 ano!r (fice are h&l$ ?r\gh trunk l9es lead+ to t o!r (fice1 z be=e describ$1 & ^! trunk l9es always t]m9ate 9 ! ,b bo>d at t (fice4 ,! ,b op]ators are1 !re=e1 ^? op]ators :o receive ! calls ov] trunk l9es & complete ! connection ) ! l9e ( ! subscrib] desir$4 ,to def9e ^! t]ms m specifically1 an ,a bo>d is a multiple swit*bo>d 9 :i* ! subscrib]'s l9es ( a giv5 (fice di/rict t]m9ate4 ,= ?is reason ! ,a bo>d is frequ5tly ref]r$ to z a subscrib]s' bo>d1 & ! op]ators :o "w at ^! bo>ds & :o answ] ! calls ( ! subscrib]s are call$ ,a op]ators or subscrib]s' op]ators4 ,b bo>ds are swit*bo>ds 9 :i* t]m9ate ! incom+ ends ( ! trunk l9es lead+ f o!r (fices 9 ! same ex*ange4 ,^! bo>ds are frequ5tly call$ incom+ trunk bo>ds1 or m]ely trunk bo>ds1 & ! op]ators :o "w at !m & :o receive ! directions f ! ,a op]ators at ! o!r bo>ds are call$ ,b op]ators1 or incom+ trunk op]ators4 ,! circuits :i* are conf9$ :olly to ! use ( op]ators & ov] :i* ! in/ructions f "o op]ator to ano!r are s5t1 z 9 ! case ( ! ,a op]ator giv+ an ord] = a connection to a ,b op]ator at ano!r swit*bo>d1 are designat$ call circuits or ord] wire circuits4 ,sometimes trunk l9es are s arrang$ t connections may be orig9at$ at ei!r ( _! ends4 ,9 o!r cases !y are s arrang$ t "o gr\p ( trunk l9es connect+ two (fices is = ! traffic 9 "o direction only1 :ile ano!r gr\p lead+ betwe5 ! same two (fices is = h&l+ only ! traffic 9 ! o!r direction4 ,trunk l9es are call$ "o-way or two-way trunks1 accord+ to :e!r !y h&le ! traffic 9 "o direction or 9 two4 ,a trunk+ sy/em1 :]e ! same trunks h&le traffic bo? ways1 is call$ a s+le-track sy/em2 &1 on ! o!r h&1 a sy/em 9 :i* !re are two gr\ps ( trunks1 "o h&l+ traffic 9 "o direction & ! o!r 9 ! o!r1 is call$ a d\ble-track sy/em4 ,?is nom5clature is obvi\sly borr[$ f railroad practice4 ,!re is /ill ano!r class ( manual swit*bo>ds call$ ! toll bo>d ( :i* x w be necess>y to treat4 ,telephone calls made by "o p]son = ano!r )9 ! limits ( ! same ex*ange di/rict are usually *>g$ = ei!r by a flat rate p] mon?1 or by a c]ta9 *>ge = ea* call4 ,?is is usually reg>dless ( ! duration ( ! conv]sation foll[+ ! call4 ,on ! o!r h&1 :]e a call is made by "o p>ty = ano!r outside ( ! limits ( ! ex*ange di/rict &1 !re=e1 9 "s o!r ex*ange di/rict1 a *>ge is usually made1 bas$ on ! "t t ! connect+ long-di/ance l9e is employ$4 ,su* calls & _! ensu+ conv]sations are *>g$ = at a v mu* high] rate ?an ! purely local calls1 ?is rate dep5d+ on ! di/ance betwe5 ! /ations involv$4 ,! mak+ up ( connections betwe5 a long-di/ance & a local l9e is usually done by means ( op]ators o!r ?an ^? employ$ 9 h&l+ ! local calls1 :o "w ei!r by means ( special equipm5t locat$ on ! local bo>d1 or by means ( a sep>ate bo>d4 ,su* equipm5ts = h&l+ long-di/ance or toll traffic are commonly t]m$ toll swit*bo>ds4 ,!y diff] f local bo>ds 7a7 9 t !y are arrang$ = a v mu* small] numb] ( l9es2 7b7 9 t !y h facilities by :i* ! toll op]ator may make up ! connections ) a m9imum am\nt ( labor on ! "p ( ! assi/+ local op]ators2 & 7c7 9 t !y h facilities = record+ ! id5tification ( ! p>ties & tim+ ! conv]sations tak+ place ov] ! toll l9es1 s t ! prop] *>ge may be made to ! prop] subscrib]4 ,,*apt] ,,xxi ,,! ,,simple ,,magneto ,,swit*bo>d ,def9itions4 ,z already /at$ ^? swit*bo>ds :i* are adapt$ to "w 9 conjunction ) magneto telephones are call$ magneto swit*bo>ds4 ,! signals on su* swit*bo>ds are electromagnetic devices capable ( respond+ to ! curr5ts ( ! magneto g5]ators at ! subscrib]s' /ations4 ,s9ce1 z a rule1 magneto telephones are equipp$ ) local batt]ies1 x foll[s t ! magneto swit*bo>d does n ne$ to be arrang$ = supply+ ! subscrib]s' /ations ) talk+ curr5t4 ,?is fact is acc\ntable = magneto swit*bo>ds (t5 be+ ref]r$ to z local-batt]y swit*bo>ds1 9 contradi/9ction to common-batt]y swit*bo>ds :i* are equipp$ s z to supply ! connect$ subscrib]s' /ations ) talk+ curr5t4 ,! t]m simple z appli$ 9 ! head+s ( ?is & ! next *apt]1 is employ$ to designate swit*bo>ds adapt$ = s small a numb] ( l9es t !y may be s]v$ by a s+le or a v small gr\p ( op]ators2 ea* l9e is provid$ ) b a s+le connection t]m9al & all ( !m1 )\t special provision1 are plac$ directly )9 ! rea* ( ! op]ator1 or op]ators if !re are m ?an "o4 ,?is di/9ction w be m app>5t "u ! discussion ( transf] & multiple swit*bo>ds4 ,mode ( ,op]ation4 ,! cycle ( op]ation ( any simple manual swit*bo>d may be briefly outl9$ z foll[s3 ,! subscrib] desir+ a connection transmits a signal to ! c5tral (fice1 ! op]ator see+ ! signal makes connection ) ! call+ l9e & places h]self 9 telephonic communication ) ! call+ subscrib] to receive 8 ord]s2 ! op]ator !n completes ! connection ) ! l9e ( ! call$ subscrib] & s5ds r++ curr5t out on t l9e s z to r+ ! bell ( t subscrib]2 ! two subscrib]s !n conv]se ov] ! connect$ l9es & :5 ! conv]sation is f9i%$ ei!r "o or bo? ( !m may s5d a signal to ! c5tral (fice = disconnection1 ?is signal be+ call$ a cle>+-out signal2 ^u receipt ( ! cle>+-out signal1 ! op]ator disconnects ! two l9es & re/ores all ( ! c5tral-(fice app>atus involv$ 9 ! connection to its normal position4 ,compon5t ,p>ts4 ,be=e consid]+ fur!r ! op]ation ( manual swit*bo>ds x w be well to ref] briefly to ! compon5t pieces ( app>atus :i* g to make up a swit*bo>d4 ,l9e ,signal4 ,! l9e signal 9 magneto swit*bo>ds is practically always 9 ! =m ( an electromagnetic annunciator or drop4 ,x consi/s 9 an electromagnet adapt$ to be includ$ 9 ! l9e circuit1 its armature controll+ a lat*1 :i* s]ves to hold ! drop or %utt] or t>get 9 its rais$ position :5 ! magnet is n en]giz$1 & to release ! drop or %utt] or t>get s z to p]mit ! display ( ! signal :5 ! magnet is en]giz$4 ,! symbolic repres5tation ( su* an electromagnetic drop is %[n 9 ,fig4 #bcc4 ,illu/ration3 ,fig4 #bcc4 ,drop ,symbol ,jacks & ,plugs4 ,ea* l9e is also provid$ ) a connection t]m9al 9 ! =m ( a swit* socket4 ,?is assumes _m =ms1 b always consi/s 9 a cyl9drical op5+ beh9d :i* are arrang$ "o or m spr+ contacts4 ,! op5+ =ms a receptacle = plugs :i* h "o or m metallic t]m9als = ! conductors 9 ! flexible cord 9 :i* ! plug t]m9ates4 ,! arrangem5t is su* t :5 a plug is ins]t$ into a jack ! contacts on ! plug w regi/] ) c]ta9 ( ! contacts 9 ! jack & ?us cont9ue ! l9e conductors1 :i* t]m9ate 9 ! jack contacts1 to ! cord conductors1 :i* t]m9ate 9 ! plug contacts4 ,usually also :5 a plug is ins]t$ c]ta9 ( ! spr+ contacts 9 ! jack are made to engage ) or dis5gage o!r contacts 9 ! jack s z to make or break auxili>y circuits4 ,illu/ration3 ,fig4 #bcd4 ,spr+ ,jack ,a simple =m ( spr+ jack is %[n 9 section 9 ,fig4 #bcd4 ,9 ,fig4 #bce is %[n a sectional view ( a plug adapt$ to co-op]ate ) ! jack ( ,fig4 #bcd4 ,9 ,fig4 #bcf ! plug is %[n ins]t$ into ! jack4 ,! cyl9drical portion ( ! jack is commonly call$ ! sleeve or ?imble & x usually =ms "o ( ! ma9 t]m9als ( ! jack2 ! spr+1 =m+ ! o!r pr9cipal t]m9al1 is call$ ! tip spr+1 s9ce x engages ! tip ( ! plug4 ,! tip spr+ usually re/s on ano!r contact :i* may be t]m$ ! anvil4 ,:5 ! plug is ins]t$ into ! jack z %[n 9 ,fig4 #bcf1 ! tip spr+ is rais$ f contact ) ?is anvil & ?us breaks ! circuit lead+ ?r\gh x4 ,x w be und]/ood t spr+ jacks are n limit$ to ?ree contacts su* z %[n 9 ^! figures nor are plugs limit$ to two contacts4 ,sometimes ! plugs h ?ree1 & ev5 m1 contacts1 & frequ5tly ! jacks correspond+ to su* plugs h n only a contact spr+ adapt$ to regi/] ) ea* ( ! contacts ( ! plug1 b sev]al o!r auxili>y contacts also1 :i* w be made or brok5 accord+ to :e!r ! plug is ins]t$ or )drawn f ! jack4 ,symbolic repres5tations ( plugs & jacks are %[n 9 ,fig4 #bcg4 ,^! are employ$ 9 diagrammatic repres5tations ( circuits & are suppos$ to repres5t ! ess5tial elem5ts ( ! plugs & jacks 9 su* a way z to be sugge/ive ( _! op]ation4 ,x w be und]/ood t su* symbols may be greatly modifi$ to express ! v>i\s peculi>ities ( ! plugs & jacks :i* !y repres5t4 ,illu/ration3 ,fig4 #bce4 ,plug ,illu/ration3 ,fig4 #bcf4 ,plug & ,jack ,illu/ration3 ,fig4 #bcg4 ,jack & ,plug ,symbols ,keys4 ,o!r important elem5ts ( manual swit*bo>ds are r++ & li/5+ keys4 ,^! are ! devices by means ( :i* ! op]ator may swit* ! c5tral-(fice g5]ator or h] telephone set into or out ( ! circuit ( ! connect$ l9es4 ,! details ( a simple r++ & li/5+ key are %[n 9 ,fig4 #bch4 ,?is consi/s ( two gr\ps ( spr+s1 "o ( f\r & "o ( six1 ! spr+s 9 ea* gr\p be+ insulat$ f ea* o!r at _! po9ts ( m\nt+4 ,two ( ^! spr+s #a & #b 9 "o gr\p--! r++ gr\p--are long] ?an ! o!rs1 & act z movable lev]s engag+ ! inn] pair ( spr+s #c & #d :5 9 _! normal positions1 & ! out] pair #e & #f :5 =c$ into _! alt]nate positions4 ,movem5t is imp>t$ to ^! spr+s by ! action ( a cam :i* is m\nt$ on a lev]1 manipulat$ by ! op]ator4 ,:5 ?is lev] is mov$ 9 "o direction ! cam presses ! two spr+s #a & #b ap>t1 ?us caus+ !m to dis5gage ! spr+s #c & #d & to engage ! spr+s #e & #f4 ,illu/ration3 ,fig4 #bch4 ,r++ & ,li/5+ ,key ,! spr+s ( ! o!r gr\p con/itute ! swit*+ elem5t ( ! li/5+ key & are v simil> 9 _! action to ^? ( ! r++ key1 diff]+ 9 ! fact t !y h no inn] pair ( spr+s su* z #c & #d4 ,! two long spr+s #g & #h1 !re=e1 normally d n re/ aga9/ any?+1 b :5 ! key lev] is press$1 s z to =ce ! cam betwe5 !m1 !y are made to engage ! two out] spr+s #i & #aj4 ,illu/ration3 ,fig4 #bci4 ,r++-& ,li/5+-,key ,symbols ,! design & con/ruction ( r++ & li/5+ keys assume _m diff]5t =ms4 ,9 g5]al1 h[ev]1 !y are adapt$ to d exactly ! same sort ( swit*+ op]ations z t ( :i* ! device ( ,fig4 #bch is capable4 ,easily und]/ood symbols ( r++ & li/5+ keys are %[n 9 ,fig4 #bci2 ! cam memb] :i* op]ates on ! two long spr+s is usually omitt$ = ease ( illu/ration4 ,x w be und]/ood 9 consid]+ ^! symbols1 !re=e1 t ! two long curv$ spr+s usually re/ aga9/ a pair ( inn] contacts 9 case ( ! r++ key or aga9/ no?+ at all 9 case ( ! li/5+ key1 & t :5 ! key is op]at$ ! two spr+s are assum$ to be spread ap>t s z to engage ! out] pair ( contacts ) :i* !y are respectively normally disconnect$4 ,l9e & ,cord ,equipm5ts4 ,! p>ts ( ! swit*bo>d t are individual to ! subscrib]'s l9e are t]m$ ! l9e equipm5t2 ?is1 9 ! case ( a magneto swit*bo>d1 consi/s ( ! l9e drop & ! jack toge!r ) ! associat$ wir+ necess>y to connect !m prop]ly 9 ! l9e circuit4 ,! p>ts ( ! swit*bo>d t are associat$ ) a connect+ l9k--consi/+ ( a pair ( plugs & associat$ cords ) _! r++ & li/5+ keys & cle>+-out drop--are ref]r$ to z a cord equipm5t4 ,! circuit ( a complete pair ( cords & plugs ) _! associat$ app>atus is call$ a cord circuit4 ,9 ord] t !re may be a numb] ( simultane\s connections betwe5 diff]5t pairs ( l9es t]m9at+ 9 a swit*bo>d1 a numb] ( cord circuits are provid$1 ?is numb] dep5d+ on ! am\nt ( traffic at ! busie/ "t ( ! day4 ,op]ator's ,equipm5t4 ,a "p ( ! equipm5t t is n individual to ! l9es or to ! cord circuits1 b :i* may1 z occasion requires1 be associat$ ) any ( !m is call$ ! op]ator's equipm5t4 ,?is consi/s ( ! op]ator's transmitt] & receiv]1 induction coil1 & batt]y connections toge!r ) ! wir+ & o!r associat$ p>ts necess>y to co-ord9ate !m ) ! re/ ( ! app>atus4 ,/ill ano!r "p ( ! equipm5t t is n individual to ! l9es nor to ! cord circuits is ! call+-curr5t g5]ator4 ,?is may be common to ! entire (fice or a sep>ate "o may be provid$ = ea* op]ator's position4 ,op]ation 9 ,detail4 ,) ^! g5]al /atem5ts 9 m9d we may take up 9 "s detail ! v>i\s op]ations ( a telephone sy/em :]e9 ! l9es c5t] 9 a magneto swit*bo>d4 ,?is may be/ be done by consid]+ ! circuits involv$1 )\t special reg>d to ! details ( ! app>atus4 ,! s]ies ( figures %[+ ! cycle ( op]ations ( ! magneto swit*bo>d ab\t to be discuss$ are typical ( ?is type ( swit*bo>d almo/ reg>dless ( make4 ,! app>atus is 9 ea* case repres5t$ symbolically1 ! repres5tations indicat+ type r ?an any p>ticul> k9d ( app>atus )9 ! g5]al class to :i* x belongs4 ,normal ,condition ( ,l9e4 ,9 ,fig4 #bdj is %[n ! circuit ( an ord9>y magneto l9e4 ,! subscrib]'s sub-/ation app>atus1 %[n at ! left1 consi/s ( ! ord9>y bridg+ telephone b might ) equal propriety be indicat$ z a s]ies telephone4 ,! subscrib]'s /ation is %[n connect$ ) ! c5tral (fice by ! two limbs ( a metallic-circuit l9e4 ,"o limb ( ! l9e t]m9ates 9 ! spr+ #a ( ! jack1 & ! o!r limb 9 ! sleeve or ?imble #b ( ! jack4 ,! spr+ #a normally re/s on ! ?ird contact or anvil #c 9 ! jack1 its con/ruction be+ su* t :5 a plug is ins]t$ ?is spr+ w be rais$ by ! plug s z to break contact ) ! anvil #c4 ,x is und]/ood1 ( c\rse1 t ! plug associat$ ) ?is jack has two contacts1 ref]r$ to respectively z ! tip & ! sleeve2 ! tip makes contact ) ! tip spr+ #a & ! sleeve ) ! sleeve or ?imble #b4 ,illu/ration3 ,fig4 #bdj4 ,normal ,condition ( ,l9e ,! drop or l9e signal is p]man5tly connect$ betwe5 ! jack sleeve & ! anvil #c4 ,z a result1 ! drop is normally bridg$ across ! circuit ( ! l9e s z to be 9 a receptive condition to signal+ curr5t s5t out by ! subscrib]4 ,x is evid5t1 h[ev]1 t :5 ! plug is ins]t$ into ! jack ?is connection betwe5 ! l9e & ! drop w be brok54 ,9 ?is normal condition ( ! l9e1 !re=e1 ! drop /&s ready at ! c5tral (fice to receive ! signal f ! subscrib] & ! g5]ator at ! sub-/ation /&s ready to be bridg$ across ! circuit ( ! l9e z soon z ! subscrib] turns its h&le4 ,simil>ly ! r+]--! call-receiv+ device at ! sub-/ation--is p]man5tly bridg$ across ! l9e s z to be responsive to any signal t may be s5t out f ! c5tral (fice 9 ord] to call ! subscrib]4 ,! subscrib]'s talk+ app>atus is1 9 ?is normal condition ( ! l9e1 cut out ( ! circuit by ! swit* hook4 ,subscrib] ,call+4 ,fig4 #bda %[s ! condition ( ! l9e :5 ! subscrib] at ! sub-/ation is mak+ a call4 ,9 turn+ 8 g5]ator ! two spr+s :i* control ! connection ( ! g5]ator ) ! l9e are br\ght into engagem5t ) ea* o!r s t ! g5]ator curr5ts may pass out ov] ! l9e4 ,! condition at ! c5tral (fice is ! same z t ( ,fig4 #bdj except t ! drop is %[n ) its %utt] fall5 s z to indicate a call4 ,illu/ration3 ,fig4 #bda4 ,subscrib] ,call+ ,illu/ration3 ,a ,,specially ,,=m$ ,,cable ,,= ,,key ,,%elf ,,( ,,mon>* ,,swit*bo>d ,op]ator ,answ]+4 ,! next /ep is = ! op]ator to answ] ! call & ?is is %[n 9 ,fig4 #bdb4 ,! subscrib] has releas$ ! h&le ( 8 g5]ator & ! g5]ator has1 !re=e1 be5 automatically cut out ( ! circuit4 ,he also has remov$ 8 receiv] f its hook1 ?us br++ 8 talk+ app>atus into ! l9e circuit4 ,! op]ator on ! o!r h& has ins]t$ "o ( ! plugs ,pa into ! jack4 ,?is action has result$ 9 ! break+ ( ! circuit ?r\gh ! drop by ! rais+ ( ! spr+ #a f ! anvil #c1 & also 9 ! cont9uance ( ! l9e circuit ?r\gh ! conductors ( ! cord circuits4 ,?us1 ! upp] limb ( ! l9e is cont9u$ by means ( ! engagem5t ( ! tip spr+ #a ) ! tip #d ( ! plug to ! conduct+ /r& #f ( ! cord circuit2 likewise ! l[] limb ( ! l9e is cont9u$ by ! engagem5t ( ! ?imble #b ( ! jack ) ! sleeve contact #e ( ! plug ,pa to ! /r& #g ( ! cord circuit4 ,! op]ator has also clos$ h] li/5+ key ,l4,k4 ,9 do+ s %e has br\ght ! spr+s #h & #i into engagem5t ) ! anvils #aj & #aa & has ?us bridg$ h] head telephone receiv] ) ! second>y ( h] induction coil across ! two /r&s #f & #g ( ! cord4 ,associat$ ) ! second>y w9d+ ( h] receiv] is a prim>y circuit conta9+ a transmitt]1 batt]y1 & ! prim>y ( ! induction coil4 ,x w be se5 t ! conditions are n[ su* z to p]mit ! subscrib] at ! call+ /ation to conv]se ) ! op]ator & ?is conv]sation consi/s 9 ! famili> ,numb] ,please on ! "p ( ! op]ator & ! response ( ! subscrib] giv+ ! numb] ( ! l9e t is desir$4 ,nei!r ! plug ,pc1 nor ! r++ key ,r4,k41 %[n 9 ,fig4 #bdb1 is us$ 9 ?is op]ation4 ,! cle>+-out drop ,c4,o4 is bridg$ p]man5tly across ! /r&s #f-g ( ! cord1 b is )\t function at ?is "t2 ! fact t x is w\nd to a high resi/ance & imp$ance prev5ts its hav+ a h>mful effect on ! transmission4 ,illu/ration3 ,fig4 #bdb4 ,op]ator ,answ]+ ,x may be /at$ at ?is po9t t ! two plugs ( an associat$ pair are commonly ref]r$ to z ! answ]+ & call+ plugs4 ,! answ]+ plug is ! "o :i* ! op]ator always uses 9 answ]+ a call z j describ$ 9 connection ) ,fig4 #bdb4 ,! call+ plug is ! "o :i* %e next uses 9 connect+ ) ! l9e ( ! call$ subscrib]4 ,x lies idle dur+ ! answ]+ ( a call & is only br\ght into play aft] ! ord] ( ! call+ subscrib] has be5 giv51 9 :i* case x is us$ 9 e/abli%+ connection ) ! call$ subscrib]4 ,illu/ration3 ,fig4 #bdc4 ,op]ator ,call+ ,op]ator ,call+4 ,we may n[ consid] h[ ! op]ator calls ! call$ subscrib]4 ,! condition exi/+ = ?is op]ation is %[n 9 ,fig4 #bdc4 ,! op]ator aft] receiv+ ! ord] f ! call+ subscrib] ins]ts ! call+ plug ,pc into ! jack ( ! l9e ( ! call$ /ation4 ,?is act at once connects ! limbs ( ! l9e ) ! /r&s #f & #g ( ! cord circuit1 & also cuts out ! l9e drop ( ! call$ /ation1 z already expla9$4 ,! op]ator is %[n 9 ?is figure z hav+ op5$ h] li/5+ key ,l4,k4 & clos$ h] r++ key ,r4,k4 ,z a result1 r++ curr5t f ! c5tral-(fice g5]ator w fl[ out ov] ! two r++ key spr+s #ab & #ac to ! tip & sleeve contacts ( ! call+ plug ,pc1 !n to ! tip spr+ #a & ! sleeve or ?imble #b ( ! jack1 & !n to ! two sides ( ! metallic-circuit l9e to ! sub-/ation & ?r\gh ! bell !re4 ,?is causes ! r++ ( ! call$ subscrib]'s bell1 aft] :i* ! op]ator releases ! r++ key & !reby all[s ! two spr+s #ab & #ac ( t key to aga9 engage _! normal contacts #ad & #ae1 ?us mak+ ! two /r&s #f & #g ( ! cord circuit cont9u\s f ! contacts ( ! answ]+ plug ,pa to ! contacts ( ! call+ plug ,pc4 ,?is e/abli%es ! condition at ! c5tral (fice = conv]sation betwe5 ! two subscrib]s4 ,illu/ration3 ,fig4 #bdd4 ,subscrib]s ,connect$ = ,conv]sation4 ,subscrib]s ,conv]s+4 ,! only o!r ?+ necess>y to e/abli% a complete set ( talk+ conditions betwe5 ! two subscrib]s is = ! call$ subscrib] to remove 8 receiv] f its hook1 :i* he does z soon z he responds to ! call4 ,! conditions = conv]sation betwe5 ! two subscrib]s are %[n 9 ,fig4 #bdd4 ,x is se5 t ! two limbs ( ! call+ l9e are connect$ respectively to ! two limbs ( ! call$ l9e by ! two /r&s ( ! cord circuit1 bo? ! op]ator's receiv] & ! c5tral-(fice g5]ator be+ cut out by ! li/5+ & r++ keys1 respectively4 ,likewise ! two l9e drops are cut out ( circuit & ! only ?+ left associat$ ) ! circuit at ! c5tral (fice is ! cle>+-out drop ,c4 ,o41 :i* rema9s bridg$ across ! cord circuit4 ,?is1 l ! two r+]s at ! respective connect$ /ations1 :i* also rema9 bridg$ across ! circuit :5 bridg+ in/rum5ts are us$1 is ( su* high resi/ance & imp$ance t x (f]s practically no pa? to ! rapidly fluctuat+ voice curr5ts to leak f "o side ( ! l9e circuit to ! o!r4 ,fluctuat+ curr5ts g5]at$ by ! transmitt] at ! call+ /ation1 = in/ance1 are conv]t$ by means ( ! induction coil into alt]nat+ curr5ts fl[+ 9 ! second>y ( ! induction coil at t /ation4 ,consid]+ a mom5t>y curr5t z pass+ up ?r\gh ! second>y w9d+ ( ! induction coil at ! call+ /ation1 x passes ?r\gh ! receiv] ( t /ation ?r\gh ! upp] limb ( ! l9e to ! spr+ #a ( ! l9e jack belong+ to t l9e at ! c5tral (fice2 !nce ?r\gh ! tip #d ( ! answ]+ plug to ! conductor #f ( ! cord2 !nce ?r\gh ! pair ( contacts #ad & #ab =m+ "o side ( ! r++ key to ! tip #d ( ! call+ plug2 !nce to ! tip spr+ #a ( ! jack ( ! call$ subscrib]'s l9e2 !nce ov] ! upp] limb ( 8 l9e ?r\gh 8 receiv] & ?r\gh ! second>y ( ! induction to "o ( ! upp] swit*-hook contacts2 !nce ?r\gh ! hook lev] to ! l[] side ( ! l9e1 back to ! c5tral (fice & ?r\gh ! sleeve contact #b ( ! jack & ! sleeve contact #e ( ! plug2 !nce ?r\gh ! o!r r++ key contacts #ac & #ae2 !nce ?r\gh ! /r& #g ( ! cord to ! sleeve contact #e & ! sleeve contact #b ( ! answ]+ plug & jack1 respectively2 !nce ?r\gh ! l[] limb ( ! call+ subscrib]'s l9e to ! hook lev] at 8 /ation2 !nce ?r\gh "o ( ! upp] contacts ( ?is hook to ! second>y ( ! induction coil1 f :i* po9t ! curr5t />t$4 ,illu/ration3 ,fig4 #bde4 ,cle>+-,out ,signal ,obvi\sly1 :5 ! call$ subscrib] is talk+ to ! call+ subscrib] ! same pa? is foll[$4 ,x w be se5 t at any "t ! op]ator may press h] li/5+ key ,l4,k41 bridge h] telephone set across ! circuit ( ! two connect$ l9es1 & li/5 to ! conv]sation or conv]se ) ei!r ( ! subscrib]s 9 case ( necessity4 ,cle>+ ,out4 ,at ! close ( ! conv]sation1 ei!r "o or bo? ( ! subscrib]s may s5d a cle>+-out signal by turn+ _! g5]ators aft] hang+ up _! receiv]s4 ,?is condition is %[n 9 ,fig4 #bde4 ,! app>atus at ! c5tral (fice rema9s 9 exactly ! same position dur+ conv]sation z t ( ,fig4 #bdd1 except t ! cle>+-out drop %utt] is %[n z hav+ fall54 ,! two subscrib]s are %[n z hav+ hung up _! receiv]s1 ?us cutt+ out _! talk+ app>atus1 & z op]at+ _! g5]ators = ! purpose ( s5d+ ! cle>+-out signals4 ,9 response to ?is act ! op]ator pulls d[n bo? ! call+ & ! answ]+ plug1 ?us re/or+ !m to _! normal seats1 & br++ bo? l9es to ! normal condition z %[n 9 ,fig4 #bdj4 ,! l9e drops are aga9 br\ght into op]ative relation ) _! respective l9es s z to be receptive to subsequ5t calls & ! call+ g5]ators at ! sub-/ations are remov$ f ! bridge circuits across ! l9e by ! op5+ ( ! automatic swit* contacts associat$ ) ^? g5]ators4 ,ess5tials ( ,op]ation4 ,! =ego+ sequ5ce ( op]ations :ile describ$ p>ticul>ly ) respect to magneto swit*bo>ds is1 ) c]ta9 modifications1 typical ( ! op]ation ( ne>ly all manual swit*bo>ds4 ,9 ! m advanc$ types ( manual swit*bo>ds1 c]ta9 ( ! functions describ$ are sometimes done automatically1 & c]ta9 o!r functions1 n necess>y 9 connection ) ! simple swit*bo>d1 are add$4 ,! ess5tial mode ( op]ation1 h[ev]1 rema9s ! same 9 practically all manual swit*bo>ds1 & = ?is reason ! /ud5t %\ld ?or\ghly famili>ize himself ) ! op]ation & circuits ( ! simple swit*bo>d z a f\ndation = ! m complex & consequ5tly m-difficult-to-und]/& swit*bo>ds t w be describ$ lat] on4 ,comm]cial ,types ( ,drops & ,jacks4 ,e>ly ,drops4 ,com+ n[ to ! comm]cial types ( swit*bo>d app>atus1 ! fir/ subject t pres5ts itself is t ( magneto l9e signals or drops4 ,! v e>ly =ms ( swit*bo>d drops _h1 9 mo/ cases1 two-coil magnets1 ! cores ( :i* 7 connect$ at _! =w>d ends by an iron yoke & ! armature ( :i* 0 pivot$ opposite ! re> end ( ! two cores4 ,to ! armature 0 atta*$ a lat* rod :i* project$ =w>dly to ! front ( ! device & 0 !re adapt$ to engage ! upp] edge ( ! h+$ %utt]1 s z to hold x 9 its rais$ or undisplay$ position :5 ! armature 0 unattract$4 ,su* a drop1 ( ,we/]n ,electric manufacture1 is %[n 9 ,fig4 #bdf4 ,illu/ration3 ,fig4 #bdf ,old-,/yle ,drop ,liability to ,cross-,talk3--,?is type ( drop is suitable = use only on small swit*bo>ds :]e space is n an important consid]ation1 & ev5 !n only :5 ! drop is entirely cut out ( ! circuit dur+ conv]sation4 ,! reason = ?is latt] requirem5t w be obvi\s :5 x is consid]$ t !re is no magnetic %ield ar\nd ! w9d+ ( ! magnet & no means = prev5t+ ! /ray field set up by ! talk+ curr5ts 9 "o ( ! magnets f affect+ by induction ! w9d+s ( adjac5t magnets conta9$ 9 o!r talk+ circuits4 ,unless ! drops are entirely cut out ( ! talk+ circuit1 !re=e1 !y are v likely to produce cross-talk betwe5 adjac5t circuits4 ,fur!rmore1 su* =m ( drop is obvi\sly n economical ( space1 two coils plac$ side by side consum+ practically twice z mu* room z 9 ! case ( lat] drops :]e9 s+le magnet coils h be5 made to answ] ! purpose4 ,tubul> ,drops4 ,9 ! case ( l9e drops1 :i* usually c readily be cut out ( ! circuit dur+ conv]sation1 ?is cross-talk feature is n s]i\s1 b sometimes ! l9e drops1 & always ! cle>+-out drops mu/ be left 9 connection ) ! talk+ circuit4 ,on acc\nt ( economy 9 space & also on acc\nt ( ?is cross-talk feature1 !re has come into exi/5ce ! s-call$ tubul> or iron-clad drop1 "o ( :i* is %[n 9 section 9 ,fig4 #bdg4 ,?is 0 develop$ a good _m ye>s ago by ,mr4 ,e4,p4 ,w>n] ( ! ,we/]n ,electric ,company1 & has s9ce1 ) modifications1 become /&>d ) practically all ! manufactur+ companies4 ,9 ?is !re is b a s+le bobb91 & ?is is enclos$ 9 a %ell ( s(t ,norway iron1 :i* is clos$ at its front end & jo9$ to ! end ( ! core z indicat$1 s z to =m a complete return magnetic pa? = ! l9es ( =ce g5]at$ 9 ! coil4 ,! re> end ( ! %ell & core are bo? cut (f 9 ! same plane & ! armature is made 9 su* =m z to practically close ?is end ( ! %ell4 ,! armature c>ries a lat* rod ext5d+ ! entire l5g? ( ! %ell to ! front portion ( ! /ructure1 :]e x engages ! upp] edge ( ! pivot$ %utt]2 ?is1 :5 releas$ by ! lat* ^u ! attraction ( ! armature1 falls s z to display a t>get beh9d x4 ,illu/ration3 ,fig4 #bdg4 ,tubul> ,drop ,illu/ration3 ,fig4 #bdh4 ,/rip ( ,tubul> ,drops ,^! drops may be m\nt$ individually on ! face ( ! swit*bo>d1 b x is m usual to m\nt !m 9 /rips ( five or t54 ,a /rip ( five drops1 z manufactur$ by ! ,kellogg ,swit*bo>d & ,supply ,company1 is %[n 9 ,fig4 #bdh4 ,! front /rip on :i* ^! drops are m\nt$ is usually ( brass or /eel1 copp] plat$1 & is suffici5tly heavy to provide a rigid support = ! entire gr\p ( drops t are m\nt$ on x4 ,?is con/ruction greatly facilitates ! assembl+ ( ! swit*bo>d & also s]ves to economize space--obvi\sly1 ! ?+ to economize on ! face ( a swit*bo>d is space z def9$ by v]tical & horizontal dim5sions4 ,^! tubul> drops1 hav+ b "o coil1 are readily m\nt$ on #a-;in* c5t]s1 bo? v]tically & horizontally4 ,sometimes ev5 small] dim5sions ?an ?is are secur$4 ,! greate/ advantage ( ?is =m ( con/ruction1 h[ev]1 is 9 ! absolute fre$om f cross-talk betwe5 two adjac5t drops4 ,s completely is ! magnetic field ( =ce kept )9 ! mat]ial ( ! %ell1 t !re is practically no /ray field & two su* drops may be includ$ 9 two diff]5t talk+ circuits & ! drops m\nt$ imm$iately adjac5t to ea* o!r )\t produc+ any cross-talk :atev]4 ,night ,al>m4 ,swit*bo>d drops 9 fall+ make b little noise1 & dur+ ! day "t1 :ile ! op]ator is suppos$ to be ne$$ cont9ually at ! bo>d1 ! visual signal :i* !y display is suffici5t to attract h] att5tion4 ,9 small ex*anges1 h[ev]1 x is frequ5tly n practicable to keep an op]ator at ! swit*bo>d at night or dur+ o!r comp>atively idle p]iods1 & yet calls t d arrive dur+ su* p]iods mu/ be att5d$ to4 ,= ?is reason "s o!r ?an a visual signal is necess>y1 & ?is ne$ is met by ! s-call$ night-al>m atta*m5t4 ,?is is m]ely an arrangem5t by :i* ! %utt] 9 fall+ closes a pair ( contacts & ?us completes ! circuit ( an ord9>y vibrat+ bell or buzz] :i* w s\nd until ! %utt] is re/or$ to its normal position4 ,su* contacts are %[n 9 ,fig4 #bdi at #a & #b4 ,night-al>m contacts h assum$ a v>iety ( =ms1 "s ( :i* w be ref]r$ to 9 ! discussion ( o!r types ( drops & jacks4 ,illu/ration3 ,fig4 #bdi4 ,drop ) ,night-,al>m ,contacts ,jack ,m\nt+4 ,jacks1 l drops1 ?\gh frequ5tly individually m\nt$ are m (t5 m\nt$ 9 /rips4 ,an individually m\nt$ jack is %[n 9 ,fig4 #bej1 & a /rip ( t5 jacks 9 ,fig4 #bea4 ,9 su* a /rip ( jacks1 ! /rips support+ ! metallic p>ts ( ! v>i\s jacks are usually ( h>d rubb] re9=c$ by brass s z to give suffici5t /r5g?4 ,v>i\s =ms ( supports = ^! /rips are us$ by diff]5t manufactur]s1 ! means = fa/5+ !m 9 ! swit*bo>d frame usually consi/+ ( brass lugs on ! end ( ! jack /rip adapt$ to be engag$ by screws ent]+ ! /ation>y portion ( ! iron framework2 or sometimes p9s are fix$ 9 ! framework1 & ! jack is held 9 place by nuts engag+ screw-?read$ ends on su* p9s4 ,illu/ration3 ,fig4 #bej4 ,individual ,jack ,illu/ration3 ,fig4 #bea4 ,/rip ( ,jacks ,me?ods ( ,associat+ ,jacks & ,drops4 ,!re are two g5]al me?ods ( arrang+ ! drops & jacks 9 a swit*bo>d4 ,"o ( ^! is to place all ( ! jacks 9 a gr\p toge!r at ! l[] portion ( ! panel 9 front ( ! op]ator & all ( ! drops toge!r 9 ano!r gr\p above ! gr\p ( jacks4 ,! o!r way is to locate ea* jack 9 imm$iate proximity to ! drop belong+ to ! same l9e s t ! op]ator's att5tion w always be call$ imm$iately to ! jack into :i* %e mu/ ins]t h] plug 9 response to ! display ( a drop4 ,?is latt] practice has sev]al advantages ov] ! =m]4 ,:]e ! drops are all m\nt$ 9 "o gr\p & ! jacks 9 ano!r1 an op]ator see+ a drop fall mu/ make m5tal note ( x & pick out ! correspond+ jack 9 ! gr\p ( jacks4 ,on ! o!r h&1 :]e ! jacks & drops are m\nt$ imm$iately adjac5t to ea* o!r1 ! fall+ ( a drop attracts ! att5tion ( ! op]ator to ! correspond+ jack )\t fur!r m5tal ef=t on h] "p4 ,! imm$iate association ( ! drops & jacks has ano!r advantage--x makes possible su* a me*anical relation betwe5 ! drop & its associat$ jack t ! act ( ins]t+ ! plug into ! jack 9 mak+ ! connection w automatically & me*anically re/ore ! drop to its rais$ position4 ,su* drops are t]m$ self-re/or+ drops1 &1 s9ce a drop & jack are (t5 made /ructurally a unit>y piece ( app>atus1 !y are frequ5tly call$ comb9$ drops & jacks4 ,manual vs4 ,automatic ,re/oration44 ,!re has be5 mu* diff]5ce ( op9ion on ! "q ( manual v]sus automatic re/oration ( drops4 ,"s h cont5d$ t !re is no advantage 9 hav+ ! drops re/or$ automatically1 claim+ t ! op]ator has pl5ty ( "t to re/ore ! drops by h& :ile receiv+ ! ord] f ! call+ subscrib] or p]=m+ "s ( h] o!r "w4 ,^? :o ?9k ?is way h claim$ t ! only place :]e an automatically re/or$ drop is really desirable is :]e1 on acc\nt ( ! lack ( space on ! front ( ! swit*bo>d1 ! drops are plac$ on su* a portion ( ! bo>d z to be n readily rea*$ by ! op]ator4 ,?is result$ 9 ! electrically re/or$ drop1 m5tion ( :i* w be made lat]4 ,o!rs h cont5d$ t ev5 ?\gh ! drop is m\nt$ )9 easy rea* ( ! op]ator1 x is advantage\s t ! op]ator %\ld be reliev$ ( ! burd5 ( re/or+ x1 claim+ t ev5 ?\gh !re are times 9 ! regul> p]=mance ( ! op]ator's duties :5 %e may )\t int]f]+ ) o!r "w re/ore ! drops manually1 su* requirem5t results 9 a d\ble use ( h] att5tion & 9 a useless /ra9 on h] :i* might bett] be devot$ to ! actual mak+ ( connections4 ,until rec5tly ! v>i\s ,bell op]at+ companies h adh]$1 9 _! small ex*ange "w1 to ! manual re/or+ me?od1 :ile mo/ ( ! s-call$ indep5d5t op]at+ companies h adh]$ to ! automatic self-re/or+ drops4 ,me?ods ( ,automatic ,re/oration4 ,two g5]al me?ods pres5t !mselves = br++ ab\t ! automatic re/oration ( ! drop4 ,fir/1 ! me*anical me?od1 :i* is accompli%$ by hav+ "s mov+ "p ( ! jack or ( ! plug z x ent]s ! jack =ce ! drop me*anically into its re/or$ position4 ,?is usually means ! m\nt+ ( ! drop & ! correspond+ jack 9 juxtaposition1 & ?is1 9 turn1 has usually result$ 9 ! unit>y /ructure conta9+ bo? ! drop & ! jack4 ,second1 ! electrical me?od :]e9 ! plug 9 ent]+ ! jack controls a re/or+ circuit1 :i* includes a batt]y or o!r s\rce ( en]gy & a re/or+ coil on ! drop1 ! result be+ t ! ins]tion ( ! plug into ! jack closes ?is auxili>y circuit & ?us en]gizes ! re/or+ magnet1 ! armature ( :i* pulls ! %utt] back into its re/or$ position4 ,?is practice has be5 foll[$ by ,bell op]at+ companies :5ev] conditions require ! drop to be m\nt$ out ( easy rea* ( ! op]ator2 n o!rwise4 ,me*anical--,direct ,contact ) ,plug4 ,"o widely us$ me?od ( me*anical re/oration ( drops1 once employ$ by ! ,we/]n ,telephone ,con/ruction ,company ) consid]able success1 0 to hang ! %utt] 9 su* position t x w\ld fall imm$iately 9 front ( ! jack s t ! op]ator 9 ord] to rea* ! jack ) ! plug w\ld h to pu% ! plug directly aga9/ ! %utt] & ?us re/ore x to its normal or rais$ position4 ,9 ?is con/ruction ! coil ( ! drop magnet 0 m\nt$ directly beh9d ! jack1 ! lat* rod controll$ by ! armature rea*+ =w>d1 p>allel ) ! jack1 to ! %utt]1 :i*1 z /at$1 0 hung 9 front ( ! jack4 ,?is result$ 9 a mo/ compact arrangem5t s f> z ! space utilization on ! front ( ! bo>d 0 conc]n$ & su* comb9$ drops & jacks 7 m\nt$ on ab\t #a-;in* c5t]s1 s t a bank ( "o hundr$ comb9$ drops & jacks occupi$ a space only a little ov] #aj in*es squ>e4 ,a modification ( ?is s*eme1 z us$ by ! ,am]ican ,electric ,telephone ,company1 0 to m\nt ! drop imm$iately ov] ! jack s t its %utt]1 :5 d[n1 occupi$ a position almo/ 9 front (1 b above1 ! jack op5+4 ,! plug 0 provid$ ) a coll>1 :i*1 z x ent]$ ! jack1 engag$ a cam on ! base ( ! %utt] & =c$ ! latt] me*anically into its rais$ position4 ,nei!r ( ^! me?ods ( re/or+--i4e41 by direct contact betwe5 ! %utt] or "p ( x & ! plug or "p ( x--is n[ z widely us$ z =m]ly4 ,x has be5 f\nd t !re is no real ne$ 9 magneto swit*bo>ds = ! v great compactness :i* ! hang+ ( ! %utt] directly 9 front ( ! drop result$ 91 & ! t5d5cy 9 lat] ye>s has be5 to make ! comb9$ drops & jacks m sub/antial 9 con/ruction at ! exp5se ( "s space on ! face ( ! swit*bo>d4 ,illu/ration3 ,fig4 #beb4 ,kellogg ,drop & ,jack ,kellogg ,type3--,a v widely us$ s*eme ( me*anical re/oration is t employ$ 9 ! ,mill] drop & jack manufactur$ by ! ,kellogg ,swit*bo>d & ,supply ,company1 ! pr9ciples ( :i* may be und]/ood 9 connection ) ,fig4 #beb4 ,9 ?is figure views ( "o ( ^! comb9$ drops & jacks 9 ?ree diff]5t positions are %[n4 ,! jack is compos$ ( ! framework ,b & ! holl[ screw ,a1 ! latt] =m+ ! sleeve or ?imble ( ! jack & be+ ext]nally screw-?read$ s z to engage & b9d 9 place ! front end ( ! framework ,b4 ,! jack is m\nt$ on ! l[] "p ( ! brass m\nt+ /rip ,c b insulat$ !refrom4 ,! tip spr+ ( ! jack is b5t d[n z usual to engage ! tip ( ! plug1 z bett] %[n 9 ! l[] cut ( ,fig4 #beb1 & !n cont9ues 9 an ext5sion ,d1 :i* passes ?r\gh a hole 9 ! m\nt+ plate ,c4 ,?is tip spr+ 9 its normal position re/s aga9/ ano!r spr+ z %[n1 :i* latt] spr+ =ms "o t]m9al ( ! drop w9d+4 ,! drop or annunciator is ( tubul> =m1 & ! %utt] is s arrang$ on ! front ( ! m\nt+ /rip ,c z to fall directly above ! ext5sion ,d ( ! tip spr+4 ,z a result1 :5 ! plug is ins]t$ into ! jack1 ! upw>d motion ( ! tip spr+ =ces ! drop into its re/or$ position1 z indicat$ 9 ! l[] cut ( ! figure4 ,^! drops & jacks are usually m\nt$ 9 banks ( five1 z %[n 9 ,fig4 #bec4 ,illu/ration3 ,fig4 #bec4 ,/rip ( ,kellogg ,drops & ,jacks ,we/]n ,electric ,type3--,! comb9$ drop & jack ( ! ,we/]n ,electric ,company rec5tly put on ! m>ket to meet ! dem&s ( ! indep5d5t trade1 diff]s f o!rs pr9cipally 9 t x employs a sph]ical drop or t>get in/ead ( ! ord9>y flat %utt]4 ,?is piece ( app>atus is %[n 9 its ?ree possible positions 9 ,fig4 #bed4 ,! %utt] or t>get normally displays a black surface ?r\gh a hole 9 ! m\nt+ plate4 ,! sph]e =m+ ! t>get is out ( balance1 & :5 ! lat* is )drawn f x by ! action ( ! electromagnet x falls into ! position %[n 9 ! middle cut ( ,fig4 #bed1 ?us display+ a r$ in/ead ( a black surface to ! view ( ! op]ator4 ,:5 ! op]ator plugs 91 ! plug engages ! l[] "p ( an ,s-%ap$ lev] :i* acts on ! pivot$ sph]e to re/ore x to its normal position4 ,a p]spective view ( "o ( ^! comb9$ l9e signals & jacks is %[n 9 ,fig4 #bee4 ,a feature t is made mu* ( 9 rec5tly design$ drops & jacks = magneto s]vice is t :i* provides = ! ready removal ( ! drop coil1 f ! re/ ( ! /ructure1 = repair4 ,! drop & jack ( ! ,we/]n ,electric ,company1 j describ$1 embodies ?is feature1 a s+le screw be+ s arrang$ t its removal w p]mit ! )drawal ( ! coil )\t di/urb+ any ( ! o!r p>ts or connections4 ,! coil w9d+s t]m9ate 9 two projections on ! front head ( ! spool1 & ^! regi/] ) spr+ clips on ! inside ( ! %ell s t ! prop] connections = ! coil are automatically made by ! m]e ins]tion ( ! coil into ! %ell4 ,illu/ration3 ,fig4 #bed4 ,we/]n ,electric ,drop & ,jack ,illu/ration3 ,fig4 #bee4 ,we/]n ,electric ,drop & ,jack ,dean ,type3--,! comb9$ drop & jack ( ! ,dean ,electric ,company is illu/rat$ 9 ,figs4 #bef & #beg4 ,! two p]spective views %[ ! g5]al features ( ! drop & jack & ! me?od by :i* ! magnet coil may be )drawn f ! %ell4 ,z w be se5 ! magnet is w\nd on a holl[ core :i* slides ov] ! iron core1 ! latt] rema9+ p]man5tly fix$ 9 ! %ell1 ev5 ?\gh ! coil be )drawn4 ,fig4 #beh %[s ! /ructural details ( ! jack employ$ 9 ?is comb9ation & x w be se5 t ! re/or+ spr+ = ! drop is n ! tip spr+ itself1 b ano!r spr+ locat$ above & insulat$ f x & me*anically connect$ !re)4 ,illu/ration3 ,fig4 #bef4 ,dean ,drop & ,jack ,illu/ration3 ,fig4 #beg4 ,dean ,drop & ,jack ,illu/ration3 ,fig4 #beh4 ,details ( ,dean ,jack ,mon>* ,type3--,/ill ano!r comb9$ drop & jack is t ( ! ,mon>* ,telephone ,manufactur+ ,company ( ,*icago1 %[n 9 sectional view 9 ,fig4 #bei4 ,?is diff]s f ! usual type 9 t ! armature is m\nt$ on ! front end ( ! electromagnet1 its lat* arm reta9+ ! %utt] 9 its normal position :5 rais$1 & releas+ x :5 depress$ by ! attraction ( ! armature4 ,z is %[n1 !re is )9 ! core ( ! magnet an adju/able spiral spr+ :i* presses =w>d aga9/ ! armature & :i* spr+ is compress$ by ! attraction ( ! armature ( ! magnet4 ,! night-al>m contact is cle>ly %[n imm$iately bel[ ! /rip :i* supports ! drop1 ?is consi/+ ( a spr+ adapt$ to be engag$ by a lug on ! %utt] & press$ upw>dly aga9/ a /ation>y contact :5 ! %utt] falls4 ,! me?od ( re/oration ( ! %utt] 9 ?is case is by means ( an auxili>y spr+ b5t up s z to engage ! %utt] & re/ore x :5 ! spr+ is rais$ by ! ins]tion ( a plug into ! jack4 ,illu/ration3 ,fig4 #bei4 ,mon>* ,drop & ,jack ,code ,signal+4 ,on bridg+ p>ty l9es1 :]e ! subscrib]s sometimes call o!r subscrib]s on ! same l9e & sometimes call ! swit*bo>d s z to obta9 a connection ) ano!r l9e1 x is n always easy = ! op]ator at ! swit*bo>d to di/+ui% :e!r ! call is = h] or = "s o!r p>ty on ! l9e4 ,on su* l9es1 ( c\rse1 code r++ is us$ & 9 mo/ cases ! op]ator's only way ( di/+ui%+ betwe5 calls = h] & ^? = "s sub-/ation p>ties on ! l9e is by li/5+ to ! rattl+ noise :i* ! drop armature makes4 ,9 ! case ( ! ,mon>* drop ! adju/able spr+ t5sion on ! armature is int5d$ to provide = su* an adju/m5t z w p]mit ! armature to give a satisfactory buzz 9 response to ! alt]nat+ r++ curr5ts1 :e!r ! l9e be long or %ort4 ,illu/ration3 ,fig4 #bfj4 ,code ,signal ,atta*m5t ,! ,mon>* ,company provides 9 ano!r way = code signal+ at ! swit*bo>d4 ,9 "s cases !re is a special atta*m5t1 %[n 9 ,fig4 #bfj1 by means ( :i* ! code signals are repeat$ on ! night-al>m bell4 ,?is is 9 ! nature ( a special atta*m5t plac$ on ! drop1 :i* consi/s ( a light1 flat spr+ atta*$ to ! armature & =m+ "o side ( a local circuit4 ,! o!r side ( ! circuit t]m9ates 9 a fixture :i* is m\nt$ on ! drop frame & is provid$ ) a screw1 hav+ a plat9um po9t =m+ ! o!r contact po9t2 ?is all[s ( consid]able adju/m5t4 ,at ! po9t :]e ! screw comes 9 contact ) ! spr+ !re is a plat9um rivet4 ,:5 an op]ator is n always 9 att5dance1 ?is code-signal+ atta*m5t has "s advantages ov] ! drop z a signal int]pret]1 9 t x p]mits ! code signals to be he>d f a di/ance4 ,( c\rse1 ! addition ( spr+ contacts to ! drop armature t5ds to complicate ! /ructure & p]haps to cut d[n ! s5sitiv5ess ( ! drop1 :i* are (fsett+ disadvantages4 ,illu/ration3 ,fig4 #bfa4 ,comb9$ ,drop & ,r+] ,= really long l9es1 ?is code signal+ by means ( ! drop is be/ provid$ = by employ+ a comb9$ drop & r+]1 al?\gh 9 ?is case :atev] advantages are secur$ by ! me*anical re/oration ( ! %utt] ^u plugg+ 9 are lo/4 ,su* a device z manufactur$ by ! ,dean ,electric ,company is %[n 9 ,fig4 #bfa4 ,9 ?is ! ord9>y pol>iz$ r+] is us$1 b 9 addition ! tapp] rod c>ries a lat* :i*1 :5 vibrat$ by ! r++ ( ! bell1 releases a %utt] & causes x to fall1 ?us giv+ a visual z well z an audible signal4 ,electrical4 ,com+ n[ to ! electrical re/oration ( drop %utt]s1 ref]5ce is made to ,fig4 #bfb1 :i* %[s 9 side section ! electrical re/or+ drop employ$ by ! ,bell companies & manufactur$ by ! ,we/]n ,electric ,company4 ,9 ?is ! coil #a is a l9e coil1 & x op]ates on ! armature #b to raise ! lat* lev] #c 9 j ! same mann] z 9 ! ord9>y tubul> drop4 ,! lat* lev] #c acts1 h[ev]1 to release ano!r armature #d in/ead ( a %utt]4 ,?is armature #d is pivot$ at its l[] end at ! opposite end ( ! device f ! armature #b &1 by fall+ outw>dly :5 releas$1 x s]ves to raise ! light %utt] #e4 ,! re/or+ coil ( ?is device is %[n at #f1 & :5 en]giz$ x attracts ! armature #d s z to pull x back "u ! cat* ( ! lat* lev] #c & also s z to all[ ! %utt] #e to fall into its normal position4 ,! me?od ( clos+ ! re/or+ circuit is by plac+ coil #f 9 circuit ) a local batt]y & ) a pair ( contacts 9 ! jack1 :i* latt] contacts are normally op5 b are bridg$ across by ! plug :5 x ent]s ! jack1 ?us en]giz+ ! re/or+ coil & re/or+ ! %utt]4 ,illu/ration3 ,fig4 #bfb4 ,electrically ,re/or$ ,drop ,a p]spective view ( ?is ,we/]n ,electric electrical re/or+ drop is %[n 9 ,fig4 #bfc1 a m complete m5tion be+ made ( ?is feature "u ! discussion ( magneto multiple swit*bo>ds1 :]e9 x f\nd its *ief use4 ,x is m5tion$ "h to r\nd out ! me?ods t h be5 employ$ = accompli%+ ! automatic re/oration ( %utt]s by ! ins]tion ( ! plug4 ,illu/ration3 ,fig4 #bfc4 ,electrically ,re/or$ ,drop ,swit*bo>d ,plugs4 ,a swit*bo>d plug su* z is commonly us$ 9 simple magneto swit*bo>ds is %[n 9 ,fig4 #bfd & also 9 ,fig4 #bce4 ,! tip contact is usually ( brass & is connect$ to a sl5d] /eel rod :i* runs ?r\gh ! c5t] ( ! plug & t]m9ates ne> ! re> end ( ! plug 9 a connector = ! tip conductor ( ! cord4 ,?is c5tral core ( /eel is c>efully insulat$ f ! out] %ell ( ! plug by means ( h>d rubb] bu%+s1 ! p>ts be+ =c$ tightly toge!r4 ,! out] %ell1 ( c\rse1 =ms ! o!r conductor ( ! plug1 call$ ! sleeve contact4 ,a h&le ( t\gh fib] tub+ is fitt$ ov] ! re> end ( ! plug & ?is also s]ves to close ! op5+ =m$ by cutt+ away a portion ( ! plug %ell1 ?us expos+ ! connector = ! tip conductor4 ,illu/ration3 ,fig4 #bfd4 ,swit*bo>d ,plug ,cord ,atta*m5t4 ,! re> end ( ! plug %ell is usually bor$ out j ab\t ! size ( ! out] cov]+ ( ! swit*bo>d cord1 & x is provid$ ) a co>se int]nal screw ?read1 z %[n4 ,! cord is atta*$ by screw+ x tightly into ?is screw-?read$ *amb]1 ! screw ?reads 9 ! brass be+ suffici5tly co>se & ( suffici5tly small int]nal diamet] to af=d a v secure me*anical connection betwe5 ! out] braid+ ( ! cord & ! plug4 ,! connection betwe5 ! tip conductor ( ! cord & ! tip ( ! plug is made by a small ma*9e screw connection z %[n1 :ile ! connection betwe5 ! sleeve conductor ( ! plug & ! sleeve conductor ( ! cord is made by b5d+ back ! latt] ov] ! out] braid+ ( ! cord be=e x is screw$ into ! %ank ( ! plug4 ,?is results 9 ! close electrical contact betwe5 ! sleeve conductor ( ! cord & ! inn] metal surface ( ! %ank ( ! plug4 ,swit*bo>d ,cords4 ,a great deal ( +5uity has be5 ex]t$ t[>d ! end ( produc+ a reliable & durable swit*bo>d cord4 ,:ile great improvem5t has result$1 ! fact rema9s t ! cords ( manual swit*bo>ds are today probably ! mo/ tr\blesome elem5t1 & !y ne$ con/ant att5tion & repairs4 ,:ile no two manufactur]s build _! cords exactly alike1 descriptions ( a few commonly us$ & successful cords may be "h giv54 ,conc5tric ,conductors4 ,9 "o ! core is made f a d\ble /r& ( /rong lock /it* tw9e1 ov] :i* is plac$ a l95 braid4 ,!n ! tip conductor1 :i* is ( /r&$ copp] t9sel1 is braid$ on4 ,?is is !n cov]$ ) two lay]s ( tussah silk1 laid 9 rev]se wrapp+s1 !n !re is a heavy cotton braid1 & ov] ! latt] a l95 braid4 ,! sleeve conductor1 :i* is also ( copp] t9sel1 is !n braid$ ov] ! /ructure s =m$1 aft] :i* two rev]se wrapp+s ( tussah silk are s]v$ on1 & ?is is cov]$ by a cotton braid & ?is 9 turn by a heavy l95 or poli%$ cotton braid4 ,! plug end ( ! cord is re9=c$ = a l5g? ( f #ab to #ah in*es by ano!r braid+ ( l95 or poli%$ cotton1 & ! :ole cord is treat$ ) melt$ beeswax to make x moi/ure-pro( & durable4 ,illu/ration3 ,fig4 #bfe4 ,swit*bo>d ,cord ,/eel ,spiral ,conductors4 ,9 ano!r cord t has f\nd mu* favor ! two conductors are =m$ ma9ly by two conc5tric spiral wrapp+s ( /eel wire1 ! conductivity be+ re9=c$ by adjac5t braid+s ( t9sel4 ,! /ructure ( su* a cord is well %[n 9 ,fig4 #bfe4 ,beg9n+ at ! "r1 ! diff]5t elem5ts %[n are1 9 ! ord] nam$1 a /r& ( lock /it* tw9e1 a l95 braid+1 into ! /r&s ( :i* are int]m+l$ t9sel /r&s1 ! inn] spiral /eel wrapp+1 a braid+ ( tussah silk1 a l95 braid+1 a loose t9sel braid+1 ! out] conductor ( r\nd spiral /eel1 a cotton braid1 & an outside l95 or poli%$ cotton braid4 ,! inn] t9sel braid+ & ! inn] spiral toge!r =m ! tip conductor :ile ! out] braid+ & spiral toge!r =m ! sleeve conductor4 ,! cord is re9=c$ at ! plug end = a l5g? ( ab\t #ad in*es by ano!r braid+ ( l954 ,! t9sel us$ is1 9 ea* case1 = ! purpose ( cutt+ d[n ! resi/ance ( ! ma9 /eel conductor4 ,^! wrapp+s ( /eel wire =m+ ! tip & sleeve conductors respectively1 h ! advantage ( af=d+ great flexibility1 & also ( mak+ x c]ta9 t :atev] /ra9 ! cord is subject$ to w fall on ! insulat$ braid+ r ?an on ! spiral /eel :i* has 9 itself no p[] to resi/ t5sile /ra9s4 ,p>allel ,t9sel ,conductors4 ,ano!r /&>d two-conductor swit*bo>d cord is manufactur$ z foll[s3 ,"o conductor is ( v heavy copp] t9sel insulat$ ) "o wrapp+ ( sea isl& cotton1 :i* prev5ts brok5 ends ( ! t9sel or knots f pi]c+ ?r\gh & %ort-circuit+ ) ! o!r conductor4 ,ov] ?is is plac$ "o braid ( tussah silk & an out] braid ( cotton4 ,?is comb9es high insulation ) consid]able /r5g?4 ,! o!r conductor is ( copp] t9sel1 n insulat$1 & ?is is laid p>allel to ! ?rice insulat$ conductor already describ$4 ,ar\nd ^! two conductors is plac$ an armor ( spr+ brass wire 9 spiral =m1 & ov] ?is a close1 /\t braid ( glaz$ cotton4 ,?is l ! o!rs is re9=c$ by an extra braid at ! plug end4 ,r++ & ,li/5+ ,keys4 ,! g5]al pr9ciples ( ! r++ key h already be5 ref]r$ to4 ,r++ keys are ( two g5]al types1 "o hav+ horizontal spr+s & ! o!r v]tical4 ,illu/ration3 ,fig4 #bff4 ,horizontal-,spr+ ,li/5+ & ,r++ ,key ,horizontal ,spr+ ,type4 ,v>i\s ,bell op]at+ companies h g5]ally adh]$ to ! horizontal spr+ type except 9 individual & f\r-p>ty-l9e keys4 ,! con/ruction ( a ,we/]n ,electric ,company horizontal spr+ key is %[n 9 ,fig4 #bff4 ,9 ?is p>ticul> key1 z illu/rat$1 !re are two cam lev]s op]at+ ^u ?ree sets ( spr+s4 ,! cam lev] at ! left op]ates ! ord9>y r++ & li/5+ set ( spr+s accord+ to :e!r x is pu%$ "o way or ! o!r4 ,9 r++ on s+le-p>ty l9es ! cam lev] at ! left is ! "o to be us$2 :ile on two-p>ty l9es ! lev] at ! left s]ves to r+ ! fir/ p>ty & ! r++ key at ! "r ! second p>ty4 ,9 ord] t ! op]ator may h an indication z to :i* /ation on a two-p>ty l9e %e has call$1 a small t>get #a c>ri$ on a lev] #b is provid$4 ,?is t>get may display a black or a :ite field1 accord+ to :i* ( its positions x occupies4 ,! lev] #b is connect$ by ! l9ks #c & #d ) ! two key lev]s & ! t>get is ?us mov$ into "o position or ! o!r1 accord+ to :i* lev] 0 la/ ?r[n into r++ position4 ,x w be notic$ t ! spr+s are m\nt$ horizontally & on edge4 ,?is on-edge feature has ! advantage ( p]mitt+ ready inspection ( ! contacts & ( avoid+ ! liability ( du/ ga!r+ betwe5 ! contacts4 ,z w be se51 at ! l[] end ( ea* swit* lev] !re is a roll] ( insulat+ mat]ial :i* s]ves z a w$ge1 :5 =c$ betwe5 ! two long spr+s ( any set1 to =ce !m ap>t & into engagem5t ) _! respective out] spr+s4 ,illu/ration3 ,fig4 #bfg4 ,v]tical-,spr+ ,li/5+ & ,r++ ,key ,v]tical ,spr+ ,type4 ,! o!r type ( r++ & li/5+ key employ+ v]tical spr+s is almo/ univ]sally us$ by ! v>i\s indep5d5t manufactur+ companies4 ,a good example ( ?is is %[n 9 ,fig4 #bfg1 :i* %[s p>tly 9 elevation & p>tly 9 section a d\ble key ( ! ,mon>* ,company4 ,! op]ation ( ?is is obvi\s f its mode ( con/ruction4 ,! "r-h& set ( spr+s ( ! "r-h& key 9 ?is cut are ! spr+s ( ! li/5+ key1 :ile ! left-h& set ( ! "r-h& key are ^? ( ! call+-plug r++ key4 ,! left-h& set ( ! left-h& key may be ^? ( a r+-back key on ! answ]+ plug1 :ile ! "r-h& set ( ! left-h& key may be = any special purpose4 ,x is obvi\s t ^! gr\ps ( spr+s may be gr\p$ 9 diff]5t comb9ations or omitt$ 9 "p1 z requir$4 ,?is same g5]al =m ( key is also manufactur$ by ! ,kellogg ,company & ! ,dean ,company1 t ( ! ,kellogg ,company be+ illu/rat$ 9 p]spective1 ,fig4 #bfh4 ,! keys ( ?is g5]al type h ! same advantages z ^? ( ! horizontal on-edge arrangem5t ) respect to ! ga!r+ ( du/1 & :ile p]haps ! contacts are n s readily get-at-able = inspection1 yet !y h ! advantage ( be+ some:at m simple1 & ( tak+ up less horizontal space on ! key %elf4 ,illu/ration3 ,fig4 #bfh4 ,v]tical ,li/5+ & ,r++ ,key ,illu/ration3 ,fig4 #bfi4 ,f\r-,p>ty ,li/5+ & ,r++ ,key ,p>ty-,l9e ,r++ ,keys4 ,= p>ty-l9e r++ ! key matt] becomes some:at m complicat$4 ,usually ! arrangem5t is su* t 9 connection ) ea* call+ plug !re are a numb] ( keys1 ea* arrang$ ) respect to ! circuits ( ! plug s z to s5d out ! prop] comb9ation & direction ( curr5t1 if ! pol>ity sy/em is us$2 or ! prop] frequ5cy ( curr5t if ! h>monic sy/em is us$2 or ! prop] numb] ( impulses if ! /ep-by-/ep or brok5-l9e sy/em is us$4 ,! numb] ( diff]5t k9ds ( arrangem5ts & comb9ations is legion1 & we w "h illu/rate only an example ( a f\r-p>ty l9e r++ key adapt$ = h>monic r++4 ,a ,kellogg p>ty-l9e li/5+ & r++ key is %[n 9 ,fig4 #bfi4 ,9 ?is1 besides ! regul> li/5+ key1 are %[n f\r pu%-button keys1 ea* adapt$1 :5 depress$1 to break ! connection back ( ! key1 & at ! same "t connect ! prop] call+ g5]ator ) ! call+ plug4 ,self-,indicat+ ,keys4 ,a complication t has giv5 a good deal ( tr\ble 9 ! matt] ( p>ty-l9e r++ is due to ! fact t x is sometimes necess>y to r+ a second or a ?ird "t on a p>ty-l9e connection1 because ! p>ty call$ may n respond ! fir/ "t4 ,! op]ator is n always able to rememb] :i* "o ( ! f\r keys associat$ ) ! plug connect$ ) ! desir$ p>ty %e has press$ on ! fir/ occasion &1 !re=e1 :5 x becomes necess>y to r+ aga91 %e may r+ ! wrong p>ty4 ,?is is provid$ = 9 a v +5i\s way 9 ! key %[n 9 ,fig4 #bfi1 by mak+ ! arrangem5t su* t aft] a giv5 key has be5 depress$ to its full ext5t 9 r++1 & !n releas$1 x does n come q back to its normal position b rema9s slightly depress$4 ,?is always s]ves z an indication to ! op]ator1 !re=e1 z to :i* key %e depress$ la/1 & 9 ! case ( a re-r+1 %e m]ely presses ! key t is already d[n a little way4 ,on ! next call if %e is requir$ to press ano!r "o ( ! f\r keys1 ! "o :i* rema9$ d[n a slight di/ance on ! la/ call w be releas$ & ! "o t is fully depress$ w be ! "o t rema9s d[n z an indication4 ,su* keys1 :]e ! key t 0 la/ us$ leaves an indication to t effect1 are call$ indicat+ r++ keys4 ,9 o!r =ms ! indication is giv5 by caus+ ! key lev] to move a little t>get :i* rema9s expos$ until "s o!r key 9 ! same set is mov$4 ,! key %[n 9 ,fig4 #bff is an example ( ?is type4 ,,note4 ,! matt] ( automatic r++ & o!r special =ms ( r++ w be ref]r$ to & discuss$ at _! prop] places 9 ?is "w1 b at ?is po9t !y are n p]t95t z !y are n employ$ 9 simple swit*bo>ds4 ,op]ator's ,telephone ,equipm5t4 ,little ne$ be said conc]n+ ! matt] ( ! op]ator's talk+ app>atus1 i4e41 ! op]ator's transmitt] & receiv]1 s9ce z transmitt]s & receiv]s !y are practically ! same z ^? 9 ord9>y use = o!r purposes4 ,! wat*-case receiv] is ne>ly always employ$ = op]ators' purposes on acc\nt ( its lightness & compactness4 ,x is us$ 9 connection ) a head b& s z to be held cont9ually at ! op]ator's e>1 all[+ bo? ( h] h&s to be free4 ,! transmitt] us$ by op]ators does n 9 itself diff] f ! transmitt]s employ$ by subscrib]s1 b ! me?ods by :i* x is support$ diff]1 two g5]al practices be+ foll[$4 ,"o ( ^! is to susp5d ! transmitt] by flexible conduct+ cords s z to be adju/able 9 a v]tical direction4 ,a good illu/ration ( ?is is giv5 9 ,fig4 #bgj4 ,! o!r me?od1 & "o t is com+ into m & m favor1 is to m\nt ! transmitt] on a light bracket susp5d$ by a flexible b& f ! neck ( ! op]ator1 a brea/ plate be+ furni%$ s t ! transmitt] w re/ on h] brea/ & be at all times )9 prop] position to receive h] spee*4 ,to facilitate ?is1 a long curv$ m\?piece is commonly employ$1 z %[n cle>ly 9 ,fig4 #dg4 ,illu/ration3 ,fig4 #bgj4 ,op]ator's ,transmitt] ,susp5sion ,cut-9 ,jack4 ,x is common to t]m9ate t portion ( ! app>atus :i* is worn on ! op]ator's p]son--t is1 ! receiv] only if ! susp5d$ type ( transmitt] is employ$1 & ! receiv] & transmitt] if ! brea/ plate type ( transmitt] is employ$--9 a plug1 & a flexible cord connect+ ! plug t]m9ates ) ! app>atus4 ,! portions ( ! op]ator's talk+ circuit t are locat$ p]man5tly 9 ! swit*bo>d cab9et are 9 su* cases t]m9at$ 9 a jack1 call$ an op]ator's cut-9 jack4 ,?is is usually m\nt$ on ! front rail ( ! swit*bo>d cab9et j bel[ ! key %elf4 ,su* a cut-9 jack is %[n 9 ,fig4 #bga & x is m]ely a specializ$ =m ( spr+ jack adapt$ to receive ! %ort1 /\t plug 9 :i* ! op]ator's transmitt]1 or transmitt] & receiv]1 t]m9ate4 ,by ?is arrangem5t ! op]ator is enabl$ readily to connect or disconnect h] talk+ app>atus1 :i* is worn on h] p]son1 :5ev] %e comes to ! bo>d = "w or leaves x at ! end ( h] "w4 ,a complete op]ator's telephone set1 or t portion t is c>ri$ on ! p]son ( ! op]ator1 toge!r ) ! cut-9 plug1 is %[n 9 ,fig4 #bgb4 ,illu/ration3 ,fig4 #bga4 ,op]ator's ,cut-9 ,jack ,illu/ration3 ,fig4 #bgb4 ,op]ator's ,talk+ ,set ,circuits ( ,complete ,swit*bo>d4 ,we may n[ discuss ! circuits ( a complete simple magneto swit*bo>d4 ,! "o %[n 9 ,fig4 #bgc is typical4 ,be=e go+ into ! details ( ?is1 x is well to in=m ! /ud5t t ?is g5]al =m ( circuit repres5tation is "o t is commonly employ$ 9 %[+ ! complete circuits ( any swit*bo>d4 ,ord9>ily two subscrib]s' l9es are %[n1 ^! connect+ _! respective subscrib]s' /ations ) two diff]5t l9e equipm5ts at ! c5tral (fice4 ,! jacks & signals ( ^! l9e equipm5ts are turn$ ar\nd s z to face ea* o!r1 9 ord] to cle>ly repres5t h[ ! connection betwe5 !m may be made by means ( ! cord circuit4 ,! elem5ts ( ! cord circuit are also spread out1 s t ! v>i\s p>ts occupy relative positions :i* !y d n assume at all 9 practice4 ,9 o!r words x mu/ be rememb]$ t1 9 circuit diagrams1 ! relative positions ( ! p>ts are sacrific$ 9 ord] to make cle> ! circuit connections4 ,h[ev]1 ?is does n mean t x is (t5 n possible to s locate ! pieces ( app>atus t !y w 9 a c]ta9 way indicate relative positions1 z may be se5 9 ! case ( ! drop & jack 9 ,fig4 #bgc1 ! drop be+ %[n imm$iately above ! jack1 :i* is ! position 9 :i* ^! p>ts are locat$ 9 practice4 ,illu/ration3 ,fig4 #bgc4 ,circuit ( ,simple ,magneto ,swit*bo>d ,little ne$ be said conc]n+ ?is circuit 9 view ( :at has already be5 said 9 connection ) ,figs4 #bdj to #bde4 ,x w be se5 9 ! p>ticul> sub-/ation circuit "h repres5t$1 t ! talk+ app>atus is arrang$ 9 ! usual mann] & t ! r+] & g5]ator are s arrang$ t :5 ! g5]ator is op]at$ ! r+] w be cut out ( circuit1 :ile ! g5]ator w be plac$ across ! circuit2 :ile1 :5 ! g5]ator is idle1 ! r+] is bridg$ across ! circuit & ! g5]ator is cut out4 ,! l9e t]m9ates 9 ea* case 9 ! tip & sleeve contacts ( ! jack1 & 9 ! normal condition ( ! jack ! l9e drop is bridg$ across ! l9e4 ,! arrangem5t by :i* ! drop is re/or$ & at ! same "t cut out ( circuit :5 ! op]ator plugs 9 ! jack1 is obvi\s f ! diagrammatic illu/ration4 ,! cord circuit is ! same z t already discuss$1 ) ! exception t two r++ keys are provid$1 "o 9 connection ) ! call+ plug1 z is univ]sal practice1 & ! o!r 9 connection ) ! answ]+ plug z is sometimes practic$ 9 ord] t ! op]ator may1 :5 occasion requires1 r+ back ! call+ subscrib] )\t ! necessity ( *ang+ ! plug 9 ! jack4 ,! out] contacts ( ^! two r++ keys are connect$ to ! t]m9als ( ! r++ g5]ator &1 :5 ei!r key is op]at$1 ! connection betwe5 ! plug1 on :i* ! r++ is to be done1 & ! re/ ( ! cord circuit w be brok51 :ile ! g5]ator w be connect$ ) ! t]m9als ( ! plug4 ,! li/5+ key & talk+ app>atus ne$ no fur!r explanation1 x be+ obvi\s t :5 ! key is op]at$ ! subscrib]'s telephone set w be bridg$ across ! cord circuit &1 !re=e1 connect$ ) ei!r or bo? ( ! talk+ subscrib]s4 ,illu/ration3 ,fig4 #bgd4 ,night-,al>m ,circuit ,night-,al>m ,circuits4 ,! circuit ( ,fig4 #bgc1 :ile ref]r$ to z a complete circuit1 is n q t4 ,! night-al>m circuit is n %[n4 ,9 ord] to cle>ly indicate h[ a s+le batt]y & bell1 or buzz]1 may s]ve 9 connect+ a numb] ( l9e drops1 ref]5ce is made to ,fig4 #bgd :i* %[s ! connection betwe5 ?ree diff]5t l9e drops & ! night-al>m circuit4 ,! night-al>m app>atus consi/s 9 ! batt]y #a & ! buzz]1 or bell1 #b4 ,a swit* #c adapt$ to be manually op]at$ is connect$ 9 ! circuit ) ! batt]y & ! buzz] s z to op5 ?is circuit :5 ! night al>m is n ne$$1 ?us mak+ x inop]ative4 ,dur+ ! portions ( ! day :5 ! op]ator is ne$$ con/antly at ! bo>d x is cu/om>y to leave ?is swit* #c op51 b dur+ ! night p]iod :5 %e is n requir$ con/antly at ! bo>d ?is swit* is clos$ s t an audible signal w be giv5 :5ev] a drop falls4 ,! night-al>m contact #d on ea* ( ! drops w be clos$ :5ev] a %utt] falls1 & z ! two memb]s ( ?is contact1 9 ! case ( ea* drop1 are connect$ respectively ) ! two sides ( ! night-al>m circuit1 any "o %utt] fall+ w complete ! necess>y conditions = caus+ ! buzz] to s\nd1 assum+ ( c\rse t ! swit* #c is clos$4 ,night ,al>m ) ,relay4 ,a good deal ( tr\ble has be5 caus$ 9 ! pa/ by unc]ta9ty 9 ! closure ( ! night-al>m circuit at ! drop contact4 ,"s ( ! companies h employ$ ! =m ( circuit %[n 9 ,fig4 #bge to ov]come ?is4 ,in/ead ( ! night-al>m buzz] be+ plac$ directly 9 ! circuit t is clos$ by ! drop1 a relay #e & a high-voltage batt]y #f are plac$ 9 ?is circuit4 ,! buzz] & ! batt]y = op]at+ x are plac$ 9 a local circuit controll$ by ?is relay4 ,x w be se5 by ref]5ce to ,fig4 #bge t :5 ! %utt] falls1 x w1 by clos+ ! contact #d1 complete ! circuit f ! batt]y #f ?r\gh ! relay #e--;assum+ swit* #c to be clos$--& ?us cause ! op]ation ( ! relay4 ,! relay1 9 turn1 by pull+ up its armature1 w close ! circuit ( ! buzz] #b ?r\gh ! batt]y #g & cause ! buzz] to s\nd4 ,illu/ration3 ,fig4 #bge4 ,night-,al>m ,circuit ) ,relay ,! advantage ( ?is me?od ov] ! direct me?od ( op]at+ ! buzz] is t any imp]fection 9 ! night-al>m contact at ! drop is mu* less likely to prev5t ! fl[ ( curr5t ( ! high-voltage batt]y #f ?an ( ! l[-voltage batt]y #a1 %[n 9 connection ) ,fig4 #bgd4 ,?is is because ! high] voltage is mu* m likely to break d[n any v ?9 bit ( insulation1 su* z might be caus$ by a m9ute p>ticle ( du/ or oxide betwe5 contacts t are suppos$ to be clos$ by ! fall+ ( ! %utt]4 ,x has be5 common to employ = batt]y #f a dry-cell batt]y giv+ ab\t #bj or #bd volts1 & = ! op]ation ( ! buzz] itself1 a simil> batt]y ( ab\t two cells giv+ approximately #c volts4 ,night-,al>m ,contacts4 ,! night-al>m contact #d ( ! drop %[n diagrammatically 9 ,figs4 #bgd & #bge w\ld1 if tak5 lit]ally1 indicate t ! %utt] itself actually =ms "o t]m9al ( ! circuit & ! contact aga9/ :i* x falls1 ! o!r4 ,?is has n be5 f\nd to be a reliable way ( clos+ ! night-al>m contacts & ?is me?od is indicat$ 9 ^! figures & 9 o!r figures 9 ?is "w m]ely z a conv5i5t way ( repres5t+ ! matt] diagrammatically4 ,z a matt] ( fact ! night-al>m contacts are ord9>ily clos$ by hav+ ! %utt] fall aga9/ "o spr+1 :i* is !reby press$ into engagem5t ) ano!r spr+ or contact1 z %[n 9 ,fig4 #bdi4 ,?is me?od employs ! %utt] only z a means = me*anically caus+ ! "o spr+ to press aga9/ ! o!r1 ! %utt] itself =m+ no "p ( ! circuit4 ,! reason :y x is n a good plan to h ! %utt] itself act z "o t]m9al ( ! circuit is t ?is necessitates ! circuit connections be+ l$ to ! %utt] ?r\gh ! trunnions on :i* ! %utt] is pivot$4 ,?is is bad because1 obvi\sly1 ! %utt] mu/ be loosely support$ on its trunnions 9 ord] to give x suffici5tly free movem5t1 &1 z is well kn[n1 loose connections are n conducive to good electrical contacts4 ,gr\nd$-& ,metallic-,circuit ,l9es4 ,:5 gr\nd$ circuits 7 ! rule r ?an ! exception1 _m ( ! swit*bo>ds 7 p>ticul>ly adapt$ = _! use & c\ld n be us$ ) metallic-circuit l9es4 ,^! gr\nd$-circuit swit*bo>ds provid$ b a s+le contact 9 ! jack & a s+le contact on ! plug1 ! cords hav+ b a s+le /r& rea*+ f "o plug to ! o!r4 ,! r++ keys & li/5+ keys 7 likewise s+le-contact keys r ?an d\ble4 ,! cle>+-out drop & ! op]ator's talk+ circuit & ! r++ g5]ator 7 connect$ betwe5 ! s+le /r& ( ! cord & ! gr\nd z 0 requir$4 ,! gr\nd$-circuit swit*bo>d has practically pass$ out ( exi/5ce1 & :ile a few ( !m may be 9 use1 !y are n manufactur$ at pres5t4 ,! reason = ?is is t :ile _m gr\nd$ circuits are /ill 9 use1 !re are v few places :]e !re are n "s metallic-circuit l9es1 & :ile ! gr\nd$-circuit swit*bo>d w n s]ve = metallic-circuit l9es1 ! metallic-circuit swit*bo>d w s]ve equally well = ei!r metallic-circuit or gr\nd$ l9es1 & w int]connect !m ) equal facility4 ,?is fact w be made cle> by a consid]ation ( ,figs4 #bgf1 #bgg1 & #bgh4 ,illu/ration3 ,fig4 #bgf4 ,connection ,betwe5 ,metallic ,l9es ,illu/ration3 ,fig4 #bgg4 ,connection ,betwe5 ,gr\nd$ ,l9es ,connection betwe5 ,two ,simil> ,l9es4 ,9 ,fig4 #bgf a common magneto cord circuit is %[n connect+ two metallic-circuit l9es2 9 ,fig4 #bgg ! same cord circuit is %[n connect+ two gr\nd$ l9es4 ,9 ?is case ! l9e wire #a ( ! left-h& l9e is1 :5 ! plugs are ins]t$1 cont9u$ to ! tip ( ! answ]+ plug1 !nce ?r\gh ! tip /r& ( ! cord circuit to ! tip ( ! call+ plug1 !n to ! tip spr+ ( ! "r-h& jack & out to ! s+le conductor ( t l9e4 ,! entire sleeve portion ( ! cord circuit becomes gr\nd$ z soon z ! plugs are ins]t$ 9 ! jacks ( su* a l9e4 ,h5ce1 we see t ! sleeve contacts ( ! plug & ! sleeve conductor ( ! cord are connect$ to gr\nd ?r\gh ! p]man5t gr\nd connection ( ! sleeve conductors ( ! jack z soon z ! plug is ins]t$ into ! jack4 ,?us1 :5 ! cord circuit ( a metallic-circuit swit*bo>d is us$ to connect two gr\nd$ circuits toge!r1 ! tip /r& ( ! cord is ! connect+ l9k betwe5 ! two conductors1 :ile ! sleeve /r& ( ! cord m]ely s]ves to gr\nd "o side ( ! cle>+-out drop & "o side ea* ( ! op]ator's telephone set & ! r++ g5]ator :5 _! respective keys are op]at$4 ,connection betwe5 ,dissimil> ,l9es4 ,fig4 #bgh %[s h[ ! same cord circuit & ! same arrangem5t ( l9e equipm5t may be us$ = connect+ a gr\nd$ l9e to a metallic-circuit l9e4 ,! metallic circuit l9e is %[n on ! left & ! gr\nd$ l9e on ! "r4 ,:5 ! two plugs are ins]t$ into ! respective jacks ( ?is figure1 ! "r-h& conductor ( ! metallic circuit %[n on ! left w be cont9u$ ?r\gh ! tip /r& ( ! cord circuit to ! l9e conductor ( ! gr\nd$ l9e %[n on ! "r4 ,! left-h& conductor ( ! metallic-circuit l9e w be connect$ to gr\nd because x w be cont9u$ ?r\gh ! sleeve /r& ( ! cord circuit to ! sleeve contact ( ! call+ plug & !nce to ! sleeve contact ( ! jack ( ! gr\nd$ l9e1 :i* sleeve contact is %[n to be gr\nd$4 ,! talk+ circuit betwe5 ! two connect$ l9es 9 ?is case may be trac$ z foll[s3 ,f ! subscrib]'s /ation at ! left ?r\gh ! "r-h& limb ( ! metallic-circuit l9e1 ?r\gh ! tip contact & tip conductor ( ! cord circuit1 to ! s+le limb ( ! gr\nd$-circuit l9e1 !nce to ! sub-/ation ( t l9e & ?r\gh ! talk+ app>atus !re to gr\nd4 ,! return pa? f ! "r-h& /ation is by way ( gr\nd to ! gr\nd connection at ! c5tral (fice1 !nce to ! sleeve contact ( ! gr\nd$ l9e jack1 ?r\gh ! sleeve conductor ( ! cord circuit1 to ! sleeve contact ( ! metallic-circuit l9e jack1 & !nce by ! left-h& limb ( ! metallic-circuit l9e to ! subscrib]'s /ation4 ,illu/ration3 ,fig4 #bgh4 ,connection ,betwe5 ,dissimil> ,l9es ,a bett] way ( connect+ a metallic-circuit l9e to a gr\nd$ l9e is by ! use ( a special cord circuit involv+ a repeat+ coil1 su* a connection be+ %[n 9 ,fig4 #bgi4 ,! cord circuit 9 ?is case diff]s 9 no respect f ^? already %[n except t a repeat+ coil is associat$ ) x 9 su* a way z to conductively divide ! answ]+ side f ! call+ side4 ,obvi\sly1 :atev] curr5ts come ov] ! l9e connect$ ) ! answ]+ plug w pass ?r\gh ! w9d+s #a & #b ( ?is coil & w induce correspond+ curr5ts 9 ! w9d+s #c & #d1 :i* latt] curr5ts w pass out ov] ! circuit ( ! l9e connect$ ) ! call+ plug4 ,:5 a gr\nd$ circuit is connect$ to a metallic circuit 9 ?is mann]1 no gr\nd is ?r[n onto ! metallic circuit4 ,! balance ( ! metallic circuit is1 !re=e1 ma9ta9$4 ,to gr\nd "o side ( a metallic circuit frequ5tly s unbalances x z to cause x to become noisy1 t is1 to h curr5ts fl[+ 9 x1 by induction or f o!r causes1 o!r ?an ! curr5ts :i* are suppos$ to be !re = ! purpose ( convey+ spee*4 ,illu/ration3 ,fig4 #bgi4 ,connection ( ,dissimil> ,l9es ?r\gh ,repeat+ ,coil ,conv]tible ,cord ,circuits4 ,! consid]ation ( ,fig4 #bgi br+s u to ! subject ( s-call$ conv]tible cord circuits4 ,"s swit*bo>ds1 s]v+ a mixture ( metallic & gr\nd$ l9es1 are provid$ ) cord circuits :i* may be conv]t$ at w by ! op]ator f ! ord9>y type %[n 9 ,fig4 #bgf to ! type %[n 9 ,fig4 #bgi4 ,! advantage ( ?is w be obvi\s f ! foll[+ consid]ation4 ,:5 a call orig9ates on any l9e1 ei!r gr\nd$ or metallic1 ! op]ator does n "k :i* k9d ( a l9e is to be call$ =4 ,%e1 !re=e1 plugs into ?is l9e ) any "o ( h] answ]+ plugs & completes ! connection 9 ! usual way4 ,if ! call is = ! same k9d ( a circuit z t ov] :i* ! call orig9at$1 %e places ! conv]t+ key 9 su* a position z w connect ! conductors ( ! cord circuit /raight ?r\gh2 :ile if ! connection is = a diff]5t k9d ( a l9e ?an t on :i* ! call orig9at$ %e ?r[s ! conv]t+ key into su* a position z to include ! repeat+ coil4 ,a /udy ( ,fig4 #bhj w %[ t :5 ! conv]t+ key1 :i* is commonly ref]r$ to z ! repeat+-coil key1 is 9 "o position1 ! cord conductors w be cut /raight ?r\gh1 ! repeat+ coil be+ left op5 9 bo? its w9d+s2 & :5 x is ?r[n to its o!r position1 ! connection betwe5 ! answ]+ & call+ sides ( ! cord circuit w be sev]$ & ! repeat+ coil ins]t$ s z to br+ ab\t ! same effects & circuit arrangem5ts z are %[n 9 ,fig4 #bgi4 ,illu/ration3 ,fig4 #bhj4 ,conv]tible ,cord ,circuit ,cord-,circuit ,consid]ations4 ,simple ,bridg+ ,drop ,type4 ,! matt] ( cord circuits 9 magneto swit*bo>ds is des]v+ ( mu* att5tion4 ,s f> z talk+ requirem5ts are conc]n$1 ! ord9>y =m ( cord circuit ) a cle>+-out drop bridg$ across ! two /r&s is adequate = ne>ly all conditions except ^? :]e a gr\nd$-& a metallic-circuit l9e are connect$ toge!r1 9 :i* case ! inclusion ( a repeat+ coil has "s advantages4 ,illu/ration3 ,fig4 #bha4 ,bridg+ ,drop-,cord ,circuit ,f ! /&po9t ( signal+1 h[ev]1 ?is type ( cord circuit has "s disadvantages "u c]ta9 conditions4 ,9 ord] to simplify ! discussion ( ?is & o!r cord-circuit matt]s1 ref]5ce w be made to "s diagrams f :i* ! r++ & li/5+ keys & talk+ app>atus h be5 entirely omitt$4 ,9 ,fig4 #bha ! regul> bridg+ type ( cle>+-out drop-cord circuit is %[n1 ?is be+ ! type already discuss$ z /&>d4 ,= ord9>y practice x is all "r4 ,c]ta9 difficulties are exp]i5c$ ) x1 h[ev]1 :]e l9es ( v>i\s l5g?s & v>i\s types ( sub-/ation app>atus are connect$4 ,= in/ance1 if a long bridg+ l9e be connect$ ) "o end ( ?is cord circuit & a %ort l9e hav+ a l[-resi/ance s]ies r+] be connect$ ) ! o!r end1 !n a /ation on ! long l9e may h "s difficulty 9 ?r[+ ! cle>+-out drop1 because ( ! l[-resi/ance %unt t is plac$ ar\nd x ?r\gh ! %ort l9e & ! l[-resi/ance r+]4 ,9 o!r words1 ! cle>+-out drop is %unt$ by a comp>atively l[-resi/ance l9e & r+] & ! feeble curr5ts arriv+ f a di/ant /ation ov] ! long l9e are n suffici5t to op]ate ! drop ?us h&icapp$4 ,! adv5t ( ! v>i\s =ms ( p>ty-l9e selective signal+ & ! use ( su* sy/ems 9 connection ) magneto swit*bo>ds has br\ght 9 ano!r difficulty t sometimes manife/s itself ) ?is type ( cord circuit4 ,if two ord9>y magneto telephones are connect$ to ! two ends ( ?is cord circuit1 x is obvi\s t :5 "o ( ! subscrib]s has hung up 8 receiv] & ! o!r subscrib] r+s (f1 ! bell ( ! o!r subscrib] w v likely be rung ev5 ?\gh ! cle>+-out drop op]ates prop]ly2 x w\ld be bett] 9 any ev5t n to h ?is o!r subscrib]'s bell rung1 = he may und]/& x to be a recall to 8 telephone4 ,:51 h[ev]1 a p>ty l9e is connect$ ?r\gh su* a cord circuit to an ord9>y l9e hav+ bridg+ in/rum5ts1 = in/ance1 ! difficulty due to r++ (f becomes ev5 great]4 ,:5 ! subscrib] on ! magneto l9e op]ates 8 g5]ator to give ! cle>+-out signal1 he is v likely to r+ "s ( ! bells on ! o!r l9e & ?is1 ( c\rse1 is an undesirable ?+4 ,?is may happ5 ev5 9 ! case ( h>monic bells on ! p>ty l9e1 s9ce x is possible t ! subscrib] on ! magneto l9e 9 turn+ 8 g5]ator w1 at "s phase ( ! op]ation1 /rike j ! prop] frequ5cy to r+ "s "o ( ! bells on ! h>monic p>ty l9e4 ,x is obvi\s1 !re=e1 t !re is a real ne$ = a cord circuit t w prev5t ?r\gh r++4 ,"o way ( elim9at+ ! ?r\gh-r++ difficulty 9 ! type ( cord circuit %[n 9 ,fig4 #bha w\ld be to use su* a v l[-w\nd cle>+-out drop t x w\ld practically %ort-circuit ! l9e ) respect to r++ curr5ts & prev5t !m f pass+ on to ! o!r l9e4 ,?is1 h[ev]1 is n a good ?+ to d1 s9ce a w9d+ suffici5tly l[ to %unt ! effective r++ curr5t w\ld also be too l[ = good telephone transmission4 ,illu/ration3 ,fig4 #bhb4 ,s]ies ,drop-,cord ,circuit ,s]ies ,drop ,type4 ,ano!r type ( cord circuit t 0 l>gely us$ by ! ,/romb]g-,c>lson ,telephone ,manufactur+ ,company at "o "t is %[n 9 ,fig4 #bhb4 ,9 ?is ! cle>+-out drop 0 n bridg$ b 0 plac$ 9 s]ies 9 ! tip side ( ! l9e & 0 %unt$ by a cond5s]4 ,! resi/ance ( ! cle>+-out drop 0 #a1jjj ohms & ! capacity ( ! cond5s] 0 #b micr(>ads4 ,x is obvi\s t ?is way ( connect+ ! cle>+-out drop 0 subject to ! r++-?r\gh difficulty1 s9ce ! circuit ?r\gh :i* ! cle>+-out curr5t necess>ily pass$ includ$ ! telephone in/rum5t ( ! l9e t 0 n s5d+ ! cle>+-out signal4 ,?is =m 0 also objectionable because x 0 necess>y = ! subscrib] to r+ ?r\gh ! comb9$ resi/ance ( two l9es1 & 9 case ! o!r l9e happ5$ to be op51 no cle>+-out signal w\ld be receiv$4 ,:ile ?is circuit1 !re=e1 0 p]haps n q s likely z ! o!r to tie up ! subscrib]1 t is1 to leave him connect$ )\t ! ability to s5d a cle>+-out signal1 yet x 0 sure to r+ ?r\gh1 = ! cle>+-out drop c\ld n be ?r[n )\t ! curr5t pass+ ?r\gh ! o!r subscrib]'s /ation4 ,illu/ration3 ,fig4 #bhc4 ,dean ,non-,r+-,?r\gh ,cord ,circuit ,non-,r+-,?r\gh ,type4 ,an e>ly attempt at a non-r+-?r\gh cord is %[n 9 ,fig4 #bhc1 ?is hav+ once be5 /&>d ) ! ,dean ,electric ,company4 ,x made use ( two cond5s]s ( #a micr(>ad ea*1 "o 9 ea* side ( ! cord circuit4 ,! cle>+-out drop 0 ( #ejj ohms resi/ance & 0 connect$ f ! answ]+ side ( ! tip conductor to ! call+ side ( ! sleeve conductor4 ,9 ?is way :atev] cle>+-out curr5t rea*$ ! c5tral (fice pass$ ?r\gh at lea/ "o ( ! cond5s]s & ! cle>+-out drop4 ,9 ord] = ! cle>+-out curr5t to pass on beyond ! c5tral (fice x 0 necess>y = x to pass ?r\gh ! two cond5s]s 9 s]ies4 ,?is arrangem5t _h ! advantage ( giv+ a positive r+-(f1 reg>dless ( ! condition ( ! connect$ l9e4 ,obvi\sly1 ev5 if ! l9e 0 %ort-circuit$1 ! r++ curr5ts f ! o!r l9e w\ld /ill be =c$ ?r\gh ! cle>+-out drop on acc\nt ( ! high effective resi/ance ( ! #a-micr(>ad cond5s] connect$ 9 s]ies ) ! %ort-circuit$ l9e4 ,also ! cle>+-out signal w\ld be prop]ly receiv$ if ! connect$ l9e 7 op51 s9ce ! cle>+-out drop w\ld /ill be directly across ! cord circuit4 ,?is arrangem5t also l>gely prev5t$ ?r\gh r++1 s9ce ! curr5ts w\ld pass ?r\gh ! #a-micr(>ad cond5s] & ! #ejj-ohm drop m readily ?an ?r\gh ! two cond5s]s connect$ 9 s]ies4 ,illu/ration3 ,fig4 #bhd4 ,mon>* ,non-,r+-,?r\gh ,cord ,circuit ,9 ,fig4 #bhd is %[n ! non-r+-?r\gh arrangem5t ( cord circuit adopt$ by ! ,mon>* ,company4 ,9 ?is sy/em ! cle>+-out drop has two w9d+s1 ei!r ( :i* w op]ate ! armature4 ,! two w9d+s are bridg$ across ! cord circuit1 ) a #a_/b-micr(>ad cond5s] 9 s]ies 9 ! tip /r& betwe5 ! two w9d+ connections4 ,:ile ! l[-capacity cond5s] w all[ ! high-frequ5cy talk+ curr5t to pass readily )\t affect+ x to any appreciable ext5t1 x (f]s a high resi/ance to a l[-frequ5cy r++ curr5t1 ?us prev5t+ x f pass+ out on a connect$ l9e & =c+ x ?r\gh "o ( ! w9d+s ( ! coil4 ,!re is a t5d5cy to trans=m] action 9 ?is arrangem5t1 "o ( ! w9d+s s]v+ z a prim>y & ! o!r z a second>y1 b ?is has n prev5t$ ! device f be+ highly successful4 ,a modification ( ?is arrangem5t is %[n 9 ,fig4 #bhe1 :]e9 a d\ble-w\nd cle>+-out drop is us$1 & a #a_/b-micr(>ad cond5s] is plac$ 9 s]ies 9 ea* side ( ! cord circuit betwe5 ! w9d+ connections ( ! cle>+-out drop4 ,?is circuit %\ld give a positive r+-(f "u all conditions & %\ld prev5t ?r\gh r++ except z x may be provid$ by ! trans=m] action betwe5 ! two w9d+s on ! same core4 ,illu/ration3 ,fig4 #bhe4 ,non-,r+-,?r\gh ,cord ,circuit ,ano!r r +5i\s me?od ( secur+ a positive r+-(f & yet ( prev5t+ 9 a c]ta9 degree ! undesirable r++-?r\gh feature is %[n 9 ! cord circuit1 ,fig4 #bhf4 ,9 ?is two non-inductive coils #a & #b are %[n connect$ 9 s]ies 9 ! tip & sleeve /r&s ( ! coils1 respectively4 ,betwe5 ! neutral po9t ( ^! two non-inductive w9d+s is connect$ ! cle>+-out drop circuit4 ,voice curr5ts f9d ready pa? ?r\gh ^! non-inductive w9d+s because ( ! fact t1 be+ non-inductive1 !y pres5t only _! /raight ohmic resi/ance4 ,! imp$ance ( ! cle>+-out drop prev5ts ! w9d+s be+ %unt$ across ! two sides ( ! cord circuit4 ,) ?is circuit a positive r+-(f is assur$ ev5 ?\gh ! l9e connect$ ) ! "o s5d+ ! cle>+-out signal is %ort-circuit$ or op54 ,if x is %ort-circuit$1 ! %unt ar\nd ! cle>+-out drop w /ill h ! resi/ance ( two ( ! non-inductive w9d+s includ$ 9 x1 & ?us ! drop w nev] be %ort-circuit$ by a v l[-resi/ance pa?4 ,obvi\sly1 an op5 circuit 9 ! l9e w n prev5t ! cle>+-out signal be+ receiv$4 ,:ile ?is is an +5i\s s*eme1 x is n "o to be highly recomm5d$ s9ce ! non-inductive w9d+s1 9 ord] to be effective s f> z signal+ is conc]n$1 mu/ be ( consid]able resi/ance & ?is resi/ance is 9 s]ies 9 ! talk+ circuit4 ,ev5 non-inductive resi/ance is to be avoid$ 9 ! talk+ circuit :5 x is ( consid]able magnitude & :]e !re are o!r ways ( solv+ ! problem4 ,illu/ration3 ,fig4 #bhf4 ,cord ,circuit ) ,diff]5tial ,w9d+s ,d\ble ,cle>+-out ,type4 ,"s p pref] two cle>+-out drops 9 ea* cord circuit1 s arrang$ t ! "o w be responsive to curr5ts s5t f ! l9e ) :i* ! answ]+ plug is connect$ & ! o!r responsive only to curr5ts s5t f ! l9e ) :i* ! call+ plug is connect$4 ,su* a s*eme1 %[n 9 ,fig4 #bhg1 is sometimes employ$ by ! ,dean1 ! ,mon>*1 & ! ,kellogg companies4 ,two #ejj-ohm cle>+-out drops ( ord9>y con/ruction are bridg$ across ! cord circuit & 9 ea* side ( ! cord circuit !re is includ$ betwe5 ! drop connections a #a-micr(>ad cond5s]4 ,r++ curr5ts orig9at+ on ! l9e ) :i* ! answ]+ plug is connect$ w pass ?r\gh ! cle>+-out drop1 :i* is across t side ( ! cord circuit1 )\t hav+ to pass ?r\gh any cond5s]s4 ,9 ord] to rea* ! o!r cle>+-out drop ! r++ curr5t mu/ pass ?r\gh ! two #a-micr(>ad cond5s]s 9 s]ies1 ?is mak+ 9 effect only #a_/b-micr(>ad4 ,z is well kn[n1 a #a_/b-micr(>ad cond5s] n only transmits voice curr5ts ) ease b also (f]s a v high app>5t resi/ance to r++ curr5ts4 ,) ! d\ble cle>+-out drop sy/em ! op]ator is enabl$ to tell :i* subscrib] is r++ (f4 ,if bo? %utt]s fall %e kn[s t bo? subscrib]s h s5t cle>+-out signals & %e1 !re=e1 pulls d[n ! connection )\t ! usual precaution ( li/5+ to see :e!r "o ( ! subscrib]s may be wait+ = ano!r connection4 ,?is d\ble cle>+-out sy/em is analog\s to ! complete d\ble-lamp sup]vision t w be ref]r$ to m fully 9 connection ) common-batt]y circuits4 ,!re is n ! ne$ = d\ble sup]vision 9 magneto "w1 h[ev]1 t !re is 9 common-batt]y "w because ( ! fact t 9 magneto "w ! subscrib]s frequ5tly fail to rememb] to r+ (f1 ?is act be+ entirely volunt>y on _! "p1 :ile 9 common-batt]y "w1 ! cle>+-out signal is giv5 automatically by ! subscrib] :5 he hangs up 8 receiv]1 ?us accompli%+ ! desir$ end )\t ! necessity ( ?\ghtfulness on 8 "p4 ,illu/ration3 ,fig4 #bhg4 ,d\ble ,cle>+-,out ,drops ,ano!r =m ( d\ble cle>+-out cord circuit is %[n 9 ,fig4 #bhh4 ,9 ?is ! call+ & ! answ]+ plugs are sep>at$ by repeat+ coils1 a cond5s] ( #a-micr(>ad capacity be+ ins]t$ betwe5 ea* pair ( w9d+s on ! two ends ( ! circuit4 ,! cle>+-out drops are plac$ across ! call+ & answ]+ cords 9 ! usual mann]4 ,! cond5s] 9 ?is case prev5ts ! drop be+ %ort-circuit$ ) respect to r++ curr5ts & yet p]mits ! voice curr5ts to fl[ readily ?r\gh x4 ,! high imp$ance ( ! drop =ces ! voice curr5ts to take ! pa? ?r\gh ! repeat+ coil r ?an ?r\gh ! drop4 ,?is circuit has ! advantage ( a repeat+-coil cord circuit 9 p]mitt+ ! connection ( metallic & gr\nd$ l9es )\t caus+ ! unbalanc+ ( ! metallic circuits by ! connection to !m ( ! gr\nd$ circuits4 ,illu/ration3 ,fig4 #bhh4 ,d\ble ,cle>+-,out ,drops ,rec5tly !re has be5 a gr[+ t5d5cy on ! "p ( "s manufactur]s to control _! cle>+-out signals by means ( relays associat$ ) cord circuits1 ^! signals sometimes be+ ord9>y cle>+-out drops & sometimes inc&esc5t lamps4 ,illu/ration3 ,fig4 #bhi4 ,relay-,controll$ ,cle>+-,out ,drop ,9 ,fig4 #bhi is %[n ! cord circuit sometimes us$ by ! ,l4,m4 ,ericsson ,telephone ,manufactur+ ,company4 ,a high-w\nd relay is normally plac$ across ! cord & ?is1 besides hav+ a high-resi/ance & imp$ance w9d+ has a l[-resi/ance lock+ w9d+ s arrang$ t :5 ! relay pulls up its armature x w close a local circuit includ+ ?is lock+ w9d+ & local batt]y4 ,:5 once pull$ up ! relay w1 !re=e1 /ay up due to ! en]giz+ ( ?is lock+ coil4 ,ano!r contact op]at$ by ! relay closes ! circuit ( a l[-w\nd cle>+-out drop plac$ across ! l9e1 ?us bridg+ x across ! l9e4 ,! condition ( high imp$ance is ma9ta9$ across ! cord circuit normally :ile ! subscrib]s are talk+2 b :5 ei!r ( !m r+s (f1 ! high-w\nd relay pulls up & locks1 ?us complet+ ! circuit ( ! cle>+-out drop across ! cords4 ,! subsequ5t impulses s5t f ! subscrib]s' g5]ators op]ate ?is drop4 ,! relay is re/or$ or unlock$ & ! cle>+-out drop disconnect$ f ! cord circuit by means ( a key :i* op5s ! lock+ circuit ( ! relay4 ,?is key is really a "p ( ! li/5+ key & s]ves to op5 ?is lock+ circuit :5ev] ! li/5+ key is op]at$4 ,! cle>+-out drop is also automatically re/or$ by ! action ( ! li/5+ key1 ?is connection be+ me*anical r ?an electrical4 ,recall ,lamp3--,! ,mon>* ,company sometimes furni%es :at x t]ms a recall lamp 9 connection ) ! cle>+-out drops on its magneto swit*bo>ds4 ,! circuit arrangem5t is %[n 9 ,fig4 #bij1 :]e9 ! drop is ! regul> d\ble-w\nd cle>+-out drop l t ( ,fig4 #bhd4 ,! armature c>ries a contact spr+ adapt$ to close ! local circuit ( a lamp :5ev] x is attract$4 ,! object ( ?is is to give ! subscrib]1 ^: l9e /ill rema9s connect$ by a cord circuit1 opportunity to recall ! c5tral (fice if ! op]ator has n re/or$ ! cle>+-out drop4 ,illu/ration3 ,fig4 #bij4 ,cord ,circuit ) ,recall ,lamp ,lamp-,signal ,type4 ,!re has be5 a t5d5cy on ! "p ( "s manufactur+ companies to advocate1 in/ead ( drop signals1 inc&esc5t lamp signals = ! cord circuits1 & sometimes = ! l9e circuits on magneto bo>ds4 ,9 mo/ cases ?is may be look$ ^u z a frill4 ,:]e l9e lamps in/ead ( drops h be5 us$ on magneto swit*bo>ds1 x has be5 ! practice to employ1 in/ead ( a drop1 a lock+ relay associat$ ) ea* lamp1 :i* 0 s arrang$ t :5 ! relay 0 en]giz$ by ! magneto curr5t f ! subscrib]'s /ation1 x w\ld pull up & lock1 ?us clos+ ! lamp circuit4 ,! local circuit1 or lock+ circuit1 :i* includ$ ! lamp 0 c>ri$ ?r\gh a pair ( contacts 9 ! correspond+ jacks s arrang$ t :5 ! plug 0 ins]t$ 9 answ] to ! call1 ?is lock+ lamp circuit w\ld be op51 !reby ext+ui%+ ! lamp & also unlock+ ! relay4 ,!re seems to be absolutely no good reason :y lamp signals %\ld be sub/itut$ = me*anical drops 9 magneto swit*bo>ds4 ,!re is no ne$ = ! economy 9 space :i* ! lamp signal af=ds1 & ! complications br\ght 9 by ! lock+ relays1 & ! requirem5ts = ma9ta9+ a local batt]y suitable = en]giz+ ! lamps are n w>rant$ = ord9>y cases4 ,illu/ration3 ,fig4 #bia4 ,cord ,circuit ) ,d\ble ,lamp ,signals ,9 ,fig4 #bia is %[n a cord circuit1 adaptable to magneto swit*bo>ds1 provid$ ) d\ble lamp signals in/ead ( cle>+-out drops4 ,two high-w\nd lock+ relays are bridg$ across ! l9e1 ! cord /r&s be+ divid$ by #a-micr(>ad cond5s]s4 ,:5 ! high-w\nd coil ( ei!r relay is en]giz$ by ! magneto curr5t f ! subscrib]'s /ation1 ! relay pulls up & closes a lock+ circuit includ+ a batt]y & a coil #b1 ! contact #c ( ! lock+ relay1 & also ! contact #d ( a re/or+ key4 ,?is circuit may be trac$ f ! gr\nd ?r\gh batt]y1 coil #b1 contact #c controll$ by ! relay1 & contact #d controll$ by ! re/or+ key1 & back to gr\nd4 ,9 multiple ) ! lock+ coil #b is ! lamp1 :i* is illum9at$1 !re=e1 :5ev] ! lock+ circuit is clos$4 ,pressure on ! re/or+ key breaks ! lock+ circuit ( ei!r ( ! lamps1 !reby putt+ out ! lamp & at ! same "t re/or+ ! lock+ relay to its normal position4 ,lamps vs4 ,drops 9 ,cord ,circuits4 ,s mu* has be5 said & writt5 ab\t ! advantages ( inc&esc5t lamps z signals 9 swit*bo>ds & ab\t ! m]its ( ! common-batt]y me?od ( supply+ curr5t to ! subscrib]s1 t !re has be5 a t5d5cy = p 9 *>ge ( ! op]ation ( small ex*anges to sub/itute ! lamp = ! drop 9 a magneto swit*bo>d 9 ord] to give ! g5]al appe>ance ( common-batt]y op]ations4 ,!re has also be5 a t5d5cy to employ ! common-batt]y sy/em ( op]ation 9 _m places :]e magneto s]vice %\ld h be5 us$1 a mi/ake :i* has n[ be5 realiz$ & correct$4 ,9 places :]e ! simple magneto swit*bo>d is ! ?+ to use1 ! simpl] x is ! bett]1 & ! employm5t ( lock+ relays & lamp signals & ! complications :i* !y c>ry ) !m1 is n w>rant$4 ,swit*bo>d ,assembly4 ,! assembly ( all ! p>ts ( a simple magneto swit*bo>d into a complete :ole des]ves f9al consid]ation4 ,! /ructure 9 :i* ! v>i\s p>ts are m\nt$1 ref]r$ to z ! cab9et1 is usually ( wood4 ,functions ( ,cab9et4 ,! purpose ( ! cab9et is n only to =m a support = ! v>i\s pieces ( app>atus b also to protect !m f du/ & me*anical injury1 & to hold ^? p>ts t mu/ be manipulat$ by ! op]ator 9 su* relation t !y may be mo/ conv5i5t = use1 & ?us be/ adapt$ = c>ry+ out _! v>i\s functions4 ,o!r po9ts to be provid$ = 9 ! design ( ! cab9et & ! arrangem5t ( ! v>i\s p>ts )9 are3 t all ! app>atus t is 9 any way liable to get out ( ord] may be readily accessible = inspection & repairs2 & t provision %all be made :]eby ! wir+ ( ^! v>i\s pieces ( app>atus may be done 9 a sy/ematic & simple way s z to m9imize ! dang] ( cross$1 gr\nd$1 or op5 circuits1 & s z to provide = ready repair 9 case any ( ^! injuries d occur4 ,wall-,type ,swit*bo>ds4 ,! simple/ =m ( swit*bo>d is t = s]v+ small communities 9 rural di/ricts4 ,ord9>ily ! telephone indu/ry 9 su* a community beg9s by a gr\p ( f>m]s along a c]ta9 road build+ a l9e connect+ ! h\ses ( sev]al ( !m & in/all+ _! own in/rum5ts4 ,?is l9e is liable to be ext5d$ to "s /ore at ! village or settlem5t1 ?us af=d+ communication betwe5 ^! f>m]s & ! c5t] ( _! community4 ,lat] on ^? resid+ on o!r roads d ! same ?+ & connect _! l9es to ! same /ore or c5tral po9t4 ,!n x is t "s =m ( swit*bo>d is e/abli%$1 & p]haps ! /orekeep]'s daught] or wife is paid a small fee = att5dance4 ,illu/ration3 ,fig4 #bib4 ,wall ,swit*bo>d ) ,telephone ,a swit*bo>d well-adapt$ = ?is class ( s]vice :]e ! numb] ( l9es is small1 is %[n 9 ,fig4 #bib4 ,9 ?is ! op]ator's talk+ app>atus & h] call+ app>atus are embodi$ 9 an ord9>y magneto wall telephone4 ,! swit*bo>d prop] is m\nt$ alongside ( ?is1 & ! two l9e b9d+ po/s ( ! telephone are connect$ by a pair ( wires to t]m9als ( ! op]ator's plug1 :i* plug is %[n hang+ f ! left-h& portion ( ! swit*bo>d4 ,! v>i\s l9es c5t]+ at ?is po9t t]m9ate 9 ! comb9$ drops & jacks on ! swit*bo>d1 ( :i* !re are #bj %[n 9 ?is illu/ration4 ,beside ! op]ator's plug !re are a numb] ( pairs ( plugs %[n hang+ f ! swit*bo>d cab9et4 ,^! are connect$ /raight ?r\gh 9 pairs1 !re be+ no cle>+-out drops or keys associat$ ) !m 9 ! arrangem5t4 ,ea* l9e %[n is provid$ ) an extra jack1 ! purpose ( :i* w be pres5tly und]/ood4 ,! me?od ( op]ation is z foll[s3 ,:5 a subscrib] on a c]ta9 l9e desires to get connection ?r\gh ! swit*bo>d he turns 8 g5]ator & ?r[s ! drop4 ,! op]ator 9 ord] to communicate ) him ins]ts ! plug 9 :i* h] telephone t]m9ates into ! jack1 & removes h] receiv] f its hook4 ,hav+ le>n$ t x is = a c]ta9 subscrib] on ano!r l9e1 %e )draws h] plug f ! jack ( ! call+ l9e & ins]ts x into ! jack ( ! call$ l9e1 !n1 hang+ up h] receiv]1 %e turns ! g5]ator crank 9 accordance ) ! prop] code to call t subscrib]4 ,:5 t subscrib] responds %e connects ! two l9es by ins]t+ ! two plugs ( a pair into _! respective jacks1 & ! subscrib]s are ?us plac$ 9 communication4 ,! extra jack associat$ ) ea* l9e is m]ely an op5 jack hav+ its t]m9als connect$ respectively ) ! two sides ( ! l9e4 ,:5ev] an op]ator desires to li/5 9 on two connect$ l9es %e does s by ins]t+ ! op]ator's plug into "o ( ^! extra jacks ( ! connect$ l9es1 & %e may ?us f9d out :e!r ! subscrib]s are ?r\gh talk+ or :e!r ei!r "o ( !m desires ano!r connection4 ,! drops 9 su* swit*bo>ds are commonly high w\nd & left p]man5tly bridg$ across ! l9e s z to s]ve z cle>+-out drops4 ,! usual night-al>m atta*m5t is provid$1 ! buzz] be+ %[n at ! upp] "r-h& portion ( ! cab9et4 ,illu/ration3 ,fig4 #bic4 ,comb9$ ,telephone & ,swit*bo>d ,ano!r type ( swit*bo>d commonly employ$ = ?is k9d ( s]vice is %[n 9 ,fig4 #bic1 9 :i* ! telephone & ! swit*bo>d cab9et are comb9$4 ,! op]ation ( ?is bo>d is practically ! same z t ( ,fig4 #bib1 al?\gh x has manually-re/or$ drops in/ead ( self-re/or+ drops2 ! diff]5ce betwe5 ^! two types1 h[ev]1 is n mat]ial = ?is class ( s]vice4 ,= su* "w ! op]ator has ample "t to att5d to ! re/or+ ( ! drop & ! only possible advantage 9 ! comb9$ drop-&-jack = ?is class ( "w is t x prev5ts ! op]ator f =gett+ to re/ore ! drops4 ,h[ev]1 %e is n likely to d ?is ) ! night-al>m circuit 9 op]ation1 s9ce ! buzz] or bell w\ld cont9ue to r+ z long z ! drop 0 d[n4 ,illu/ration3 ,fig4 #bid4 ,upright ,magneto ,swit*bo>d ,illu/ration3 ,fig4 #bie4 ,upright ,magneto ,swit*bo>d--,re> ,view ,upright ,type ,swit*bo>d4 ,by f> ! mo/ common type ( magneto swit*bo>d is ! s-call$ upright type1 :]e9 ! drops & jacks are m\nt$ on ! face ( upright panels ris+ f a horizontal %elf1 :i* %elf conta9s ! plugs1 ! keys1 & any o!r app>atus :i* ! op]ator mu/ manipulate4 ,front & re> views ( su* a swit*bo>d1 z manufactur$ by ! ,kellogg ,company1 are %[n 9 ,figs4 #bid & #bie4 ,?is p>ticul> bo>d is provid$ ) fifty comb9$ drops & jacks &1 !re=e1 equipp$ = fifty subscrib]s' l9es4 ,! drops & jacks are m\nt$ 9 /rips ( five1 & arrang$ 9 two panels4 ,! cle>+-out drops1 ( :i* !re are t51 are arrang$ at ! bottom ( ! two panels 9 a s+le r[ & may be se5 imm$iately above ! swit*bo>d plugs4 ,!re are t5 pairs ( cords & plugs ) _! associat$ r++ & li/5+ keys1 ! plugs be+ m\nt$ on ! re> portion ( ! %elf1 :ile ! r++ & li/5+ keys are m\nt$ on ! h+$ portion ( ! %elf 9 front ( ! plugs4 ,illu/ration3 ,fig4 #bif4 ,details ( ,drop1 ,jack1 ,plug1 & ,key ,arrangem5t ,illu/ration3 ,fig4 #big4 ,cross-,section ( ,upright ,swit*bo>d ,a bett] idea ( ! arrangem5t ( drops1 jacks1 plugs1 & keys may be _h f an illu/ration ( a ,dean magneto swit*bo>d %[n 9 ,fig4 #bif4 ,! cle>+-out drops & ! arrangem5t ( ! plugs & keys are cle>ly %[n4 ,! portion ( ! swit*bo>d on :i* ! plugs are m\nt$ is always immovable1 ! plugs be+ provid$ ) seats ?r\gh :i* holes are bor$ ( suffici5t size to p]mit ! swit*bo>d cord to pass b5ea? ! %elf4 ,:5 "o ( ^! plugs is rais$1 ! cord is pull$ up ?r\gh ?is hole ?us all[+ ! plug to be plac$ 9 any ( ! jacks4 ,! key arrangem5t %[n 9 ?is p>ticul> cut is in/ructive4 ,x w be notic$ t ! "r-h& five pairs ( plugs are provid$ ) ord9>y r++ & li/5+ keys1 :ile ! left-h& five are provid$ ) p>ty-l9e r++ keys & li/5+ keys4 ,! li/5+ key 9 ea* case is ! "o 9 ! re> & is alike = all ( ! cord pairs4 ,! "r-h& five r++ keys are s arrang$ t press+ ! lev] to ! re> w r+ on ! answ]+ cord1 :ile press+ x t[>d ! front w cause r++ curr5t to fl[ on ! call+ plug4 ,9 ! left-h& five pairs ( cords %[n 9 ?is cut1 ! pressure ( any "o ( ! keys causes a r++ curr5t ( a c]ta9 frequ5cy to fl[ on ! call+ cord1 ?is frequ5cy dep5d+ ^u :i* "o ( ! keys is press$4 ,illu/ration3 ,fig4 #bih4 ,cord ,weight ,an excell5t idea ( ! gr\p+ ( ! v>i\s pieces ( app>atus 9 a complete simple magneto swit*bo>d may be _h f ,fig4 #big4 ,:ile ! arrangem5t "h %[n is applicable p>ticul>ly to ! app>atus ( ! ,dean ,electric ,company1 ! /ructure indicat$ is none-!-less g5]ally in/ructive1 s9ce x repres5ts good practice 9 ?is respect4 ,9 ?is draw+ ! /ation>y plug %elf ) ! plug seat is cle>ly %[n & also ! h+$ key %elf4 ,! h+e ( ! key %elf is an important feature & is univ]sally f\nd 9 all swit*bo>ds ( ?is g5]al type4 ,! key %elf may be rais$ & ?us expose all ( ! wir+ lead+ to ! keys1 z well z ! v>i\s contacts ( ! keys !mselves1 to inspection4 ,illu/ration3 ,fig4 #bii4 ,magneto ,swit*bo>d1 ,t>get ,signals ,z w be se51 ! swit*bo>d cords lead+ f ! plugs ext5d d[n to a po9t ne> ! bottom ( ! cab9et :]e !y pass ?r\gh pulley weights & !n up to a /ation>y cord rack4 ,on ?is cord rack are provid$ t]m9als = ! v>i\s conductors 9 ! cord1 & x is at ?is po9t t ! cord conductors jo9 ! o!r wires lead+ to ! o!r portions ( ! app>atus z requir$4 ,a good =m ( cord weight is %[n 9 ,fig4 #bih2 & obvi\sly ! function ( ^! weights is to keep ! cords taut at all times & to prev5t _! tangl+4 ,illu/ration3 ,fig4 #cjj4 ,re> ,view ( ,t>get ,signal1 ,magneto ,swit*bo>d ,! draw+1 ,fig4 #big1 also gives a good idea ( ! me?od ( m\nt+ ! h& g5]ator t is ord9>ily employ$ ) su* magneto swit*bo>ds4 ,! %aft ( ! g5]ator is m]ely cont9u$ out to ! front ( ! key %elf :]e ! usual crank is provid$1 by means ( :i* ! op]ator is able to g5]ate ! necess>y r++ curr5t4 ,beside ! h& g5]ator at ea* op]ator's position1 x is q common 9 magneto bo>ds1 ( o!r ?an ! smalle/ sizes1 to employ "s =m ( r++ g5]ator1 ei!r a p[]-driv5 g5]ator or a pole *ang] driv5 by batt]y curr5t = furni%+ r++ curr5t )\t ef=t on ! "p ( ! op]ator4 ,illu/ration3 ,fig4 #cja4 ,dean ,two-,position ,swit*bo>d ,swit*bo>ds z %[n 9 ,figs4 #bid & #bie1 are call$ s+le-position swit*bo>ds because !y af=d room = a s+le op]ator4 ,ord9>ily = ?is class ( "w a s+le op]ator may h&le f "o to two hundr$ l9es1 al?\gh ( c\rse ?is dep5ds on ! am\nt ( traffic on ! l9e1 & ?is1 9 turn1 dep5ds on ! "* ( ! subscrib]s s]v$1 & also on ! av]age numb] ( /ations on a l9e4 ,ano!r s+le-position swit*bo>d is %[n 9 ,figs4 #bii & #cjj1 be+ a front & re> view ( ! simple magneto swit*bo>d ( ! ,we/]n ,electric ,company1 :i* is provid$ ) ! t>get signals ( t company r ?an ! usual =m ( drop4 ,:]e a swit*bo>d mu/ accommodate m l9es ?an c be h&l$ by a s+le op]ator1 ! cab9et is made wid] s z to af=d room = m ?an "o op]ator to be seat$ be=e x4 ,sometimes ?is is accompli%$ by build+ ! cab9et wid]1 or by putt+ two su* swit*bo>d sections z are %[n 9 ,figs4 #bid or #bii side by side4 ,a two-position swit*bo>d section is %[n 9 front & re> views 9 ,figs4 #cja & #cjb4 ,illu/ration3 ,fig4 #cjb4 ,re> ,view ( ,dean ,two-,position ,swit*bo>d ,sectional ,swit*bo>ds4 ,! problem ( provid+ = gr[? 9 a swit*bo>d is v mu* ! same z t :i* confronts "o 9 buy+ a bookcase = 8 libr>y4 ,! ,we/]n ,electric ,company has met ?is problem1 = v small rural ex*anges1 9 mu* ! same way t ! sectional bookcase manufactur]s h provid$ = ! possible increase 9 bookcase capacity4 ,l ! sectional bookcase1 ?is sectional swit*bo>d may />t ) ! smalle/ ( equipm5t--a s+le sectional unit--& may be add$ to v]tically z ! requirem5ts increase1 ! orig9al equipm5t be+ usable 9 its m ext5d$ surr\nd+s4 ,illu/ration3 ,fig4 #cjc4 ,sectional ,swit*bo>d--,wall ,type ,?is l9e ( swit*bo>ds is illu/rat$ 9 ,figs4 #cjc to #cjf4 ,! beg9n+ may be made ) ei!r a wall type or an upright type ( swit*bo>d1 ! =m] be+ m\nt$ on brackets secur$ to ! wall1 & ! latt] on a table4 ,a good idea ( ! wall type is %[n 9 ,fig4 #cjc4 ,?ree diff]5t k9ds ( sectional units are involv$ 9 ?is3 fir/1 ! unit :i* includes ! cords1 plugs1 cle>+-out drops1 li/5+ jacks1 op]ator's telephone set & g5]ator2 second1 ! unit conta9+ ! l9e equipm5t1 includ+ a /rip ( t5 magneto l9e signals & _! correspond+ jacks2 ?ird1 ! f9i%+ top1 :i* includes no equipm5t except ! support = ! op]ator's talk+ app>atus4 ,illu/ration3 ,fig4 #cja4 ,sectional ,swit*bo>d--,wall ,type ,! fir/ ( ! units 9 ,fig4 #cjc =ms ! f\ndation on :i* ! o!rs are built4 ,two ( ! l9e-equipm5t units are %[n2 ^! provide = a total ( tw5ty l9es4 ,! top re/s on ! upp] l9e-equipm5t unit1 & :5 x becomes necess>y to add "o or m l9e-equipm5t units z ! swit*bo>d gr[s1 ?is top is m]ely tak5 (f1 ! o!r l9e-equipm5t units put 9 place on top ( ^? already exi/+1 & ! top replac$4 ,! wall type ( sectional swit*bo>d is s arrang$ t ! entire /ructure may be swung out f ! wall1 z indicat$ 9 ,fig4 #cjd1 expos+ all ( ! app>atus & wir+ = inspection4 ,ea* ( ! sectional units is provid$ ) a sep>ate door1 z indicat$1 s t ! re> door equipm5t is add$ to automatically z ! sections are add$4 ,9 ! embodim5t ( ! sectional swit*bo>d idea %[n 9 ^! two figures j ref]r$ to1 no r++ & li/5+ keys are provid$1 b ! op]ator's telephone & g5]ator t]m9ate 9 a special plug--! left-h& "o %[n 9 ,fig4 #cjc--;& :5 ! op]ator desires to conv]se ) ! connect$ subscrib]s1 %e does s by ins]t+ ! op]ator's plug into "o ( ! jacks imm$iately bel[ ! cle>+-out drop correspond+ to ! pair ( plugs us$ 9 mak+ ! connection4 ,! arrangem5t 9 ?is case is exactly ! same 9 pr9ciple z t describ$ 9 ,fig4 #bib4 ,! op]ator's g5]ator is s arrang$ 9 connection ) ?is left-h& op]ator's plug t ! turn+ ( ! g5]ator crank automatically swit*es ! op]ator's telephone set (f & swit*es ! g5]ator on1 j ! same z a swit* hook may d 9 a subscrib]'s s]ies telephone4 ,illu/ration3 ,fig4 #cje4 ,sectional ,swit*bo>d--,table ,type ,illu/ration3 ,fig4 #cjf4 ,sectional ,swit*bo>d--,table ,type ,! upright type ( sectional swit*bo>d is %[n 9 ,figs4 #cje & #cjf1 :i* ne$ no explanation 9 view ( ! =ego+1 except to say t1 9 ! p>ticul> in/rum5t illu/rat$1 r++ & li/5+ keys are provid$ in/ead ( ! jack-&-plug arrangem5t ( ! wall type4 ,9 ?is case also1 ! top section c>ries an arm = support+ a sw++ transmitt] in/ead ( ! hook support = ! comb9$ transmitt] & receiv]4 ,,review ,,que/ions ,blank ,page ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #aa--fb 99 99 99 99 99 #a4 ,:5 0 ! telephone inv5t$ & by :om8 #b4 ,/ate ! velocity ( s\nd 9 air4 ,is x high] 9 air ?an 9 a d5s] m$ium8 #c4 ,/ate & def9e ! *>act]i/ics ( s\nd4 #d4 ,make sket* ( ,bell's orig9al magneto telephone )\t p]man5t magnets4 #e4 ,describe & sket* ,hughes' microphone4 #f4 ,:i* is1 at pres5t1 ! be/ mat]ial = v>y+ ! resi/ance 9 transmitt]s8 #g4 ,give ! fundam5tal diff]5ces betwe5 ! magneto transmitt] & ! c>bon transmitt]4 #h4 ,:at is ! function ( ! induction coil 9 ! telephone circuit8 #i4 ,describe & sket* ! diff]5t k9ds ( visible signals4 #aj4 ,:at %\ld be ! diamet] ( h>d drawn copp] wire 9 ord] to all[ economical spac+ ( poles8 #aa4 ,/ate ! f\r pr9cipal prop]ties ( a telephone l9e4 #ab4 ,if 9 te/+ a l9e ! capacity is *ang$ :at are ! results f\nd on ! receiv] & transmitt] end8 #ac4 ,:y is pap] us$ z an insulator ( telephone cables8 #ad4 ,h[ does a conductor behave 9 connection ) direct curr5t & h[ ) alt]nat+ curr5t8 #ae4 ,:at influ5ce has inductance on ! telephone8 #af4 ,def9e imp$ance & give ! =mula = x4 #ag4 ,:at is ! usual specification = insulation ( resi/ance 9 telephone cables8 #ah4 ,if #gej feet ( cable h an insulation resi/ance ( #i1ace megohms1 h[ great is ! insulation resi/ance = #g miles & #a1gdd feet ( cable8 #ai4 ,:at is ! practical limit+ conv]sation di/ance = ,no4 #aj ,b4 & ,s4 wire8 #bj4 ,describe ,pr(essor ,pup9's me?od ( ins]t+ inductance into ! telephone l9e4 #ba4 ,:at does mho d5ote8 #bb4 ,:y are ,pup9's coils n s successful on op5 wires8 #bc4 ,:at is a repeat]8 #bd4 ,def9e reactive int]f]5ce4 #be4 ,/ate ! frequ5cies ( ! pit*es ( ! human voice4 #bf4 ,:at is ! (fice ( a diaphragm 9 a telephone app>atus8 #bg4 ,:at transmitt] mat]ial has greatly increas$ ! ranges ( spee*8 #bh4 ,describe ! diff]5t me?ods ( measurem5ts ( telephone circuits4 #bi4 ,:at are ! two k9ds ( electric calls8 #cj4 ,h[ _m conductors has a telephone l9e8 #ca4 ,give =mula = capacity reactance & ! mean+ ( ! symbols4 #cb4 ,:i* ,am]ican cities are jo9$ by und]gr\nd l9es at pres5t8 #cc4 ,/ate ! two practical ways ( improv+ telephone transmission4 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #fc--ada 99 99 99 99 99 #a4 ,on :at g5]al pr9ciple are mo/ ( ! telephone transmitt]s ( today con/ruct$8 #b4 ,make sket* ( ! new ,we/]n ,electric transmitt] & describe its work+4 #c4 ,make sket* & describe ! ,kellogg transmitt]4 #d4 ,:at tr\bles 7 enc\nt]$ 9 ! e>li] =ms ( granul> c>bon transmitt]s & h[ 7 !y ov]come8 #e4 ,:at limits ! curr5t-c>ry+ capacity ( ! transmitt]8 ,h[ may ?is capacity be increas$8 #f4 ,/ate 9 :at k9d ( transmitt]s a maximum degree ( s5sitiv5ess is desirable4 #g4 ,%[ ! conv5tional symbols = transmitt]s4 #h4 ,describe a telephone receiv]4 #i4 ,sket* a ,we/]n ,electric receiv] & po9t out its defici5cies4 #aj4 ,make a diagram ( ! ,kellogg receiv]4 #aa4 ,describe ! direct-curr5t receiv] ( ! ,automatic ,electric ,company4 #ab4 ,describe & sket* ! ,dean receiv]4 #ac4 ,%[ ! conv5tional symbols ( a receiv]4 #ad4 ,describe exactly h[1 9 a cell compos$ ( a t9 & a silv] plate ) dilute sulphuric acid z electrolyte1 ! curr5t inside & outside ( ! cell w fl[4 #ae4 ,describe ! ph5om5on ( pol>ization4 #af4 ,:at is local action ( a cell8 ,h[ may x be prev5t$8 #ag4 ,into h[ _m classes may cells be divid$8 ,:i* class is mo/ us$ 9 telephony8 #ah4 ,describe ! ,le,clanch cell4 #ai4 ,sket* & describe an excell5t =m ( dry cell4 #bj4 ,%[ ! conv5tional symbols = batt]ies4 #ba4 ,sket* & describe ! g5]ator %unt swit* & ! g5]ator cut-9 swit*4 #bb4 ,h[ may a pulsat+ curr5t be d]iv$ f a magneto g5]ator8 #bc4 ,%[ conv5tional symbols = magneto g5]ators4 #bd4 ,sket* & describe ! ,we/]n ,electric pol>iz$ bell4 #be4 ,give conv5tional r+] symbols4 #bf4 ,:at is ! purpose ( ! hook swit*8 #bg4 ,make sket* & give description ( ,kellogg's long lev] hook swit*4 #bh4 ,describe & sket* ! ,we/]n ,electric %ort lev] hook swit*4 #bi4 ,po9t out ! pr9cipal diff]5ce betwe5 ! desk /& hook swit*es ( ! ,we/]n ,electric ,company & ( ! ,kellogg ,swit*bo>d & ,supply ,company4 #cj4 ,give conv5tional symbols ( hook swit*es4 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #adc--bbe 99 99 99 99 99 #a4 ,describe an electromagnet & its function 9 telephony4 #b4 ,sket* an iron-clad electromagnet4 #c4 ,:at is a diff]5tial electromagnet8 ,sket* & describe "o type4 #d4 ,/ate ! desirable *>act]i/ics ( good enamel insulation = magnet wire4 #e4 ,if y h a coil ( ,no4 #bc d\ble cotton ,b4 & ,s4 wire ( #aae ohms resi/ance & y h to rew9d x = #a1jgj ohms resi/ance ) d\ble cotton wire1 :at numb] ( wire w\ld y take8 ,%[ calculation4 ,,note4 ,no4 #bc d4 c wire has res4 #a4ggb ohms p] cubic in*2 = ! core1 #aae ohms4 ,!re are requir$ 9 ! coil #a1jgj ohms1 t is1 #i4c times z mu*4 #a4ggb x #i4c #af4dg ohms1 :i* mu/ be ! resi/ance p] cu4 94 ,?is resi/ance gives1 accord+ to ,table ,,iv1 ,no4 #bi wire4 #f4 ,:at is an imp$ance coil8 ,/ate h[ x diff]s f an electromagnet coil4 #g4 ,describe ! diff]5t k9ds ( imp$ance coils4 #h4 ,give symbol ( imp$ance coil4 #i4 ,:at are ! pr9cipal p>ts ( an induction coil8 #aj4 ,:at is ! function ( an induction coil 9 telephony8 #aa4 ,:at is a repeat+ coil & h[ does x diff] f an induction coil8 #ab4 ,give conv5tional symbols ( induction coils & repeat+ coils4 #ac4 ,enum]ate ! diff]5t types ( non-inductive resi/ance devices & give a %ort description ( ea*4 #ad4 ,def9e cond5s]4 #ae4 ,:at is ! mean+ ( ! ^w dielectrics8 #af4 ,/ate :at y und]/& by ! specific inductive capacity ( a dielectric4 #ag4 ,^u :at factors does ! capacity ( a cond5s] dep5d8 #ah4 ,:at is ! usual capacity ( cond5s]s 9 telephone practice8 #ai4 ,give conv5tional cond5s] symbols4 #bj4 ,by :at two me?ods may ! curr5t be suppli$ to a telephone transmitt]8 #ba4 ,make sket* ( local-batt]y /ations ) metallic circuit4 #bb4 ,sket* common-batt]y circuit 9 s]ies ) two l9es4 #bc4 ,/ate ! objections aga9/ ! prec$+ arrangem5t4 #bd4 ,make sket* ( ! /&>d arrangem5t ( ! ,we/]n ,electric ,company 9 bridg+ ! common batt]y ) repeat+ coils4 #be4 ,sket* ! arrangem5t ( bridg+ ! batt]y ) imp$ance coils & /ate ! purpose ( ! coils4 #bf4 ,make diagram ( a common-s\rce curr5t supply = _m l9es ) repeat+ coils & po9t out ! travel ( ! voice curr5ts4 #bg4 ,"n ! diff]5t p>ts :i* comprise a telephone set4 #bh4 ,:at is a magneto telephone8 #bi4 ,make diagram ( ! circuit ( a s]ies magneto set ) receiv] on ! hook & expla9 h[ ! diff]5t curr5ts are fl[+4 #cj4 ,%[ diagram ( ! ,/romb]g-,c>lson magneto desk telephone circuit & describe its work+4 #ca4 ,give sket* ( ! ,/romb]g-,c>lson common-batt]y wall set circuit4 #cb4 ,describe briefly ! microtelephone set4 #cc4 ,make sket* ( ! ,mon>* common-batt]y wall set4 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #bbg--bhf 99 99 99 99 99 #a4 ,:at is a p>ty l9e8 #b4 ,:at is usually und]/ood by private l9es8 #c4 ,:at problem is !re to ov]come 9 connection ) p>ty l9es8 #d4 ,/ate ! two g5]al classes ( p>ty-l9e sy/ems4 #e4 ,po9t out ! defects ( ! s]ies sy/em4 #f4 ,make sket* ( a metallic bridg+ l9e & %[ ! circuit = ! voice curr5ts4 #g4 ,:at is a signal code8 #h4 ,give classification ( selective p>ty-l9e sy/ems ) %ort def9itions4 #i4 ,describe ! pr9ciple ( selection by pol>ity & make sket* illu/rat+ ?is pr9ciple4 #aj4 ,make diagram ( ! circuit ( a f\r-p>ty /ation ) relay4 #aa4 ,describe ! process ( tun+ 9 ! h>monic sy/em4 #ab4 ,:at is ! diff]5ce betwe5 ! "u-tune & 9-tune sy/ems8 #ac4 ,sket* circuit ( ,kellogg's h>monic sy/em4 #ad4 ,illu/rate ! pr9ciple ( a brok5-l9e sy/em by a sket*4 #ae4 ,9 :at p>ticul>s does ! p>ty-l9e sy/em 9 rural di/ricts diff] f t )9 urban limits8 #af4 ,describe & sket* ,pool's lock-out sy/em4 #ag4 ,make diagram ( ! ,k4,b4 lock-out sy/em4 #ah4 ,:at is ! object ( ! rat*et 9 ?is sy/em8 #ai4 ,make diagram ( simplifi$ circuits ( ,rob]ts sy/em4 #bj4 ,sket* & describe ,rob]ts lat*+ key & connections4 #ba4 ,sket* circuits ( bridg+ /ation = non-selective p>ty l9e4 #bb4 ,h[ w\ld y arrange ! signal code = six /ations on a non-selective p>ty l9e8 #bc4 ,:at is ! limit ( numb] ( /ations on a non-selective p>ty l9e "u ord9>y circum/ances8 #bd4 ,/ate ! objections aga9/ ! p>ty pol>ity sy/em z %[n 9 ,fig4 #agb4 #be4 ,:at are ! advantages ( ! h>monic p>ty-l9e sy/em8 #bf4 ,to h[ _m frequ5cies is ! h>monic sy/em usually limit$8 #bg4 ,:at c y say ab\t ! comm]cial success ( ! /ep-by-/ep me?od8 #bh4 ,/ate ! pr9ciples ( a lock-out p>ty l9e4 #bi4 ,= :at purpose is a cond5s] plac$ 9 ! receiv] circuit ( ea* /ation 9 ! ,k4,b4 lock-out sy/em8 #cj4 ,h[ are ! select+ relays 9 ,rob]ts l9e re/or$ to _! normal position aft] a conv]sation is f9i%$8 #ca4 ,:at are ! objections aga9/ ! ,rob]ts sy/em8 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #bhg--cae 99 99 99 99 99 #a4 ,:at are electrical haz>ds8 #b4 ,:5 is ! lightn+ haz>d lea/8 #c4 ,:at actions c electricity produce8 ,:i* involves ! great] haz>d to ! value ( prop]ty8 #d4 ,:5 is a piece ( app>atus call$ self-protect+8 #e4 ,:y mu/ a protector = telephone app>atus "w m quickly = a l>ge curr5t ?an = a small "o8 #f4 ,/ate ! g5]al problem :i* heat+ haz>ds pres5t ) relation to telephone app>atus4 #g4 ,:at is ! mo/ ne>ly univ]sal electrical haz>d8 #h4 ,sket* & describe ! saw-too? lightn+ arre/]4 #i4 ,make diagram ( ! c>bon-block arre/] & /ate its advantages4 #aj4 ,describe a vacuum arre/]4 #aa4 ,expla9 ! reason = plac+ an imp$ance 9 connection ) ! lightn+ arre/]4 #ab4 ,:at is ! purpose ( ! globule ( l[-melt+ alloy 9 ! ,we/]n ,electric ,company's arre/]8 #ac4 ,:y are n fuses good lightn+ arre/]s8 #ad4 ,:at is ! prop] function ( a fuse8 #ae4 ,make sket* ( a mica slip fuse4 #af4 ,def9e sneak curr5ts4 #ag4 ,make a diagram ( a sneak-curr5t arre/] & describe its pr9ciples & work+4 #ah4 ,describe a heat coil4 #ai4 ,sket* a complete l9e protection4 #bj4 ,:]e is ! prop] position ( ! fuse8 #ba4 ,:i* wires are consid]$ expos$ & :i* unexpos$8 #bb4 ,:y is x n necess>y to in/all sneak-curr5t arre/]s 9 c5tral-batt]y subscrib]s' /ations8 #bc4 ,sket* & describe ! action ( a comb9$ sneak-curr5t & air-gap arre/]1 z widely us$ by ,bell companies4 #bd4 ,describe ! self-sold]+ heat-coil arre/]4 #be4 ,:at is ! purpose ( ribbon fuses8 #bf4 ,:at is a dra9age coil8 ,,review ,,que/ions ,,on ,,! ,,subject ,,( ,,telephony ,,pages #cag--chf 99 99 99 99 99 #a4 ,:at is a c5tral (fice8 #b4 ,:at are 7a7 subscrib]'s l9es8 7b7 ,trunk l9es8 7c7 ,toll l9es8 #c4 ,= :at purpose is ! swit*bo>d8 #d4 ,give %ort descriptions ( ! diff]5t classes ( swit*bo>ds4 #e4 ,h[ are manual swit*bo>ds subdivid$8 ,describe briefly ! diff]5t types4 #f4 ,def9e ,a & ,b bo>ds4 #g4 ,:at is a call circuit8 #h4 ,:at k9d ( calls are h&l$ on a toll swit*bo>d8 #i4 ,give drop symbol & describe its pr9ciples4 #aj4 ,:at is a jack8 #aa4 ,make a sket* ( a plug ins]t$ into a jack4 #ab4 ,give jack & plug symbols4 #ac4 ,:at are r++ & li/5+ keys8 #ad4 ,%[ symbols = r++ & li/5+ keys4 #ae4 ,/ate ! p>ts ( :i* a cord equipm5t consi/s4 #af4 ,%[ /ep by /ep ! v>i\s op]ations ( a telephone sy/em :]e9 ! l9es c5t] 9 a magneto swit*bo>d4 ,make all ! necess>y diagrams & give brief descriptions to %[ t y und]/& ea* op]ation4 #ag4 ,on :at pr9ciple does a drop ) night-al>m contact op]ate8 #ah4 ,:at is ! advantage ( associat+ jacks & drops8 #ai4 ,describe ! me*anical re/oration z employ$ 9 ! ,mill] drop & jack4 #bj4 ,describe ! electrical re/oration ( drop %utt]s z manufactur$ by ! ,we/]n ,electric ,company4 #ba4 ,:at complications arise 9 r++ ( p>ty l9es & h[ are !y ov]come8 #bb4 ,give diagram ( ! complete circuit ( a simple magneto swit*bo>d4 #bc4 ,sket* night-al>m circuit ) relay4 #bd4 ,:at is a conv]tible cord circuit8 #be4 ,/ate :at disadvantages may be enc\nt]$ "u c]ta9 conditions ) a bridg+ drop-cord circuit4 #bf4 ,are lamps 9 cord circuits to be advocat$ on magneto swit*bo>ds8 #bg4 ,:at is ! function ( ! cab9et8 #bh4 ,give cross-section ( upright swit*bo>d z us$ 9 ! magneto sy/em4 #bi4 ,:at is ! purpose ( a sectional swit*bo>d8 #cj4 ,give a %ort description ( ! ess5tial p>ts ( a sectional swit*bo>d4 ,,index ,,index ,! page numb]s ( ?is volume w be f\nd at ! bottom ( ! pages2 ! numb]s at ! top ref] only to ! section4 ,a ,ac\/icon transmitt] ,ac\/ics *>act]i/ics ( s\nd l\dness pit* timbre human e> human voice propagation ( s\nd ,air-gap vs4 fuse arre/]s ,amalgamat$ z9cs ,arre/] sep>ators ,audible signals magneto bell telegraph s\nd] telephone receiv] vibrat+ bell ,automatic ,electric ,company direct-curr5t receiv] transmitt] ,automatic %unt ,b ,b> electromagnet ,batt]y bell ,batt]y symbols ,blake s+le electrode ,braz$ bell ,brok5-back r+] ,brok5-l9e me?od ( selective signal+ ,c ,capacity reactance ,c>bon adaptability limitations prep>ation ( sup]iority ,c>bon air-gap arre/] ,c>bon-block arre/] ,c>ry+ capacity ( transmitt] ,c5tral-(fice protectors ,*>act]i/ics ( s\nd l\dness pit* timbre ,*loride ( silv] cell ,clos$-circuit cells ,clos$-circuit imp$ance coil ,common-batt]y telephone sets ,cond5s]s capacity *>ge conv5tional symbols def9ition ( dielectric dielectric mat]ials functions means = assort+ curr5t sizes !ory ,conductivity ( conductors ,conductors1 conductivity ( ,conv5tional symbols ,cook air-gap arre/] arre/] arre/] = magneto /ations ,cr[foot cell ,curr5t supply to transmitt]s common batt]y advantages bell sub/ation arrangem5t bridg+ batt]y ) imp$ance coils bridg+ batt]y ) repeat+ coil curr5t supply f di/ant po9t curr5t supply ov] limbs ( l9e 9 p>allel ,dean sub/ation arrangem5t d\ble batt]y ) imp$ance coil ,kellogg sub/ation arrangem5t ,nor? ,electric ,company sy/em s]ies batt]y s]ies sub/ation arrangem5t ,/romb]g-,c>lson sy/em supply _m l9es f common s\rce repeat+ coil ret>dation coil local batt]y ,d ,dean drop & jack receiv] wall telephone hook ,desk /& hooks ,kellogg ,we/]n ,electric ,dielectric ,dielectric mat]ials dry pap] mica ,diff]5tial electromagnet ,direct-curr5t receiv] ,dra9age coils ,e ,electric lamp signal ,electrical haz>ds ,electrical reproduction ( spee* c>bon conv]sion f s\nd waves to vibration ( diaphragm conv]sion f vibration to voice curr5ts conv]sion f voice curr5ts to vibration cycle ( conv]sion detrim5tal effects ( capacity e>ly conceptions electro/atic telephone induction coil limitations ( magneto transmitt] loose contact pr9ciple magneto telephone measurem5ts ( telephone curr5ts v>iation ( electrical pressure v>iation ( resi/ance ,electrical signals audible magneto-bell telegraph s\nd] telephone receiv] vibrat+ bell visible electric lamp signal electromagnetic signal ,electrodes arrangem5t ( c>bon prep>ation multiple s+le ,electrolysis ,electromagnetic me?od ( measur+ telephone curr5ts ,electromagnetic signal ,electromagnets & inductive coils conv5tional symbols diff]5tial electromagnet direction ( armature motion direction ( l9es ( =ce electromagnets l[-resi/ance circuits horse%oe =m iron-clad =m special horse%oe =m imp$ance coils k9d ( iron numb] ( turns types clos$-circuit op5-circuit toroidal induction coil curr5t & voltage ratios design functions use & advantage magnet wire enamel silk & cotton insulation space utilization wire gauges magnetic flux magnetization curves magnetiz+ =ce me*anical details p]meability reluctance repeat+ coil w9d+ me?ods w9d+ calculations w9d+ data w9d+ t]m9als ,electro/atic capacity unit ( ,electro/atic telephone ,enamel ,f ,five-b> g5]ator ,full] cell ,g ,galvani ,g5]ator armature ,g5]ator cut-9 swit* ,g5]ator %unt swit* ,g5]ator symbols ,granul> c>bon ,gravity cell ,h ,h& receiv]s ,h>monic me?od ( selective signal+ advantages circuits 9-tune sy/em limitations pr9ciples tun+ "u-tune sy/em ,head receiv]s ,heat coil ,holtz]-,cabot arre/] ,hook swit* automatic op]ation contact mat]ial design desk /& hooks ,kellogg ,we/]n ,electric purpose symbols wall telephone hooks ,dean ,kellogg ,we/]n ,electric ,horse%oe electromagnet ,human e> ,human voice ,i ,imp$ance coils k9d ( iron numb] ( turns symbols ( types clos$-circuit op5-circuit toroidal ,inductance vs4 capacity ,induction coil curr5t & voltage ratios design functions use & advantage ,inductive neutrality ,inductive reactance ,insulation ( conductors ,introduction to telephony ,iron-clad electromagnet ,iron wire balla/ ,k ,kellogg air-gap arre/] desk /& hook drop & jack receiv] r+] transmitt] wall telephone hook ,l ,lal&e cell ,lamp filam5t ,le ,clan* cell ,l5z law ,l9e signals ,l9es ( =ce1 direction ( ,load+ coils ,lock-out p>ty-l9e sy/ems brok5-l9e me?od op]ation ,poole sy/em /ep-by-/ep sy/em ,l\dness ( s\nd ,l[-reluctance circuits horse%oe =m iron-clad =m ,m ,magnetic flux ,magnetization curves ,magnetiz+ =ce ,magneto bell ,magneto op]ator ,magneto signal+ app>atus armature automatic %unt batt]y bell g5]ator symbols magneto bell magneto g5]ator me?od ( signal+ pol>iz$ r+] pulsat+ curr5t r+] symbols !ory ,magneto swit*bo>d automatic re/oration me*anical ,dean type ,kellogg type ,mon>* type ,we/]n ,electric type circuits ( complete swit*bo>d code signal+ comm]cial types ( drops & jacks e>ly drops jack m\nt+ manual vs4 automatic re/oration me?ods ( associat+ night al>m tubul> drops compon5t p>ts jacks & plugs keys l9e & cord equipm5ts l9e signal op]ators' equipm5t cord-circuit consid]ations d\ble cle>+-out type lamp-signal type non-r+ ?r\gh type s]ies drop type simple bridg+ drop type def9itions electrical re/oration gr\nd$ & metallic-circuit l9es mode ( op]ation night-al>m circuits op]ation 9 detail cle>+ out ess5tials ( op]ation normal condition ( l9e op]ator answ]+ op]ator call+ subscrib] call+ subscrib]s conv]s+ op]ator's telephone equipm5t cut-9 jack r++ & li/5+ keys horizontal spr+ type p>ty-l9e r++ keys self-indicat+ keys v]tical spr+ type swit*bo>d assembly functions ( cab9et sectional swit*bo>ds upright type ( swit*bo>d wall type swit*bo>d swit*bo>d cords conc5tric conductors p>allel t9sel conductors /eel spiral conductors swit*bo>d plugs ,magneto telephone ,magneto telephone sets ,mica c>d resi/ance ,mica slip fuse ,microtelephone set ,mon>* drop & jack ,mon>* receiv] ,mon>* transmitt] ,multiple electrode ,mutual induction ,n ,non-inductive resi/ance devices inductive neutrality provisions aga9/ heat+ temp]ature coeffici5t types diff]5tially-w\nd unit iron wire balla/ lamp filam5t mica c>d unit ,non-selective p>ty-l9e sy/ems bridg+ limitations s]ies signal code ,o ,op5-circuit cells ,op5-circuit imp$ance coil ,op]ator's receiv] ,p ,pack+ ( transmitt]s ,p]meability ,pit* ,doppl]'s pr9ciple vibration ( diaphragms ,pol>ity me?od ( selective signal+ ,pol>ization ( cells ,pol>iz$ r+] braz$ bell ,kellogg ,we/]n ,electric ,poole lock-out sy/em ,prim>y cells conv5tional symbol s]ies & multiple connections simple voltaic types ( clos$-circuit ,full] gravity ,lal&e prev5tion ( creep+ sett+ up op5-circuit ,le ,clan* /&>d *loride ( silv] ,propagation ( s\nd ,protective means aga9/ high pot5tials air-gap arre/] advantages ( c>bon comm]cial types cont9u\s arcs dis*>ge across gaps du/ betwe5 c>bons introduction ( imp$ance metallic electrodes vacuum arre/]s aga9/ sneak curr5ts heat coil sneak-curr5t arre/]s aga9/ /rong curr5ts fuses enclos$ mica prop] functions c5tral-(fice protectors self-sold]+ heat coils sneak-curr5t & air-gap arre/] city ex*ange requirem5ts complete l9e protection electrolysis subscrib]s' /ation protectors ribbon fuses ,pulsat+-curr5t commutator ,r ,receiv]s ,dean direct-curr5t e>ly ,kellogg mod]n ,mon>* op]ator's s+le-pole symbols ,we/]n ,electric ,reluctance ,repeat+ coil ,ribbon fuses ,r+] symbols ,r++ & li/5+ key ,rob]t's lat*+ relay ,rob]t's self-cleans+ arre/] ,roll$ cond5s] ,s ,saw-too? arre/] ,selective p>ty-l9e sy/ems brok5-l9e me?od classification brok5-l9e sy/ems h>monic sy/ems pol>ity sy/ems /ep-by-/ep sy/ems h>monic me?od pol>ity me?od /ep-by-/ep me?od ,self-induction ,signal code ,signal+1 me?od ( ,silk & cotton insulation ,s+le electrode ,s+le-pole receiv] ,sneak-curr5t arre/]s ,solid-back transmitt] ,s\nd *>act]i/ics ( l\dness pit* timbre ,/&>d cell ,/ep-by-/ep lock-out sy/em ,/ep-by-/ep me?od ( selective signal+ ,subscrib]s' /ation protectors ,swit*bo>d cords ,swit*bo>d plugs ,swit*bo>d transmitt] ,symbols batt]y cond5s] g5]ator hook swit* imp$ance coil induction coil receiv] repeat+ coil r+] r++ & li/5+ key transmitt] ,t ,table cond5s] data copp] wire ,g]man silv] wire--#ah p] c5t ,g]man silv] wire--#cj p] c5t metals1 behavior (1 9 diff]5t electrolysis signal code specific inductive capacities temp]ature coeffici5ts transmission di/ances1 limit+ w9d+ data = insulat+ wires ,t&em diff]5tial electromagnet ,telegraph s\nd] ,telephone curr5ts1 measurem5ts ( electromagnetic me?od !rmal me?od ,telephone ex*ange1 features ( di/ricts subscrib]s' l9es swit*bo>ds toll l9es trunk l9es ,telephone l9es conductivity ( conductors electro/atic capacity inductance ( circuit inductance vs4 capacity insulation ( conductors transmission ,telephone sets classification ( common-batt]y telephone magneto telephone wall & desk telephones common-batt]y desk hotel wall magneto circuits ( bridg+ s]ies desk wall ,temp]ature coeffici5ts ,!rmal me?od ( measur+ telephone curr5ts ,timbre ,toroidal imp$ance coil ,toroidal repeat+ coil ,transmission1 ways ( improv+ ,transmitt]s ac\/icon ,automatic ,electric ,company c>ry+ capacity conv5tional diagram electrode arrangem5t ( multiple s+le granul> c>bon ,kellogg mat]ials ,mon>* pack+ s5sitiv5ess swit*bo>d symbols v>iable resi/ance ,we/]n ,electric solid-back ,u ,"u-tun$ r+] ,v ,vacuum arre/] ,v>iable resi/ance ,vibrat+ bell ,visible signals electric lamp electromagnetic ,volta ,voltaic cell amalgamat$ z9cs diff]5ce ( pot5tial local action pol>ization !ory ,w ,wall telephone hooks ,dean ,kellogg ,we/]n ,electric ,we/]n ,electric air-gap arre/] desk /& hook drop & jack receiv] r+] solid-back transmitt] /ation arre/] wall telephone hook ,:ite transmitt] ,wire gauges