,illu/ration3 ,,fir/ ,,direct-,,connect$ ,,electric ,,g5]ator ,,unit ,,( ,,l>ge ,,capacity ,,ev] ,,con/ruct$ ,,up ,,to ,,! ,,"t ,,x ,,0 ,,made ,,by ,,?omas ,a4 ,,edison ,,9 ,,june1 #ahha4 ,,capacity1 #abjj ,,inc&esc5t ,,lamps ,,( #af ,,c&le-,,p[] ,,ea* ,a-,b-,c ,,( ,,electricity ,,by ,,william ,h4 ,,mead[cr(t ,,h>p] ,,bro!rs ,,publi%]s ,,new ,,york ,,london ,a-,b-,c ( ,electricity ,,copyright1 #ahhh1 #aiji1 ,,by ,,william ,h4 ,,mead[cr(t ,,copyright1 #aiae1 ,,by ,,h>p] ,,bro!rs ,,pr9t$ ,,9 ,,! ,,unit$ ,,/ates ,,( ,,am]ica ,,publi%$ ,,may1 #aiae ,,f ,,! ,,laboratory ,,( ,,?omas ,a4 ,,edison ,,orange1 ,n4 ,j4 ,,mr4 ,w4 ,h4 ,,mead[cr(t1 ,new ,york ,city4 ,,de> ,,sir3 ,i h read ! ,,ms4 ( y\r ,a-,b-,c ( ,electricity1 & f9d t ! /atem5ts y h made !re9 are correct4 ,y\r treatm5t ( ! subject1 & arrangem5t ( ! matt]1 h impress$ me favorably4 ,y\rs truly1 ,,?os4 ,a4 ,,edison ,,cont5ts ,,*ap4 ,,page ,,introduction ,,to ,,new ,,edition viii ,,preface x ,i4 #a ,,ii4 ,,def9itions #c ,,iii4 ,,magnetism #af ,,iv4 ,,! ,,telegraph #bc ,v4 ,,wireless ,,telegraphy #cc ,,vi4 ,,! ,,telephone #dj ,,vii4 ,,electric ,,light #ed ,,viii4 ,,electric ,,p[] #hg ,,ix4 ,,batt]ies #ie ,x4 ,,conclusion #abg ,,introduction ,,to ,,new ,,edition ,! favor ) :i* ?is book has be5 receiv$ has br\ght ab\t ! prep>ation ( ?is new edition4 ,! pres5t volume has be5 enl>g$ by ! addition ( c]ta9 new mat]ial & x has be5 entirely reset4 ,"s new illu/rations h be5 made1 & 9 its new dress ! book1 x is hop$1 w be f\nd to af=d an ev5 l>g] measure ( usefulness4 ,! pr9ciples ( ! sci5ce rema9 ! same1 b ! au?or is glad ( ! opportunity to note c]ta9 developm5ts 9 _! application4 ,w4 ,h4 ,m4 ,,edison ,,laboratory1 ,april1 #aiae4 ,,preface ,:ile !re is no lack ( mo/ excell5t text-books = ! /udy ( ^? bran*es ( ,electricity :i* are above ! elem5t>y /age1 !re is a decid$ ne$ ( text-books :i* %all expla91 9 simple language1 to "y p (1 say1 f\rte5 ye>s & upw>d1 a g5]al outl9e ( ! sci5ce1 z well z ! gr\nd-"w ( ^? electrical inv5tions :i* are to-day ( su* va/ comm]cial importance4 ,!re is also a ne$ = su* a book among a l>ge "p ( ! adult population1 = ! reason t !re h be5 great & radical *anges 9 ?is sci5ce s9ce ! "t !y complet$ _! /udies1 & !y h n ! "t to foll[ up ! subject 9 ! advanc$ books4 ,z in/ances ( ^? *anges j spok5 (1 ! electric light1 telephone1 & /orage batt]ies may be m5tion$1 :i* h be5 develop$ dur+ ! la/ t5 or twelve ye>s1 ) ! result ( add+ v _m features t 7 entirely new to electricians4 ,) ^! ideas 9 view ,i h prep>$ ?is little volume4 ,x is n int5d$1 9 ! slighte/ degree1 to be put =w>d z a sci5tific "w1 b x w probably give to _m ! in=mation !y desire )\t requir+ too great a rese>* into books :i* treat m ext5sively & deeply ( ?is subject4 ,w4 ,h4 ,m4 ,a-,b-,c ,,( ,,electricity ,a-,b-,c ,,( ,,electricity ,i ,we n[ obta9 s _m ( our com=ts & conv5i5ces by ! use ( electricity t all "y p ought to le>n some?+ ( ?is wond]ful =ce1 9 ord] to und]/& "s ( ! pr9ciples :i* are br\ght into practice4 ,y all "k t we h ! telegraph1 ! telephone1 ! electric light1 electric motors on /reet-c>s1 electric bells1 etc41 besides _m o!r conv5i5ces :i* ! use ( electricity gives u4 ,e "o kn[s t1 by ! laws ( multiplication1 twice two makes f\r1 & t twice two c nev] make any?+ b f\r4 ,well1 ^! useful inv5tions h be5 made by apply+ ! laws ( electricity 9 c]ta9 ways1 j z well kn[n1 s z to enable u to s5d 9 a few mom5ts a message to our abs5t fri5ds at any di/ance1 to speak ) !m at a great di/ance1 to light our h\ses & /reets ) electric light1 & to d _m o!r useful ?+s ) quickness & ease4 ,b y mu/ rememb] t we d n "k :at electricity itself really is4 ,we only "k h[ to produce x by c]ta9 me?ods1 & we also "k :at we c d ) x :5 we h obta9$ x4 ,9 ?is little book we w try to expla9 ! v>i\s ways by :i* electricity is obta9$1 & h[ x is appli$ to produce ! useful results t we see ar\nd u4 ,we w try & make ?is explanation su* t x w enc\rage _m ( y to /udy ?is v important & int]e/+ subject m deeply4 ,9 ! advanc$ books on electricity !re are _m te*nical t]ms :i* are some:at difficult to und]/&1 b 9 ?is book x w only be necess>y to use a few ( ! m simple ones1 :i* x w be well = y to le>n & und]/& be=e go+ fur!r4 ,,ii ,,def9itions ,! ?ree measurem5ts mo/ frequ5tly us$ 9 electricity are ,! ,volt1 ,! ,ampre1 ,! ,ohm4 ,we w expla9 ^! 9 _! ord]4 ,illu/ration3 ,fig4 #a ,! ,volt4--,?is t]m may be bett] und]/ood by mak+ a comp>ison ) some?+ y all "k (4 ,suppose we h a tank conta9+ "o hundr$ gallons ( wat]1 & we want to dis*>ge x ?r\gh a half-in* pipe at ! bottom ( ! tank4 ,suppose1 fur!r1 t we want$ to make ! wat] sp\t upw>d1 & = ?is purpose ! pipe 0 b5t upw>d z 9 ,fig4 #a4 ,if y op5$ ! tap ! wat] w\ld sp\t out & upw>d z 9 ,fig4 #a4 ,illu/ration3 ,fig4 #b ,! cause ( its sp\t+ upw>d w\ld be ! weight or pressure ( ! wat] 9 ! tank4 ,?is pressure is reckon$ z s _m p\nds to ! squ>e in* ( wat]4 ,n[1 if ! tank 7 plac$ on ! ro( ( ! h\se & ! pipe br\ght to ! gr\nd z %[n 9 ,fig4 #b1 ! wat] w\ld sp\t up v mu* high]1 because !re w\ld be _m m p\nds ( pressure on acc\nt ( ! height ( ! pipe4 ,s1 y see1 ! =ce or pressure ( wat] is measur$ 9 p\nds1 &1 !re=e1 a p\nd is ! unit ( pressure1 or =ce1 ( wat]4 ,n[1 9 electricity ! unit ( pressure1 or =ce1 is call$ a volt4 ,?is ^w volt does n mean any weight1 z ! ^w p\nd weight does4 ,y all "k t if y h a p\nd ( wat] y mu/ h some?+ to hold x1 because x has weight1 &1 consequ5tly1 occupies "s space4 ,b electricity itself has no weight & !re=e _c occupy any space4 ,:5 we desire to c>ry wat] into a h\se or o!r build+ we d s by means ( holl[ pipes1 :i* are usually made ( iron4 ,?is is ! way t wat] is br\ght into h\ses 9 cities & t[ns1 s t x may be drawn & us$ 9 any "p ( a dwell+4 ,n[1 ! pr9cipal supply usually comes f a res]voir :i* is plac$ up on high gr\nd s z to give ! necess>y p\nds ( pressure to =ce ! wat] up to ! upp] "p ( ! h\ses4 ,if "s arrangem5t ( ?is k9d 7 n made we c\ld get no wat] 9 our b$rooms1 because1 z y "k1 wat] w n rise above its own level unless by =ce4 ,! wat] _c escape z long z !re are no holes or leaks 9 ! iron pipes1 b if !re %\ld be ! slighte/ crevice 9 !m ! wat] w run out4 ,9 electricity we f9d simil> effects4 ,! electricity is c>ri$ into h\ses by means ( wires :i* are cov]$1 or insulat$1 ) v>i\s sub/ances1 su*1 = in/ance1 z rubb]4 ,j z ! iron ( ! pipes prev5ts ! wat] f escap+1 ! insulation ( ! wire prev5ts ! escape ( ! electricity4 ,n[1 if we 7 to cause ! p\nds ( pressure ( wat]1 9 pipes ( ord9>y ?ickness1 to be v greatly increas$1 ! pipes c\ld n /& ! /ra9 & w\ld bur/ & ! wat] escape4 ,s x is ) electricity4 ,if !re 7 too _m volts ( pressure ! insulation w\ld n be suffici5t to hold x & ! electricity w\ld escape ?r\gh ! cov]+1 or insulation1 ( ! wire4 ,x is a simple & easy matt] to /op ! fl[ ( wat] f an ord9>y faucet by plac+ y\r f+] ov] ! op5+4 ,z ! wat] _c !n fl[1 y\r f+] is :at we w call a non-conductor & ! wat] w be reta9$ 9 ! pipe4 ,we h j ! same effects 9 electricity4 ,if we place "s sub/ance :i* is practically a non-conductor1 or insulator1 su* z rubb]1 ar\nd an electric wire1 or 9 ! pa? ( an electric curr5t1 ! electricity1 act$ ^u by ! volts ( pressure1 _c escape1 because ! insulation keeps x f do+ s1 j z ! iron ( ! pipe keeps ! wat] f escap+4 ,?us1 y see1 ! volt does n itself repres5t electricity1 b only ! pressure :i* =ces x ?r\gh ! wire4 ,!re are o!r words & expressions 9 electricity :i* are sometimes us$ 9 connection ) ! ^w volt4 ,^! words are pressure & int5sity4 ,we might say1 = in/ance1 t a c]ta9 dynamo ma*9e _h an electromotive =ce ( #aaj volts2 or t ! int5sity ( a cell ( a batt]y 0 #b volts1 etc4 ,we might m5tion1 z ano!r analogy1 ! pressure ( /eam 9 a boil]1 :i* is measur$ or calculat$ 9 p\nds1 j z ! pressure ( wat] is measur$4 ,s1 we might say t #ajj p\nds /eam pressure us$ ?r\gh ! m$ium ( a /eam-eng9e to drive a dynamo c\ld ?us be *ang$ to electricity at #ajj volts pressure4 ,! ,ampre4--,n[1 9 comp>+ ! p\nds pressure ( wat] ) ! volts ( pressure ( electricity we us$ z an illu/ration a tank ( wat] conta9+ #ajj gallons1 & we saw t ?is wat] _h a d[nw>d =ce or pressure 9 p\nds4 ,let u n[ see :at ?is pressure 0 act+ ^u4 ,x 0 =c+ ! quantity ( wat] to sp\t upw>d ?r\gh ! end ( ! pipe4 ,n[1 z ! quantity ( wat] 0 #ajj gallons1 x c\ld n all be =c$ at once out ( ! end ( ! pipe4 ,! p\nds pressure ( wat] act+ on ! #ajj gallons w\ld =ce x out at a c]ta9 rate1 :i*1 let u say1 w\ld be "o gallon p] m9ute4 ,?is w\ld be ! rate ( ! fl[ ( wat] out ( ! tank4 ,?us1 y see1 we f9d a second measurem5t to be consid]$ 9 dis*>g+ ! wat]-tank4 ,! fir/ 0 ! =ce1 or p\nds ( pressure1 & ! second ! rate at :i* ! quantity ( wat] 0 be+ dis*>g$ p] m9ute by t pressure4 ,?is second measurem5t tea*es u t a c]ta9 quantity w pass out ( ! pipe 9 a c]ta9 "t if ! pressure is /eady1 su* quantity dep5d+1 ( c\rse1 on ! size or friction resi/ance ( ! pipe4 ,9 electricity ! volts ( pressure act s z to =ce ! quantity ( curr5t to fl[ ?r\gh ! wires at a c]ta9 rate p] second1 & ! rate at :i* x fl[s is measur$ 9 ampres4 ,= in/ance1 let u suppose t an electric lamp requir$ a pressure ( #ajj volts & a curr5t ( "o ampre to light x up1 we %\ld h to supply a curr5t ( electricity fl[+ at ! rate ( "o ampre1 act$ ^u by an electromotive =ce ( #ajj volts4 ,y w see1 !re=e1 t :ile ! volt does n repres5t any electricity1 b only its pressure1 ! ampre repres5ts ! rate ( fl[ ( ! curr5t itself4 ,y %\ld rememb] t !re are sev]al words sometimes us$ 9 connection ) ! ^w ampre--= in/ance1 we might say t a lamp requir$ a curr5t ( "o ampre or t a dynamo w\ld give a quantity ( #bj ampres4 ,! ,ohm4--,y h le>n$ t ! pressure w\ld dis*>ge ! quantity ( wat] at a c]ta9 rate ?r\gh ! pipe4 ,n[1 suppose we 7 to fix two dis*>ge-pipes to ! tank1 ! wat] w\ld run away v mu* quick]1 w\ld x n8 ,if we try to f9d a reason = ?is1 we %all see t a pipe c only1 at a giv5 pressure1 admit s mu* wat] ?r\gh x at a "t4 ,!re=e1 y see1 ?is pipe w\ld pres5t a c]ta9 am\nt ( resi/ance to ! passage ( ! total quantity ( wat]1 & w\ld only all[ a limit$ quantity at once to g ?r\gh4 ,b1 if we 7 to atta* two or m pipes to ! tank1 or "o l>ge pipe1 we %\ld make x easi] = ! wat] to fl[1 &1 !re=e1 ! total am\nt ( resi/ance to ! passage ( ! wat] w\ld be v mu* less1 & ! tank w\ld quickly be empti$4 ,n[1 z y already "k1 wat] has sub/ance & weight & !re=e occupies "s space1 b electricity has nei!r sub/ance nor weight1 & !re=e _c occupy any space2 consequ5tly1 to c>ry electricity f "o place to ano!r we d n ne$ to use a pipe1 :i* is holl[1 b we use a solid wire4 ,^! solid wires h a c]ta9 am\nt ( resi/ance to ! passage ( ! electricity1 j z ! wat]-pipe has to ! wat]1 & 7z x is 9 ! case ( ! wat]7 ! effect ( ! resi/ance to ! passage ( electricity is great] if y pass a l>g] quantity ?r\gh ?an a small] quantity4 ,if y want$ to c>ry a quantity ( electricity to a c]ta9 di/ance1 & = t purpose us$ a wire1 !re w\ld be a c]ta9 am\nt ( resi/ance 9 t wire to ! passage ( ! curr5t ?r\gh x2 b if y us$ two or m wires ( ! same size1 or "o l>ge wire1 ! resi/ance w\ld be v mu* less & ! curr5t w\ld fl[ m easily4 ,suppose t1 in/ead ( empty+ ! wat]-tank f ! ro( ?r\gh ! pipe1 we _h j turn$ ! tank ov] & let ! wat] all p\r out at once d[n to ! gr\nd4 ,t w\ld dispose ( ! wat] v quickly & by a %ort way1 w\ld x n8 ,t is v easy to be se51 because !re w\ld be no resi/ance to its passage to ! gr\nd4 ,well1 suppose we _h an electric batt]y giv+ a c]ta9 quantity ( curr5t1 say five ampres1 & we %\ld take a l>ge wire t w\ld (f] no resi/ance to t quantity & put x f "o side ( ! batt]y to ! o!r1 a l>ge curr5t w\ld fl[ at once & t5d to exhau/ ! batt]y4 ,?is is call$ a %ort circuit because !re is little or no resi/ance1 & x provides ! curr5t ) an easy pa? to escape4 ,rememb] ?is1 t electricity always takes ! easie/ pa?4 ,x w take z _m pa?s z are (f]$1 b ! l>ge/ quantity w always take ! easie/4 ,z ! subject ( resi/ance is "o ( ! mo/ important 9 electricity1 we w give y "o m example1 because if y c obta9 a good und]/&+ ( ?is pr9ciple x w help y to compreh5d ! :ole subject m easily 9 y\r future /udies4 ,we />t$ by comp>ison ) a tank hold+ #ajj gallons ( wat]1 dis*>g+ ?r\gh a half-in* pipe1 & %[$ y t ! p\nds ( pressure w\ld =ce ! quantity ( gallons ?r\gh ! pipe4 ,:5 ! tap 0 fir/ op5$ ! wat] w\ld sp\t up v high1 b z ! wat] 9 ! tank became l[] ! pressure w\ld be less1 &1 consequ5tly1 ! wat] w\ld n sp\t s high4 ,s1 if x 7 desir$ to keep ! wat] sp\t+ up to ! height x />t$ )1 we %\ld h to keep ! tank full1 s z to h ! same p\nds ( pressure all ! "t4 ,b1 if we want$ ! wat] to sp\t /ill high] we %\ld h to use o!r means1 su* z a =ce-pump1 to obta9 a great] pressure4 ,n[1 if we %\ld use too _m p\nds pressure x w\ld =ce ! quantity ( wat] m rapidly ?r\gh ! pipe & w\ld cause ! wat] to become heat$ because ( ! resi/ance ( ! pipe to ! passage ( t quantity act$ ^u by s great a pressure4 ,?is is j ! same 9 electricity1 except t ! wire itself w\ld become heat$1 "s ( ! electricity be+ turn$ into heat & lo/4 ,if a wire 7 too small = ! volts pressure & ampres ( curr5t ( electricity ! resi/ance ( su* wire w\ld be ov]come1 & x w\ld become r$-hot & p]haps melt4 ,electricians are !re=e v c>eful to calculate ! resi/ance ( ! wires !y use be=e putt+ !m up1 especially :5 !y are = electric light+1 9 ord] to make all[ances = ! ampres ( curr5t to fl[ ?r\gh !m1 s t b little ( ! electricity w be turn$ into heat & ?us r5d]$ useless = _! purpose4 ,! unit ( resi/ance is call$ ! ohm 7pron\nc$ l home )\t ! h74 ,all wires h a c]ta9 resi/ance p] foot1 accord+ to ! nature ( ! metal us$ & ! size ( ! wire--t is to say1 ! f9] ! wire ! great] numb] ( ohms resi/ance x has to ! foot4 ,wat] & electricity fl[ "u v simil> conditions--t is to say1 ea* ( !m mu/ h a *annel1 or conductor1 & ea* ( !m requires pressure to =ce x onw>d4 ,wat]1 h[ev]1 be+ a tangible sub/ance1 requires a holl[ conductor2 :ile electricity1 be+ intangible1 w fl[ ?r\gh a solid conductor4 ,! iron ( ! wat]-pipe & ! insulation ( ! electric wire s]ve ! same purpose--namely1 t ( s]v+ to prev5t escape by reason ( ! pressure ex]t$4 ,!re is ano!r t]m :i* %\ld be m5tion$ 9 connection ) resi/ance1 z !y are closely relat$1 & t is opposition4 ,!re is no g5]al electrical t]m ( ?is "n1 b1 z x w be mo/ easily und]/ood f ! mean+ ( ! ^w itself1 we h us$ x4 ,let u give an example ( :at opposition w\ld mean if appli$ to wat]4 ,probably e "o kn[s t a wat]-:eel is a :eel hav+ l>ge blades1 or paddles1 ar\nd its circumf]5ce4 ,:5 ! wat]1 9 try+ to =ce its passage1 ru%es aga9/ "o ( ^! paddles x meets ) its opposition1 b ov]comes x by pu%+ ! paddle away4 ,?is br+s ar\nd m opposition 9 ! %ape ( ano!r paddle1 :i* ! wat] also pu%es away4 ,& s ?is goes on1 ! wat] ov]com+ ?is opposition & turn+ ! :eel ar\nd1 by :i* means we c get wat] to d useful "w = u4 ,y mu/ rememb]1 h[ev]1 t x is only by putt+ opposition 9 ! pa? ( a pressure & quantity ( wat] t we c get ?is "w4 ,! same pr9ciple holds good 9 electricity4 ,we make electricity 9 diff]5t ways1 & 9 ord] to obta9 useful "w we put 9 its pa? ! in/rum5ts1 lamps1 or ma*9es :i* (f] ! prop] am\nt ( resi/ance1 or opposition1 to its passage1 & ?us obta9 f ?is wond]ful ag5t ! "w we desire to h done4 ,y h le>n$ t ?ree important measurem5ts 9 electricity are z foll[s3 ,! volt is ! practical unit ( measurem5t ( pressure2 ,! ampre is ! practical unit ( measurem5t ( ! rate ( fl[2 & ,! ohm is ! practical unit ( measurem5t ( resi/ance4 ,,iii ,,magnetism ,n[ we w try to expla9 to y some?+ ab\t magnets & magnetism4 ,!re are v few boys :o h n se5 & play$ ) ! ord9>y magnets1 %ap$ l a horse%oe1 :i* are sold 9 all toy-/ores z well z by ^? :o sell electrical goods4 ,well1 y "k t ^! magnets w attract & hold fa/ any?+ t is made ( iron or /eel1 b !y h no effect on brass1 copp]1 z9c1 gold1 or silv]1 yet !re is no?+ t y c see :i* %\ld cause any su* effect4 ,y w notice1 !n1 t magnetism is l electricity2 we _c see x1 b we c tell t x exi/s1 because x produces c]ta9 effects4 ,& "h is ano!r curi\s ?+--magnetism produces electricity1 & electricity produces magnetism4 ,?is seems to be a v conv5i5t sort ( a family affair1 & x is ow+ to ?is close relation t we are able to obta9 s _m wond]ful ?+s by ! use ( electricity4 ,we %all n[ %[ y h[ electricity produces magnetism1 &1 :5 we come to ! subject ( electric light+ we w expla9 h[ magnetism produces electricity4 ,illu/ration3 ,fig4 #c ,! easie/ way to %[ h[ electricity makes magnetism is to f9d out h[ magnets are made4 ,suppose we want$ to make a horse%oe magnet1 j m5tion$ above2 we w\ld take a piece ( /eel & w9d ar\nd x "s f9e copp] wire1 comm5c+ on "o leg ( ! horse%oe & w9d+ ar\nd until we came to ! end ( ! o!r leg4 ,!n we %\ld h two ends ( wire left1 z %[n 9 ! sket*4 7,fig4 #c47 ,we connect ^! two ends ) an electric batt]y1 giv+1 say1 two volts1 & !n ! ampres ( curr5t ( electricity w travel ?r\gh ! wire1 & 9 do+ s has su* an influ5ce on ! /eel t x is conv]t$ into a magnet1 su* z y h play$ )4 ,! curr5t is brok5--t is to say1 x is %ut (f sev]al times 9 mak+ a magnet ( ?is k9d1 & !n ! wire is tak5 away f ! batt]y & is unw\nd f ! /eel horse%oe1 leav+ x free f wire1 j z y h se5 x4 ,?is horse%oe is n[ a p]man5t magnet--t is1 x w always attract & hold pieces ( iron & /eel4 ,n[1 if y 7 to d ! same ?+ ) a horse%oe made ( s(t iron in/ead ( /eel x w\ld n be a magnet aft] y /opp$ ! curr5t ( electricity f go+ ?r\gh ! wires1 al?\gh ! piece ( iron w\ld be a /rong] magnet :ile ! electricity 0 go+ ?r\gh ! wire ar\nd x4 ,! /eel magnet is call$ a p]man5t magnet1 & its ends1 or poles1 are nam$ ,nor? & ,s\?4 ,!re is usually a loose piece ( /eel or iron1 call$ an armature1 put across ! ends1 :i* has ! peculi> prop]ty ( keep+ ! magnetism f becom+ weak]1 & !reby reta9+ ! /r5g? ( ! magnet4 ,! /ronge/ "p ( ! magnet is at ! poles1 :ile1 at ! po9t m>k$ 7:i* is call$ ! neutral po9t7 !re is sc>cely any magnetism4 ,x w be well to rememb] ! object ( ! armature z we %all meet x aga9 9 describ+ dynamo ma*9es4 ,! magnets made ( iron are call$ electromagnets because !y exhibit magnetism only :5 ! ampres ( curr5t ( electricity are fl[+ ar\nd !m4 ,!y also h two poles1 nor? & s\?1 z h p]man5t magnets4 ,electromagnets are us$ 9 ne>ly all electrical in/rum5ts1 n only because !y are /rong] ?an p]man5t magnets1 b because !y c be made to act in/antly by pass+ a curr5t ( electricity ?r\gh !m at ! mo/ conv5i5t mom5t1 z y w see :5 we expla9 "s ( ! electrical in/rum5ts :i* are us$ to produce c]ta9 effects4 7,fig4 #d47 ,illu/ration3 ,fig4 #d ,( c\rse !re are a great _m diff]5t %apes 9 :i* magnets are made4 ,! simple/ is ! b> magnet1 :i* is simply a flat or r\nd piece ( iron or /eel4 ,suppose y made a magnet ( a flat piece ( /eel & put on top ( x a %eet ( pap]1 & !n ?rew on ! pap] "s iron fil+s1 y w\ld see !m arrange !mselves z is %[n 9 ! foll[+ sket*4 7,fig4 #e47 ,! fil+s w\ld always arrange !mselves 9 ?is %ape1 no matt] h[ l>ge or small ! magnets 74 ,&1 if y 7 to cut x into two or half a doz5 pieces1 ea* piece w\ld h ! same effect4 ,?is %[s y t ea* piece w\ld itself become a magnet & w\ld h its poles exactly z ! l>ge "o _h4 ,illu/ration3 ,fig4 #e ,n[1 we h ano!r curi\s ?+ to tell y ab\t magnets4 ,if y pres5t ! nor? pole ( a magnet to ! s\? pole ( ano!r magnet1 !y w attract & hold fa/ to ea* o!r1 b if y pres5t a s\? pole to ano!r s\? pole1 or a nor? pole to a nor? pole1 !y w repel ea* o!r1 & !re w be no attraction4 ,y c p]=m "s int]e/+ exp]im5ts by reason ( ?is fact4 ,we w give y "o ( !m4 ,take1 say1 a doz5 ne$les & draw !m sev]al times 9 ! same direction across ! ends ( a magnet s t !y become magnetiz$4 ,n[ /ick ea* ne$le half-way ?r\gh a piece ( cork1 & put ! corks1 ) ! ne$les /ick+ ?r\gh !m1 into a b[l ( wat]4 ,!n take a b> magnet & br+ x gradually t[>d ! middle ( ! b[l & y w see ! corks advance or back away f ! magnet4 ,if ! ends ( ! ne$les /ick+ up out ( ! wat] are s\? poles & ! end ( ! magnet y pres5t is a nor? pole1 ! ne$les w come to ! c5t]2 b w g to ! side ( ! b[l if y pres5t ! s\? pole4 ,y c v>y ?is pretty exp]im5t by turn+ up ! o!r ends ( "p ( ! ne$les4 ,y w rememb] t :5 we expla9$ :at resi/ance meant1 we told y t electricity w\ld always take ! easie/ pa?1 & :ile "p ( x w fl[ 9 a small wire1 ! l>ge/ portion w take an easi] pa? if x c get to some?+ l>g] t is a metallic sub/ance4 ,electricity w only fl[ easily ?r\gh any?+ t is made ( metal4 ,y w also rememb] t y le>n$ t :5 electricity took a %ort cut to get away f its prop] pa? x 0 call$ a %ort circuit4 ,all ?is mu/ be tak5 into consid]ation :5 magnets are be+ made4 ,9 ! fir/ place1 ! wire we w9d ar\nd /eel or iron to make magnets mu/ always be cov]$ ) an insulator ( electricity4 ,magnet wire is usually cov]$ ) cotton or silk4 ,if x 7 left b>e1 ea* turn ( ! wire w\ld t\* ! next turn1 & s we %\ld make su* an easy pa? = ! electricity t x w\ld all g back to ! batt]y by a %ort circuit1 & !n we w\ld get no magnetic effect 9 ! /eel or iron4 ,! only way we c get electricity to d useful "w = u is to put "s resi/ance or opposition 9 its way4 ,s y see t if we make x travel ?r\gh ! wire ar\nd ! iron or /eel1 !re is j en\gh resi/ance or opposition 9 its way to give x "w to get ?r\gh ! wire1 & ?is "w produces ! peculi> effect ( mak+ ! iron or /eel magnetic4 ,! cov]+ on ! wire1 z y w rememb]1 is call$ insulation4 ,,iv ,,! ,,telegraph ,e "o kn[s h[ v conv5i5t ! telegraph is1 b !re are n _m :o ?9k h[ wond]ful x is t we c s5d a message 9 a few seconds ( "t to a di/ant place1 ev5 ?\gh x 7 ?\s&s ( miles away4 ,& yet1 ?\gh ! pres5t sy/em ( telegraph+ is a wond]ful "o1 ! me?od ( s5d+ a telegram is simple en\gh4 ,! app>atus t is us$ 9 s5d+ a telegram is z foll[s3 ,! ,batt]y4 ,! ,wire4 ,! ,telegraph ,key4 ,! ,s\nd]4 ,! diff]5t k9ds ( electric batt]ies w be m5tion$ aft]w>d1 s we w n /op n[ to describe !m1 b simply /ate t a batt]y is us$ to produce ! necess>y electricity4 ,z y all "k :at wire is1 !re is no necessity ( describ+ x fur!r4 ,! telegraph key is %[n 9 ! sket* bel[4 7,fig4 #f47 ,illu/ration3 ,fig4 #f ,?is in/rum5t is usually made ( brass1 except t ^u ! h&le !re is ! little knob :i* is ( h>d rubb]4 ,! h&le1 or lev]1 moves d[n :5 ?is knob is press$1 & a little spr+ b5ea? pu%es x up aga9 :5 let g4 ,y w see a second small] knob1 ! use ( :i* we w expla9 lat]4 ,! s\nd] is %[n on ! foll[+ page4 7,fig4 #g47 ,! "p consi/+ ( ! two black pill>s is an electromagnet1 & across ! top ( ^! pill>s is a piece ( iron call$ ! armature1 :i* is held up by a spr+4 ,illu/ration3 ,fig4 #g ,n[ let u see h[ ! batt]y & wire are plac$ 9 connection ) ^! in/rum5ts4 ,y h se5 t we usually h two wires = ! electricity to travel 91 "o wire = x to leave ! batt]y1 & ! o!r to return on4 ,b y w easily see t if two wires _h to be us$ 9 telegraph+ x w\ld be a v exp5sive matt]1 especially :5 !y _h to be c>ri$ ?\s&s ( miles4 ,s1 in/ead ( us+ a second wire1 we use ! e>? to c>ry back ! electricity to ! batt]y1 because ! e>? is a bett] conductor ev5 ?an wire4 ,al?\gh a quantity ( gr\nd equal 9 size to ! wire w\ld (f] ?\s&s ( times great] resi/ance ?an ! wire1 yet1 ow+ to ! great body ( our e>?1 its total resi/ance is ev5 less ?an any telegraph wire us$4 ,:5 two electric wires are run f a batt]y & connect$ toge!r ?r\gh "s in/rum5t1 ?is is call$ a circuit1 because ! electricity has a pa? 9 :i* x c travel back to ! batt]y4 ,?is w\ld be a metallic circuit2 b :5 "o wire only is us$1 & ! o!r side ( ! batt]y is connect$ ) ! e>?1 x is call$ a gr\nd or e>? circuit1 because ! electricity returns ?r\gh ! e>?4 ,illu/ration3 ,fig4 #h ,if y look at ?is sket* 7,fig4 #h7 y w see h[ ! telegraph in/rum5ts are connect$ & w !n be able to und]/& h[ a message c be s5t4 ,"h we h two sets ( telegraph app>atus1 "o ( :i*1 let u say1 is 9 ,new ,york & ! o!r 9 ,philadelphia4 ,y w see t "o wire f ! batt]y is connect$ ) ! e>?1 & ! o!r wire ) ! s\nd]4 ,ano!r wire goes f ! s\nd] to "o leg ( ! key s z to make ! brass base ( ! key "p ( ! circuit4 ,! o!r leg ( ! key is insulat$ f ! brass base by be+ sep>at$ !refrom ) "s sub/ance :i* w n c>ry electricity1 su*1 = in/ance1 z h>d rubb]4 ,we w suppose t !re is already a wire /rung up on poles betwe5 ,new ,york & ,philadelphia1 & t ! key1 s\nd]1 & batt]y 9 ! latt] city are connect$ 9 ! same way z ^? 9 ,new ,york4 ,n[1 to enable u to s5d a message f "o city to ! o!r we mu/ connect ! ends ( ! wires to ! in/rum5ts 9 ea* city2 s we connect "o end to ! insulat$ leg ( ! key 9 ,new ,york1 & ! o!r end to ! insulat$ leg ( ! key 9 ,philadelphia4 ,ev]y?+ is n[ complet$1 &1 z soon z we f9d out :at is ! use ( t "p ( ! key t has a little r\nd1 black h&le1 we %all be ready to />t4 ,?is is call$ ! swit*4 ,if y w look once m at ! picture ( ! key y w see "u ! long h&le 7or lev]7 a little po9t :i* ! lev] w t\* :5 x is press$ d[n4 ,n[ ?is little po9t is "p ( t insulat$ leg1 &1 !re=e1 ?is po9t is also insulat$ f ! base4 ,if a curr5t ( electricity 7 s5t along ! wire x c\ld n get any f>!r ?an ?is po9t unless we put 9 "s arrangem5t to complete ! pa?1 or circuit1 = x to travel 94 ,we !re=e put 9 ! swit*4 ,"o end ( ! swit* 7:i* is made ( brass ) a rubb] h&le7 is fa/5$ on ! base ( ! key1 s t x may be mov$ to ! "r or left4 ,! o!r end1 :5 ! swit* is mov$ to ! left 7or clos$71 t\*es a piece ( brass fa/5$ to ! little po9t we h m5tion$1 & s makes a free pa? = ! electricity to g ?r\gh ! base ( ! key & ?r\gh ! wire to ! s\nd]1 & f !re to ! batt]y1 & s back to ! e>?4 ,?is swit* mu/ be op5$ be=e ! s\nd] ne> x w respond to its neighbor+ key4 ,n[ we are ready to s5d a message4 ,suppose we want to s5d a telegram f ,new ,york to ,philadelphia4 ,! op]ator 9 ,new ,york op5s 8 swit* & presses d[n 8 key sev]al times4 ,! swit* on ! ,philadelphia key be+ clos$1 ! electricity goes ?r\gh to ! s\nd]1 &1 ?is be+ made an electromagnet by ! curr5t pass+ ?r\gh ! wire1 ! iron armature is attract$ by ! magnetism & drawn d[n to ! magnet ) a snap4 ,x w /ay !re z long z ! ,new ,york op]ator keeps 8 lev] press$ d[n1 b1 :5 he all[s x to spr+ up1 !re is no curr5t pass+ ?r\gh ! ,philadelphia s\nd] & !re is no magnetism1 consequ5tly ! armature spr+s up aga9 ) a click4 ,z (t5 z ! op]ator presses d[n 8 key lev] & lets x spr+ up aga91 ! same action takes place 9 ! s\nd]1 & x makes t click1 click1 :i* y h he>d if y h ev] se5 telegraph in/rum5ts 9 op]ation4 ,let u cont9ue1 h[ev]1 to s5d our message4 ,! ,new ,york op]ator1 hav+ press$ d[n 8 key sev]al times to signal ! ,philadelphia op]ator1 closes 8 swit* to receive ! answ] f ,philadelphia4 ,! op]ator 9 ! latt] city !n op5s 8 swit* & presses d[n 8 key sev]al times1 :i* makes ! ,new ,york s\nd] click1 9 ! same way1 to let ! op]ator !re "k t he is ready to receive ! message4 ,he !n closes 8 swit* & receives ! telegram :i* ! ,new ,york op]ator s5ds aft] op5+ 8 key4 ,telegraphic messages are s5t & receiv$ 9 ?is way & are read by ! s\nd ( ! clicks4 ,^! s\nds may be repres5t$ on pap] by dots1 da%es1 & spaces4 ,= in/ance1 if y press d[n ! key & let x spr+ back quickly1 t w\ld repres5t a dot4 ,if y press d[n ! key & hold x a little long] be=e lett+ x spr+ up aga91 x w\ld repres5t a da%4 ,a space w\ld be repres5t$ by wait+ a little :ile be=e press+ d[n ! key aga94 ,we %[ y bel[ ! alphabet 9 ^! dots1 da%es1 & spaces1 & ^! are ! ones n[ us$ 9 s5d+ all telegraphic messages4 ,illu/ration ,?us1 y see1 if y 7 telegraph+ ! ^w & y w\ld press d[n y\r key & let x return quickly1 !n press d[n aga9 & return aft] a long] pause1 :i* w\ld give ! lett] ,a2 !n sl[ly & quickly1 :i* w\ld be ,n2 !n sl[ly & twice quickly1 :i* w\ld be ,d4 ,any p]sev]+ boy c le>n to op]ate a telegraph in/rum5t by a little /udy & regul> practice2 &1 z complete le>n]'s sets c be pur*as$ v *eaply1 ?is af=ds a pleasant & useful recreation = boys4 ,!re are _m cases :]e two boys liv+ ne> ea* o!r h a set ( telegraph in/rum5ts 9 _! homes & run a wire f "o h\se to ! o!r1 ?us af=d+ _m h\rs ( pleasant & pr(itable amusem5t4 ,9 giv+ ! above explanation ( telegraph+ we h describ$ only ! simple & elem5t>y =m4 ,9 l>ge telegraph l9es1 su* z ^? ( ! ,we/]n ,union1 !re are _m m additional in/rum5ts us$1 :i* are v complicat$ & difficult to und]/&2 su*1 = in/ance1 z ! quadruplex1 by :i* f\r di/9ct messages c be s5t ov] ! same wire at ! same "t4 ,we h1 !re=e1 describ$ only ! simple/ =m 9 ord] to give ! g5]al idea ( ! work+ ( ! telegraph by electromagnetism1 :i* is ! pr9ciple ( all telegraph+4 ,:5 y /udy electricity m deeply y w f9d ?is subject & ! _m diff]5t in/rum5ts v int]e/+ & wond]ful4 ,v ,,wireless ,,telegraphy ,if x has seem$ extraord9>y to y t only "o wire %\ld be necess>y = s5d+ a message by ! electric telegraph1 & t our e>? c be us$ in/ead ( a second wire1 h[ mu* m wond]ful x is to realize t 9 ^! days we c ex*ange telegraphic messages ) diff]5t po9ts )\t any connect+ wires at all betwe5 !m1 ev5 ?\gh ! places be _m hundr$ miles ap>t4 ,?us1 two %ips on ! ocean1 entirely out ( sight ( ea* o!r1 may int]communicate1 or may telegraph to or receive despat*es f a f>-di/ant %ore2 inde$1 telegraphy )\t wires has be5 accompli%$ across ! ,atlantic ,ocean4 ,9 ! language ( ! day1 ?is is call$ wireless telegraphy1 al?\gh x is m correct to ?9k ( x z a]ial1 or space1 telegraphy4 ,z y w naturally want to "k h[ ?is is effect$1 we w try to expla9 ! ma9 pr9ciples 9 a simple mann]4 ,if y drop a /one into a quiet pond1 y w see ! wat] =m into r+-l waves1 or ripples1 :i* travel on & on until !y die away 9 ! f> di/ance4 ,^! waves are caus$1 z we h se51 by a di/urbance ( ! body ( wat]4 ,probably y h already le>n$ 9 s*ool t all kn[n space is said to be fill$ ) a m$ium call$ e!r1 & t ?is m$ium is s exce$+ly ?9 t x p5etrates1 or p]meates1 ev]y?+1 s t x exi/s 9 ! d5se/ bodies z well z 9 free space4 ,= ! sake ( obta9+ a cle> idea ( ?is !ory we may imag9e t ! e!r envelops & p]meates e ?+ 9 ! entire univ]se4 ,h5ce we c easily realize t1 al?\gh we _c see or feel ! e!r1 any di/urbance ( x w set x 9 wavelike motion4 ,mod]n sci5ce acc\nts = light1 radiant heat1 & electrical ph5om5a by reason ( wavelike di/urbances1 vibrations1 or pulsations ( ?is e!r4 ,?us1 if y %\ld /rike a light1 ! e!r w\ld be di/urb$1 caus+ waves to =m1 :i*1 l ! waves 9 ! wat]1 w\ld travel 9 e direction4 ,:5 ^! waves rea*$ ! eyes ( ano!r p]son )9 see+ di/ance1 t p]son's eyes w\ld be s act$ ^u by ! waves t he w\ld see ! light :i* y _h made1 & w\ld see x in/antly1 = light waves travel ab\t #ahf1jjj miles p] second4 ,s1 if y create an electrical di/urbance1 ! same k9d ( an effect w be produc$2 t is to say1 waves 9 ! e!r w be creat$1 or propagat$1 & w travel on & on 9 e direction4 ,n[1 if "s =m ( electrical appliance c be made t w be ( ! "r k9d to respond to !m 7z ! eye responds to light rays71 ^! electric waves c be made practically useful = transmitt+ messages ?r\gh space4 ,?is is j :at has be5 done1 & we w n[ give y a brief g5]al description ( "o k9d ( app>atus us$4 ,= s5d+1 or transmitt+1 z x is usually t]m$1 !re is us$ an induction-coil1 hav+ r l>ge brass balls on ! second>y t]m9als2 suitable batt]ies1 a cond5s]1 a ,morse telegraph key1 & an a]ial1 or wire :i* is c>ri$ away up into ! air v]tically1 & is made fa/ to a pole or special t[]4 ,:5 ^! are connect$ prop]ly1 ! clos+ ( ! circuit ) ! key w cause sp>ks to jump betwe5 ! brass balls4 ,?is electrical dis*>ge1 or oscillation1 is c>ri$ by ! a]ial into ! upp] air & causes int5se pulsations 9 ! e!r1 :i* set up waves z already m5tion$4 ,if ! circuit is op5$ aga9 ! di/urbance ceases4 ,s1 by alt]nately clos+ & op5+ ! circuit1 ! ,morse *>act]s c be imitat$4 ,b h[ c ^! signals be receiv$ by ! man = :om !y are int5d$1 :o may be a hundr$ miles or m away8 ,he has a receiv+ set1 consi/+ ( a s5sitive relay1 batt]ies1 resi/ance-coils1 a ,morse regi/]1 an a]ial1 & a special device call$ a coh]]4 ,?is is ! important "p ( ! :ole set1 because x is s5sitive to ! electrical waves4 ,x consi/s ( a little glass tube ab\t z l>ge ar\nd z an ord9>y lead-p5cil1 & p]haps two in*es long4 ,9 ! tube are two metallic plugs1 ea* hav+ a wire atta*$ s t "o wire projects f ea* end ( ! tube4 ,! plugs are sep>at$ inside ! tube by a v small space1 & 9 ?is space are "s metal fil+s4 ,"o wire f ! coh]] is connect$ to ! a]ial & ! o!r to ! gr\nd4 ,:5 !re are no electrical e!r waves to influ5ce !m1 ^! fil+s1 be+ loosely sep>at$1 are at re/ & (f] high resi/ance2 b :5 ! e!r is di/urb$ by electrical vibrations & ! waves arrive at ! coh]] 7?r\gh ! a]ial71 ^! fil+s are drawn toge!r1 or coh]e4 ,?is l[]s _! resi/ance & !y become a bett] conductor4 ,n[1 ! coh]] wires are also connect$ ?r\gh a batt]y to ! relay1 :i* 9 turn is connect$ ?r\gh ano!r batt]y to a ,morse regi/]4 ,!re=e1 :5 ! fil+s become a conductor1 ! curr5t fl[s ?r\gh !m & ! circuit to ! relay is clos$4 ,t attracts an armature :i* closes ! circuit ( ! ,morse regi/] & ?us m>ks ! electrical impulse on a /rip ( pap] tape4 ,9 ! mean "t1 a re/or+ device1 call$ a decoh]]1 op]at$ also by ! relay circuit1 has tapp$ ^u ! coh]]1 ?us %ak+ ! fil+s loose aga91 s t !y are ready to coh]e aga9 & regi/] ano!r impulse1 or "*4 ,?us1 by press+ ! key at ! transmitt+ end = long or %ort p]iods1 to repres5t ,morse *>act]s1 long & %ort waves are propagat$ 9 ! e!r & are receiv$ & record$ at ! receiv+ end ?r\gh ! coh]] & o!r p>ts ( ! receiv+ set4 ,9 ?is way telegraphic messages are s5t & receiv$ ?r\gh space1 betwe5 po9ts sep>at$ by hundr$s or ?\s&s ( miles4 ,we h tri$ to describe to y ! g5]al pr9ciples und]ly+ ! art ( wireless telegraphy z pla9ly z possible1 us+ = illu/ration ! simple/ k9d ( app>atus employ$ = ! practical s5d+ & receiv+ ( messages4 ,at ! pres5t day !re are sev]al sy/ems 9 actual practice1 & ) ! gr[? ( ! art !re h be5 _m elaborations ( app>atus t h come into use4 ,= in/ance1 ! coh]] is n z mu* us$ z =m]ly4 ,9 its place !re are employ$ sev]al k9ds ( wave-detectors z !y are n[ t]m$1 & 9 _m ( ! sy/ems ! electrical pulsations are g5]at$ by a dynamo-ma*9e in/ead ( batt]ies4 ,!n1 aga91 in/ead ( ! messages be+ record$ by a ,morse regi/] at ! receiv+ end1 ! op]ator receives !m by means ( a telephone receiv]1 ?r\gh :i* he he>s ! ,morse *>act]s & writes !m d[n 9 words z he he>s !m4 ,g5]ally ! a]ial1 or ant5n1 z x is sometimes nam$1 consi/s ( sev]al wires1 sometimes a l>ge numb]1 c>ri$ to a consid]able height4 ,!re are a great _m o!r details :i* might be writt5 to expla9 all ! complicat$ app>atus :i* is us$ 9 "s ( ! sy/ems1 b x is n int5d$ 9 ?is book to (f] m ?an a g5]al explanation ( ma9 pr9ciples4 ,we mu/ leave x to y to /udy ! details else:]e if y s desire aft] y h read ^! pages4 ,,vi ,,! ,,telephone ,y probably all "k t ! telephone is an electrical in/rum5t by :i* "o p]son may talk to ano!r :o is at a di/ance4 ,n only c we talk to a p]son :o is 9 a diff]5t "p ( ! city1 b su* great improvem5ts h be5 made 9 ^! in/rum5ts t we c talk ?r\gh ! telephone to a p]son 9 ano!r city1 ev5 ?\gh x be hundr$s ( miles away4 ,! ma9 pr9ciple ( ! telephone is electromagnetism1 z 9 ! telegraph1 b !re are o!r important po9ts 9 addition to ^? we m5tion$ 9 describ+ ! latt]4 ,let u take fir/ ! ,,induction-,,coil ,y w rememb] t an electromagnet is made by w9d+ _m turns ( wire ar\nd a piece ( iron & s5d+ a curr5t ( electricity ?r\gh ?is wire4 ,n[1 suppose ?is curr5t ( electricity 0 be+ suppli$ by two cells ( a batt]y4 ,if y took 9 y\r h&s ! wires com+ f ^! two cells1 giv+1 say1 f\r volts1 y c\ld n feel any %ock2 b if y 7 to take hold ( ! ends ( ! wires on ! electromagnet & sep>ate !m :ile ?is same curr5t 0 go+ ?r\gh1 y w\ld get a decid$ %ock4 ,?is sep>ation w\ld break ! circuit1 & ! reason y w\ld get a %ock is t1 :ile ! electricity is act+ on ! wire1 ! iron itself is magnetiz$1 & on break+ ! circuit reacts ^u ! wire1 produc+ = a mom5t m volts ( pressure 9 e turn ( x4 ,?us1 y see1 ?is weak pressure ( electricity z x travels ?r\gh ! wire c yet produce1 ?r\gh its magnetism1 /rong mom5t>y effects1 b y _c feel x unless y break ! circuit4 ,,h[ ,,! ,,induction-,,coil ,,is ,,made ,! object ( ! induction-coil is to produce high int5sity1 or pressure1 f a comp>atively weak pressure & l>ge curr5t ( electricity2 s1 if we add /ill m wire1 ! magnet has a l>g] numb] ( turns to act ^u & ?us makes a v /rong pressure1 or l>ge numb] ( volts1 b a less] numb] ( ampres4 ,in/ead ( tak+ "o piece ( iron1 z we w\ld = an ord9>y electromagnet1 we take a bundle ( iron wires 9 mak+ an induction-coil1 z ^! give a /rong] effect4 ,ar\nd ?is bundle ( wires we wrap _m turns ( insulat$ copp] wire4 ,?is is call$ ! prim>y coil1 & ! ends ( ?is wire are to be atta*$ to ! batt]y4 ,illu/ration3 ,fig4 #i ,on top (1 or ov]1 ?is prim>y coil we wrap a great _m turns ( v f9e wire1 ( :i*1 z x is s f9e1 a great l5g? c be us$4 ,?is is call$ ! second>y coil1 & x is 9 ?is coil t ! volts1 or pressure1 ( electricity become /ronge/4 ,above we %[ y a sket* ( an induction-coil4 7,fig4 #i47 ,at ! left-h& side ( ! cut is a circuit-break]1 :i* is simply a piece ( iron 7armature7 on a spr+ plac$ opposite ! iron core4 ,?is armature is made a "p ( ! wire lead+ to ! prim>y coil4 ,:5 ! curr5t f ! batt]y is s5t ?r\gh ! wires1 ! core becomes magnetiz$ & draws ?is armature away f a fix$ contact po9t1 ?us break+ ! circuit1 b ! spr+ pulls x back1 aga9 complet+ ! circuit1 & s x keeps go+ back & =? v rapidly ) a br-r-r-+ s\nd4 ,if y 7 n[ to take hold ( ! ends ( ! second>y coil y w\ld get a cont9u\s s]ies ( quick %ocks :i* w\ld feel l p9s & ne$les runn+ into y4 ,p]haps mo/ ( y h tak5 hold ( ! h&les ( a m$ical batt]y & h _h %ocks !refrom4 ,9 s do+1 y h simply _h ! curr5t f ! second>y ( an induction-coil4 ,! curr5t may be made weak] by slid+ a metallic cov] ov] "p ( ! iron core & s %utt+ (f "p ( ! magnetic effect4 ,,sp>k+ ,,coils ,:ile on ?is subject we may add t ^! coils w produce sp>ks f ! two ends ( ! wire ( ! second>y coil4 ,^! sp>ks v>y 9 l5g? accord+ to ! am\nt ( wire 9 ! coil4 ,small ones are made :i* give a sp>k a qu>t] ( an in* 9 l5g?1 :ile o!rs are made :i* w give sp>ks #aj1 #ab1 & #af in*es 9 l5g?4 ,9 ! latt]1 h[ev]1 !re are _m miles ( wire 9 ! second>y coil4 ,! l>ge/ induction-coil kn[n is "o :i* 0 made = an ,engli% sci5ti/4 ,!re are #cda1hej turns1 or #bhj miles1 ( wire 9 ! second>y coil4 ,) #cj cells ( ,grove batt]y ?is coil w give a sp>k #db in*es 9 l5g?4 ,y may =m "s idea ( ! effect ( ?is induction-coil :5 we /ate t if we desir$ to produce ! same l5g? ( sp>k direct f batt]ies1 )\t us+ an induction-coil1 we %\ld require ! comb9$ volts ( pressure ( #fj1jjj to #ajj1jjj cells ( batt]y4 ,hav+ expla9$ to y briefly ! induction-coil--h[ x is made & its action--we mu/ ask y to be> ^! pr9ciples 9 m9d1 & pres5tly we w tell y h[ x is us$ 9 ! telephone4 ,! next ?+ we %all try to expla9 w be ,,! ,,vibrat+ ,,diaphragm ,did y ev] take ! end ( a cane 9 y\r h&1 raise x up ov] y\r head1 & !n br+ x d[n sudd5ly & %>ply1 s t x ne>ly t\*$ ! gr\nd1 z ?\gh y 7 ab\t to /rike some?+8 ,if n1 try x n[ ) a ?9 walk+-cane or ) a p9e /ick ab\t ?ree feet long & "o-half in* ?ick1 & y w f9d t !re is a peculi> s\nd giv5 out4 ,x is n ! /ick t makes ?is s\nd1 b x is ow+ to ! fact t y h caus$ ! air to vibrate1 or tremble1 & ?us give out a s\nd4 ,illu/ration3 ,fig4 #aj ,if y /rike a tun+-=k %>ply y w see ! ends vibrate & a s\nd w be giv54 ,if y put y\r f+]s on top ( a silk hat & speak ne> x y w feel vibrations ( y\r voice4 ,e "t y speak y cause vibrations ( ! air2 & ! l\d] & high] y speak ! great] ! numb] ( vibrations4 ,suppose y take a ?9 piece ( wood 9 y\r h&s 7say1 = in/ance1 ! lid ( a cig>-box cut 9 ! %ape %[n 9 ! picture1 ,fig4 #aj7 & hold x ab\t two in*es f y\r m\? & !n speak4 ,y w feel ! wood tremble 9 y\r h&4 ,?is is because ! vibrations ( ! air cause ! wood to vibrate 9 ! same mann]4 ,^! vibrations are v m9ute & _c be se5 ) ! nak$ eye1 b !y actually take place1 & c\ld be measur$ ) a delicately balanc$ in/rum5t4 ,illu/ration3 ,fig4 #aa ,n[ let u try ano!r exp]im5t 9 fur!r illu/ration ( ?is pr9ciple4 ,we w take a tube ab\t ?ree in*es long & "o & "o-half or two in*es 9 diamet]4 ,?is tube may be made ( c>dbo>d4 ,n[ cut out a piece ( ?9 c>dbo>d :i* w j fit ov] "o end ( ! tube4 ,?is piece we w call ! diaphragm4 ,fa/5 ! diaphragm by pa/+ x ) two /rips ( ?9 pap] to ! tube4 ,^! /rips ( pap] %\ld be fa/5$ only on ! ends1 & ! middle ( ! pap] all[$ to be slack1 z %[n 9 ! picture1 s t ! diaphragm may "w backw>d & =w>d easily4 ,take a small %ot ab\t ! size se5 9 ! sket* & tie x to a s+le ?read ( f9e silk1 !n let x hang z %[n 9 ! sket* 7,fig4 #aa71 s t x w only j t\* ! diaphragm4 ,n[1 if y speak into ! op5 end ( ! tube ! diaphragm w vibrate & ! %ot w be se5 to move to & f x accord+ to ! /r5g? ( ! vibrations4 ,if we c\ld by any means make a diaphragm 9 ano!r tube reproduce ^! same vibrations1 we %\ld he> ! same words respok51 if ! tube 7 held to ! e>4 ,illu/ration3 ,fig4 #ab ,:ile ! vibrations caus$ by ! human voice are too m9ute to be se51 x may seem surpris+ t !y c be made to produce p[]4 ,?is is done by an +5i\s me*anism call$ a ,phonomotor1 p]fect$ by ! great inv5tor ,?omas ,a4 ,edison1 ( :om e "o has probably he>d4 ,?is me*anism1 :5 spok5 or sung at 7or into7 imm$iately responds by caus+ a :eel to revolve4 ,no am\nt ( bl[+ w />t ! :eel1 b x c in/antly be set 9 motion by ! vibrations caus$ by s\nd4 ,! ,phonomotor 7:i* is %[n 9 ! engrav+ ,fig4 #ab7 has a diaphragm & m\?piece4 ,a spr+1 :i* is secur$ to ! b$piece1 re/s on a piece ( rubb] tub+ plac$ aga9/ ! diaphragm4 ,?is spr+ c>ries a pawl t acts on a rat*et or r\gh5$ :eel on ! fly-:eel %aft4 ,a s\nd made 9 ! m\?piece creates vibrations 9 ! diaphragm2 ! vibrations ( ! diaphragm move ! spr+ & pawl ) ! same impulses1 & z ! pawl ?us moves back & =? on ! rat*et-:eel x is made to revolve4 ,! in/rum5t1 !re=e1 is ( great value = measur+ ! me*anical =ce ( s\nd waves1 or vibrations1 produc$ by ! human voice4 ,,! ,,transmitt] ,t "p ( ! telephone into :i* we speak is call$ ! transmitt]4 ,?is is usually a piece ( h>d rubb] hav+ a r\nd m\?piece cut ?r\gh x4 ,at ! o!r side ( ?is m\?piece is plac$ a diaphragm made ( a ?9 piece ( metal1 :i* is held m place by a light spr+4 ,beh9d ?is diaphragm1 & v close to x1 is plac$ a c>bon button4 ,betwe5 ?is c>bon button & ! diaphragm is a small piece ( plat9um1 :i* is plac$ s z to t\* bo? ! button & diaphragm v lightly4 ,?is plat9um contact piece is connect$ ) "o ( ! wires runn+ to ! prim>y ( ! induction-coil1 & ! spr+ atta*$ to ! c>bon button is connect$ ) ! batt]y to :i* ! o!r wire ( ! prim>y is connect$4 ,?is is all %[n 9 ! sket* ( a transmitt]4 7,fig4 #ac47 ,illu/ration3 ,fig4 #ac ,a is ! m\?piece2 ,b1 ! diaphragm2 ,c1 ! c>bon button2 ,d1 ! wire at ! end ( :i* is ! plat9um contact2 ,e1 ! batt]y2 & ,f1 ! induction-coil2 ,p1 ,p are ! wires to ! prim>y1 & ,s1 ,s to ! second>y wires4 ,we w n[ say a few words ab\t ! receiv]1 & !n describe ! mann] 9 :i* ! telephone works4 ,,! ,,receiv] ,?is is t "p ( ! telephone :i* is held to ! e>1 & by :i* we c he> ! words spok5 into ! transmitt] ( ! telephone at ! o!r end ( ! l9e4 ,illu/ration3 ,fig4 #ad ,! receiv] is made ( h>d rubb]1 & conta9s a p]man5t b> magnet1 :i* is w\nd ) wire s z to make x also an electromagnet :5 desir$4 ,9 front ( ?is magnet is plac$ loosely a diaphragm ( ?9 %eet iron4 ,?is diaphragm is plac$ s z to be )9 ! influ5ce ( ! magnet1 b j s t nei!r "o c t\* ! o!r4 ,fig4 #ad is a sket* ( ! receiv]4 ,a & ,b are ! wires lead+ to ! magnet1 ,c1 & ,d is ! diaphragm4 ,e & ,f are :]e ! wires connect1 "o f ! second>y ( ! induction-coil 9 ! o!r telephone1 & ! o!r connect$ ) ! e>?4 ,,! ,,c>bon ,,button ,! little c>bon button plays an important "p 9 ! telephone4 ,y w see f ! sket* ( ! transmitt] t ! curr5t ( electricity w fl[ ?r\gh ! c>bon button to ! contact po9t & ?r\gh ! wire to ! prim>y ( ! induction-coil4 ,n[1 c>bon has a peculi>ity1 :i* is ?is1 t if we press ?is c>bon button1 ev] s slightly1 aga9/ ! plat9um contact1 !re w\ld be less resi/ance to ! fl[ ( ! electricity ?r\gh ! wire to ! prim>y1 & ! m we press x ! less ! resi/ance becomes4 ,! consequ5ce ( ?is w\ld be t m curr5t w\ld g to ! prim>y1 & ! second>y w\ld become correspond+ly /rong]4 ,if ! c>bon button 7 left unt\*$1 & no?+ press$ aga9/ x1 ! fl[ ( curr5t ?r\gh x w\ld be p]fectly ev54 ,hav+ exam9$ ! inside ( ! transmitt] & receiv]1 & und]/&+ ! effect ( pressure on ! c>bon button1 let u n[ see ,,h[ ,,! ,,telephone ,,works ,:5 we speak into ! m\?piece ( ! transmitt]1 ! vibrations ( ! air cause ! diaphragm to vibrate v rapidly1 &1 ( c\rse1 e movem5t ( ! diaphragm presses m or less aga9/ ! c>bon button1 9 consequ5ce ( :i* ! curr5ts pass+ ?r\gh ! prim>y ( ! induction-coil are con/antly increas$ or dim9i%$ & ?us produce simil> effects1 b magnifi$1 9 ! second>y4 ,! effect ( ?is is t ! magnet 9 ! receiv] ( ! o!r telephone is receiv+ a rapidly *ang+ curr5t1 :i*1 produc+ correspond+ magnetic *anges1 makes ! magnet alt]nately weak] or /rong]4 ,?is influ5ces1 by magnetism1 ! iron diaphragm accord+ly1 & makes x reproduce ! same vibrations t 7 caus$ by ! spee* at ! transmitt] ( ! s5d+ telephone4 ,?us1 ! same vibrations be+ reproduc$1 ! orig9al s\nds are giv5 out1 & we c he> :at ! p]son at ! s5d+ telephone is say+4 ,! action ( ! telephone illu/rates well ! wond]fully quick action ( ! electric curr5t by ! reproduction ( ^! s\nd waves1 or air vibrations1 = !y numb] _m ?\s&s 9 "o m9ute's spee*4 ,,vii ,,electric ,,light ,we h n[ arriv$ at a v int]e/+ "p ( ! /udy ( electricity1 z well z a m difficult "p ?an we h yet told y (1 b "o :i* y c easily und]/& if y read c>efully4 ,y mu/ all h se5 electric lights1 ei!r 9 ! /reets or 9 "s l>ge build+s1 = s _m electric lights are n[ us$ t !re are v few p :o h n se5 !m4 ,b p]haps "s ( y h only se5 ! l>ge1 dazzl+ lights t are us$ 9 ! /reets1 & d n "k t !re is ano!r k9d ( electric light :i* is 9 a globe ab\t ! size & %ape ( a l>ge pe>1 & gives ab\t ! same light z a good gas-jet4 ,^! two k9ds ( electric lights h diff]5t names4 ,! l>ge1 dazzl+ lights :i* y see 9 ! /reets are call$ arc-lights1 & ! small1 pe>-%ap$ lamps1 :i* give a s(t1 /eady light1 are call$ inc&esc5t lights4 ,we w tell y lat] :y ^! names are giv5 to !m4 ,illu/ration3 ,fig4 #ae ,! inc&esc5t lights are g5]ally us$ 9 h\ses1 /ores1 !at]s1 factories1 /eamboats1 & o!r places :]e a numb] ( small lights are m pleasant to ! eyes4 ,! arc-lights 7,fig4 #ae7 are us$ to light /reets & l>ge spaces :]e a great quantity ( light is want$4 ,x w\ld n be pleasant to h "o ( ^! dazzl+ arc-lamps 9 y\r p>lor--al?\gh x w\ld give a great deal ( light--because y\r eyes w\ld soon become tir$4 ,b two or ?ree ( ! small inc&esc5t lights 7,fig4 #af7 w\ld be v agreeable1 because !y w\ld give y a nice1 s(t light to read or "w by1 & w\ld n tire y\r eyes4 ,s1 y see1 ^! two diff]5t k9ds ( lamps are v useful 9 _! prop] places4 ,n[1 if y w read pati5tly & c>efully1 we w try & expla9 h[ bo? ^! lights are made4 ,illu/ration3 ,fig4 #af ,y h se5 t ! telegraph1 telephone1 electric bells1 etc41 are work$ by batt]ies4 ,electric lights1 h[ev]1 require su* a l>ge am\nt ( curr5t t x is too exp5sive to produce !m 9 l>ge quantities by batt]ies4 ,a small numb] ( lamps c\ld be light$ by batt]ies1 b if we 7 to attempt to use !m to light #ejj or #a1jjj lamps toge!r1 ! exp5se w\ld be s enorm\s z to make x entirely out ( ! "q4 ,!re are _m millions ( inc&esc5t lamps 9 use 9 ! ,unit$ ,/ates1 b y w easily see t !re c\ld n be t numb] us$ if we _h to dep5d on batt]ies to light !m4 ,y w und]/& ?is m ?or\ghly :5 y h f9i%$ read+ ?is little book4 ,well1 y w ask1 if we _c use batt]ies1 :at is us$ to produce ^! electric lights8 ,ma*9es call$ dynamo-electric ma*9es1 or g5]ators1 :i* are driv5 by /eam-eng9es or wat]-p[]1 are us$ to produce ! electricity :i* makes ^! lamps give u light4 ,y w rememb] t 9 ! *apt] on ,magnetism we expla9$ to y h[ electricity makes magnetism1 & n[ we w expla9 h[1 9 ! dynamo1 magnetism makes electricity4 ,illu/ration3 ,fig4 #ag ,x has be5 f\nd t ! influ5ce ( a magnet is v /rong at its poles1 & t ?is influ5ce is always 9 ! same l9es4 ,?is influ5ce has be5 describ$ z l9es ( =ce1 :i* y w see repres5t$ 9 ! sket* above by ! dott$ l9es 7,fig4 #ag74 ,( c\rse1 ^! l9es ( =ce are only imag9>y & _c be se5 9 any magnet1 b !y are always pres5t4 ,! mean+ ( ?is t]m l9es ( =ce1 !n1 is us$ to designate ! /r5g? ( ! magnet4 ,_m ye>s ago ! great sci5ti/ ,f>aday made ! discov]y t1 by pass+ a clos$ loop ( wire ?r\gh ! magnetic l9es ( =ce exi/+ betwe5 ! poles ( a magnet1 ! magnetism produc$ ! peculi> effect ( creat+ a curr5t ( electricity 9 ! wire4 ,if ! clos$ loop ( wire 7 pass$ d[n1 say f ,u to ,d1 ! curr5t fl[$ 9 ! wire 9 "o direction1 & if x 7 pass$ upw>d1 f ,d to ,u1 ! curr5t fl[$ 9 ! o!r direction4 ,?us1 y see1 magnetism produces electricity 9 ! clos$ loop ( wire z x cuts ?r\gh ! magnetic l9es ( =ce4 ,j :y or h[1 nobody kn[s2 we only "k t electricity is produc$ 9 t way1 & to-day we make practical use ( ?is me?od ( produc+ x by embody+ ?is pr9ciple 9 dynamo-ma*9es1 z we w %ortly expla94 ,9 c>ry+ ?is discov]y into practice 9 mak+ dynamo-ma*9es we use copp] wire4 ,if iron 7 us$1 !re w\ld be a curr5t ( electricity g5]at$1 b x w\ld be mu* less 9 quantity1 because iron wire has mu* great] resi/ance to ! passage ( electricity ?an ! same size ( copp] wire4 ,p]haps y c und]/& x m ?or\ghly if we /ate t :5 a clos$ loop ( wire is pass$ up & d[n betwe5 ! poles ( a /rong magnet !re is a v p]ceptible opposition felt to ! passage ( ! wire to & fro4 ,?is is due to ! influ5ce ( ! magnetism ^u ! curr5t produc$ 9 ! wire z x cuts ?r\gh ! l9es ( =ce1 &1 inasmu* z ^! l9es ( =ce are always pres5t at ! poles ( a magnet1 y w see t1 no matt] h[ _m times y pass ! loop ( wire up & d[n1 !re w be creat$ 9 x a curr5t ( electricity by its passage ?r\gh ! l9es ( =ce4 ,illu/ration3 ,fig4 #ah ,suppose t1 in/ead ( us+ "o s+le loop ( copp] wire1 y w\nd ^u a spool a long piece ( wire l t 9 ,fig4 #ah1 & t y turn$ ?is spool ar\nd rapidly betwe5 ! poles ( ! magnet1 y w\ld ?us be cutt+ ! l9es ( =ce by ! same wire a great _m times1 & e "t "o l5g? ( ! wire cut ?r\gh ! l9es ( =ce "s electricity w\ld be g5]at$ 9 x1 & ?is w\ld cont9ue z long z ! spool 0 revolv$4 ,b1 z ea* l5g? w\ld only be a "p ( ! "o piece ( wire1 y w easily see t !re w\ld be a great deal ( electricity g5]at$ 9 ! :ole piece ( wire4 ,illu/ration3 ,fig4 #ai ,all we h to d1 !n1 is to collect ?is electricity f ! two ends ( ! wire1 & use x4 ,if we %\ld atta* two wires to ! two ends ( ?is wire on ! spool1 !y w\ld be brok5 (f :5 x turn$ ar\nd1 s we mu/ use "s o!r me?od4 ,we fix on ! end ( ! spool 7:i* is call$ an armature7 two pieces ( copp]1 s t !y w n t\* ea* o!r 7z 9 ,fig4 #ai71 & fa/5 ! ends ( ! wire to ^! pieces ( copp]4 ,?is is call$ a commutator1 &1 z y see1 is really ! ends ( ! wire on ! spool4 ,n[ we get two ?91 flat pieces ( copp] & fix !m s t !y w re/ ^u ! copp] b>s ( ! commutator1 b w n g r\nd ) x4 ,^! two flat pieces ( copp] are call$ ! bru%es1 & !y w collect f ! commutator ! electricity :i* is ga!r$ 9 ! wire ar\nd ! spool4 ,z ! bru%es /& /ill1 two wires c be fa/5$ to !m1 & ?us ! ampres ( curr5t ( electricity1 act$ ^u by ! volts pressure1 c be c>ri$ away to be us$ 9 ! lamps1 = y mu/ rememb] t z long z ! spool turns ar\nd x ga!rs m electricity :ile !re is any magnetism = ! wire on ! spool to pass ?r\gh4 ,! con/ant revolv+ ( ! spool creates s mu* electricity t x is driv5 out f ! wire on ! spool1 ?r\gh ! commutator to ! bru%es1 & !re x f9ds a pa? to travel away f ! pressure ( ! new electricity :i* is all ! "t be+ made4 ,9 ?is way we get a cont9u\s curr5t ( electricity 9 ! two wires lead+ f ! commutator1 & c use x to light electric lamps or = o!r useful purposes4 ,9 expla9+ ?is to y1 s f>1 we h us$ z an illu/ration ( ! magnet "o ( ! /eel p]man5t magnets 9 ord] to make ! explanation m simple1 b n[ t y und]/& h[ ! electricity is made1 we mu/ expla9 to y some?+ ab\t ! magnets t are us$ 9 dynamo-ma*9es4 ,we c p]haps make ?is m cle> by giv+ ano!r example4 ,suppose y _h a dynamo :i* 0 light+ up #ajj ( ! inc&esc5t lamps1 ea* ( #bjj ohms resi/ance & ea* requir+ #ajj volts pressure4 ,n[ ea* lamp w\ld take j a c]ta9 quantity ( electricity1 say half an ampre2 s1 ! #ajj lamps w\ld require "o hundr$ times t quantity4 ,b1 if y turn$ (f #ej ( ^! lamps at once1 ! t5d5cy w\ld be = ! pressure to rise above ! #ajj volts requir$ = ! o!r #ej1 & !y w\ld be apt to burn out quick]4 ,x is pla9ly to be se51 !n1 t we mu/ h "s means ( regulat+ ! magnetism s z to regulate ! l9es ( =ce = ! wire on ! armature to cut ?r\gh4 ,we c d ?is ) an electromagnet1 b n ) a p]man5t magnet1 because we _c easily regulate ! am\nt ( magnetism :i* a p]man5t magnet w give4 ,!re is ano!r reason :y we _c use p]man5t magnets 9 a dynamo1 & t is because !y _c be made to give z mu* magnetism z an electromagnet w give4 ,?us y w see t !re are v good reasons = us+ electromagnets 9 mak+ dynamo-ma*9es4 ,let u see n[ h[ ^! electromagnets & dynamos are made1 & !n exam9e ! me?ods :i* are foll[$ to op]ate & use !m4 ,y mu/ rememb]1 to beg9 )1 t 9 ref]r+ to wire us$ on magnets & armatures & = c>ry+ ! electricity away to ! lamps1 we always mean wire t is cov]$ or insulat$4 ,9 electric light+1 insulat$ wire is always us$1 except at ! po9ts :]e x is connect$ )1 ! dynamo1 ! lamps1 a swit*1 or any po9t :]e we make :at is call$ a connection4 ,z ! %ape ( ! magnets is diff]5t 9 ! dynamos ( v>i\s inv5tors1 we w take = illu/ration ! "o t is ne>e/ ! %ape ( ! horse%oe & ! %ape t is g5]ally us$ 9 illu/rat+ ! pr9ciple ( ! dynamo4 ,?is is ! =m us$ by ,mr4 ,edison1 :om we h previ\sly m5tion$4 ,?is =m is %[n 9 ,fig4 #bj4 ,n[1 al?\gh ?is magnet appe>s to be 9 "o piece1 x really consi/s ( five p>ts screw$ toge!r s z to make1 practically1 "o piece4 ,! names ( ! p>ts are z foll[s3 ,f1 ,f are ! cores2 ,c ! yoke1 :i* b9ds !m toge!r2 & ,p1 ,p ! pole pieces1 :]e ! magnetism is ! /ronge/4 ,^! pole pieces are r\nd$ out to receive ! armature1 :i*1 z y w rememb]1 is ! "p t turns ar\nd4 ,illu/ration3 ,fig4 #bj ,! cores1 ,f1 ,f1 are fir/ w\nd ) a c]ta9 am\nt ( wire1 :i* dep5ds ^u ! use ! dynamo is to be made =4 ,?us1 y w see1 !re w be on ea* core two loose ends ( ! wire t is w\nd ar\nd x--namely1 ! beg9n+ ( ! wire & ! end :]e we leave (f w9d+1 :i* on ! two cores toge!r w make f\r ends ( wire4 ,we w tell y pres5tly :at is done ) !m4 ,aft] ! cores are w\nd1 !y are screw$ firmly to ! yoke & to ! pole pieces1 s z to make1 = all practical purposes1 "o :ole piece pretty ne>ly ! %ape ( a horse%oe magnet4 ,illu/ration3 ,fig4 #ba ,n[1 to make ! dynamo complete1 we mu/ put 9 ! armature betwe5 ! poles1 :i* are r\nd$ (f1 z y w see1 to accommodate x4 ,! armature is held up by two be>+s1 :i* y w see 9 ! sket* ( ! complete dynamo above4 7,fig4 #ba47 ,! armature 9 a practical dynamo-ma*9e consi/s ( a l>ge spool made ( ?9 %eets ( iron firmly fa/5$ toge!r & hav+ a /eel %aft run ?r\gh ! c5t]1 ^u :i* x revolves4 ,?is spool1 or armature1 is w\nd ) a numb] ( /r&s ( copp] wire4 ,! commutator1 in/ead ( consi/+ ( two b>s1 is made 9 _m dynamos ) z _m b>s z !re are /r&s ( wire1 & ! ends ( ^! wires are fa/5$ to ! b>s ( ! commutator s z to make1 practically1 "o long piece ( wire1 j z we %[$ y 9 expla9+ h[ ! electricity 0 produc$4 ,! bru%es1 re/+ ^u ! commutator1 c>ry away ! electricity f x into ! wires ) :i* !y are connect$4 ,n[ we h our dynamo all put toge!r & ready to />t z soon z we prop]ly connect ^! f\r loose ends ( wire on ! cores4 ,if y w turn back to ,fig4 #bj y w see t two ( ! wires are m>k$ ,i1 & ! o!r two ,o4 ,! lett] ,i means ! inside wire1 or :]e ! w9d+ began1 & ! lett] ,o means ! outside wire1 or :]e we left (f w9d+4 ,n[1 if we fa/5 toge!r 7or connect7 ! two ends ( wires1 ,i & ,o1 ne> ! top ( ! magnet1 we make ! two wires r\nd ! cores into "o wire1 :i* />ts1 say1 at ,i ne> ! poles1 goes all ar\nd "o core1 crosses ov] & ar\nd ! o!r core d[n to ! o!r end ( ! wire to ,o1 ne> ! poles4 ,s f> we h call$ ! iron a magnet1 al?\gh x is n a magnet until electricity is put into x2 s1 :5 ! dynamo is />t$ = ! fir/ "t1 ^! two ends ( wire1 ,i & ,o1 are connect$ to a batt]y or o!r s\rce ( curr5t = ! purpose ( s5d+ electricity ?r\gh ! wire on ! cores4 ,:5 ! electricity goes into ?is wire ! iron imm$iately becomes a magnet1 & ! l9es ( =ce are pres5t at ! poles4 ,n[1 ! armature is turn$ ar\nd rapidly by a /eam-eng9e1 &1 z ! wire on ! armature cuts ! l9es ( =ce ) great rapidity & s frequ5tly1 !re is quickly g5]at$ a l>ge quantity ( electricity1 :i* passes out z fa/ z x is made ?r\gh ! commutator & ! bru%es to ! lamp4 ,& s long z ! armature is revolv$ & ! batt]y atta*$1 ! electricity w be made1 or1 z x is usually t]m$1 g5]at$4 ,z we /at$ above1 a batt]y is us$ ! fir/ "t ! dynamo is run1 & n[ we w expla9 :y x is n ne$$ aft]w>d4 ,al?\gh iron w n become a p]man5t magnet1 l /eel1 x does n lose all its magnetism aft] x has be5 once ?or\ghly *>g$4 ,:5 ! dynamo is /opp$1 aft] ! fir/ trial1 & ! batt]y is tak5 away1 y w discov] only traces ( magnetism ab\t ! poles4 ,!y w n readily attract ev5 a ne$le or iron fil+s2 b !re is1 nev]!less1 a v small am\nt ( magnetism left 9 ! iron4 ,small z ?is magnetism is1 h[ev]1 x is en\gh to make v fa9t & weak l9es ( =ce at ! poles ( ! magnet4 ,aft] ! batt]y is tak5 away1 ! ends ( ! wire on ! cores1 :i* 7 connect$ to ! batt]y1 are connect$1 in/ead1 to ! wires :i* c>ry away ! electricity f ! bru%es to ! lamps4 ,?us1 y w see1 if any electricity goes f ! dynamo to ! lamps1 "p ( x mu/ also f9d its way ?r\gh ! wires :i* are ar\nd ! cores4 ,we w n[ />t up ! dynamo )\t hav+ any batt]y atta*$ & see :at happ5s4 ,! armature turns ar\nd & ! wires ^u x cut ?r\gh ^? v fa9t l9es ( =ce :i* are always at ! poles4 ,?is1 z y "k1 makes "s electricity2 v little1 to be sure1 b x comes out ?r\gh ! bru%es to ! wires lead+ to ! lamps1 & !re x f9ds ! wires lead+ back to ! cores4 ,well1 "p ( ?is weak curr5t ( electricity goes into ^! wires & travels back r\nd ! cores & s makes ! magnetism /rong]4 ,! consequ5ce ( ?is is t ! l9es ( =ce become /rong] &1 z ! armature keeps turn+ ar\nd1 ! electricity naturally becomes /rong]1 & s !re is m ( x go+ ?r\gh ! wires back to ! cores & increas+ ! /r5g? ( ! magnet all ! "t1 until ! dynamo becomes /rong en\gh to g5]ate all ! curr5t x 0 int5d$ to give = ! lamps4 ,( c\rse1 y und]/& t ! /rong] ! magnet becomes1 ! great] w be ! l9es ( =ce & ! great] ! am\nt ( electricity made by ! turn+ ( ! armature4 ,n[1 !re is naturally a limit to :at c be done ) any p>ticul> dynamo2 s1 :ile ! electricity cont9ues to /r5g!n ! magnetism & ! magnetism increases ! electricity1 ?is _c g beyond :at is call$ ! saturation po9t ( ! magnet4 ,saturation means t ! iron is full ( magnetism1 & w hold t mu* b no m4 ,y w le>n m z to ! saturation ( magnets :5 y /udy electricity m deeply1 & we !re=e d n int5d to ent] into t subject 9 ?is book4 ,we w only /ate1 h[ev]1 t ! magnets ( dynamos are n always *>g$ up to _! saturation po9t4 ,,! ,,lamps ,s f> y h le>n$ h[ ! curr5t ( electricity is produc$1 & n[ we w foll[ along ! wires to f9d out h[ x makes ! lamps give out bo? /rong lights & ! small]1 pleasant ones4 ,suppose we take fir/ ! l>ge1 dazzl+ lights we see 9 ! /reets1 :i*1 z y "k1 are call$ ,,arc-,,lights ,^? :o h se5 ! arc-lamps w readily recognize !m f ! picture 9 ,fig4 #bb4 ,y w see t !re are two /icks1 or p5cils1 ( c>bon4 ,n[ y w rememb] t 9 ! *apt] on ,magnetism we told y t 9 ord] to h electricity d "w = u we mu/ put "s resi/ance or opposition 9 its way4 ,:5 we get light f an electric lamp x is because we make ! electricity d "s "w 9 ! lamp1 & ?is "w is 9 pu%+ its way ?r\gh a resi/ance or opposition :i* is 9 ! lamp4 ,illu/ration3 ,fig4 #bb ,:5 we g5]ate electricity 9 ! dynamo & put two wires = x to travel 91 ! curr5t goes away f ! dynamo ?r\gh "o ( ! wires & w g back to ! dynamo ?r\gh ! o!r "o if x c possibly get a *ance to get to ?is o!r "o4 ,n[1 ! electricity :i* is con/antly be+ made fills ! wires & acts z a pressure to =ce ! curr5t ?r\gh ! wires back to ! dynamo1 &1 if we put no resi/ance or opposition 9 ! way1 x w\ld h a v easy pa? to travel 9 & w\ld d no "w at all4 ,! wires lead+ to an electric lamp %\ld h v little resi/ance1 n suffici5t to require any "w f ! curr5t 9 pass+ ?r\gh4 ,s1 if we br+ ! two c>bons 9 an arc-lamp toge!r !y really =m "p ( ! wire1 & d n int]rupt ! curr5t 9 its travels1 b1 if we sep>ate ! c>bons1 we make a gap :i* ! curr5t mu/ jump across if x wants to g on4 ,z ! volts1 or pressure1 is s great1 ! curr5t mu/ jump1 & ?is aga9/ ! resi/ance or opposition 9 an arc-lamp is t :i* gives ! curr5t s mu* "w to d4 ,inde$1 s h>d is x = ! curr5t to jump across ?is gap t x breaks (f f "o c>bon a %[] ( t9y p>ticles z f9e z ! f9e/ du/1 & makes !m :ite hot 9 pass+ to ! o!r4 ,?is %[] ( f9e c>bon du/1 toge!r ) ! ends ( ! c>bons1 be+ :ite hot1 ( c\rse makes a light1 & ?is is ! dazzl+ light :i* y see 9 ! arc-lamp4 ,( c\rse1 :5 ! electricity has jump$ ov] f "o c>bon to ! o!r1 x goes ?r\gh x to ! wire1 & s passes on to ! next lamp1 :]e x has to jump aga91 & s on until x has gone ?r\gh ! la/ lamp1 !n x has an easy pa? to get back to ! dynamo4 ,n[1 we want y to und]/& m ?or\ghly h[ t mu* resi/ance or opposition w cause heat1 s we w try to give y a simple example4 ,mo/ ( y "k t if y 7 hold+ a rope tightly 9 y\r h&s & "s "o pull$ x ?r\gh !m quickly & sudd5ly1 x w\ld get v hot & y\r h&s w\ld feel z ?\gh !y 7 be+ burn$4 ,?is is heat caus$ by y\r h&s resi/+ or oppos+ ! passage ( ! rope ?r\gh !m1 & if y c\ld hold on tightly en\gh & ! rope 0 drawn ?r\gh quickly en\gh1 x w\ld take fire4 ,?is fire w\ld1 !re=e1 cause heat & light4 ,x is j ?is pr9ciple ( resi/ance to ! passage ( ! curr5t :i* causes ! light 9 an arc-lamp1 z we h %[n y4 ,,inc&esc5t ,,lamps ,y h j le>n$ t ! light 9 an arc-lamp is caus$ by ! curr5t =c+ (f f ! c>bon /icks t9y p>ticles & heat+ !m up until !y give a brilliant light4 ,s1 y see1 9 an arc-light !re is a we>+ away ( c>bon by electricity1 & !re=e ^! /icks1 or p5cils1 ( c>bon 9 "t are all burn$ away4 ,9 practice ! c>bon p5cils la/ ab\t eight or t5 h\rs1 & !n new ones mu/ be put 94 ,n[1 9 ! inc&esc5t lamp !re is also c>bon us$1 b ! light is n produc$ by ! combu/ion or wa/+ away ( ! c>bon1 z we w %[ y4 ,! picture bel[ w %[ y ! appe>ance ( an inc&esc5t lamp4 7,fig4 #bc47 ,illu/ration3 ,fig4 #bc ,y w see t ?is lamp consi/s ( a pe>-%ap$ globe1 & inside is a long ,u-%ap$ /rip ( c>bon no ?ick] ?an an ord9>y ?read4 ,?is is a /rip ( bamboo cane#a :i* has be5 c>boniz$ to a ?read ( *>coal4 ,x is jo9$ to two wires :i* come ?r\gh ! glass4 ,^! two wires come d[n ?r\gh ! bottom ( ! globe1 & "o is fa/5$ to a brass screw-r+1 :ile ! o!r wire is fa/5$ to a brass button at ! bottom ( ! lamp4 ,^! two 7! r+ & button7 mu/1 z y "k1 be sep>at$ f ea* o!r by some?+ :i* w n c>ry electricity1 or !y w\ld make a %ort circuit :5 ! electricity 0 appli$4 ,we sep>ate ! r+ & ! button 9 v>i\s ways4 ,n[1 if we took ! ends ( two wires :i* 7 *>g$ ) ! prop] am\nt ( electricity & put "o wire on ! screw-r+ & ! o!r on ! button1 ! lamp w\ld light up1 because !re w\ld be a complete pa? = ! curr5t to travel 94 ,illu/ration3 ,fig4 #bd ,x w1 h[ev]1 be pla9 to y t x w\ld be awkw>d to light ! lamps 9 ?is way1 s we use a socket into :i* ! lamp is screw$4 7,fig4 #bd47 ,! wires f ! dynamo c>ry+ ! electricity are connect$ 9 ! socket1 "o wire ) ! screw ?read into :i* ! screw-r+ fits1 & ! o!r ) a button :i* ! button on ! lamp t\*es :5 ! lamp is screw$ into ! socket4 ,?us we h a connect$ pa? = ! curr5t to travel 91 or1 z x is t]m$1 a complete circuit4 ,y w notice t 9 ! inc&esc5t lamp ! electricity does n ne$ to jump1 z x does 9 ! arc-light1 because we give x "o cont9u\s l9e to travel 94 ,9 ord]1 h[ev]1 to get ! curr5t to d "w = u1 we put "s resi/ance 9 its pa?1 :i* x mu/ ov]come 9 ord] to travel back to ! dynamo4 ,! resi/ance 9 an inc&esc5t lamp is ! ,u-%ap$ c>bon /rip 7or1 z x is call$1 filam5t74 ,?is *>coal filam5t has s mu* great] resi/ance ?an ! wires t x opposes1 or resi/s1 ! passage ( ! electricity ?r\gh x2 b ! electricity mu/ g ?r\gh1 &1 z x is /rong en\gh to =ce its way1 x ov]comes ?is resi/ance & passes on ?r\gh ! c>bon to ! wire at ! o!r end4 ,y see x is a /ruggle betwe5 ! c>bon & ! electricity1 ! curr5t be+ det]m9$ to g on & ! c>bon try+ to keep x back2 &1 9 ! end1 ! electricity1 be+ ! /rong]1 gets ! be/ ( x2 b ! /ruggle has be5 s h>d t ! c>bon has be5 rais$ to a :ite heat1 or inc&esc5ce1 & s gives out a beautiful light1 :i* cont9ues z long z ! curr5t ( electricity fl[s4 ,y w rememb] t 9 ! arc-light ! c>bons are sl[ly consum$ & new ones mu/ be put 94 ,if ! c>bon 9 ! inc&esc5t light 7 consum$1 x w\ld n la/ _m m9utes1 because x is only ab\t ! size ( a horsehair4 ,n[1 y w naturally inquire :y ?is f9e /rip is n burn$ up :5 x is rais$ to s high a heat4 ,well1 we w tell y4 ,y "k t if y light a mat* & let x burn ! wood w all be consum$4 ,b did y ev] light a mat*1 put x into a small bottle1 & put ! cork 98 ,if y nev] did1 d s n[ z an exp]im5t1 & y w see t ! mat* w keep light$ = an in/ant & !n g out )\t consum+ ! wood4 ,! reasons = ?is are v simple4 ,9 ord] to burn any?+ up entirely x is absolutely necess>y to h ! gas call$ oxyg5 pres5t1 &1 z ! air y live 9 conta9s a v l>ge am\nt ( oxyg51 !re is m ?an suffici5t 9 y\r room to cause ! wood ( ! mat* to be entirely consum$ aft] x is light$4 ,b !re is su* a small quantity ( oxyg5 9 ! bottle t x is n en\gh to keep ! fire go+ 9 ! mat*1 &1 consequ5tly1 x w n burn up ! wood4 ,! reason ! filam5t 9 an inc&esc5t lamp is n burn$ up is because !re is no oxyg5 inside ! globe4 ,aft] ! c>bon is put 9 its place all ! oxyg5 is drawn out ?r\gh a tube1 & ! glass is seal$ up s t no m oxyg5 c get 94 ,?is is call$ obta9+ a vacuum1 & vacuum means a space )\t air4 ,!re be+ no oxyg5 9 ! globe1 x is impossible = ! c>bon to burn up2 s ! inc&esc5t lamp w cont9ue to give its light = a v long "t1 "s ( !m la/+ = ?\s&s ( h\rs4 ,"s day1 h[ev]1 f a great v>iety ( obscure causes1 ! filam5t becomes weak 9 "s p>ticul> spot & breaks1 & ! light ceases4 ,:5 ?is happ5s1 we unscrew ! lamp & put ano!r "o 91 & ! light goes on z usual4 ,n[ y h le>n$ h[ ! inc&esc5t lamp is made to give light4 ,we w add t x is a beautiful1 s(t1 :ite light1 almo/ )\t heat1 x w n explode1 ?r[s (f no poison\s fumes l gas or oil lamps1 & has _m o!r po9ts ( com=t & conv5i5ce :i* make x v desirable4 ,,electric-,,light ,,wires ,be=e clos+ ! subject ( electric light y w\ld p]haps l to "k some?+ ab\t ! way 9 :i* we place ! wires lead+ to ! lamps4 ,illu/ration3 ,fig4 #be ,if y rememb] :at we told y ab\t measurem5ts 9 ! beg9n+ ( ?is book1 x w be easy to und]/& :at foll[s3 ,y "k t if y h a v great pressure y c =ce a quantity ?r\gh a small conductor4 ,?is is ! pr9ciple ^u :i* ! arc-lamps are run4 ,e arc-lamp takes ab\t #dj to #ej volts & f #e to #aj ampres to produce ! light1 & !y are connect$ ) ! wires z %[n 9 ,fig4 #be4 ,?is is call$ runn+ lamps 9 s]ies1 &1 z y w see f ! sket*1 ! wire />ts out f ! dynamo & connects ) "o c>bon ( ! fir/ arc-lamp1 & to ! o!r c>bon is connect$ ano!r wire :i* goes on to ! next lamp1 & s on until ! la/ lamp is rea*$1 & !n ! wire goes back to ! dynamo4 ,?is =ms1 practically1 "o cont9u\s loop f "o bru% to ! o!r ( ! dynamo4 ,! curr5t />ts out1 makes its way ?r\gh ! fir/ lamp1 goes on to ! next1 makes its way ?r\gh t1 & s on till x has jump$ ! la/ "o2 !n x goes back to ! dynamo4 ,n[1 z ea* ( ^! jumps requires a pressure ( #dj or #ej volts1 y w easily see t ! total pressure1 9 volts1 ( ! electricity mu/ be z _m times #dj or #ej volts z !re are lamps to be light$2 s1 if !re 7 #fj lamps 9 circuit1 !re w\ld be #b1djj to #c1jjj volts pressure1 :i*1 :ile x gives v f9e lights1 might cause in/ant dea? to any "o t\*+ ! wires4 ,suppose any?+ happ5$ to ! fir/ lamp1 :i* /opp$ ! curr5t f jump+ ?r\gh x4 ,!re w\ld be no pa? = ! curr5t to travel f>!r1 &1 consequ5tly1 all ! lights w\ld g out4 ,to get ov] ?is difficulty !re is sometimes us$ :at is call$ a %unt1 :i* only acts :5 ! lamp w n light4 ,?is %unt c>ries ! curr5t r\nd ! lamp to ! o!r wire1 s t x may travel on & light up ! o!r lamps4 ,,wires ,,= ,,inc&esc5t ,,lamps ,! wir+ = inc&esc5t lamps is c>ri$ out 9 an entirely diff]5t way1 :i* y c see by comp>+ ,fig4 #be ,a ) ,fig4 #be :i* %[s ! wir+ = arc-lamps4 ,illu/ration3 ,fig4 #be ,a ,?is is call$ connect+ 9 multiple arc4 ,y w notice t ! two wires runn+ out f ! dynamo 7:i* are call$ ! ma9 wires7 d n =m "o cont9u\s loop z 9 ! arc-light sy/em1 b t a small] wire is atta*$ to "o ( ! ma9 wires & !n connect$ ) ! screw-r+ 9 ! lamp-socket2 !n ano!r wire is connect$ ) ! button 9 ! socket & aft]w>d to ! o!r ma9 wire4 ,e lamp =ms an indep5d5t pa? ?r\gh :i* ! curr5t c travel back to ! dynamo4 ,n[1 if we turn "o ( ^! inc&esc5t lamps out1 we simply %ut (f "o ( ^! pa?s & ! electricity travels ?r\gh ! o!r lamps1 &1 if we wi%1 we c turn out all ! lamps b "o & !re w /ill be a way = ! electricity to g back to ! dynamo4 ,9 ! arc-lamps we mu/ h a v high numb] ( volts pressure1 because ! electricity has only "o pa?1 & x all has to pass ?r\gh ! fir/ & o!r lamps till x comes to ! la/ "o4 ,9 ! inc&esc5t light ! electricity has z _m pa?s z !re are lamps1 s we only ne$ to keep "o c]ta9 pressure 9 volts 9 ! ma9 wires all ! "t4 ,?is pressure is ev5 all ! way ?r\gh ! ma9 wires1 &1 !re=e1 x is ready to light a lamp ! in/ant x is turn$ on1 because1 z y h se51 electricity w always get back to ! dynamo if !re is a possible *ance1 & ! lamp op5s a pa?4 ,! volts pressure us$ to op]ate any numb] ( inc&esc5t lamps is altoge!r v mu* less ?an = a numb] ( arc-lights4 ,= example1 9 ! ,edison sy/em ! pressure 7sometimes call$ electromotive =ce7 is only ab\t #aaj volts1 :i* is v mild & n at all dang]\s4 ,?is electromotive =ce w\ld be ! same if !re 7 "o lamp or t5 ?\s& light$4 ,:ile ?is ,edison curr5t w\ld n hurt any "o1 y %\ld rememb] t x is mu* ! bett] plan n to t\* any electric-light wires until y h le>n$ a great deal m on ?is subject4 ,we may add t ea* ( ! /&>d inc&esc5t lamps requires only ab\t "o-qu>t] ( an ampre ( curr5t to make !m give a light ( #af c&le-p[]1 :i* is ab\t ! light giv5 by a v good gas-jet1 & :ile ! electromotive =ce1 or pressure1 w\ld only be ab\t #aaj volts1 :e!r !re 7 "o lamp or t5 ?\s& light$1 !re mu/ be suffici5t ampres 9 ! wires to give ea* lamp its prop] quantity4 ,,swit*es ,we h made m5tion sev]al times ( turn+ on or (f "o or m lights1 & n[1 p]haps1 y w\ld l to "k h[ ?is is done4 ,suppose ! electricity 0 travel+ ?r\gh wires to "o or sev]al lamps1 x w\ld light up ^? lamps z long z ! wires provid$ a pa? to travel 91 b if y 7 to cut out "o ( !m1 :i* is call$ break+ ! circuit1 !re w\ld be no road = ! electricity to foll[1 &1 consequ5tly1 its c\rse w\ld be /opp$ %ort & ! lamps w\ld g out4 ,y w rememb] t electricity mu/ h a complete circuit or x c d no "w1 & 9 electric light+ x is always a metallic circuit t is us$4 ,n[1 ! swit* is simply a device :i* is us$ to break ! circuit s t ! curr5t _c pass on4 ,! simple/ =m ( swit* is se5 9 ! sket*4 7,fig4 #bf47 ,illu/ration3 ,fig4 #bf ,y w see t !re is a wire cut 9 two1 & to "o piece is atta*$ a metallic piece1 ,a1 :i* turns "o way or ! o!r1 & :5 x is turn$ s z to t\* ! o!r "p ( ! wire ! circuit is clos$ & ! electricity goes f ! l[] "p ( ! wire ?r\gh ! metallic piece ,a to ! o!r "p ( ! wire1 ?us mak+ a complete circuit or pa? = ! electricity to travel 94 ,if we turn ! piece ,a away f ! upp] wire ?is breaks ! circuit & cuts (f ! pa?1 &1 ( c\rse1 ! lamps w\ld g out4 ,?is is ! pr9ciple ( ! swit*1 &1 al?\gh !y are made 9 ?\s&s ( ways1 swit*es all h ! same object--namely1 ! clos+ & break+ ( ! circuit1 :e!r x is = "o or a hundr$ lamps4 ,,wire ,,on ,,dynamos ,9 expla9+ to y ! con/ruction & work+ ( dynamo-ma*9es1 we did n /ate any?+ ab\t ! am\nts ( wire us$ 9 w9d+ ! ma*9e4 ,x is n our int5tion to say exactly h[ mu* is us$ on any "o dynamo1 because t is among ! ?+s y w h to le>n :5 y come to /udy ! subject ( electricity m deeply4 ,we simply want to h y und]/& t ^u ! numb] ( turns ( wire on any "o ma*9e dep5ds ! effect t t am\nt ( wire1 c>ry+ electricity1 w h ^u a c]ta9 weight ( iron :5 ! armature is revolv$ a c]ta9 numb] ( turns p] m9ute4 ,a c]ta9 numb] ( /r&s ( wire on an armature w only d a c]ta9 am\nt ( "w at ! mo/1 s y w see t a small dynamo w n produce z mu* electricity z a l>g] "o conta9+ m iron & wire4 ,= high pressure !re mu/ be m /r&s ( wire cutt+ ! l9es ( =ce m frequ5tly ?an w\ld be requir$ = l[ pressure2 &1 to produce a great _m ampres1 ! armature mu/ be l>g] & ! wire ^u x ?ick] ?an x w\ld ne$ to be if only a small numb] ( ampres 7 want$4 ,?is ( itself is a v deep & complicat$ subject1 & _m books h be5 writt5 ^u x alone4 ,we %all1 !re=e1 n attempt to g m deeply into x 9 ?is little book1 b simply cont5t ourselves ) giv+ y ! g5]al idea1 :i* w be suffici5t until y make a ?or\gh /udy ( ! subject4 ,,viii ,,electric ,,p[] ,"o ( ! mo/ conv5i5t uses to :i* electricity is put is 9 produc+ motive p[] = driv+ all k9ds ( ma*9es1 f a sew+-ma*9e to a railway tra91 & we w n[ try to expla9 h[ we c get ?is k9d ( "w f electricity4 ,to beg9 )1 y all "k t a piece ( ma*9]y is usually made to "w by revolv+ a :eel :i* is "p ( ! ma*9e1 ei!r by means ( a /eam-eng9e or by wat]-p[]1 or1 z a sew+-ma*9e1 by foot-p[]4 ,n[1 :5 we "w a piece ( ma*9]y by electricity we d j ! same ?+ by us+1 in/ead ( ! /eam-eng9e or wat] or foot p[]1 an electric-eng9e call$ an electromotor1 :i* op]ates 9 ! same way--namely1 by turn+ ! :eel ( ! ma*9e x is appli$ to4 ,foot-p[] is h>d "w = ! p]son :o is apply+ ! p[]1 &1 z y c easily see1 "o p]son c make only a v little p[] by use ( ! feet4 ,/eam & wat] p[] c be us$ = any l>ge am\nt ( "w1 b ! "w mu/ be )9 a few hundr$ feet ( ! eng9e or ! p[] _c be us$4 ,if !re 7 a factory us+ /eam-p[] a block or two away f :]e y liv$1 & y _h a la! 9 y\r h\se :i* y w\ld l to h run by ! /eam-p[] 9 ! factory1 x w\ld be practically impossible to d ?is4 ,n[1 if ! factory 7 /ill f>!r away f y\r h\se1 x w\ld be /ill m impossible1 & if x 7 a mile away x w\ld be fooli% to dream ( tak+ /eam-p[] f a place s f> away4 ,suppose1 h[ev]1 t ?is factory 0 light$ by electric lights1 x w\ld be a v easy matt] to take "s ( ! p[] ov] to y\r h\se4 ,?is c\ld be done1 ev5 if ! factory 7 miles away1 by tak+ two wires f _! electric-light wires & runn+ !m into y\r h\se to an electromotor connect$ ) y\r la!4 ,?is electromotor w\ld !n run y\r la! j z well z if x 7 belt$ to a /eam-eng9e4 ,s1 y see1 p[] c be c>ri$ 9 ! =m ( electricity ?r\gh two wires ov] v great di/ances & made to d "w at a long way f ! eng9e :i* is turn+ ! dynamo to make ! electricity4 ,?us1 y may h br\ght into y\r h\se wires :i* w give lights &1 at ! same "t1 p[] to run a sew+-ma*9e1 a la!1 or any o!r piece ( ma*9]y4 ,hav+ le>n$ s f> t a dynamo w make a cont9u\s curr5t ( electricity1 & t two wires w c>ry ?is curr5t to any place :]e x is want$1 let u n[ see :at takes place 9 ! electromotor to trans=m ! electricity into p[]4 ,an electromotor 7:i* we w n[ call by its %ort "n1 motor7 is simply a ma*9e made l a dynamo4 ,curi\s z x may seem to y1 x is a fact t if y take two dynamo-ma*9es exactly alike1 & run "o ) ! /eam-eng9e s z to produce electricity1 & !n take ! two ma9 wires & atta* !m to ! bru%es ( ! o!r dynamo1 ! electricity w drive ?is o!r dynamo s z to produce a great deal ( p[] :i* c\ld be us$ = driv+ o!r ma*9es4 ,?us1 ! second dynamo w\ld become a motor4 ,9 ! *apt] on dynamos we expla9$ some?+ ab\t ! way !y 7 made & h[ ! electricity 0 produc$4 ,,! ,,motor ,y w rememb] t ! armature consi/s ( a spool w\nd ) wire4 ,?is spool is made ( iron plates fa/5$ toge!r s z to =m "o solid piece4 ,! armature ( a motor may be made 9 ! same way2 9 fact1 ! :ole motor is practically a dynamo-ma*9e4 ,!re is some?+ m ab\t magnetism :i* we w tell y ( "h1 because y w m easily und]/& x 9 its relation to an electromotor4 ,if we take an ord9>y piece ( iron & br+ "o end ( x ne> to 7b n t\*+7 "o pole ( a magnet1 ?is piece ( iron w itself become a weak] magnet z long z x rema9s 9 ?is position4 ,?is is said to be magnetism by induction4 ,! end ( ! piece ( iron ne>e/ to ! magnet w be ( ! opposite pol>ity4 ,= in/ance1 if ! pole ( ! magnet 7 nor?1 ! end ( ! iron :i* 0 ne>e/ to ?is nor? pole w\ld be s\?1 &1 ( c\rse1 ! o!r end w\ld be nor?4 ,to make ?is m pla9 we %[ x 9 ! foll[+ sket*4 7,fig4 #bg47 ,?is w\ld be ! same :e!r ! magnet 7 a p]man5t or an electromagnet4 ,y w rememb] also t ! nor? pole ( "o magnet w attract ! s\? pole ( ano!r magnet1 b w repel a nor? pole4 ,^! are ! pr9ciples made use ( 9 an electromotor1 & we w n[ try to %[ y h[ ?is is c>ri$ into practice4 ,illu/ration3 ,,/eel ,,p]man5t ,,magnet ,,iron ,fig4 #bg ,al?\gh a motor is made l a dynamo1 we w %[ a diff]5t =m ( ma*9e f ! dynamo already illu/rat$1 because x w help y to und]/& m easily4 7,fig4 #bh47 ,"h we h an electromagnet ) its poles1 & an iron armature w\nd ) wire1 j z 9 ! dynamo we h describ$1 except t its =m is diff]5t4 ,illu/ration3 ,fig4 #bh ,a commutator & bru%es are also us$1 b ! electricity1 in/ead ( be+ tak5 away f ! bru%es1 is tak5 to !m by ! wires connect$ ) !m4 ,two wires are also connect$ :i* take "p ( ! electricity ar\nd ! magnet1 j z 9 ! dynamo4 ,n[1 :5 ! volts pressure & ampres ( electricity com+ f a dynamo or batt]y are turn$ into ! wires lead+ to ! bru%es ( ! motor1 !y g ?r\gh ! commutator into ! armature & r\nd ! magnet1 & s create ! l9es ( =ce at ! poles & magnetize ! iron ( ! armature4 ,let u see :at ! effect ( ?is is4 ,! poles ( ! magnet become nor? & s\?1 & ! f\r ends on ! armature also become nor? & s\?1 two ( ea*4 ,by ref]r+ to ,fig4 #bh aga9 we %all see :at takes place4 ,! nor? pole ( ! magnet is do+ two ?+s3 x is repell+1 or =c+ away1 ! upp] nor? pole ( ! armature & at ! same "t draw+ t[>d itself ! l[] s\? pole ( ! armature4 ,9 ! mean "t ! s\? pole ( ! magnet is repell+ ! s\? pole ( ! armature & at ! same "t draw+ t[>d itself ! nor? pole ( ! armature4 ,?is1 ( c\rse1 makes ! armature turn ar\nd1 & ! same poles are aga9 pres5t$ to ! magnet1 :5 !y are act$ ^u 9 ! same mann]1 :i* makes ! armature revolve aga91 & ?is action cont9ues z long z electricity is br\ght ?r\gh ! wires to ! bru%es4 ,?us1 ! armature turns ar\nd ) great spe$ & /r5g?1 & w !n drive a ma*9e to :i* x is atta*$4 ,! spe$ & /r5g? ( ! motor are regulat$ by ! am\nt ( iron & wire ^u x1 & by ! volts pressure & ampres ( electricity suppli$ to ! bru%es4 ,motors are made f a small size t w run a sew+-ma*9e up to a size l>ge en\gh to run a railway tra91 & are (t5 op]at$ ?r\gh wires at a great di/ance f ! place :]e ! electricity is be+ made1 sometimes miles away4 ,!y are also made 9 a great _m diff]5t =ms1 b ! pr9ciple is practically ! same z we h j describ$ to y4 ,,ix ,,batt]ies ,s f> we h only describ$ "o way ( produc+ electricity--namely1 by means ( a dynamo-ma*9e driv5 by /eam or wat] p[]4 ,! supply ( electricity s obta9$ is regul> & con/ant z long z ! /eam or wat] p[] is appli$ to ! dynamo4 ,!re is ano!r & v diff]5t way ( produc+ electricity1 & ?is is by means ( a *emical process 9 :at is call$ a batt]y4 ,to obta9 electricity f ! dynamo we mu/ sp5d money = ! coal to make ! /eam :i* op]ates ! /eam-eng9e1 or = ! wat] :i* turns ! wat]-:eel1 z well z = an eng9e] 9 bo? cases4 ,:5 we obta9 electricity f a batt]y we mu/ sp5d money = ! *emicals & metals :i* are con/antly consum$ 9 ! batt]y4 ,,prim>y ,,batt]ies ,an electrical batt]y is a device 9 :i* "o or m *emical sub/ances act ^u a metal & a c>bon1 or ^u two diff]5t metals1 produc+ !reby a curr5t ( electricity1 :i* w cont9ue z long z !re is any action ( ! *emicals ^u ! metal & c>bon1 or ^u ! two metals4 ,batt]ies = produc+ electricity may be divid$ into two classes1 call$ op5 circuit batt]ies & clos$ circuit batt]ies4 ,op5-circuit batt]ies are ^? :i* are us$ :]e ! electricity is n requir$ con/antly )\t int]mission--= in/ance1 9 telephones1 electric bells1 burgl> al>ms1 gas-light+1 annunciators1 etc4 ,clos$-circuit batt]ies are ^? :i* are us$ :]e ! effect produc$ mu/ be cont9u\s e mom5t1 z1 = in/ance1 9 electric lights & motors4 ,! op5-circuit batt]y is made 9 _m diff]5t ways1 s we only describe two ( ! pr9cipal ones4 ,z we told y 9 an e>ly "p ( ?is book1 we d n "k j :at electricity is1 nor :y x is produc$ "u ! conditions exi/+ 9 a batt]y4 ,b we d "k t by foll[+ c]ta9 processes & mak+ c]ta9 *emical comb9ations we c make z mu* electricity & 9 su* proportions z we want4 ,! two metals1 or ! metal & c>bon1 9 a batt]y are call$ ! elem5ts1 & to ^! are connect$ ! wires :i* lead f ! batt]y to ! in/rum5ts to be work$ by x4 ,! ,leclan* ,batt]y4--,?is =m ( op5-circuit batt]y consi/s ( a glass j> 9 :i* is plac$ ! elem5ts4 ,"o elem5t consi/s ( a rod ( z9c1 & ! o!r elem5t is c>bon & p[d]$ black oxide ( manganese4 ,^! two 7! c>bon & black oxide ( manganese7 are plac$ 9 an e>!nw>e vessel call$ a por\s cup4 ,?is is simply a small j> made ( clay :i* is n glaz$4 ,?us1 ! liquid :i* is 9 ! glass j> p5etrates ?r\gh ! por\s cup to ! c>bon & manganese :i* x conta9s1 & s ! *emicals affect bo? ^! & ! z9c at once1 =1 9 ord] to obta9 electricity1 y w rememb] t ! *emical action mu/ take place at ! same "t ^u bo? ! elem5ts 9 ! same vessel4 7,fig4 #bi47 ,! *emical sub/ance us$ 9 ?is batt]y is sal-ammoniac1 or salts ( ammonia4 ,a c]ta9 quantity ( ?is salt is dissolv$ 9 wat]1 & ?is solution is p\r$ into ! glass j>4 ,:5 ?is is done ! batt]y w g5]ate electricity at once4 ,illu/ration3 ,fig4 #bi ,x %\ld be rememb]$ t ! prop] t]m = ! *emical mixture :i* acts ^u ! elem5ts 9 any batt]y is electrolyte4 ,! ,dry ,batt]y4--,! cleanl9ess1 conv5i5ce1 high effici5cy1 & comp>atively l[ int]nal resi/ance ( ! dry cell has br\ght x into great favor 9 ! la/ few ye>s4 ,x is n[ ext5sively us$ 9 pref]5ce to ! ,leclan* & o!r op5-circuit batt]ies hav+ liquid electrolyte = light "w1 su* z bells1 gas-light+1 burgl> al>ms1 ignition on motor-boats1 automobiles1 etc4 ,! dry cell is also us$ 9 great numb]s = pocket fla%-lamps1 & 9 o!r ways :]e x w\ld be impossible to employ batt]ies conta9+ liquids4 ,a dry cell consi/s ( z9c1 c>bon1 & ! electrolyte1 :i* is a mixture s made t x is 9 ! =m ( a gelat9\s or semi-solid mass1 s t x w n run or slop ov]4 ,a piece ( %eet z9c is =m$ into a long tube1 & a r\nd1 flat piece ( z9c is sold]$ at "o end1 ?us mak+ a cup op5 at "o end4 ,?is =ms ! cell itself1 & at ! same "t becomes "o ( ! elem5ts4 ,! o!r elem5t is a piece ( batt]y c>bon :i* is long en\gh to project out ( ! top ( ! cell ab\t half an in* or m4 ,:ile ! cell is be+ fill$ ) ! electrolyte ! c>bon is held up by a support s t x does n t\* ! z9c at ! bottom ( ! cup4 ,( c\rse1 ! z9c cup & ! c>bon are provid$ ) prop] b9d+-po/s or o!r atta*m5ts1 s t conduct+ wires c be connect$4 ,! electrolyte is pack$ into ! cup & ar\nd ! c>bon 9 su* a way t ! cup is entirely fill$ )9 ab\t half an in* f ! top1 & !n "s melt$ t> or pit* is p\r$ ov] ! top ( ! electrolyte4 ,?is seals ! cell & b9ds ! cont5ts solidly toge!r4 ,j be=e ! seal+ comp\nd h>d5s1 "o or two holes are made 9 x s t ! gases may escape4 ,! composition ( ! electrolyte itself is n exactly alike 9 all dry cells1 z ! v>i\s manufactur]s foll[ _! own p>ticul> =mulas4 ,h[ev]1 z y may be curi\s to "k some?+ ab\t x1 we w\ld /ate t "o =mula embraces fl\r1 wat]1 pla/] ( ,p>is1 granulat$ c>bon1 z9c *loride1 ammonium *loride1 & manganese b9oxide4 ,y w rememb] t ! ,leclan* & ! dry batt]ies are purely op5-circuit cells1 & t !y c be us$ to advantage = electric bells1 annunciators1 burgl> al>ms1 gas ignition1 etc41 :]e ! curr5t ( electricity is n do+ cont9u\s "w1 b only = a few seconds at a "t4 ,consequ5tly1 ! batt]ies h a little re/ 9 betwe51 if only = a few seconds4 ,n[1 if we 7 to attempt to use op5-circuit batt]ies = electric lights or motors1 :]e ! electricity mu/ "w con/antly e second1 ! batt]ies w\ld pol>ize--t is to say1 !y w\ld only "w a few m9utes & !n /op1 because ! *emicals us$ 9 !m are ( t k9d t !y w only all[ ! batt]y to d a little "w at a "t4 ,! batt]ies we h be5 describ+ w d ! ord9>y "w = :i* !y are int5d$ = sometimes a ye> )\t requir+ any att5tion1 b if we try to make !m d "w = :i* !y 7 n int5d$1 !y w\ld only la/ a few days4 ,if we %\ld want to op]ate electric lights or motors cont9u\sly f a batt]y we mu/1 !re=e1 use ,,clos$-,,circuit ,,batt]ies ,!re is a great v>iety ( ways 9 :i* clos$-circuit batt]ies are made1 b1 z ! ma9 pr9ciples are v mu* alike1 we w only describe two g5]al k9ds1 ^? ) & ^? )\t a por\s cup4#b ,9 ! fir/ place1 we mu/ /ate t clos$-circuit batt]ies prop] usually consi/ ( a glass j> & two elem5ts--c>bon & z9c4 ,sometimes a por\s cup is us$2 = :at reason y w soon le>n4 ,! *emicals t are us$ are usually diff]5t f ^? us$ 9 ! op5-circuit batt]ies & are mu* /rong]4 ,^! *emicals are usually sulphuric acid & bi*romate ( pota% 7or *romic acid71 :i* are mix$ ) wat]4 ,we w n[ exam9e two ( ! types ( clos$-circuit batt]ies1 tak+ fir/ ! "o )\t ! por\s cup1 ( :i* ! ,gr5et is a good example4 ,illu/ration3 ,fig4 #cj ,?is batt]y1 z y see1 consi/s ( a glass j>1 9 :i* are plac$ two plates ( c>bon & "o ( z9c4 7,fig4 #cj47 ,! latt] is betwe5 ! two c>bon plates & is movable up & d[n1 s t x may be drawn up out ( ! solution :5 x is n desir$ to use ! batt]y4 ,:5 ! z9c is 9 ! solution !re is a /eady & cont9u\s curr5t ( electricity develop$1 :i* c be tak5 away by wires f ! connections on top ( ! batt]y4 ,if ! z9c 7 left 9 ! solution :5 ! batt]y 0 n 9 use1 ! acid w\ld act ^u x almo/ z mu* z ?\gh ! electricity 7 n be+ us$1 & ?us ! z9c w\ld be eat5 away & ! acid w\ld be neutraliz$1 s t no m action c\ld be _h :5 we want$ m electricity4 ,n[1 9 ! ,gr5et batt]y we c light a lamp or run a motor = sev]al h\rs cont9u\sly1 b at ! end ( t "t ! solution w\ld become black & x w\ld d no m "w4 ,!n we mu/ ?r[ out t solution & put 9 fre%1 & ! batt]y w d ! same "w aga91 & s on4 ,if y %\ld only want to light y\r lamp or run y\r motor = a few m9utes1 y c\ld pull ! z9c up f ! solution & put x d[n aga9 :5 y want$ ! electricity once m4 ,! c>bon elem5t 9 ! batt]y is n consum$ by ! acid1 al?\gh ! z9c is4 ,illu/ration3 ,fig4 #ca ,n[ y w see ! use ( ! por\s cup4 ,we w take z an illu/ration ( ?is type an ord9>y batt]y 9 :i* a por\s cup is us$4 7,fig4 #ca47 ,"h1 y w see1 ! c>bon is plac$ 9 ! por\s cup1 :ile ! z9c is outside 9 ! glass j>4 ,9 ! glass cell ) ! z9c is usually us$ wat] made slightly acid1 & ! /rong solution ( sulphuric acid & bi*romate ( pota% 7or *romic acid7 is p\r$ 9 ! por\s cup1 :]e ! c>bon is plac$4 ,! /rong solution p5etrates ! por\s cup v sl[ly & gets to ! z9c1 :5 x imm$iately produces a curr5t ( electricity4 ,b ! acid does n get at ! z9c s freely z x does 9 ! batt]y )\t a por\s cup1 &1 consequ5tly1 nei!r ! acid nor ! z9c is s rapidly us$ up4 ,:]e por\s cups are us$1 ! batt]ies w give a cont9u\s curr5t = a v mu* long] "t ?an )\t !m1 & w1 sometimes1 give _m h\rs' "w e day = sev]al mon?s )\t requir+ any *ange ( solution4 ,pol>ization4--,!re is "o o!r reason :y a long] work+ "t c be _h f a batt]y ) a por\s cup1 & t is1 9 a batt]y )\t a por\s cup ! action ( ! acid ^u ! z9c is s rapid t ! c>bon plates become cov]$ ) gas1 &1 !re=e1 ! prop] action by ! acid _c take place ^u !m4 ,?us1 ! batt]y ceases to "w1 & is said to be pol>iz$4 ,:5 a por\s cup is us$1 ! action ( ! acid ^u ! z9c is sl[ en\gh to give (f only a small am\nt ( gas1 & ?us ! acid has a *ance to act ^u ! c>bon plates & develop a /eady curr5t ( electricity4 ,,! ,,"w ,,done ,,by ,,batt]ies ,! pressure & quantity ( electricity giv5 (f cont9u\sly by op5 & clos$ circuit batt]ies is v diff]5t4 ,! pressure 7or electromotive =ce7 ( "o cell ( an ord9>y op5-circuit batt]y is only ab\t "o volt1 & ! curr5t is usually v mu* less ?an "o ampre1 except 9 a dry cell1 :i* may give m4 ,9 ! clos$-circuit batt]ies describ$1 ! electromotive =ce ( ea* cell is ab\t two volts1 :ile ! curr5t v>ies f #a to p]haps #ej ampres1 accord+ to ! size ( ! z9c & c>bon plates4 ,x w\ld n matt] if y made "o cell z big z a b>rel1 nor if y put 9 a doz5 c>bons & z9cs1 ! electromotive =ce w\ld n exce$ ! volts m5tion$ = ea* type ( batt]y1 b ! ampre capacity w\ld be great] ?an 9 a small] cell on acc\nt ( ! l>g] size ( ! c>bon & z9c plates4 ,int]nal ,resi/ance4--,!re is "o o!r po9t :i* affects ! numb] ( ampres :i* c be obta9$ f a clos$-circuit batt]y1 & t is :e!r !re is a l>ge or small int]nal resi/ance 9 ! batt]y itself4 ,?is dep5ds ^u ! solution :i* is us$ & ! arrangem5t ( ! plates4 ,if !re is a high resi/ance 9 ! batt]y itself 7call$ int]nal resi/ance71 ! electricity mu/ d "w to ov]come ?is resi/ance be=e x c get out ( ! batt]y to d useful "w ?r\gh ! wires1 &1 consequ5tly1 ! capacity 9 ampres is limit$4 ,if1 on ! o!r h&1 !re is v little resi/ance 9 ! batt]y1 ! curr5t has v little "w to fl[ to ! wires lead+ f ! batt]y1 & we c get a l>g] quantity1 or great] numb] ( ampres4 ,?us1 y w see t :ile ! clos$-circuit batt]y is ! /rong]1 & w d all t ! op5-circuit batt]y w d1 & ev5 m1 9 a %ort "t ! latt]1 ?\gh weak]1 w d ab\t z mu* "w = ! same am\nt ( z9c & c>bon z ! =m]1 b takes a mu* long] "t4 ,,batt]ies ,,= ,,electric ,,light ,z we h expla9$ to y1 clos$-circuit batt]ies are us$ = produc+ inc&esc5t electric lights 9 small numb]s1 z well z = runn+ motors4 ,to op]ate inc&esc5t lights1 a numb] ( batt]ies connect$ toge!r are us$4 ,! numb] us$ dep5ds ^u ! pressure :i* ! lamps require to make !m give ! requir$ light4 ,we w n[ expla9 h[ ! batt]ies are connect$ toge!r = ?is purpose4 ,illu/ration3 ,fig4 #cb ,suppose y wi%$ to light an inc&esc5t lamp (1 say1 ?ree c&le-p[]1 :i* requir$ six volts4 ,we w\ld take ?ree clos$-circuit batt]ies :i* w\ld ea* give two volts1 & connect by a piece ( wire ! z9c ( ! fir/ to ! c>bon ( ! second1 & ! z9c ( ! second to ! c>bon ( ! ?ird1 z %[n 9 ! sket*4 7,fig4 #cb47 ,we w\ld !n atta* a wire to ! c>bon ( ! fir/ & "o to ! z9c ( ! ?ird1 & !re w\ld be six volts 9 ^! two wires1 :i* w\ld light up "o six-volt lamp nicely4 ,?is is call$ connect+ 9 s]ies1 or = int5sity4 ,n[ if ea* ( ^! cells gave t5 ampres alone1 ! ?ree w only give t5 ampres toge!r :5 !y are connect$ 9 s]ies4 ,if our lamp only requir$ "o ampre1 y w\ld naturally ?9k t t5 simil> lamps put on ! wires w\ld give z good light z ! "o1 b t is n s4 ,al?\gh y might light up two lamps1 ! pressure w\ld drop & ! lights w\ld become less brilliant if y put on ! :ole numb]4 ,s1 if we wi%$ to put on ! :ole t5 lights we w\ld connect ano!r batt]y & ?us increase ! pressure1 :i* w\ld probably make ^! t5 lamps burn brightly4 ,^! rules hold good = connect+ any numb] ( batt]ies = lamps ( any numb] ( volts--t is to say1 !re %\ld be calculat$ ab\t two volts = ea* cell & an all[ance made = drop 9 pressure4 ,,connect+ ,,9 ,,multiple ,!re is ano!r way ( connect+ batt]ies1 & t is to obta9 a l>g] numb] ( ampres4 ,?is is call$ connect+ 9 multiple arc1 or = quantity4 ,illu/ration3 ,fig4 #cc ,let u take aga9 = an illu/ration ! ?ree cells giv+ ea* #b volts & #aj ampres4 ,?is "t we connect ! c>bon ( ! fir/ to ! c>bon ( ! second1 & ! c>bon ( ! second to t ( ! ?ird2 !n we connect ! z9c ( ! fir/ to t ( ! second1 & ! z9c ( ! second to t ( ! ?ird1 z %[n 9 ! sket*4 7,fig4 #cc47 ,we !n atta* a wire to ! z9c & "o to ! c>bon 9 ! ?ird cell1 & we !n c obta9 f ^! two wires only #b volts1 b #cj ampres4 ,!re are1 aga91 _m ways ( connect+ sev]al ( ^! sets toge!r1 b x is n int5d$ 9 ?is book to g into ^! at l5g?1 = ! reason t we only set out to give a simple explanation ( ! fir/ pr9ciples ( ?is subject4 ,we %all !re=e only give an illu/ration ( "o m me?od ( connect+ batt]ies :i* w be easy to und]/&4 ,?is is call$ ,,multiple ,,s]ies ,! sket* we h la/ giv5 %[s ?ree batt]ies connect$ 9 multiple4 ,^! we w call set ,no4 #a4 ,n[1 suppose we take ?ree m batt]ies exactly simil> & connect !m toge!r j 9 ! same mann]4 ,let u call ?is set ,no4 #b4 ,n[ take ! wire lead+ f ! c>bon ( set ,no4 #b & connect x ) ! wire lead+ f ! z9c ( set ,no4 #a4 ,!n take a wire lead+ f ! z9c ( set ,no4 #b1 & a wire lead+ f ! c>bon ( set ,no4 #a1 & connect !m ) ! lamps or motors4 ,^! two sets be+ connect$ 9 multiple s]ies1 we %all get #d volts & #cj ampres4 ,?is is call$ connect+ 9 multiple s]ies1 & may be ext5d$ indef9itely ) any numb] ( batt]ies4 ,we %\ld add t "o ( ! elem5ts 9 a batt]y is call$ positive1 & ! o!r negative4 ,,! ,,edison ,,prim>y ,,batt]y ,z ?is type ( batt]y w "w effici5tly on ei!r op5 or clos$ circuit1 we h ?\ght be/ to describe x sep>ately at ?is place1 9 ord] n to confuse y\r ideas :ile read+ ab\t batt]ies g5]ally4 ,! type ( cell we w n[ describe 0 orig9at$ by an inv5tor nam$ ,lal&e1 & 0 kn[n by t "n2 b x has be5 greatly improv$ & r5d]$ m effici5t by ,edison1 & is n[ manufactur$ & sold by him "u ! "n ( ! ,edison ,prim>y ,batt]y4 ,be=e describ+ ! cell itself1 let u consid] ! action t takes place 9 a batt]y ( ?is k9d4 ,if c]ta9 metals are plac$ 9 a suitable solution1 & are connect$ toge!r1 outside ( ! solution1 by wires1 vigor\s *emical action w take place at ! surfaces ( ! metals1 & electrical en]gy w be produc$4 ,! plates mu/ be ( diff]5t metals1 & ! solution %\ld be "o t w dissolve nei!r ( !m except :5 an electric curr5t is all[$ to fl[4 ,"o ( ! metals is usually z9c1 :i* is gradually eat5 away or dissolv$ by ! solution :ile ! batt]y is deliv]+ electrical en]gy4 ,x is ! *emical comb9ation ( ! z9c & ! solution t produces ?is en]gy1 :i* leaves ! z9c 9 ! =m ( an electric curr5t1 & passes ?r\gh ! solution to ! o!r metal1 out ( ! cell to ! wire1 & !nce back by ano!r wire to ! z9c1 :]e x is once m />t$ on its circuit4 ,at ! surface ( ! o!r metal1 :i* may be1 & frequ5tly is1 copp]1 small bubbles ( ! gas call$ hydrog5 are produc$4 ,?is gas rises to ! surface ( ! liquid & gradually passes (f into ! air4 ,b its pres5ce (f]s resi/ance to ! passage ( ! curr5t2 s t g5]ally !re is associat$ ) ! copp] a supply ( ! gas oxyg54 ,oxyg5 & hydrog5 are always v eag] to mix ) ea* o!r1 &1 !re=e1 :5 ! hydrog5 bubbles appe> !y are quickly tak5 up by ! oxyg5 ne> by4 ,! mixture ( ^! two gases =ms wat]1 :i* becomes "p ( ! solution4 ,all ( ?is happ5s s quickly t ! hydrog5 _c be p]ceiv$ s long z !re is any oxyg5 left 9 ! copp]-oxide plate4 ,illu/ration3 ,fig4 #cd ,9 ! ,edison ,prim>y ,batt]y 7,fig4 #cd7 ! plates are z9c1 kn[n z ! negative1 & copp] oxide 7copp] & oxyg571 or ! positive4 ,^! are susp5d$ 9 a solution ( cau/ic soda & wat]1 ! plates & solution be+ conta9$ 9 j>s ( glass or porcela94 ,! plates are provid$ ) suitable wires = connect+ ! cells ) "o ano!r & ) ! lamps1 motors1 or o!r devices :i* !y are to op]ate4 ,!re are usually two z9c plates & "o copp]-oxide plate1 or multiples !re(4 ,! quantity ( curr5t t may be )drawn dep5ds on ! size & numb] ( ! plates1 z well z ^u _! con/ruction & arrangem5t4 ,! voltage ( ^! cells is l[1 be+ ab\t #j4fe volt ea*2 b ?is is m ?an comp5sat$ = by ! fact t ! int]nal resi/ance ( ! batt]y is s l[ t ! voltage is n p]ceptibly affect$ ev5 at cont9u\s high-dis*>ge rates1 & t ! voltage rema9s practically con/ant ?r\gh\t ! life ( ! cell4 ,fur!rmore1 :5 ! batt]y is n 9 use !re is practically no local action4 ,consequ5tly1 ! cells may rema9 on op5 circuit 7t is1 do+ no "w7 = ye>s & !re w be no loss ( en]gy4 ,! cell w !n op]ate ) ! same practical effici5cy z if x 7 new4 ,9 "s classes ( "w ?is batt]y rema9s 9 s]vice f f\r to six ye>s )\t att5tion4 ,ano!r peculi> advantage ( ?is batt]y lies 9 ! fact t ! plates & ! electrolyte are s well proportion$ t !y are all exhau/$ at ! same "t1 & !n new plates & solution c be put 9 ! j>1 re/or+ x to its orig9al condition4 ,^! batt]ies are us$ 9 great numb]s = railway signal "w & = o!r purposes1 su* z fire & burgl> al>m sy/ems1 v>i\s telephone functions1 op]ation ( electric self-w9d+ & programme clock sy/ems1 small electric-motor "w1 = l[ c&le-p[] electric lamps1 gas-eng9e ignition1 electro-plat+1 telegraph sy/ems1 *emical analysis1 & o!r exp]im5tal "w :]e batt]ies are requir$ t w rema9 9 use = long p]iods ( "t )\t requir+ any att5tion or r5ewal4 ,! rem>ks t h be5 made on previ\s pages ab\t connect+ up batt]ies 9 s]ies1 multiple1 & multiple s]ies apply also to ^! ,edison ,prim>y ,cells4 ,fig4 #ce %[s a batt]y ( f\r ( ^! cells connect$ 9 s]ies4 ,,second>y1 ,,or ,,/orage1 ,,batt]ies ,! op5 & clos$ circuit batt]ies we h s f> describ$ are us$ to produce electricity by ! action ( ! *emicals ^u ! elem5ts conta9$ 9 !m4 ,!y are call$ prim>y batt]ies4 ,illu/ration3 ,fig4 #ce ,! batt]ies :i* we w n[ tell y ( are call$ second>y1 or /orage1 batt]ies1 & d n ( !mselves make any prim>y curr5t1 b simply act z res]voirs1 s to speak1 to hold ! en]gy ( ! electric curr5t :i* is l$ into !m f a dynamo or prim>y batt]y4 ,at ! prop] "t & "u prop] conditions ^! second>y batt]ies w give back a l>ge p]c5tage ( ! en]gy ( ! electric curr5t :i* has be5 /or$ 9 !m4 ,?is class ( batt]y has be5 call$ by ^! ?ree names3 second>y batt]y1 accumulator1 & /orage batt]y2 b z ! latt] "n is us$ almo/ exclusively 9 ?is c\ntry1 we %all use x 9 ! foll[+ description4 ,,two ,,types ,!re are two di/9ct types ( /orage batt]y4 ,"o is call$ ! lead or acid /orage batt]y1 & ! o!r ! alkal9e or nickel-iron /orage batt]y4 ,ea* ( !m simply acts z a res]voir to hold ! en]gy ( ! electric curr5t :i* is l$ into x1 & ea* ( !m1 "u prop] conditions1 w give back t en]gy4 ,z ! lead /orage batt]y is ! olde/ 9 po9t ( discov]y & inv5tion1 we w describe x fir/4 ,,! ,,lead ,,/orage ,,batt]y ,a lead /orage batt]y usually consi/s ( a glass or h>d-rubb] j> conta9+ lead plates & a solution consi/+ ( wat] & sulphuric acid4 ,a s+le unit is usually call$ a cell4 7,fig4 #cf47 ,!re are always at lea/ two lead plates 9 a /orage-batt]y cell ( ?is k9d1 al?\gh !re may be any numb] above t4 ,= ! sake ( mak+ a cle>] explanation to y1 we w take z an illu/ration a cell conta9+ only two plates4#c ,illu/ration3 ,fig4 #cf ,we h1 !n1 a glass or h>d-rubb] j> conta9+ two lead plates & a solution consi/+ ( wat] & sulphuric acid4 ,^! plates are call$ ! elem5ts1 & "o is call$ ! positive & ! o!r ! negative elem5t4 ,! solution is call$ ! electrolyte4 ,! positive elem5t is a %eet ( lead ^u :i* is spread a pa/e made ( r$-lead4 ,! negative elem5t is a simil> %eet ( lead ^u :i* is spread a pa/e made ( li?>ge4 ,n[1 :5 ^! plates are ?us prep>$1 !y are put into ! acid solution 9 ! j>1 & a wire atta*$ to ea* plate is connect$ ) ! two wires f a dynamo or o!r s\rce ( electric curr5t1 j z a lamp w\ld be connect$4 ,! electric curr5t !n goes into ! /orage-batt]y cell1 ent]+ by ! positive plate & com+ out by ! negative4 ,^! plates & ! pa/e ^u !m (f] "s resi/ance1 or opposition1 to ! passage ( ! curr5t1 s ! electricity mu/ d "s "w to get f "o to ! o!r4 ,! "w x does 9 ?is case is to s act ^u ! pa/e t its *emical nature is *ang$4 ,s1 aft] ! prim>y curr5t has be5 pass$ f "o plate to ! o!r = "s "t1 & aft] sev]al dis*>ges1 ! /orage batt]y may be disconnect$1 be+ n[ =m$4 ,! pa/e on ! lead plates is n[ f\nd to h *ang$ its *emical nature1 ! pa/e on ! positive plate hav+ be5 trans=m$ into p]oxide ( lead1 & t on ! negative plate into spongy lead4 ,on arriv+ at ?is condition1 ! pa/e on ! plates is call$ active mat]ial4 ,?is process ( =mation is absolutely ess5tial be=e ! lead /orage batt]y is ready to be us$ = actual "w4 ,s1 :5 ! plates h be5 fully =m$1 ! /orage batt]y may be aga9 connect$ ) a s\rce ( electric curr5t :i* aga9 ent]s by ! positive plate & leaves by ! negative4 ,?is curr5t s acts on ! active mat]ial t x comb9es ) ! acid solution &1 ?r\gh ! en]gy ( ! *>g+ curr5t1 =ms o!r *emical comp\nds :i* may = conv5i5ce be call$ sulphates4 ,:5 ! *>g+ curr5t has fl[$ ?r\gh ! batt]y long en\gh to produce ^! *anges 9 ! active mat]ial ! batt]y is said to be *>g$1 & is ready = useful "w4 ,if ! two wires atta*$ to ! plates are n[ connect$ ) electric lamps1 or a motor1 or o!r device1 ! active mat]ial w develop en]gy 9 ! ef=t to aga9 *ange its nature4 ,?is en]gy takes ! =m ( an electric curr5t1 :i* leaves ! batt]y & passes ?r\gh ! conductors & op]ates ! lamps1 motors1 or o!r devices 9 its passage4 ,9 ?is way ! batt]y is said to be dis*>g$1 & at ! end ( its dis*>ge x c aga9 be *>g$ & dis*>g$ 9 a simil> mann] = a long "t1 until ! active mat]ial is ei!r us$ up or drops (f ! plates4 ,s f> z ! actual details ( con/ruction are conc]n$1 lead /orage batt]ies are made 9 a great _m diff]5t ways1 b ! mat]ials are1 9 g5]al1 ( ! same nature z ^? we h m5tion$ above4 ,,! ,,alkal9e ,,/orage ,,batt]y ,we %all n[ describe an entirely diff]5t type ( /orage batt]y1 :i* conta9s nei!r lead nor acid4 ,x is "o ( ! _m inv5tions ( ,?omas ,a4 ,edison4 ,9 ! alkal9e /orage batt]y ! gas call$ oxyg5 plays a v important "p1 & we w try to make x cle> to y :at ?is "p is4 ,y are well aw>e ( ! fact t if y leave y\r pocket-knife out 9 ! air x w get ru/y4 ,! reason = ?is is t iron or /eel quickly t5ds to comb9e ) ! oxyg5 ( ! air1 & ?is comb9ation ( oxyg5 & iron is ru/1 o!rwise call$ oxide ( iron1 or iron oxide4 ,?is iron oxide1 or ru/1 is !re=e ! result ( a *emical action betwe5 ! iron & ! oxyg54 ,n[ z all *emical actions require ! exp5diture ( en]gy1 !re has be5 develop$ ei!r heat or electricity 9 ! process4 ,! oxyg5 may be tak5 away f ! iron oxide1 *emically2 b "h aga9 w\ld be ano!r *emical action :i* w\ld require en]gy to be once m exp5d$4 ,iron oxide may be made *emically 9 _m diff]5t ways4 ,x is frequ5tly made 9 ! =m ( a p[d]4 ,!re=e1 we d n h to dep5d ^u iron ru/ = a supply ( ?is mat]ial4 ,be=e go+ fur!r we mu/ consid] ano!r oxide--namely1 nickel oxide4 ,x is *>act]i/ic ( nickel t :5 x is comb9$ ) oxyg5 to a c]ta9 degree s z to =m ! comp\nd kn[n z nickel oxide1 x w receive /ill m oxyg54 ,n[1 if "u prop] conditions we compel iron oxide to give up its oxyg5 to "s o!r k9d ( *emical comp\nd1 su* z nickel oxide1 we mu/ exp5d en]gy4 ,b1 on ! o!r h&1 if ?is nickel oxide gives back ! oxyg5 to ! iron--:i* x w d if opportunity is giv5--!re is en]gy produc$ aga9 9 receiv+ ! oxyg54 ,9 o!r words1 ! en]gy previ\sly exp5d$1 or "p ( x1 is n[ return$4 ,?is action & reaction are practically ^? t take place 9 ! ,edison alkal9e /orage batt]y4 ,= simplicity ( illu/ration we w consid] a cell conta9+ only two plates1 "o positive & "o negative4 ,! negative plate is made up ( a numb] ( small1 flat1 p]=at$ pockets conta9+ iron oxide 9 ! =m ( a f9e p[d]4 ,! positive plate is made up ( small1 p]=at$ tubes conta9+ nickel oxide mix$ ) v ?9 flakes ( metallic nickel4 7,fig4 #cg illu/rates ^! plates1 ! positive be+ 9 front47 ,illu/ration3 ,fig4 #cg ,^! two elem5ts1 positive & negative1 hav+ wires or conductors atta*$1 are plac$ 9 a nickel$-/eel c conta9+ ! electrolyte1 :i* consi/s ( a pota% solution4 ,y w see t ?is diff]s f a lead /orage batt]y1 9 :i* ! electrolyte is sulphuric acid & wat]4 ,if we 7 to put ?is acid solution into a metallic c 7except "o made ( lead7 ! c w\ld n la/ long1 z ! acid w\ld quickly eat holes ?r\gh x4 ,n[ let u see :at takes place 9 ! ,edison alkal9e /orage batt]y4 ,if an electric curr5t f a dynamo or o!r s\rce ( electricity is caus$ to pass ?r\gh ! positive to ! negative plate ! oxyg5 pres5t 9 ! iron oxide passes to & rema9s ) ! nickel oxide4 ,dur+ all ! "t ?is is go+ on ! batt]y is said to be *>g+1 & :5 all ! oxyg5 has be5 remov$ f ! iron oxide & is tak5 up by ! nickel oxide1 !n ! batt]y is said to be *>g$1 & ! fl[ ( curr5t into ! batt]y is /opp$4 ,a *ange has n[ tak5 place4 ,! p[d] 9 ! negative plate is no long] iron oxide1 b has be5 r$uc$ to metallic iron1 because ! oxyg5 has be5 remov$4 ,! p[d] 9 ! positive plate is n[ rais$ to a high] or sup] oxide ( nickel1 because x has tak5 ! oxyg5 t 0 9 ! iron4 ,b ! nickel oxide w readily give up its excess ( oxyg51 & ! iron w receive x back freely if p]mitt$4 ,if ! prop] conditions are e/abli%$1 ?is transf] ( oxyg5 w take place1 b ! iron _c receive x )\t deliv]+ en]gy4 ,illu/ration3 ,fig4 #ch ,! prop] conditions are e/abli%$ by provid+ a conduct+ circuit betwe5 ! two elem5ts1 9 :i* lamps1 motors1 or o!r electrical devices are plac$4 ,z soon z ?is circuit is provid$1 ! opportunity is giv5 to ! iron to receive ! oxyg54 ,?is x does1 & 9 s do+ develops electrical en]gy4 ,?is en]gy is 9 ! =m ( electric curr5t :i* is !n deliv]$ by ! batt]y on :at is call$ ! dis*>ge1 & ?is curr5t may be us$ = light+ lamps or = op]at+ motors or o!r electrical devices4 ,! batt]y is said to be dis*>g+ z long z ! iron is receiv+ oxyg5 f ! nickel oxide4 ,z soon z x becomes iron oxide once m1 ! giv+ out ( en]gy ceases & ! batt]y is said to be dis*>g$1 & mu/ aga9 be *>g$ to obta9 fur!r "w f x4 ,su* a batt]y c be *>g$ & dis*>g$ an indef9ite numb] ( times4 ,?is type ( batt]y is v rugg$1 & its comb9ations are n self-de/ructive4 ,x is v simple1 z x provides *iefly = ! movem5t ( ! oxyg5 back & =?2 besides1 x gives mu* m curr5t = its weight ?an ! lead type ( /orage batt]y4 7,fig4 #ch %[s ! plates ( a /&>d ,edison cell remov$ f conta9]47 ,,connect+ ,,/orage ,,batt]ies ,on ! dis*>ge1 "o cell ( a lead /orage batt]y gives an av]age ( ab\t #b volts1 & a cell ( alkal9e /orage batt]y ab\t #a4b volts1 no matt] :at its size or ! numb] ( plates may be4 ,:5 !re are m ?an two plates 9 "o cell1 all ! positives 9 t cell are connect$ toge!r by metallic /rips or b&s1 & all negatives 9 ! cell are connect$ toge!r 9 a simil> way4 ,al?\gh we _c obta9 m ?an ! above-nam$ electromotive =ce f "o cell ( ei!r type ( /orage batt]y1 we c obta9 a great] ampre capacity by us+ l>ge plates in/ead ( small ones1 or by us+ a l>g] numb] ( small size4 ,! same effects are produc$ by connect+ ! cells 9 s]ies1 or multiple1 or multiple s]ies1 z we %[$ y 9 reg>d to prim>y batt]ies2 & ! /orage batt]ies may be *>g$ z well z dis*>g$ :5 connect$ 9 any "o ( ^! ways4 ,,*>g+ ,,curr5t ,! curr5t :i* is us$ = *>g+ mu/ always be great] 9 pressure ?an t ( ! /orage batt]ies :i* are be+ *>g$4 ,if x is n1 ! /orage batt]ies w be ! /rong] ( ! two & w ov]p[] ! *>g+ curr5t & s dis*>ge !mselves4 ,x ,,conclusion ,we w n[ br+ ?is little volume to a close1 hav+ giv5 y a brief outl9e ( ! simple/ rudim5ts ( t wond]ful p[] ( nature1 ,electricity4 ,we may comp>e ?is subject to a beautiful h\se ! inside ( :i* y w\ld l to exam9e f top to bottom4 ,we h op5$ ! door = y2 n[ walk 9 & exam9e ev]y?+4 ,!re may be a great _m /airs to climb1 b :at y see & le>n w repay = all ! tr\ble4 ,,! ,,end ,,footnotes3 #a ,! filam5ts 9 mod]n ,mazda lamps1 z made at ! ,edison ,lamp ,works1 are /rips ( metallic tung/54 #b ,! batt]ies we w n[ describe are = clos$-circuit "w only1 & !y are nev] us$ = op5-circuit "w4 ,b !re is a type ( batt]y made t is available = ei!r op5 or clos$ circuit op]ation4 ,?is is ! ,edison ,prim>y ,batt]y1 :i* w be describ$ lat] on4 #c ,practically1 !re is always "o m negative plate ?an positive plates 9 a regul> /orage-batt]y cell4 ,consequ5tly1 a /&>d cell always conta9s an odd numb] ( plates4 ,,transcrib]',s ,,note -,pla9 pr9t & punctuation errors fix$4